JP2008226643A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having a particularly excellent electric characteristic and high capacity. <P>SOLUTION: This nonaqueous electrolyte secondary battery is provided with: a positive electrode containing a positive electrode active material capable of releasing and storing lithium ions by charge/discharge; a negative electrode containing carbon capable of releasing and storing lithium ions by charge/discharge, and having irreversible capacity of 39-61 mAh/g and theoretical capacity not smaller than 350 mAh/g; and a nonaqueous electrolyte. The nonaqueous electrolyte secondary battery is characterized in that, when it is assumed that the irreversible capacity of the positive electrode and the irreversible capacity of a part of a negative electrode mix layer facing a positive electrode mix layer are A and B, respectively, 0.73≤A/B≤1.14 is satisfied; and the positive electrode active material is a lithium nickel composite oxide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and particularly relates to a combination of a positive electrode active material and a negative electrode active material.

  In recent years, electronic devices have become portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Among non-aqueous electrolyte secondary batteries having high voltage and high energy density, expectations for lithium secondary batteries are particularly high. In addition, recent electronic devices are being further enhanced in functionality and power, and there is a demand for further increase in energy density of non-aqueous electrolyte secondary batteries.

Conventionally, lithium composite cobalt oxide (hereinafter abbreviated as LiCoO ₂ ) is often used as the positive electrode active material of the non-aqueous electrolyte secondary battery. In addition, nickel-containing lithium composite oxide and spinel-type lithium are also used. Complex manganese oxide (LiMn ₂ O ₄ ), or a solid solution or a mixture of these different elements is used.

  On the other hand, various carbon materials are used for the negative electrode. In particular, the reason why graphite is frequently used is that the capacity per weight is large, the carbon density of the negative electrode mixture layer is increased, and the difference between the initial initial charge capacity and the initial discharge capacity (irreversible capacity) of the negative electrode is reduced. Is mentioned.

LiCoO ₂ as a positive electrode active material conventionally used has a small initial irreversible capacity, and its initial charge / discharge efficiency is almost 100%. For such a positive electrode, since the reversible capacity of the negative electrode becomes the battery capacity as it is, a high capacity battery can be designed by combining a negative electrode with a small irreversible capacity.

  As a negative electrode active material having a small irreversible capacity, research and development have been conventionally conducted, and as a negative electrode active material having good electrical characteristics, a method using a carbon material made of, for example, spherical natural graphite and graphitized carbon fiber has been proposed (for example, , See Patent Document 1).

Further, the nickel-containing lithium composite oxide that can be expected to have a higher capacity than LiCoO ₂ as the positive electrode active material has a large charge / discharge capacity difference between the first charge (lithium release reaction) and the discharge (lithium insertion reaction). It is known.
JP 2004-95529 A

  When improving a negative electrode active material in order to improve electrical characteristics, for example, discharge temperature characteristics and cycle characteristics, for example, the specific surface area of the negative electrode active material is generally increased to increase the reaction active area. As a result, although the electrical characteristics are improved, the reaction area with the electrolytic solution is increased, so that side reactions are also increased, so that the irreversible capacity of the negative electrode is increased.

In order to ensure high capacity and excellent electrical characteristics, when using a positive electrode with a charge / discharge efficiency close to 100%, such as LiCoO ₂ that has been used in the past, when combined with the above negative electrode, for example, Since the capacity is governed by the irreversible capacity of the negative electrode, it is difficult to achieve both high capacity and excellent battery characteristics.

When a positive electrode such as a nickel-containing lithium composite oxide with a large irreversible capacity of the positive electrode and a negative electrode with a small irreversible capacity are combined, that is, when the irreversible capacity of the positive electrode is larger than the irreversible capacity of the negative electrode, the capacity of the battery is the irreversible capacity of the positive electrode Will be dominated by. In addition, lithium ions in an amount equivalent to the irreversible capacity of the positive electrode remain in the negative electrode even after the end of discharge, and the lithium ion remaining in the negative electrode is charged / discharged in spite of being originally dischargeable. I can't get involved. In a state where lithium ions that cannot participate in charge / discharge are held in the negative electrode carbon, the reversible electric capacity of the negative electrode that can be charged after the second cycle is reduced. For this reason, since the electric capacity which can be charged / discharged of a battery reduces, the electric quantity exceeding the limit of a reversible electric capacity becomes easy to energize at the time of charge, and there exists a problem that metal lithium tends to precipitate on the negative electrode surface. The deposited metallic lithium is thermally unstable and is not preferable in view of battery safety.

  An object of the present invention is to solve these conventional problems and to provide a non-aqueous electrolyte secondary battery having excellent electrical characteristics and high energy density.

  In order to solve the conventional problems, the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode including a positive electrode active material capable of releasing and storing lithium ions by charge and discharge, and a negative electrode capable of inserting and extracting lithium ions by charge and discharge. In a non-aqueous electrolyte secondary battery comprising a negative electrode containing an active material and a non-aqueous electrolyte, the negative electrode active material is carbon having an irreversible capacity of 39 mAh / g or more and 61 mAh / g or less, and the positive electrode active material When the irreversible capacity of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the positive electrode mixture layer is B, 0.73 ≦ A / B. ≦ 1.14.

Further, the positive and negative electrodes are formed by combining a negative electrode having an irreversible capacity with excellent battery characteristics of 39 mAh / g or more and 61 mAh / g or less and a lithium composite nickel oxide having a larger capacity per weight than LiCoO ₂ and a larger irreversible capacity. By satisfying the ratio of irreversible capacity, the irreversible capacity of the positive electrode is applied to the irreversible capacity of the negative electrode, for example, the formation of the negative electrode surface coating, etc., so that lithium ions that do not participate in charge / discharge do not remain in the negative electrode active material. In terms of battery design, the center load design value of the negative electrode can be set higher than when combined with a negative electrode having an irreversible capacity of 39 mAh / g or less, so that it has excellent electrical characteristics and high energy density. The high capacity design of the battery becomes possible.

  Moreover, since precipitation of metallic lithium is also suppressed, safety is enhanced.

  According to the present invention, it is possible to design a battery in which positive and negative electrode active materials that do not contribute to the battery capacity are not built in the battery, and it is possible to design a high capacity battery. In addition, it is possible to provide a non-aqueous electrolyte secondary battery with increased safety as well as high capacity.

  The non-aqueous electrolyte secondary battery according to the embodiment of the present invention has an electrode plate group in which a positive electrode and a negative electrode are insulated with a separator interposed therebetween, and the positive electrode active material has an irreversible capacity A and a positive electrode composite. When the irreversible capacity of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the agent layer is B, 0.73 ≦ A / B ≦ 1.14, and the positive electrode active material is a lithium composite nickel oxide It consists of

In this way, the positive electrode active material LiCoO ₂ having a charge / discharge efficiency of almost 100%, which has been used conventionally, has excellent electrical characteristics but is not suitable for increasing the capacity of the battery because of its large irreversible capacity. The positive and negative electrode active materials that do not contribute to the battery capacity are incorporated in the battery by combining the negative electrode with lithium composite nickel oxide having a larger capacity per weight than LiCoO ₂ having an irreversible capacity corresponding to the irreversible capacity of the negative electrode. Therefore, it is possible to design a high-capacity battery having excellent electrical characteristics.

As the negative electrode active material, carbon materials such as various natural graphites and various artificial graphites can be used. As described above, the positive electrode active material LiCoO ₂ has an excellent irreversible capacity due to the large irreversible capacity but the irreversible capacity corresponding to the irreversible capacity of the negative electrode. Although a high-capacity battery design is possible by combining lithium composite nickel oxide having a larger capacity per weight than LiCoO ₂ having, carbon materials (for example, mesocarbon microbeads) having a large irreversible capacity and a small theoretical capacity are high. It is not suitable for capacity battery design, and the effects of the present invention cannot be fully utilized. The theoretical capacity of the negative electrode active material is preferably at least 350 mAh / g.

In the non-aqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the positive electrode active material is represented by the general formula Li _x Ni _y M _1-y O ₂ (x: 0.95 ≦ x ≦ 1.10, M is Co, A lithium composite nickel oxide represented by at least one of Mn, Cr, Fe, Mg, Ti and Al, y: 0.3 ≦ y ≦ 0.95) is preferable.

Thus, when LiCoO ₂ is used as the positive electrode active material, the capacity per unit volume is about 120 mAh / cc, but the general formula of the positive electrode active material is Li _x Ni _y M _1-y O ₂ (x: 0 .95 ≦ x ≦ 1.10, M is one or more of Co, Mn, Cr, Fe, Mg, Ti and Al, y: 0.3 ≦ y ≦ 0.95) By using nickel oxide, it is possible to obtain a non-aqueous electrolyte secondary battery having a high energy density with a capacity of 130 mAh / cc or more per unit volume.

Here, the positive electrode active material is represented by the general formula Li _x Ni _y M _1-y O ₂ (x: 0.95 ≦ x ≦ 1.10, M is at least one of Co, Mn, Cr, Fe, Mg, Ti, and Al. LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co ₀ .0 as representatives of lithium composite nickel oxide represented by y = 0.3 ≦ y ≦ 0.95) _{. 3} Al _0.1 O ₂ , LiNi _0.6 Co _0.3 Ti _0.1 O ₂ , and LiNi _0.5 Co _0.5 O ₂ .

  As the binder used for the positive electrode, a fluororesin such as polyvinylidene fluoride (hereinafter abbreviated as PVDF) or a rubbery polymer containing an acrylonitrile unit can be used. From the viewpoint of sufficiently exerting the function of charge / discharge characteristics, a rubber-like polymer containing an acrylonitrile unit that swells or wets in the non-aqueous electrolyte is preferable to PVDF. This is considered that the binder is wetted or swollen in the electrolytic solution, thereby creating a path for lithium ions to move between the electrode plates during charge and discharge, thereby improving the charge and discharge characteristics.

  As the conductive agent, acetylene black, ketjen black (registered trademark), various graphites, and the like can be used. These may be used alone or in combination of two or more.

  The negative electrode includes at least a negative electrode active material and a binder.

  As the binder, various binders such as PVDF and modified products thereof can be used.

Various lithium salts such as lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) can be used as the solute in the electrolyte solution composed of a non-aqueous solvent. As the non-aqueous solvent, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC) and the like are preferably used, but are not limited thereto. Although a non-aqueous solvent can also be used individually by 1 type, it is preferable to use combining 2 or more types. Moreover, as an additive, vinylene carbonate (VC), cyclohexylbenzene (CHB), those modified bodies, etc. can also be used.

  As a separator, what is comprised by the single layer or multilayer structure which consists of a microporous film | membrane and nonwoven fabrics of polyolefin resins, such as a polyethylene resin and a polypropylene resin, is preferable.

  Examples of the present invention will be described below. However, the present invention is not limited to the examples described below.

(Example 1)
A so-called 18650 size cylindrical lithium ion secondary battery having a diameter of 18 mm and a height of 65 mm was produced as follows.

(A) Production of positive electrode plate 100 parts by weight of a powder of LiNi _0.6 Co _0.3 Al _0.1 O ₂ as a positive electrode active material, 5 parts by weight of acetylene black as a conductive material, and PVDF as a binder 5 parts by weight and an appropriate amount of N-methylpyrrolidone (NMP) were added to an organic solvent to prepare a paste-like positive electrode mixture. This mixture paste was applied to an aluminum foil having a thickness of 15 μm, dried and rolled to form a positive electrode mixture layer. Thereafter, the positive electrode plate was cut into a size of 56 mm in width and 660 mm in length.

(B) Production of negative electrode plate 100 parts by weight of carbon powder obtained by heat-treating coke as a negative electrode active material was mixed with 10 parts by weight of a styrene-based binder as a binder, and this was mixed with carboxymethyl cellulose (CMC). A paste-like negative electrode mixture was prepared by suspending in an aqueous solution. This mixture paste was applied to a copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode mixture layer. Thereafter, the negative electrode plate was cut into a size having a width of 58 mm and a length of 740 mm.

(C) Preparation of Electrolytic Solution LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent in which EC and MEC were mixed at a volume ratio of 1: 3 to prepare an electrolytic solution.

(D) Assembly of battery The positive electrode plate and the negative electrode plate were wound through a separator having a thickness of 16 μm to form an electrode plate group. At this time, it was confirmed that the positive electrode mixture layer was completely covered with the negative electrode mixture layer.

  And this electrode group was inserted in the battery case. Next, 5.0 g of the aforementioned electrolyte is weighed and poured into the battery case, and the opening of the case is sealed. Thus, a cylindrical lithium ion secondary battery was produced.

  The irreversible capacity of the positive electrode active material and the negative electrode active material was measured by preparing an electrochemical cell as described below.

The irreversible capacity of the positive electrode is an upper limit on the basis of the lithium potential at 25 ° C. by forming an electrode using a predetermined amount of the same electrode plate as the positive electrode that actually constitutes the battery, and forming an electrochemical cell using metallic lithium as the counter electrode. The difference in charge / discharge capacity when charging / discharging at a constant current of 0.2 mA / cm ² between a voltage of 4.3 V and a lower limit voltage of 3.0 V was defined as an irreversible capacity.

The irreversible capacity of the negative electrode is similar to that of the positive electrode in that an electrochemical cell using metallic lithium is used as the counter electrode, and at 25 ° C., the current density is between the upper limit voltage 1.5V and the lower limit voltage 0V on the basis of the lithium potential. The difference in charge / discharge capacity when charging / discharging at a constant current of 0.2 mA / cm ^{2 was} defined as the irreversible capacity.

  The irreversible capacity of the positive electrode active material measured by an electrochemical cell using metallic lithium as a counter electrode was 25 mAh / g. The negative electrode active material used had an irreversible capacity of 39 mAh / g and a theoretical capacity of 370 mAh / g as measured by an electrochemical cell using metallic lithium as the counter electrode. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 15.992 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 400 mAh.

  The weight of the negative electrode plate minus the weight of the copper foil, that is, the weight of the negative electrode mixture layer was 10.933 g. The portion of the negative electrode mixture layer facing the positive electrode mixture layer is 92.3% of the negative electrode application area, and the weight of the negative electrode active material in the negative electrode mixture (the negative electrode mixture minus the binder and CMC) is It becomes 89.3%. The weight of the negative electrode active material thus calculated was 9.011 g, and the irreversible capacity of the negative electrode as a battery, that is, the irreversible capacity B of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer. Was calculated to be 351 mAh. That is, a battery with A / B = 1.14 was produced.

(Example 2)
A negative electrode active material having an irreversible capacity of 51 mAh / g and a theoretical capacity of 370 mAh / g measured with an electrochemical cell using metallic lithium as a counter electrode was used. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 16.010 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 400 mAh.

  From the negative electrode mixture weight of 10.918 g, the negative electrode active material weight present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated in the same manner as in Example 1 was 8.999 g, The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated to be 459 mAh. That is, it carried out like Example 1 except having produced the battery used as A / B = 0.87.

(Example 3)
A negative electrode active material having an irreversible capacity of 61 mAh / g and a theoretical capacity of 370 mAh / g measured with an electrochemical cell using metallic lithium as a counter electrode was used. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 15.982 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 400 mAh.

  The weight of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated from the negative electrode mixture weight of 10.902 g in the same manner as in Example 1 was 8.986 g. The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated to be 548 mAh. That is, it carried out like Example 1 except having produced the battery used as A / B = 0.73.

(Comparative Example 1)
A negative electrode active material having an irreversible capacity of 30 mAh / g and a theoretical capacity of 370 mAh / g measured with an electrochemical cell using metallic lithium as a counter electrode was used. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 16.009 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 400 mAh.

  From the negative electrode mixture weight of 10.925 g, the negative electrode active material weight present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated in the same manner as in Example 1 was 9.005 g. The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated to be 270 mAh. That is, it carried out like Example 1 except having produced the battery used as A / B = 1.48.

(Comparative Example 2)
A negative electrode active material having an irreversible capacity of 71 mAh / g and a theoretical capacity of 370 mAh / g measured with an electrochemical cell using metallic lithium as a counter electrode was used. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 15.979 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 399 mAh.

  The weight of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated from the negative electrode mixture weight of 10.85 g in the same manner as in Example 1 was 8.972 g. The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated to be 637 mAh. That is, it carried out like Example 1 except having produced the battery used as A / B = 0.63.

(Comparative Example 3)
A negative electrode active material having an irreversible capacity of 39 mAh / g and a theoretical capacity of 330 mAh / g as measured by an electrochemical cell using metallic lithium as a counter electrode was used. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 14.002 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 350 mAh.

  The weight of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated from the negative electrode mixture weight of 10.422 g in the same manner as in Example 1 was 9.019 g. The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated to be 351 mAh. That is, it carried out like Example 1 except having produced the battery used as A / B = 1.00.

(Comparative Example 4)
When measured with an electrochemical cell using LiCoO ₂ as the positive electrode active material and metallic lithium as the counter electrode, the irreversible capacity was 2 mAh / g. The negative electrode active material used had an irreversible capacity of 40 mAh / g and a theoretical capacity of 370 mAh / g as measured by an electrochemical cell using metallic lithium as the counter electrode. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 17.980 g, and the irreversible capacity A of the positive electrode as the battery was calculated to be 36 mAh.

  The weight of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated from the negative electrode mixture weight of 8.471 g in the same manner as in Example 1 is 6.982 g. The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated as 279 mAh. That is, a battery having A / B = 0.13 was produced.

(Comparative Example 5)
A negative electrode active material having an irreversible capacity of 30 mAh / g and a theoretical capacity of 370 mAh / g measured with an electrochemical cell using metallic lithium as a counter electrode was used. The weight of the positive electrode active material in the positive electrode mixture layer of the produced battery was 17.991 g, and the irreversible capacity A of the positive electrode as a battery was calculated to be 36 mAh.

The weight of the negative electrode active material present in the portion of the negative electrode mixture layer facing the positive electrode mixture layer calculated from the negative electrode mixture weight of 8.517 g in the same manner as in Example 1 was 7.020 g. The irreversible capacity, that is, the irreversible capacity B of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the positive electrode mixture layer was calculated to be 211 mAh. That is, it carried out similarly to the comparative example 1 except having produced the battery used as A / B = 0.17.

<Charge / discharge test>
At an environmental temperature of 25 ° C., the charge / discharge capacity was measured under the following conditions.

Charging conditions: constant current and constant voltage charging
4.2V, 0.7 ItmA, 50 mA termination Discharge condition: constant current discharge
0.2 ItmA, 2.5V termination (Comparative Examples 4 and 5 are 3.0V termination)
<Charge / discharge cycle characteristics test>
At an environmental temperature of 25 ° C., the charge / discharge cycle characteristics were evaluated under the following conditions.

Charging conditions: constant current and constant voltage charging
4.2V, 0.7 ItmA, 50 mA termination Discharge condition: constant current discharge
1 ItmA, 2.5V termination (Comparative Examples 4 and 5 are 3.0V termination)
With these charging and discharging as one cycle, the discharge capacity at the first cycle was set to 100%, and the number of cycles at which the discharge capacity maintenance ratio calculated by the following equation was 50% was measured.

Discharge capacity maintenance rate (%) = discharge capacity at the time of cycle (mAh) / 1st cycle discharge capacity (mAh) × 100
These results are shown in (Table 1).

  In Example 1 and Comparative Example 1, since the irreversible capacity of the positive electrode is larger than the irreversible capacity of the negative electrode, the reversible capacity of the positive electrode becomes the battery capacity. From this, in the batteries of Example 1 and Comparative Example 1, the difference between the charge capacity and the discharge capacity in the first cycle is almost the same in each battery.

  In Comparative Example 3, the irreversible capacity of the positive electrode is larger than the irreversible capacity of the negative electrode, so that the reversible capacity of the positive electrode is the battery capacity. However, since the theoretical capacity of the negative electrode is as low as 330 mAh / g and the same battery design as in Example 1 and Comparative Example 1 cannot be performed, the charging capacity itself is smaller than in Examples 1, 2, 3 and Comparative Examples 1 and 2, and further It can be said that it is disadvantageous for high capacity and high energy density.

  In Examples 2 and 3 and Comparative Example 2, since the irreversible capacity of the negative electrode is larger than the irreversible capacity of the positive electrode, the reversible capacity of the negative electrode becomes the battery capacity.

  Therefore, in the batteries of Examples 2 and 3 and Comparative Example 2, the difference between the charge capacity and the discharge capacity at the first cycle is larger than that of the batteries of Example 1 and Comparative Example 1.

Since Comparative Example 4 and Comparative Example 5 use LiCoO ₂ having a lower capacity per weight than LiNi _0.6 Co _0.3 Al _0.1 O _{2 as the} positive electrode active material, the charge capacity itself is LiNi _{0. It} is smaller than Examples 1, 2, 3 and Comparative Examples 1, 2, 3 using ₆ Co _0.3 Al _0.1 O ₂ , and is disadvantageous for further increase in capacity and energy density. Moreover, since LiCoO ₂ has a charge / discharge efficiency of almost 100%, the capacity of this battery is dominated by the negative electrode reversible capacity.

  Regarding the cycle test, Examples 2 and 3 were good.

  As a result of disassembling and observing the battery after the cycle test, deposition of lithium metal having metallic luster was observed on the negative electrode surface of the battery of Comparative Example 1, and Examples 1, 2, 3, Comparative Examples 2, 3, 4, No precipitation was observed in the battery of No. 5.

  From this result, in Comparative Example 1, even though the battery capacity at the beginning of the cycle is the same as in Example 1, it is remarkable that the charge / discharge cycle proceeds with the irreversible capacity of the positive electrode remaining in the carbon of the negative electrode. The reversible capacity is reduced, and charging is performed beyond the reversible charge / discharge capacity of the negative electrode, so that the lithium metal is deposited on the surface of the negative electrode plate and the discharge capacity is remarkably reduced. Incidentally, in this case, a battery with good cycle characteristics can be realized by reducing the amount of the positive electrode active material or reducing the charging voltage, thereby providing a reversible capacity of the negative electrode, but the discharge capacity itself is reduced. Higher battery capacity cannot be realized.

From the above results, considering the balance between high capacity battery design and cycle characteristics, the irreversible capacity of the positive electrode / irreversible capacity of the negative electrode is preferably 0.73 or more and 1.14 or less. Lithium composite that has excellent electrical characteristics but large irreversible capacity, in particular, a negative active material having an irreversible capacity of 39 mAh / g or more and 61 mAh / g or less, a larger capacity per weight than LiCoO ₂ , and a large irreversible capacity By matching with the nickel oxide positive electrode, the irreversible capacity of the positive and negative electrodes becomes almost equal, and it is possible to design a higher capacity with a longer life.

  In the above examples, evaluation was performed using a cylindrical battery, but the same effect can be obtained even if the battery shape is different, such as a rectangular battery.

  INDUSTRIAL APPLICABILITY The present invention can be used for a non-aqueous electrolyte secondary battery, and is particularly useful as a power source for portable electronic devices, notebook computers, and the like that are required to have a high capacity.

Claims (3)

A non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material capable of releasing and storing lithium ions by charge and discharge, a negative electrode including a negative electrode active material capable of storing and releasing lithium ions by charge and discharge, and a non-aqueous electrolyte In
The negative electrode active material is carbon having an irreversible capacity of 39 mAh / g or more and 61 mAh / g or less,
When the positive electrode active material is lithium composite nickel oxide, the irreversible capacity thereof is A, and the irreversible capacity of the negative electrode active material existing in the portion of the negative electrode mixture layer facing the positive electrode mixture layer is B. A nonaqueous electrolyte secondary battery in which 73 ≦ A / B ≦ 1.14.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material has a theoretical capacity of 350 mAh / g or more. The positive electrode active material is a general formula Li _x Ni _y M _1-y O ₂ (x: 0.95 ≦ x ≦ 1.10, M is at least one of Co, Mn, Cr, Fe, Mg, Ti, and Al) The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium composite nickel oxide is represented by y: 0.3 ≦ y ≦ 0.95).