JP5135913B2 - Positive electrode active material for lithium secondary battery, method for producing the same, positive electrode for lithium secondary battery and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, a positive electrode for a lithium secondary battery using the positive electrode active material, and a lithium secondary battery including the positive electrode for the lithium secondary battery.

  Lithium secondary batteries are excellent in energy density and output density, and are effective in reducing the size and weight. Therefore, the demand for power supplies for portable devices such as notebook computers, mobile phones, and handy video cameras is growing rapidly. ing. Lithium secondary batteries are also attracting attention as power sources for electric vehicles and power load leveling, and in recent years, demand for power sources for hybrid electric vehicles is rapidly expanding. In particular, in electric vehicle applications, it is necessary to be excellent in low cost, safety, life (particularly under high temperature) and load characteristics, and improvements in materials are desired.

Among the materials constituting the lithium secondary battery, as the positive electrode active material, a substance having a function capable of desorbing and inserting lithium ions can be used. There are various types of these positive electrode active material materials, each having its own characteristics. In addition, a common problem for improving performance is to improve load characteristics, and improvements in materials are strongly desired.
Furthermore, there is a demand for a material with a good performance balance that is excellent in low cost, safety, and life (particularly under high temperatures).

  Currently, lithium manganese composite oxides having a spinel structure, layered lithium nickel composite oxides, layered lithium cobalt composite oxides, and the like have been put into practical use as positive electrode active material materials for lithium secondary batteries. All of the lithium secondary batteries using these lithium-containing composite oxides have advantages and disadvantages in terms of characteristics. That is, a lithium manganese composite oxide having a spinel structure is inexpensive and relatively easy to synthesize, and is excellent in safety when used as a battery, but has a low capacity and inferior high-temperature characteristics (cycle and storage). Layered lithium-nickel composite oxides have high capacity and excellent high-temperature characteristics, but are difficult to synthesize, have inferior safety when used as batteries, and have drawbacks such as requiring careful storage. Layered lithium cobalt-based composite oxides are widely used as power sources for portable devices because they are easy to synthesize and have an excellent balance of battery performance. However, they are not sufficient in safety and costly. It is a drawback.

  Under such circumstances, lithium nickel manganese cobalt-based composite oxides with a layered structure have been proposed as promising candidates for active material materials that can overcome or reduce the shortcomings of these positive electrode active material materials and are excellent in battery performance balance. Has been. Particularly, in recent years, demands for lowering costs, higher voltages, and increasing safety demands are promising as positive electrode active material materials that can meet any of the demands.

  However, the degree of cost reduction, higher voltage, and safety will vary depending on the composition ratio. Therefore, for further cost reduction, use with a higher upper limit voltage, and higher safety requirements. Therefore, it is necessary to select and use one having a limited composition range such as a manganese / nickel atomic ratio of approximately 1 or more, or a reduction in the cobalt ratio. However, a lithium secondary battery using a lithium nickel manganese cobalt based composite oxide having such a composition range as a positive electrode material has reduced load characteristics such as rate and output characteristics. It was necessary.

  Therefore, in order to solve the problem of improving load characteristics such as rate and output characteristics, the present inventor, while firing the active material at a higher temperature to achieve sufficiently high crystallinity, After obtaining the addition of a compound containing a specific element such as W as a result of diligent research, it is important to obtain morphological particles that are difficult to surface area, and more preferably to obtain fine particles by suppressing grain growth and sintering. , Layered lithium nickel manganese cobalt composite oxide powder composed of fine particles (high specific surface area, high pore volume) with high crystallinity and suppressed grain growth and sintering by firing under a certain high temperature condition As a positive electrode material for lithium secondary batteries, in addition to cost reduction, higher voltage resistance and higher safety, load characteristics such as rate and output characteristics are improved. It was assumed possible. However, further improvement is necessary to achieve higher output and higher capacity while taking advantage of the above characteristic merits.

  In the present invention, a layered lithium nickel manganese cobalt based composite oxide containing Li in a larger amount than the stoichiometric ratio is heat-treated in a carbon dioxide-containing atmosphere, and this is used as a positive electrode active material for a lithium secondary battery. The following Patent Documents 1 to 3 are disclosed as well-known documents in which a positive electrode active material for a lithium secondary battery is conventionally heat-treated in a carbon dioxide gas atmosphere. ing.

In Patent Document 1, LiNiO ₂ having a Li / Ni ratio of stoichiometric composition (1/1) is left in a carbon dioxide atmosphere at 150 ° C. for 2 to 3 minutes, or in air at 200 ° C. for 10 minutes. It is described. However, since the positive electrode active material having such a stoichiometric composition is very easily carbonated and far exceeds the c / S value defined by the present invention, there is a risk of causing a significant decrease in charge / discharge capacity, rate characteristics, and output characteristics. There is.

  Patent Document 2 describes that lithium nickelate or composite lithium nickelate is treated in an atmosphere containing carbon dioxide gas. However, in the technique described in this document, since the treatment temperature is low, it is extremely difficult to perform carbonation to a desired state for a composition that is hardly carbonated as defined in the present invention.

On the other hand, Patent Document 3 discloses that the Li-excess layered lithium nickel manganese cobalt based composite oxide according to the present invention is heat-treated in a carbon dioxide-containing atmosphere. However, according to the examples in this patent document, the carbonate ion concentration per unit specific surface area, that is, the c / S value is 0.5 to 6.2, which is outside the scope of the present invention.
JP 7-245105 A JP-A-9-153360 JP 2004-335345 A

  As described above, the present inventor first added a compound containing a specific element such as W and then baked it at a high temperature condition above a certain level, thereby achieving high crystallinity and fine grain growth and sintering suppressed. Found that layered lithium nickel manganese cobalt composite oxide powders composed of fine particles (high specific surface area, high pore capacity) can be obtained. In addition to safety, load characteristics such as rate and output characteristics can be improved. However, improvements are desired to achieve higher output and higher capacity.

  An object of the present invention is to increase capacity while further improving load characteristics such as rate and output characteristics in use as a positive electrode active material for a lithium secondary battery, and more preferably, good high temperature cycle performance, low Positive electrode active material for lithium secondary battery capable of achieving both cost reduction, high voltage resistance and high safety, positive electrode for lithium secondary battery using this positive electrode active material, and for this lithium secondary battery It is in providing a lithium secondary battery provided with a positive electrode.

  As a result of intensive studies to further increase the output and capacity, the present inventor has obtained a layered lithium nickel manganese cobalt based composite oxide containing Li in a larger amount than the stoichiometric ratio in a carbon dioxide-containing atmosphere. It was found that further higher output and higher capacity can be achieved by using this as a positive electrode active material for a lithium secondary battery, and the present invention has been completed.

That is, the positive electrode active material for a lithium secondary battery of the present invention is composed of a Li-excess layered lithium nickel manganese cobalt-based composite oxide heat-treated in a carbon dioxide-containing atmosphere, and the carbonate ion concentration measured by ion chromatography is c [ % By weight] and the specific surface area measured by the BET method is S [m ² / g], the c / S value is 0.055 or more and 0.30 or less (Claim 1).

Positive electrode active material for lithium secondary battery of the present invention, BET specific surface area of 1.5 m ² / g or more, ^{5 m} 2 / g or less it is not preferable.

The positive electrode active material for lithium secondary battery of the present invention, the carbonate ion concentration measured by ion chromatography 0.15 wt% or more, yet preferably be 0.50 wt% or less.

The positive electrode active material for lithium secondary battery of the present invention, the composition is not preferred those represented by the following formula (I).
LiMO ₂ (I)
[However, in the above formula (I),
M is an element composed of Li, Ni and Mn, or Li, Ni, Mn and Co. Mn / Ni molar ratio is 0.8 or more and 5 or less Co / (Mn + Ni + Co) molar ratio is 0 or more, 0 .35 or less,
Li molar ratio in M is 0.001 or more and 0.2 or less. ]

The positive electrode active material for lithium secondary battery of the present invention, M in the composition formula (I) is not preferred those represented by the following formula (II) formula.
M = Liz _{/ (2 + z)} {(Ni _{(1 + y) / 2} Mn _{(1-y) / 2} ) _1-x Co _x } _{2 / (2 + z)} (II)
[However, in the above formula (II),
0 ≦ x ≦ 0.1
−0.1 ≦ y ≦ 0.1
(1-x) (0.05-0.98y) ≤z≤ (1-x) (0.20-0.88y)
It is. ]

The positive electrode active material for lithium secondary battery of the present invention, Mo, W, Nb, Ta, and it is not preferable to contain at least one element selected from the group consisting of Re.

In addition, the positive electrode active material for a lithium secondary battery of the present invention is set to a refractive index of 1.24 using a laser diffraction / scattering particle size distribution measuring device, and the ultrasonic wave for 5 minutes with the particle size reference as the volume reference. The median diameter measured after dispersion (output 30 W, frequency 22.5 kHz) is preferably 0.5 μm or more and 10 μm or less (Claim 3 ).

The positive electrode active material for a lithium secondary battery of the present invention preferably has a bulk density of 0.5 g / cm ³ or more and 2.5 g / cm ³ or less (claim 4 ).

Moreover, the positive electrode active material for a lithium secondary battery of the present invention preferably has a volume resistivity of 1 × 10 ³ Ω · cm or more and 1 × 10 ⁶ Ω · cm or less when consolidated at a pressure of 40 MPa. (Claim 5 ).

The method for producing a positive electrode active material for a lithium secondary battery according to the present invention includes a Li-excess layered structure in an atmosphere gas having a carbon dioxide concentration of 1% by volume or more and 100% by volume or less at a temperature condition of 200 ° C. or more and 800 ° C. or less. The lithium nickel manganese cobalt composite oxide is heat-treated while being held for 0.5 hours or more and 48 hours or less (Claim 6 ).

The positive electrode for a lithium secondary battery of the present invention has a positive electrode active material layer containing at least the positive electrode active material for a lithium secondary battery and a binder on a current collector (claim). 7 ).

The lithium secondary battery of the present invention is a lithium secondary battery comprising a negative electrode capable of inserting and extracting lithium, a non-aqueous electrolyte containing a lithium salt, and a positive electrode capable of inserting and extracting lithium. Such a positive electrode for a lithium secondary battery of the present invention is used (claim 8 ).

  The positive electrode active material for a lithium secondary battery of the present invention, when used as a lithium secondary battery positive electrode material, achieves both low cost and high safety, high cycle characteristics, improved load characteristics and high capacity. Can be planned. Therefore, according to the present invention, a lithium secondary battery that is inexpensive, highly safe, and excellent in performance is provided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the gist of the present invention. The content of is not specified.

[Positive electrode active material for lithium secondary battery]
The positive electrode active material for a lithium secondary battery of the present invention (hereinafter sometimes referred to as “positive electrode active material”) is composed of a Li-excess layered lithium nickel manganese cobalt based composite oxide that has been heat-treated in a carbon dioxide-containing atmosphere.

  The lithium nickel manganese cobalt-based composite oxide (hereinafter simply referred to as “lithium nickel manganese cobalt-based composite oxide of the present invention”) used as the positive electrode active material of the present invention has a Li / (Ni + Mn + Co) molar ratio of 1. It is a powder of a lithium nickel manganese cobalt based composite oxide that is larger, that is, contains an excess of Li and has a layered structure, that is, a layered structure.

The lithium nickel manganese cobalt based composite oxide of the present invention is characterized in that it is heat-treated in an atmosphere containing carbon dioxide gas, and is thereby carbonated to a predetermined degree.
Specifically, for the lithium nickel manganese cobalt composite oxide of the present invention, the carbonate ion concentration measured by ion chromatography is c [wt%], and the specific surface area measured by the BET method is S [m ² / g]. The c / S value is in the range of 0.055 or more and 0.30 or less. In the present invention, the “carbonate ion concentration” refers to a carbonate ion concentration in a broad sense including “bicarbonate ion concentration”.

  The lower limit of the c / S value is usually 0.055 or more, preferably 0.057 or more, more preferably 0.060 or more, particularly preferably 0.062 or more, and the upper limit is usually 0.30 or less. However, it is preferably 0.25 or less, more preferably 0.20 or less, and particularly preferably 0.15 or less. If the lower limit is not reached, the improvement effect of the present invention may not be obtained. If the upper limit is exceeded, the battery performance may be deteriorated.

Although the BET specific surface area of the lithium nickel manganese cobalt based composite oxide of the present invention is arbitrary, it is usually 1.5 m ² / g or more, preferably 1.7 m ² / g or more, more preferably 2.0 m ² / g or more. , particularly preferably 2.5 m ² / g or more, and usually ^{5 m} 2 / g or less, preferably 4.5 m ² / g or less, more preferably ^4m 2 / g or less, particularly preferably 3.5 m ² / g or less. If the BET specific surface area is too small, the rate characteristics and output characteristics of the battery and the battery capacity will be reduced. On the other hand, if the BET specific surface area is too large, it will be difficult to handle as a material or cause an undesirable reaction with the electrolyte in the positive electrode. There is a possibility that the life characteristics may be deteriorated.

  The BET specific surface area can be measured by a known BET type powder specific surface area measuring device. In the present invention, an OMS Riken: AMS8000 type automatic powder specific surface area measuring device was used, nitrogen was used as an adsorption gas, and helium was used as a carrier gas. Specifically, the powder sample was heated and deaerated with a mixed gas at a temperature of 150 ° C., then cooled to liquid nitrogen temperature to adsorb the mixed gas, and then heated to room temperature with water to be adsorbed. Nitrogen gas was desorbed, the amount was detected by a heat conduction detector, and the specific surface area of the sample was calculated therefrom.

  The range of the carbonate ion concentration c of the lithium nickel manganese cobalt based composite oxide of the present invention is usually 0.15% by weight or more, preferably 0.16% by weight or more, more preferably 0.17% by weight or more, particularly preferably. 0.18% by weight or more, usually 0.50% by weight or less, preferably 0.40% by weight or less, more preferably 0.35% by weight or less, still more preferably 0.31% by weight or less, particularly preferably 0. Less than 30% by weight. If the carbonate ion concentration is too low, the improvement effect of the present invention may not be obtained. If the carbonate ion concentration is too high, swelling may occur due to gas generation when a battery is produced.

  The carbonate ion concentration c can be measured by ion chromatography. Although there is no restriction | limiting in the specific method of ion chromatography, For example, 5 ml of demineralized water immediately after preparation is added to 30-100 mg of lithium nickel manganese cobalt based composite oxides, and carbonate ions are extracted by ultrasonic dispersion for 30 minutes. It can be determined by analyzing the extracted aqueous phase with an ion chromatograph.

  The composition of the lithium nickel manganese cobalt based composite oxide of the present invention is not particularly limited as long as it does not depart from the gist of the present invention, but is preferably one represented by the following formula (I).

LiMO ₂ (I)
[However, in the above formula (I),
M is an element composed of Li, Ni and Mn, or Li, Ni, Mn and Co. Mn / Ni molar ratio is 0.8 or more and 5 or less Co / (Mn + Ni + Co) molar ratio is 0 or more, 0 .35 or less,
Li molar ratio in M is 0.001 or more and 0.2 or less. ]

In the above formula (I), M is an element composed of Li, Ni and Mn, or Li, Ni, Mn and Co. Mn / Ni molar ratio is usually 0.8 or more, preferably 0.82. Or more, more preferably 0.85 or more, further preferably 0.88 or more, most preferably 0.9 or more, usually 5 or less, preferably 4 or less, more preferably 3 or less, still more preferably 2.5 or less, most preferably Preferably it is 1.5 or less.
The Co / (Mn + Ni + Co) molar ratio is usually 0 or more, preferably 0.01 or more, more preferably 0.02 or more, further preferably 0.03 or more, most preferably 0.05 or more, usually 0.30 or less, preferably Is 0.20 or less, more preferably 0.15 or less, still more preferably 0.10 or less, and most preferably 0.099 or less.
The Li molar ratio in M is usually 0.001 or more, preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more, most preferably 0.05 or more, usually 0.2 or less, Preferably it is 0.19 or less, More preferably, it is 0.18 or less, More preferably, it is 0.17 or less, Most preferably, it is 0.15 or less.

  In the above composition formula (I), the atomic ratio of the oxygen amount is described as 2 for convenience, but there may be some non-stoichiometry. In the case of non-stoichiometry, the atomic ratio of oxygen is usually in the range of 2 ± 0.2, preferably in the range of 2 ± 0.15, more preferably in the range of 2 ± 0.12, and even more preferably 2 ± 0.10. And particularly preferably in the range of 2 ± 0.05.

  The lithium nickel manganese cobalt-based composite oxide of the present invention is particularly preferably one in which the atomic configuration in the M site in the composition formula (I) is represented by the following formula (II).

M = Liz _{/ (2 + z)} {(Ni _{(1 + y) / 2} Mn _{(1-y) / 2} ) _1-x Co _x } _{2 / (2 + z)} (II)
[However, in the above formula (II),
0 ≦ x ≦ 0.1
−0.1 ≦ y ≦ 0.1
(1-x) (0.05-0.98y) ≤z≤ (1-x) (0.20-0.88y)
It is. ]

In the above formula (II), the value of x is usually 0 or more, preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more, most preferably 0.04 or more, usually 0.1. Hereinafter, it is preferably 0.099 or less, and most preferably 0.098 or less.
The value of y is usually −0.1 or more, preferably −0.05 or more, more preferably −0.03 or more, most preferably −0.02 or more, usually 0.1 or less, preferably 0.05 or less, More preferably, it is 0.03 or less, and most preferably 0.02 or less.
The value of z is usually (1-x) (0.05-0.98y) or more, preferably (1-x) (0.06-0.98y) or more, more preferably (1-x) (0. 07-0.98y) or more, more preferably (1-x) (0.08-0.98y) or more, most preferably (1-x) (0.10-0.98y) or more, usually (1- x) (0.20-0.88y) or less, preferably (1-x) (0.18-0.88y) or less, more preferably (1-x) (0.17-0.88y), most Preferably, it is (1-x) (0.16-0.88y) or less.

  If the value falls below this lower limit, the conductivity will decrease, and if the value exceeds the upper limit, the amount of substitution to transition metal sites will increase and the battery capacity will decrease, leading to a decrease in the performance of lithium secondary batteries using this. there is a possibility. On the other hand, if z is too large, the carbon dioxide absorbability of the active material powder increases, so that it becomes easy to absorb carbon dioxide in the atmosphere. As a result, it is estimated that the concentration of contained carbon increases.

  Here, when the x value is in the range of 0 ≦ x ≦ 0.1 and the amount of Co is small, in addition to reducing the cost, it is used as a lithium secondary battery designed to be charged at a high charging potential. In this case, charge / discharge capacity, cycle characteristics, and safety are improved.

  In addition, in the composition range of the above formula (II), the closer the z value is to the lower limit that is a constant ratio, the lower the rate characteristics and output characteristics of the battery, and the z value is closer to the upper limit. As the battery is used, the rate characteristics and output characteristics increase, but on the other hand, the capacity tends to decrease. In addition, the lower the y value, that is, the smaller the manganese / nickel atomic ratio, the higher the capacity is obtained at a lower charging voltage. However, the cycle characteristics and safety of batteries set at a higher charging voltage tend to be reduced. As the value is closer to the upper limit, the cycle characteristics and safety of the battery set at a higher charge voltage are improved, while the discharge capacity, rate characteristics, and output characteristics tend to decrease. In addition, the closer the x value is to the lower limit, the lower the load characteristics such as rate characteristics and output characteristics when the battery is used. Conversely, the closer the x value is to the upper limit, the rate characteristics when the battery is used. However, if this upper limit is exceeded, the cycle characteristics and safety when set at a high charge voltage are reduced, and the raw material cost is increased. Setting the composition parameters x, y, and z within a specified range is an important component of the present invention.

  Here, the chemical meaning of the Li composition (z and x) in the lithium-lithium-nickel-manganese-cobalt composite oxide, which is a component of the present invention, will be described in more detail below.

（以下「層状Ｒ（−３）ｍ構造」と表記することがある。）に帰属される。 The lithium nickel manganese cobalt composite oxide of the present invention has a crystal structure belonging to a layered structure.
Here, the layered structure will be described in more detail. As a typical crystal system having a layered structure, there are those belonging to the α-NaFeO ₂ type such as LiCoO ₂ and LiNiO ₂ , which are hexagonal and have a space group due to their symmetry.

(Hereinafter referred to as “layered R (−3) m structure”).

However, the layered LiMeO ₂ is not limited to the layered R (−3) m structure. In addition to this, LiMnO ₂ called so-called layered Mn is an orthorhombic and space-group Pm2m layered compound, and Li ₂ MnO ₃ called so-called 213 phase is Li [Li _1/3 Mn _2/3 ]. O ₂ , which is a monoclinic space group C2 / m structure, is also a layered compound in which a Li layer, a [Li _1/3 Mn _2/3 ] layer, and an oxygen layer are stacked.
Thus, the layered structure is not necessarily limited to the R (−3) m structure, but it is preferable from the aspect of electrochemical performance that it can be attributed to the R (−3) m structure.

  In order to obtain x, y, z of the composition formula of the lithium nickel manganese cobalt based composite oxide, each transition metal and Li are analyzed by an inductively coupled plasma emission spectrometer (ICP-AES), and Li / Ni. It is calculated by obtaining the ratio of / Mn / Co.

  From a structural point of view, it is considered that Li related to z is substituted for the same transition metal site. Here, due to Li related to z, the average valence of Ni becomes larger than divalent (trivalent Ni is generated) by the principle of charge neutrality. Since z raises the Ni average valence, it becomes an index of the Ni valence (the ratio of Ni (III)).

となる。この計算結果は、Ｎｉ価数はｚのみで決まるのではなく、ｘ及びｙの関数となっていることを意味している。ｚ＝０かつｙ＝０であれば、ｘの値に関係なくＮｉ価数は２価のままである。ｚが負の値になる場合は、活物質中に含まれるＬｉ量が化学量論量より不足していることを意味し、あまり大きな負の値を有するものは本発明の効果が出ない可能性がある。一方、同じｚ値であっても、Ｎｉリッチ（ｙ値が大きい）及び／又はＣｏリッチ（ｘ値が大きい）な組成ほどＮｉ価数は高くなるということを意味し、電池に用いた場合、レート特性や出力特性が高くなるが、反面、容量低下しやすくなる結果となる。このことから、ｚ値の上限と下限はｘ及びｙの関数として規定するのがより好ましいと言える。 From the above composition formula, when calculating the Ni valence (m) accompanying the change of z, the Co valence is trivalent and the Mn valence is tetravalent,

It becomes. This calculation result means that the Ni valence is not determined only by z but is a function of x and y. If z = 0 and y = 0, the Ni valence remains divalent regardless of the value of x. When z is a negative value, it means that the amount of Li contained in the active material is less than the stoichiometric amount, and those having a very large negative value may not have the effect of the present invention. There is sex. On the other hand, even if the z value is the same, it means that the Ni valence becomes higher as the composition is rich in Ni (large y value) and / or rich in Co (large x value). The rate characteristics and output characteristics are improved, but on the other hand, the capacity tends to decrease. From this, it can be said that it is more preferable to define the upper and lower limits of the z value as a function of x and y.

  Further, the lithium nickel manganese cobalt based composite oxide of the present invention has at least one element selected from the group consisting of Mo, W, Nb, Ta, and Re (hereinafter, these elements are referred to as “additive elements”) It is preferable that it contains. These additive elements are used in the production of the lithium nickel manganese cobalt-based composite oxide of the present invention, using the compound containing these additive elements as an additive as a raw material compound for constituting the lithium nickel manganese cobalt-based composite oxide. It is preferable that it is contained in the lithium nickel manganese cobalt based composite oxide of the present invention by firing after adding to the firing precursor. The reason for this is that these additives exhibit the action of suppressing sintering during the high-temperature firing of lithium nickel manganese cobalt based composite oxides, resulting in high crystallinity, high specific surface area, and high pore volume. This is because a powder having the above can be obtained.

  There is no particular limitation on the type of the additive compound as long as it exhibits such a sintering suppression effect, but an oxide material is usually used.

Exemplary compounds as additives include MoO, MoO ₂ , MoO ₃ , MoOx, Mo ₂ O ₃ , Mo ₂ O ₅ , Li ₂ MoO ₄ , WO, WO ₂ , WO ₃ , WO _x , W ₂ O ₃ , W _2. O ₅ , W ₁₈ O ₄₉ , W ₂₀ O ₅₈ , W ₂₄ O ₇₀ , W ₂₅ O ₇₃ , W ₄₀ O ₁₁₈ , Li ₂ WO ₄ , NbO, NbO ₂ , Nb ₂ O, Nb ₂ O ₅ , Nb ₄ O , Nb ₆ O, LiNbO ₃ , TaO, TaO ₂ , Ta ₂ O ₅ , LiTaO ₃ , ReO ₂ , ReO ₃ , Re ₂ O _{3 and the} like, preferably MoO ₃ , Li ₂ MoO ₄ , WO ₃ , Li ₂ WO ₄ , LiNbO ₃ , Ta ₂ O ₅ , LiTaO ₃ , ReO ₃ are mentioned, more preferably WO ₃ , Li ₂ WO ₄ , ReO ₃ are mentioned, the most preferred. Another example is WO ₃ .
These additives may be used alone or in combination of two or more.

  As the range of the addition amount of these additives, the ratio of the additive element is usually 0.01 mol% or more with respect to the total molar amount of the transition metal elements constituting the main component raw material of the lithium nickel manganese cobalt composite oxide. , Preferably 0.03 mol% or more, more preferably 0.04 mol% or more, particularly preferably 0.05 mol% or more, usually less than 2 mol%, preferably 1.8 mol% or less, more preferably 1. The amount is 5 mol% or less, particularly preferably 1.3 mol% or less. If the additive amount is less than this lower limit, the effect may not be obtained, and if it exceeds the upper limit, battery performance may be deteriorated.

  Further, foreign elements may be introduced into the lithium nickel manganese cobalt based composite oxide of the present invention. The different elements include B, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ru, Rh, Pd, Ag, In , Sn, Sb, Te, Ba, Os, Ir, Pt, Au, Pb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, N , F, P, S, Cl, Br, and I. These foreign elements may be incorporated into the crystal structure of the lithium nickel manganese cobalt-based composite oxide, or may not be incorporated into the crystal structure of the lithium nickel manganese cobalt-based composite oxide. It may be unevenly distributed as a single substance or a compound in the boundary.

<Median diameter and 90% integrated diameter ( _D90 )>
The median diameter of the positive electrode active material for a lithium secondary battery of the present invention is usually 0.5 μm or more, preferably 1 μm or more, more preferably 1.3 μm or more, further preferably 1.6 μm or more, and most preferably 2 μm or more. Usually, it is 10 μm or less, preferably 9 μm or less, more preferably 8 μm or less, further preferably 7 μm or less, and most preferably 6 μm or less. If the median diameter is less than this lower limit, there is a possibility of causing a problem in applicability at the time of forming the positive electrode active material layer, and if it exceeds the upper limit, battery performance may be deteriorated.

The 90% cumulative diameter (D ₉₀ ) of the secondary particles of the positive electrode active material for a lithium secondary battery of the present invention is usually 20 μm or less, preferably 18 μm or less, more preferably 13 μm or less, and most preferably 10 μm or less. Usually, it is 1 μm or more, preferably 2 μm or more, more preferably 3 μm or more, and most preferably 4 μm or more. If the 90% cumulative diameter (D ₉₀ ) exceeds the above upper limit, the battery performance may be deteriorated, and if it is less than the lower limit, there is a possibility of causing a problem in the coating property when forming the positive electrode active material layer.

In the present invention, the median diameter and the 90% integrated diameter (D ₉₀ ) as the average particle diameter are set to a refractive index of 1.24 using a known laser diffraction / scattering particle size distribution measuring device, and the particle diameter standard is determined. Measured as a volume reference. In the present invention, a 0.1 wt% sodium hexametaphosphate aqueous solution was used as a dispersion medium used in the measurement, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

<Bulk density>
The bulk density of the positive electrode active material for a lithium secondary battery of the present invention is usually 0.5 g / cm ³ or more, preferably 0.7 g / cm ³ or more, more preferably 0.9 g / cm ³ or more, most preferably 1. in .0g / cm ³ or more, usually 2.5 g / cm ³ or less, preferably 2.0 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and most preferably is 1.5 g / cm ³ or less . While the bulk density exceeding this upper limit is preferable for improving powder filling properties and electrode density, the specific surface area may become too low, and battery performance may be reduced. If the bulk density is below this lower limit, there is a possibility of adversely affecting the powder filling property and electrode preparation.

In the present invention, the bulk density is determined as the powder packing density (tap density) g / cm ³ when 5 to 10 g of the positive electrode active material is put in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of about 20 mm. .

<Volume resistivity>
The volume resistivity value when the positive electrode active material for a lithium secondary battery of the present invention is compacted at a pressure of 40 MPa is preferably 1 × 10 ³ Ω · cm or more as a lower limit, and 5 × 10 ³ Ω · cm. The above is more preferable, and 1 × 10 ⁴ Ω · cm or more is more preferable. The upper limit is preferably 1 × 10 ⁶ Ω · cm or less, more preferably ⁵ × 10 5 Ω · cm or less, more preferably less than 1 × 10 ⁵ Ω · cm. If this volume resistivity exceeds this upper limit, the load characteristics when used as a battery may be reduced. On the other hand, if the volume resistivity is below this lower limit, the safety of the battery may be reduced.

  In the present invention, the positive electrode active material for the lithium secondary battery has a volume resistivity of four probe / ring electrodes, an electrode interval of 5.0 mm, an electrode radius of 1.0 mm, a sample radius of 12.5 mm, and an applied voltage limiter. Is a volume resistivity measured in a state in which the lithium transition metal-based compound powder is compacted at a pressure of 40 MPa, with 90V being set. The volume resistivity can be measured, for example, by using a powder resistance measuring device (for example, Lorester GP powder resistance measuring system manufactured by Dia Instruments Co., Ltd.) with a powder probe unit on a powder under a predetermined pressure. It can be carried out.

<Average primary particle size>
The average primary particle diameter (average primary particle diameter) of the positive electrode active material for a lithium secondary battery of the present invention is not particularly limited, but the lower limit is preferably 0.1 μm or more, more preferably 0.15 μm or more. More preferably, it is 0.2 μm or more, most preferably 0.25 μm or more, and the upper limit is preferably 3 μm or less, more preferably 2.5 μm or less, further preferably 2 μm or less, and most preferably 1.5 μm or less. is there. If the average primary particle size exceeds the above upper limit, it may adversely affect the powder filling property or the specific surface area will decrease, which may increase the possibility that the battery performance such as rate characteristics and output characteristics will decrease. If the value falls below the lower limit, there is a possibility that problems such as inferior reversibility of charge and discharge may occur due to undeveloped crystals.

  In addition, the average primary particle diameter in this invention is an average diameter observed with the scanning electron microscope (SEM), and the average particle diameter of about 10-30 primary particles using a SEM image of 30,000 times. It can be obtained as a value.

<Reason why the positive electrode active material for a lithium secondary battery of the present invention provides the above-mentioned effect>
The reason why the positive electrode active material for a lithium secondary battery of the present invention brings about improvement in the rate characteristics and output characteristics of the battery is considered as follows.
On the surface of the Li-rich layered lithium nickel manganese cobalt composite oxide powder heat-treated in an atmosphere containing carbon dioxide, a carbon dioxide film formed by reacting with the adsorbed carbon dioxide or carbon dioxide is formed. Has been. When a battery is manufactured using such a positive electrode active material, LiPO ₂ F ₂ (lithium hexafluorophosphate) is generated by reacting with the coating layer and, for example, LiPF ₆ which is a supporting salt contained in the electrolytic solution. Therefore, it is considered that this has acted on the positive electrode surface and the negative electrode surface, thereby improving the rate characteristics and output characteristics.

[Method for producing positive electrode active material for lithium secondary battery]
The positive electrode active material for a lithium secondary battery of the present invention is a method of heat-treating a Li-excess layered lithium nickel manganese cobalt based composite oxide in a carbon dioxide-containing atmosphere, specifically, in an atmosphere gas containing carbon dioxide. The Li-rich layered lithium nickel manganese cobalt-based composite oxide (hereinafter referred to as “raw material compound” as appropriate) as a raw material can be produced by holding it for a certain period of time in a heating environment.

  As a raw material compound, a powder of Li-excess layered lithium nickel manganese cobalt based composite oxide that has not been heat-treated in a carbon dioxide-containing atmosphere can be used. Since the physical properties such as composition of constituent elements and powder properties do not change greatly before and after the treatment, the Li-excess layered lithium nickel manganese cobalt-based composite oxide used as a raw material in accordance with the physical properties of the target positive electrode active material The physical properties may be selected as appropriate.

  When the treatment with carbon dioxide gas is performed, it is preferably performed in a dry atmosphere in order to prevent adsorption of water molecules to the raw material compound. As the environment of the dry atmosphere, the treatment is performed in an environment where the dew point is usually 0 ° C. or lower, preferably −30 ° C. or lower, more preferably −40 ° C. or lower.

  Further, it is preferable to perform processing by setting parameters such as processing temperature, carbon dioxide concentration in the atmosphere, and processing time within predetermined ranges. These parameters can be set independently, and appropriate conditions may be arbitrarily determined according to the type of the raw material compound.

  The treatment temperature is usually 200 ° C. or higher, preferably 250 ° C. or higher, more preferably 300 ° C. or higher, particularly preferably 350 ° C. or higher, and usually 800 ° C. or lower, preferably 600 ° C. or lower, more preferably 500 ° C. or lower, especially Preferably it is 450 degrees C or less. If the treatment temperature is lower than the above range, the treatment takes too much time, which is not preferable. On the other hand, if the treatment temperature exceeds the above range, the carbonation progresses remarkably, and it is difficult to control within the range of the c / S value defined in the present invention.

  The carbon dioxide concentration of the atmospheric gas is usually 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and usually 100% by volume or less, preferably 80% by volume or less, more preferably 60% by volume or less, most preferably 30% by volume or less. When carbon dioxide and other mixed gases are used as the atmospheric gas, the type of other gases mixed with carbon dioxide is not limited as long as it does not adversely affect the raw material compound, but Li-excess layered lithium nickel Oxygen gas and air gas are preferable in that the manganese cobalt-based composite oxide phase is easily allowed to exist stably. Moreover, the other gas mixed with a carbon dioxide gas may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The treatment time is usually 0.5 hours or longer, preferably 1 hour or longer, more preferably 2 hours or longer, and usually 48 hours or shorter, preferably 36 hours or shorter, more preferably 24 hours or shorter. In general, the processing time can be shortened as the processing temperature and / or carbon dioxide concentration is high, and conversely, the processing time needs to be increased as the processing temperature and / or carbon dioxide concentration is low.

  As described above, after the treatment, the carbonic acid or bicarbonate ion concentration contained in the obtained Li-excess layered lithium nickel manganese cobalt based composite oxide of the present invention is within the specified range of the above c / S value. This can be confirmed by ion chromatography.

[Positive electrode for lithium secondary battery]
The positive electrode for a lithium secondary battery of the present invention is obtained by forming a positive electrode active material layer containing a positive electrode active material for a lithium secondary battery of the present invention and a binder on a current collector.

  The positive electrode active material layer is usually formed by mixing a positive electrode material, a binder, and a conductive material and a thickener, which are used if necessary, in a dry form into a sheet shape, and then pressing the positive electrode current collector on the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a slurry, which is applied to the positive electrode current collector and dried.

  As the material for the positive electrode current collector, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper are usually used. Of these, metal materials are preferable, and aluminum is particularly preferable. As for the shape, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, a foam metal, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder Etc. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape.

  When a thin film is used as the positive electrode current collector, its thickness is arbitrary, but it is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 100 mm or less, preferably 1 mm or less, more preferably 50 μm or less. The range of is preferable. If it is thinner than the above range, the strength required for the current collector may be insufficient. On the other hand, if it is thicker than the above range, the handleability may be impaired.

  The binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of a coating method, any material that is stable with respect to the liquid medium used during electrode production may be used. Specific examples include polyethylene, Resin polymers such as polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose, SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), fluorine rubber, isoprene rubber, butadiene rubber, ethylene・ Rubber polymers such as propylene rubber, styrene / butadiene / styrene block copolymers and hydrogenated products thereof, EPDM (ethylene / propylene / diene terpolymers), styrene / ethylene / butadiene / ethylene copolymers, Styrene / isoprene styrene bromide Copolymer and its hydrogenated thermoplastic elastomeric polymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer, etc. Fluorine polymers such as soft resinous polymers, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymers, ion conductivity of alkali metal ions (especially lithium ions) And a polymer composition having the same. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

  The ratio of the binder in the positive electrode active material layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less. More preferably, it is 40% by weight or less, most preferably 10% by weight or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained and the positive electrode has insufficient mechanical strength, which may deteriorate battery performance such as cycle characteristics. Battery capacity and conductivity may be reduced.

  The positive electrode active material layer usually contains a conductive material in order to increase conductivity. There are no particular restrictions on the type, but specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. And carbon materials. In addition, these substances may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios. The proportion of the conductive material in the positive electrode active material layer is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 30%. % By weight or less, more preferably 20% by weight or less. If the proportion of the conductive material is too low, the conductivity may be insufficient, and conversely if it is too high, the battery capacity may be reduced.

  As a liquid medium for forming a slurry, it is possible to dissolve or disperse a lithium transition metal compound powder as a positive electrode material, a binder, and a conductive material and a thickener used as necessary. If it is a solvent, there is no restriction | limiting in particular in the kind, You may use either an aqueous solvent or an organic solvent. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N , N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran (THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. be able to. In particular, when an aqueous solvent is used, a dispersant is added together with the thickener, and a slurry such as SBR is slurried. In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  The content ratio of the positive electrode active material for a lithium secondary battery of the present invention as the positive electrode material in the positive electrode active material layer is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, Usually, it is 99.9% by weight or less, preferably 99% by weight or less. If the proportion of the positive electrode active material material for lithium secondary batteries of the present invention in the positive electrode active material layer is too large, the strength of the positive electrode tends to be insufficient, and if it is too small, the capacity may be insufficient.

  The thickness of the positive electrode active material layer is usually about 10 to 200 μm.

The positive electrode active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.
Thus, the positive electrode for a lithium secondary battery of the present invention is prepared.

[Lithium secondary battery]
The lithium secondary battery of the present invention includes the above-described positive electrode for a lithium secondary battery of the present invention capable of occluding and releasing lithium, a negative electrode capable of occluding and releasing lithium, and a non-aqueous electrolyte using a lithium salt as an electrolytic salt, Is provided. Further, a separator for holding a nonaqueous electrolyte may be provided between the positive electrode and the negative electrode. In order to effectively prevent a short circuit due to contact between the positive electrode and the negative electrode, it is desirable to interpose a separator in this way.

<Negative electrode>
The negative electrode is usually configured by forming a negative electrode active material layer on a negative electrode current collector, similarly to the positive electrode.
As a material of the negative electrode current collector, a metal material such as copper, nickel, stainless steel, nickel-plated steel, or a carbon material such as carbon cloth or carbon paper is used. Among these, in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder, etc. are mentioned. Among these, metal thin films are preferable because they are currently used in industrialized products. In addition, you may form a thin film suitably in mesh shape. When a metal thin film is used as the negative electrode current collector, the preferred thickness range is the same as the range described above for the positive electrode current collector.

  The negative electrode active material layer includes a negative electrode active material. The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions, but it can usually occlude and release lithium from the viewpoint of high safety. A carbon material is used.

  Although there is no restriction | limiting in particular as a carbon material, Graphite (graphite), such as artificial graphite and natural graphite, and the thermal decomposition thing of organic substance on various thermal decomposition conditions are mentioned. Examples of pyrolysis products of organic matter include coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke, phenol resin, crystalline cellulose, etc. And carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fibers, and the like. Among them, graphite is preferable, and particularly preferable is artificial graphite, purified natural graphite, or graphite material containing pitch in these graphites, which is manufactured by subjecting easy-graphite pitch obtained from various raw materials to high-temperature heat treatment. Therefore, those subjected to various surface treatments are mainly used. One of these carbon materials may be used alone, or two or more thereof may be used in combination.

When a graphite material is used as the negative electrode active material, the d value (interlayer distance: d ₀₀₂ ) of the lattice plane (002 plane) determined by X-ray diffraction by the Gakushin method is usually 0.335 nm or more, and usually 0.34 nm. In the following, it is preferable that the thickness is 0.337 nm or less.

  Further, the ash content of the graphite material is usually 1% by weight or less, particularly 0.5% by weight or less, and particularly preferably 0.1% by weight or less, based on the weight of the graphite material.

  Further, the crystallite size (Lc) of the graphite material determined by X-ray diffraction by the Gakushin method is usually 30 nm or more, preferably 50 nm or more, and particularly preferably 100 nm or more.

  The median diameter of the graphite material determined by the laser diffraction / scattering method is usually 1 μm or more, especially 3 μm or more, more preferably 5 μm or more, especially 7 μm or more, and usually 100 μm or less, especially 50 μm or less, more preferably 40 μm or less, especially 40 μm or less. It is preferable that it is 30 micrometers or less.

Moreover, the BET specific surface area of the graphite material is usually 0.5 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1.0 m ² / g or more, and further preferably 1.5 m ² / g. or more, and usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more preferably 15.0 m ² / g or less, still more preferably 10.0 m ² / g or less.

Further, when performing Raman spectroscopy using argon laser light for graphite material, and strength _{I A} of the peak _{P A} is detected in the range of 1580~1620cm ^-1, 135
Intensity ratio _I A / _{I B} of the intensity _{I B} of a peak _{P B} detected in the range of 0～1370Cm ^-1 is intended preferably 0 or more and 0.5 or less. Further, the half width of the peak _{P A} is preferably 26cm ^-1 or less, 25 cm ^-1 or less is more preferable.

In addition to the above-mentioned various carbon materials, it can also be used as a negative electrode active material of other materials capable of inserting and extracting lithium. Specific examples of negative electrode active materials other than carbon materials include metal oxides such as tin oxide and silicon oxide, nitrides such as Li _2.6 Co _0.4 N, and lithium alloys such as lithium alone and lithium aluminum alloys. Can be mentioned. One of these materials other than the carbon material may be used alone, or two or more thereof may be used in combination. Moreover, you may use in combination with the above-mentioned carbon material.

As in the case of the positive electrode active material layer, the negative electrode active material layer is usually prepared by slurrying the above-described negative electrode active material, a binder, and optionally a conductive material and a thickener in a liquid medium. It can manufacture by apply | coating to a negative electrode electrical power collector, and drying. As the liquid medium, the binder, the thickener, the conductive material, and the like that form the slurry, the same materials as those described above for the positive electrode active material layer can be used.

<Nonaqueous electrolyte>
As the non-aqueous electrolyte, for example, known organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes, and the like can be used. Of these, organic electrolytes are preferable. The organic electrolytic solution is configured by dissolving a solute (electrolyte) in an organic solvent.

  Here, the type of the organic solvent is not particularly limited. For example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides. A phosphoric acid ester compound or the like can be used. Typical examples include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2- Pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile Benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, etc. Et compounds, hydrogen atoms may be partially substituted with a halogen atom. Moreover, these single or 2 or more types of mixed solvents can be used.

  The organic solvent described above preferably contains a high dielectric constant solvent in order to dissociate the electrolytic salt. Here, the high dielectric constant solvent means a compound having a relative dielectric constant of 20 or more at 25 ° C. Among the high dielectric constant solvents, it is preferable that ethylene carbonate, propylene carbonate, and compounds in which hydrogen atoms thereof are substituted with other elements such as halogen or alkyl groups are contained in the electrolytic solution. The proportion of the high dielectric constant solvent in the electrolyte is preferably 20% by weight or more, more preferably 25% by weight or more, and most preferably 30% by weight or more. If the content of the high dielectric constant solvent is less than the above range, desired battery characteristics may not be obtained.

In addition, in the organic electrolyte, a gas such as CO ₂ , N ₂ O, CO, and SO ₂ , vinylene carbonate, polysulfide S _x ^{2−, and the} like that enables efficient charge and discharge of lithium ions on the negative electrode surface You may add the additive which forms a film in arbitrary ratios. Among these additives, vinylene carbonate is particularly preferable.

  Furthermore, an additive that exhibits an effect of improving cycle life and output characteristics, such as lithium difluorophosphate, may be added to the organic electrolyte at an arbitrary ratio.

The type of the electrolytic salt is not particularly limited, and any conventionally known solute can be used. Specific examples include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiBOB, LiCl, LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) _{2 and the} like. Any one of these electrolytic salts may be used alone, or two or more thereof may be used in any combination and ratio.

  The lithium salt of the electrolytic salt is usually contained in the electrolytic solution so as to have a concentration of 0.5 mol / L to 1.5 mol / L. Even if the lithium salt concentration in the electrolytic solution is less than 0.5 mol / L or more than 1.5 mol / L, the electric conductivity may be lowered, and the battery characteristics may be adversely affected. The lower limit of this concentration is preferably 0.75 mol / L or more and the upper limit is 1.25 mol / L or less.

Even when a polymer solid electrolyte is used, the type thereof is not particularly limited, and any known crystalline / amorphous inorganic substance can be used as the solid electrolyte. Examples of the crystalline inorganic solid electrolyte include LiI, Li ₃ N, Li _{1 + x} J _x Ti _2-x (PO ₄ ) ₃ (J = Al, Sc, Y, La), Li _0.5-3x RE _{0. .5 + x} TiO ₃ (RE = La, Pr, Nd, Sm) and the like. Examples of the amorphous inorganic solid electrolyte include oxide glasses such as 4.9LiI-34.1Li ₂ O-61B ₂ O ₅ and 33.3Li ₂ O-66.7SiO ₂ . Any one of these may be used alone, or two or more may be used in any combination and ratio.

<Separator>
When the above-described organic electrolyte is used as the electrolyte, a separator is interposed between the positive electrode and the negative electrode in order to prevent a short circuit between the electrodes. The material and shape of the separator are not particularly limited, but those that are stable with respect to the organic electrolyte used, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable. Preferable examples include microporous films, sheets, nonwoven fabrics and the like made of various polymer materials. Specific examples of the polymer material include polyolefin polymers such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene. In particular, from the viewpoint of chemical and electrochemical stability, which is an important factor for separators, polyolefin polymers are preferable. From the viewpoint of self-occluding temperature, which is one of the purposes of use of separators in batteries, polyethylene is preferred. Is particularly desirable.

  When using a separator made of polyethylene, it is preferable to use ultra-high molecular weight polyethylene from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. This is because if the molecular weight is too large, the fluidity becomes too low, and the pores of the separator may not close when heated.

<Battery shape>
The lithium secondary battery of the present invention is produced by assembling the above-described positive electrode for a lithium secondary battery of the present invention, a negative electrode, an electrolyte, and a separator used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various commonly employed shapes according to the application. Examples of commonly used shapes include a cylinder type with a sheet electrode and separator in a spiral shape, a cylinder type with an inside-out structure combining a pellet electrode and a separator, and a coin type with stacked pellet electrodes and a separator. Can be mentioned. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

  The general embodiment of the lithium secondary battery of the present invention has been described above. However, the lithium secondary battery of the present invention is not limited to the above-described embodiment, and various modifications are possible as long as the gist thereof is not exceeded. Can be implemented.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

[Measurement method of physical properties]
The physical properties and the like of lithium transition metal-based compound powders produced in each Example and Comparative Example described below were measured as follows.

<Composition (Li / Ni / Mn / Co)>
It was determined by ICP-AES analysis.

<Quantification of additive element (W)>
It was determined by ICP-AES analysis.

<Median diameter of secondary particles and 90% integrated diameter ( _D90 )>
Using a known laser diffraction / scattering particle size distribution measuring device, the refractive index was set to 1.24, and the particle diameter standard was measured as the volume standard. As a dispersion medium, a 0.1 wt% sodium hexametaphosphate aqueous solution was used, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

<Bulk density>
4 to 10 g of the sample powder was put into a 10 ml glass graduated cylinder, and the powder packing density when tapped 200 times with a stroke of about 20 mm was obtained.

<Specific surface area>
As described above, a BET one-point method measurement was performed by a continuous flow method using an AMS8000 type fully automatic powder specific surface area measuring device manufactured by Okura Riken, using nitrogen as an adsorption gas and helium as a carrier gas.

<Volume resistivity>
Using a powder resistivity measuring device (Dia Instruments: Lorester GP powder low-efficiency measurement system PD-41), the sample weight is set to 2 to 3 g, and a powder probe unit (four probe / ring electrodes, electrode spacing 5) The volume resistivity [Ω · cm] of the powder under various pressures was measured at an applied voltage limiter of 90 V using an electrode radius of 1.0 mm, an electrode radius of 1.0 mm, and a sample radius of 12.5 mm. The rate values were compared.

<Median diameter of pulverized particles in slurry>
Using a known laser diffraction / scattering particle size distribution measuring device, the refractive index was set to 1.24, and the particle diameter standard was measured as the volume standard. As a dispersion medium, a 0.1 wt% sodium hexametaphosphate aqueous solution was used, and measurement was performed after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz).

[Production of cathode active material for lithium secondary battery (Examples and Comparative Examples)]
Example 1
Li ₂ CO ₃ , Ni (OH) ₂ , Mn ₃ O ₄ , CoOOH, WO ₃ are mixed with Li: Ni: Mn: Co: W = 1.12: 0.45: 0.45: 0.10: 0. After weighing and mixing so as to have a molar ratio of 01, pure water was added thereto to prepare a slurry. While stirring this slurry, the solid content in the slurry was pulverized to a median diameter of 0.23 μm using a circulating medium agitation type wet pulverizer.

  Next, this slurry (solid content 16.5% by weight, viscosity 1650 cp) was spray-dried using a four-fluid nozzle type spray dryer (manufactured by Fujisaki Electric Co., Ltd .: MDP-50 type). At this time, air was used as the dry gas, the dry gas introduction amount G was 1600 L / min, and the slurry introduction amount S was 780 mL / min (gas-liquid ratio G / S = 2051). The drying inlet temperature was 200 ° C. About 370 g of particulate powder obtained by spray drying with a spray dryer is charged into an alumina square bowl and fired at 1000 ° C. for 2 hours in an air atmosphere (temperature increase rate: about 1.7 ° C./min., Temperature decrease rate) : About 3.3 ° C./min.), And then classified using a Puffer footer (manufactured by TSUKASA KOGYO Co., Ltd.) with a 45 μm mesh to obtain a Li-excess layered lithium nickel manganese cobalt based composite oxide powder.

The Li excess layered lithium nickel manganese cobalt based composite oxide powder, lithium nickel manganese cobalt composite oxide having a composition having a layered structure of _{Li (Li 0.053 Ni 0.425 Mn 0.427} Co 0.095) O 2 (In the composition formulas (I) and (II), x = 0.100, y = −0.002, z = 0.111), and the total molar amount of (Ni, Mn, Co) The content molar ratio of W was 1.0 mol%.

Next, this Li-excess layered lithium nickel manganese cobalt based composite oxide powder is subjected to an atmosphere of 5% by volume-CO ₂ /95% by volume—O ₂ mixed gas (dew point = −58 ° C.) under a condition of 400 ° C. The positive electrode active material was obtained by heat-treating by holding for 2 hours.
To 30 mg of the obtained positive electrode active material, 5 ml of demineralized water immediately after preparation was added, and ultrasonic dispersion extraction was performed for 30 minutes. The extracted aqueous phase was analyzed with an ion chromatograph to determine the carbonate ion concentration c. Dionex DX-120 was used as the ion chromatograph, Dionex IonPac ICE-AS1 was used as the column, and water was used as the eluent. As a result of the measurement, the carbonate ion concentration c was 0.252% by weight. The BET specific surface area was 2.9 m ² / g. From these, the c / S value was calculated to be 0.087 and was within the specified range of the present invention.
As other physical properties of the positive electrode active material, the volume resistivity is 7.0 × 10 ⁴ Ω · cm, the median diameter is 2.7 μm, the 90% cumulative diameter (D ₉₀ ) is 5.1 μm, and the bulk density is 0.00. It was 9 g / cm ³ .

(Example 2)
A positive electrode active material was prepared and analyzed in the same manner as in Example 1 except that the heat treatment time was 6 hours.
The positive electrode active material had a carbonate ion concentration c of 0.307% by weight. The BET specific surface area was 3.0 m ² / g. From these, the c / S value was calculated as 0.102 and was within the specified range of the present invention.
As other physical properties of the positive electrode active material, the volume resistivity is 7.7 × 10 ⁴ Ω · cm, the median diameter is 2.1 μm, the 90% cumulative diameter (D ₉₀ ) is 3.9 μm, and the bulk density is 1. It was 0 g / cm ³ .

(Example 3)
A positive electrode active material was prepared and analyzed in the same manner as in Example 1 except that the heat treatment time was 12 hours.
The positive electrode active material had a carbonate ion concentration c of 0.204% by weight. The BET specific surface area was 3.0 m ² / g. From these, the c / S value was calculated to be 0.068 and was within the specified range of the present invention.
Other physical properties of this positive electrode active material include a volume resistivity of 6.4 × 10 ⁴ Ω · cm, a median diameter of 2.7 μm, a 90% cumulative diameter (D ₉₀ ) of 4.9 μm, and a bulk density of 0.8. It was 9 g / cm ³ .

Example 4
A positive electrode active material was prepared and analyzed in the same manner as in Example 1 except that the heat treatment time was 24 hours. The positive electrode active material had a carbonate ion concentration c of 0.186% by weight. The BET specific surface area was 2.9 m ² / g. From these, the c / S value was calculated to be 0.064 and was within the specified range of the present invention.
Other physical properties of this positive electrode active material include a volume resistivity of 6.3 × 10 ⁴ Ω · cm, a median diameter of 2.2 μm, a 90% cumulative diameter (D ₉₀ ) of 4.2 μm, and a bulk density of 0.2. It was 9 g / cm ³ .

(Comparative Example 1)
A Li-excess layered lithium nickel manganese cobalt based composite oxide produced in the same manner as in Example 1 was used as a positive electrode active material without being subjected to heat treatment in a carbon dioxide-containing atmosphere. The positive electrode active material had a carbonate ion concentration c of 0.146% by weight. The BET specific surface area was 2.8 m ² / g. From these, the c / S value was calculated to be 0.052, which was outside the specified range of the present invention.
As other physical properties of the positive electrode active material, the volume resistivity is 6.3 × 10 ⁴ Ω · cm, the median diameter is 2.7 μm, the 90% cumulative diameter (D ₉₀ ) is 4.9 μm, and the bulk density is 1. It was 0 g / cm ³ .

  The physical property values of the positive electrode active materials produced in Examples 1 to 4 and Comparative Example 1 are summarized in Table 1.

By the way, in the above Examples 1 to 4, it was observed that the c-value tends to decrease when the heat treatment time of the lithium nickel manganese cobalt based composite oxide is 6 hours at maximum, and the heat treatment is longer than that. For example, it is presumed that the reaction shown by the following formula proceeds on the surface of the active material, and a transitional state such as LiOH.CO ₂ occurs, and a temporary maximum value of c value appears.

[Production and evaluation of battery]
Using the positive electrode active materials produced in Examples 1 to 4 and Comparative Example 1 described above, lithium secondary batteries were produced and evaluated by the following method. The results are shown in Table 2.

(1) Rate test:
75% by weight of each of the positive electrode active materials produced in Examples 1 to 4 and Comparative Example 1, 20% by weight of acetylene black, and 5% by weight of polytetrafluoroethylene powder were thoroughly mixed in a mortar, The thin sheet was punched out using a 9 mmφ punch. At this time, the total weight was adjusted to about 8 mg. This was pressure-bonded to an aluminum expanded metal to obtain a 9 mmφ positive electrode.

This 9 mmφ positive electrode is used as a test electrode, a lithium metal plate is used as a counter electrode, and LiPF ₆ is added to a solvent of EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 3: 3: 4 (volume ratio). Using an electrolytic solution dissolved at 1 mol / L, a coin-type cell was assembled using a porous polyethylene film having a thickness of 25 μm as a separator.

The obtained coin-type cell was subjected to a constant current constant voltage charge of 0.2 mA / cm ² at an upper limit voltage of 4.2 V and a constant current discharge test of 0.2 mA / cm ² at a lower limit voltage of 3.0 V for the first cycle. In the second cycle, a constant current constant voltage charge of 0.5 mA / cm ² at an upper limit voltage of 4.2 V and a constant current discharge test of 0.2 mA / cm ² at a lower limit voltage of 3.0 V were conducted. the cycle, constant current charge of 0.5 mA / cm ^2, was constant current discharge test of 11 mA / cm ^2.

As an acceptance criterion for the examples, the initial discharge capacity in the first cycle was set to 146 mAh / g or more, and the high rate discharge capacity at 11 mA / cm ² in the third cycle was set to 110 mAh / g or more.

(2) Low temperature load characteristic test:
75% by weight of each of the positive electrode active materials produced in Examples 1 to 4 and Comparative Example 1, 20% by weight of acetylene black, and 5% by weight of polytetrafluoroethylene powder were thoroughly mixed in a mortar, A thin sheet was punched out using a 12 mmφ punch. At this time, the total weight was adjusted to about 18 mg. This was pressure-bonded to an aluminum expanded metal to obtain a 12 mmφ positive electrode.

  Using the results of charge and discharge in the first cycle in the rate test of (1), the initial charge capacity per unit weight of the positive electrode active material is Qs (C) [mAh / g], and the initial discharge capacity is Qs (D) [mAh / g].

Graphite powder having an average particle size of 8 to 10 μm (d ₀₀₂ = 3.35 Å) was used as the negative electrode active material, and polyvinylidene fluoride was used as the binder, and these were weighed at a weight ratio of 92.5: 7.5. Were mixed in an N-methylpyrrolidone solution to obtain a negative electrode mixture slurry. This slurry was applied to one side of a 20 μm thick copper foil, dried to evaporate the solvent, punched to 12 mmφ, and pressed at 0.5 ton / cm ² (49 MPa) to form a negative electrode. At this time, the amount of the negative electrode active material on the electrode was adjusted to be about 5 to 12 mg.

A test in which a negative electrode is used as a test electrode, a battery cell is assembled using lithium metal as a counter electrode, and lithium ions are occluded in the negative electrode by a constant current-constant voltage method (cut current 0.05 mA) of 0.2 mA / cm ² -3 mV. The initial occlusion capacity per unit weight of the negative electrode active material at a lower limit of 0 V was defined as Qf [mAh / g].

The positive electrode and the negative electrode were combined, a test battery was assembled using a coin cell, and the battery performance was evaluated. That is, the above-described positive electrode prepared is placed on the positive electrode can of the coin cell, a porous polyethylene film having a thickness of 25 μm is placed thereon as a separator, pressed with a polypropylene gasket, and then EC ( An electrolytic solution in which LiPF ₆ was dissolved at a rate of 1 mol / L in a solvent of ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 3: 3: 4 (volume ratio) was added to the can. After fully infiltrating the separator, the above-described negative electrode B was placed, a negative electrode can was placed and sealed, and a coin-type lithium secondary battery was produced. At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material was set so as to satisfy the following expression.
Positive electrode active material weight [g] / Negative electrode active material weight [g]
= (Qf [mAh / g] /1.2) Qs (C) [mAh / g]

In order to measure the low temperature load characteristics of the battery thus obtained, the 1 hour rate current value of the battery, that is, 1C, was set as shown in the following equation, and the following tests were performed.
1C [mA] = Qs (D) × positive electrode active material weight [g] / hour [h]

First, a constant current 0.2C charge / discharge cycle and a constant current 1C charge / discharge cycle were performed at room temperature. The upper limit of charging was 4.1 V, and the lower limit voltage was 3.0 V. Next, when a coin cell adjusted to a charging depth of 40% is held in a low temperature atmosphere of −30 ° C. for 1 hour or longer by 1/3 C constant current charging / discharging and then discharged for 10 seconds at a constant current of 0.5 C [mA]. Assuming that the voltage after 10 seconds is V [mV] and the voltage before discharge is V ₀ [mV], the resistance value R [Ω] is calculated from the following equation as ΔV = V−V ₀ .
R [Ω] = ΔV [mV] /0.5C [mA]

  The smaller the low temperature resistance value, the better the low temperature load characteristic. In addition, it set that the low temperature resistance value was 350 ohms or less as an acceptance criterion of an Example.

  Table 2 shows that according to the lithium secondary battery positive electrode active material of the present invention, a lithium secondary battery having a high capacity and excellent load characteristics can be realized.

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, automobile power sources, and the like.

Claims (8)

It consists of a Li-excess layered lithium nickel manganese cobalt based composite oxide heat-treated in an atmosphere containing carbon dioxide gas, the carbonate ion concentration measured by ion chromatography is c [wt%], and the specific surface area measured by the BET method is S [m ² / g] and when, c / S value of 0.055 or more, a positive electrode active material for a 0.30 der ruri lithium secondary battery,
Containing W,
The BET specific surface area is 1.5 m ² / g or more and 5 m ² / g or less,
The carbonate ion concentration measured by ion chromatography is 0.15 wt% or more and 0.50 wt% or less,
A positive electrode active material for a lithium secondary battery, wherein the composition is represented by the following formula (I), and M in the formula (I) is represented by the following formula (II).
LiMO ₂ (I)
[However, in the above formula (I),
M is an element composed of Li, Ni, and Mn, or Li, Ni, Mn, and Co.
Mn / Ni molar ratio is 0.8 or more and 5 or less
Co / (Mn + Ni + Co) molar ratio is 0 or more, 0.35 or less,
Li molar ratio in M is 0.001 or more and 0.2 or less
It is. ]
M = Liz _{/ (2 + z)} {(Ni _{(1 + y) / 2} Mn _{(1-y) / 2} ) _1-x Co _x } _{2 / (2 + z)} (II)
[However, in the above formula (II),
0 ≦ x ≦ 0.1
−0.1 ≦ y ≦ 0.1
(1-x) (0.05-0.98y) ≤z≤ (1-x) (0.20-0.88y)
It is. ] 2. The positive electrode active material for a lithium secondary battery according to claim 1, comprising at least one element selected from the group consisting of Mo 2 , Nb , Ta, and Re. The median diameter measured after 5 minutes of ultrasonic dispersion (output 30 W, frequency 22.5 kHz) using a laser diffraction / scattering particle size distribution analyzer with a refractive index of 1.24 and a particle size standard as a volume standard. There 0.5μm or more, the positive electrode active material for lithium secondary battery according to claim 1 or 2, characterized in that at 10μm or less. Bulk density 0.5 g / cm ³ or more, 2.5 g / cm ³ positive electrode active material for lithium secondary battery according to any one of claims 1 to 3, wherein the less. Volume resistivity when compacted at a pressure of 40MPa is 1 × 10 ³ Ω · cm or more, lithium according to any one of claims 1 to 4, characterized in that 1 × 10 ⁶ Ω · cm or less Positive electrode active material for secondary batteries. In an atmosphere gas having a carbon dioxide concentration of 1% by volume or more and 100% by volume or less, the Li-excess layered lithium nickel manganese cobalt based composite oxide is added for 0.5 hours or more and 48 hours at a temperature condition of 200 ° C. or more and 800 ° C. or less. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5 , wherein the heat treatment is performed after the heat treatment. Lithium secondary characterized by having a positive electrode active material layer containing at least on a current collector and a lithium secondary battery positive electrode active material and a binder according to any one of claims 1 to 5 Battery positive electrode. A lithium secondary battery comprising a negative electrode capable of inserting and extracting lithium, a non-aqueous electrolyte containing a lithium salt, and a positive electrode capable of inserting and extracting lithium, wherein the lithium secondary battery according to claim 7 is used as the positive electrode. A lithium secondary battery using a positive electrode for a battery.