WO2021069951A1

WO2021069951A1 - Lithium ion secondary battery positive electrode active material

Info

Publication number: WO2021069951A1
Application number: PCT/IB2019/001263
Authority: WO
Inventors: 小野正樹; 光山知宏; 諸岡正浩; 金澤昭彦
Original assignee: 日産自動車株式会社; ルノーエス．ア．エス．
Priority date: 2019-10-09
Filing date: 2019-10-09
Publication date: 2021-04-15
Also published as: JPWO2021069951A1; JP7248136B2

Abstract

The present invention provides a means for achieving a high-capacity, high-output lithium ion secondary battery that has excellent rate characteristics and high charge/discharge cycle durability. The present invention is a lithium ion secondary battery positive electrode active material that contains at least carbon and sulfur. The ratio B/A of the height B of a peak that is at a Raman shift of 980–1000 cm^-1 on a Raman spectrum for the lithium ion secondary battery positive electrode active material to the height A of a main peak that is at 1430–1450 cm^-1 is at least 0.3.

Description

Positive electrode active material for lithium ion secondary batteries

The present invention relates to a positive electrode active material for a lithium ion secondary battery.

In recent years, there is an urgent need to reduce carbon dioxide emissions in order to deal with global warming. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and non-water batteries such as secondary batteries for driving motors, which hold the key to their practical application. The development of secondary electrolyte batteries is being actively carried out.

The secondary battery for driving the motor is required to have extremely high output characteristics and high energy as compared with the consumer lithium ion secondary battery used for mobile phones, notebook computers, and the like. Therefore, the lithium-ion secondary battery, which has the highest theoretical energy among all realistic batteries, is attracting attention and is currently being rapidly developed.

Here, the lithium ion secondary battery currently widely used uses a flammable organic electrolyte as an electrolyte. In such a liquid-based lithium-ion secondary battery, safety measures against liquid leakage, short circuit, overcharge, etc. are required more strictly than other batteries.

Therefore, in recent years, research and development on an all-solid-state lithium-ion secondary battery using an oxide-based or sulfide-based solid electrolyte as the electrolyte has been actively carried out. The solid electrolyte is a material composed mainly of an ionic conductor capable of conducting ions in a solid. Therefore, in the all-solid-state lithium ion secondary battery, various problems caused by the flammable organic electrolytic solution do not occur in principle unlike the conventional liquid-based lithium ion secondary battery. Further, in general, when a high potential / large capacity positive electrode material and a large capacity negative electrode material are used, the output density and energy density of the battery can be significantly improved. An all-solid-state lithium-ion secondary battery using elemental sulfur (S) or a sulfide-based material as the positive electrode active material is a promising candidate.

Among them, organic sulfur compounds such as polycarbon sulfide containing carbon and sulfur as main constituent elements are attracting attention because they have a high energy density. For example, Japanese Patent Application Laid-Open No. 2002-154815 describes a lithium ion secondary battery using polycarbon sulfide as a positive electrode active material. Japanese Patent Application Laid-Open No. 2002-154815 describes polycarbon sulfide showing a predetermined Raman spectrum in response to the problem that the charge / discharge cycle life of a battery is shortened when the sulfur content of polycarbon sulfide is increased in order to increase the capacity. We are proposing to use it. That is, in the polycarbon sulfide described in JP-A-2002-154815, ^{the peak existing in the region of 400 to 525 cm -1} of the Raman spectrum is assigned to a disulfide bond (SS bond) around ^{490 cm -1.} There is only one peak. As a result, the proportion of polysulfide compounds and polysulfide bonds that decompose during charging and discharging and cause a decrease in life is smaller than that of materials showing multiple peaks indicating that many polysulfide bonds are present in the region, and charging and discharging are performed. It is said that the cycle life can be improved.

However, according to the studies by the present inventors, when polycarbon sulfide described in JP-A-2002-154815 is applied to an all-solid-state battery as a positive electrode active material, high reversible capacity and high charge / discharge characteristics can be obtained. However, it has been found that the rate characteristics may be significantly reduced.

Therefore, an object of the present invention is to provide a means capable of achieving a high output lithium ion secondary battery having a high capacity, high charge / discharge cycle durability, and excellent rate characteristics.

The present inventors have made diligent studies to solve the above problems. As a result, the ratio of height B of the peak of 980 ~ 1000 cm ^-1 attributed to the = C-S bond with respect to the height A of the main peak of 1430 ~ 1450 cm ^-1 attributed to the C = C bond in the Raman spectrum It has been found that the above-mentioned problems can be solved by setting the temperature above a certain level, and the present invention has been completed.

That is, the present invention contains at least carbon and sulfur, in the Raman spectrum, the height of the peaks present in 980 ~ 1000 cm ^-1 of the main peak existing on the 1430 ~ 1450 cm ^-1 Raman shift relative to height A B It is a positive electrode active material for a lithium ion secondary battery having a ratio B / A of 0.3 or more.

It is a figure which shows (a) the positive electrode active material of this invention, and (b) the estimated structure of the conventional positive electrode active material. It is sectional drawing which represented typically the laminated type all-solid-state lithium ion secondary battery which is one Embodiment of this invention. It is sectional drawing which represented typically the bipolar type all-solid-state lithium ion secondary battery which is one Embodiment of this invention. It is a perspective view which showed the appearance of the laminated type all-solid-state lithium ion secondary battery which concerns on one Embodiment of this invention. It is a figure which shows the Raman spectrum of the polycarbon sulfide prepared in Example 1, 3 and Comparative Example 2. 3 is a graph showing the rate characteristics of the lithium ion secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 3.

One form of the present invention contains at least carbon and sulfur, in the Raman spectrum, the height of the peaks present in 980 ~ 1000 cm ^-1 of the main peak existing on the 1430 ~ 1450 cm ^-1 Raman shift relative to height A It is a positive electrode active material for a lithium ion secondary battery having a ratio B / A of B of 0.3 or more.

According to the present invention, a battery having a high capacity and high charge / discharge cycle durability can be obtained by using a positive electrode active material containing carbon and sulfur. Further, in the positive electrode active material containing sulfur and carbon, the electrode reaction activity is set by setting the ratio of the peak height B of ^{980 to 1000 cm -1 of the Raman shift attributed to the CS bond to a certain value or more.} High = Positive electrode active material with a high proportion of sulfur atoms in the CS bond. As a result, the rate characteristics of the battery can be improved.

Organosulfur compounds containing carbon and sulfur as the main constituent elements have a high capacity and are more reversible than elemental sulfur, so they are attracting attention as positive electrode active materials that can achieve high capacity of lithium ion secondary batteries. Has been done.

However, it is difficult to control the sulfur content of the obtained compound in the organic sulfur compound, and the produced compound may contain a low molecular weight or high molecular weight polysulfide compound. When the sulfur content is increased in order to increase the capacity, the proportion of the polysulfide compound increases, but there is a problem that the cycle durability of the battery is lowered due to decomposition of the polysulfide compound during charging and discharging. On the other hand, in the technique described in JP-A-2002-154815, the life is improved by reducing the proportion of polysulfide bonds. However, when polycarbon sulfide as described in JP-A-2002-154815 is applied to an all-solid-state battery, sufficient rate characteristics cannot be obtained.

In contrast, the present inventors have found that in the Raman spectrum of the cathode active material containing carbon and sulfur, the peak of 980 ~ 1000 cm ^-1 of the main peak existing on the 1430 ~ 1450 cm ^-1 Raman shift relative to height A It was found that the above-mentioned problems can be solved by setting the ratio of the height B of the above to a certain level or more.

Here, the main peak existing on the 1430 ~ 1450 cm ^-1 of Raman shift is a peak derived from C = C bond, a peak derived from the peak present in the 980 ~ 1000 cm ^-1 Raman shift = C-S bond Is.

The positive electrode active material of the present invention is considered to be a polycarbon sulfide having a structure as shown in FIG. 1A, although it is not clear because it is insoluble in a solvent and analysis means are limited. In the positive electrode active material of the present invention, the ratio of = CS bond is above a certain level. In other words, included in the polysulfide carbon = C-S bond of the sulfur atom, i.e. the ratio of sulfur atoms bonded to sp ² carbon is higher than the conventional polysulfide carbon. Since the sulfur atom bonded to sp ² carbon is considered to electrode reaction activity is high (high activity sulfur) = positive electrode active material of the present invention which is a C-S containing more binding polysulfide carbon, conventional polysulfide carbon The electrode reaction activity is high as compared with. Therefore, it is considered that excellent rate characteristics can be obtained.

On the other hand, as shown in FIG. 1 (b), = a C-S bond is relatively small poly hydrogen sulfide, which is a low active sulfur -C-S bond of the sulfur atom (sp ³ sulfur atoms bonded to carbon) High proportion, low proportion of highly active sulfur. As a result, the electrode reaction activity becomes low, and it is considered that it is difficult to obtain sufficient rate characteristics in the all-solid-state battery.

Hereinafter, this embodiment will be described with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. The dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

FIG. 2 schematically shows the overall structure of a laminated (internal parallel connection type) all-solid-state lithium-ion secondary battery (hereinafter, also simply referred to as “laminated secondary battery”) according to an embodiment of the present invention. It is a cross-sectional view. The laminated secondary battery 10a shown in FIG. 2 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated film 29 which is a battery exterior.

As shown in FIG. 2, the power generation element 21 of the laminated secondary battery 10a of the present embodiment includes a positive electrode in which positive electrode active material layers 13 are arranged on both sides of a positive electrode current collector 11', a solid electrolyte layer 17, and a negative electrode. It has a structure in which a negative electrode in which a negative electrode active material layer 15 is arranged is laminated on both sides of a current collector 11 ″. Specifically, the positive electrode, the solid electrolyte layer, and the negative electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other via the solid electrolyte layer 17. ing. As a result, the adjacent positive electrode, solid electrolyte layer, and negative electrode form one cell cell layer 19. Therefore, it can be said that the laminated secondary battery 10a shown in FIG. 2 has a configuration in which a plurality of single battery layers 19 are laminated and electrically connected in parallel. The positive electrode current collectors in the outermost layers located in both outermost layers of the power generation element 21 have the positive electrode active material layer 13 arranged on only one side, but active material layers may be provided on both sides. .. That is, instead of using a current collector dedicated to the outermost layer in which the active material layer is provided on only one side, a current collector having active material layers on both sides may be used as it is as the current collector in the outermost layer. Further, by reversing the arrangement of the positive electrode and the negative electrode as in FIG. 2, the negative electrode current collector of the outermost layer is located on both outermost layers of the power generation element 21, and one side of the negative electrode current collector of the outermost layer or Negative electrode active material layers may be arranged on both sides.

A positive electrode current collector plate 25 and a negative electrode current collector plate 27 that are conductive to each electrode (positive electrode and negative electrode) are attached to the positive electrode current collector 11'and the negative electrode current collector 11', respectively, and the end portion of the laminate film 29 is attached. It has a structure that is led out to the outside of the laminated film 29 so as to be sandwiched between the two. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are connected to the positive electrode current collector 11'and the negative electrode current collector 11'of each electrode via the positive electrode terminal lead and the negative electrode terminal lead (not shown), respectively, as necessary. It may be attached to'by ultrasonic welding, resistance welding, or the like.

In the above description, one embodiment of the all-solid-state battery has been described by taking a laminated type (internal parallel connection type) all-solid-state lithium-ion secondary battery as an example. However, the type of all-solid-state battery to which the present invention can be applied is not particularly limited, and the positive electrode active material layer electrically bonded to one surface of the current collector and the opposite surface of the current collector are electrically connected. It is also applicable to a bipolar (bipolar) all-solid-state battery including a bipolar electrode having a coupled negative electrode active material layer.

FIG. 3 is a sectional view schematically showing a bipolar type (bipolar type) all-solid-state lithium ion secondary battery (hereinafter, also simply referred to as “bipolar type secondary battery”) according to an embodiment of the present invention. .. The bipolar secondary battery 10b shown in FIG. 3 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminated film 29 which is a battery exterior.

As shown in FIG. 3, in the power generation element 21 of the bipolar secondary battery 10b of the present embodiment, a positive electrode active material layer 13 electrically bonded to one surface of the current collector 11 is formed, and the current collector 11 has a positive electrode active material layer 13. It has a plurality of bipolar electrodes 23 having an electrically coupled negative electrode active material layer 15 formed on the opposite surface. Each bipolar electrode 23 is laminated via a solid electrolyte layer 17 to form a power generation element 21. The solid electrolyte layer 17 has a structure in which the solid electrolyte is formed into layers. At this time, the positive electrode active material layer 13 of the one bipolar electrode 23 and the negative electrode active material layer 15 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other via the solid electrolyte layer 17. , The bipolar electrodes 23 and the solid electrolyte layer 17 are alternately laminated. That is, the solid electrolyte layer 17 is sandwiched between the positive electrode active material layer 13 of the one bipolar electrode 23 and the negative electrode active material layer 15 of the other bipolar electrode 23 adjacent to the one bipolar electrode 23. Has been done.

The adjacent positive electrode active material layer 13, the solid electrolyte layer 17, and the negative electrode active material layer 15 constitute one cell cell layer 19. Therefore, it can be said that the bipolar secondary battery 10b has a configuration in which the cell cell layers 19 are laminated. The positive electrode active material layer 13 is formed on only one side of the outermost layer current collector 11a on the positive electrode side located in the outermost layer of the power generation element 21. Further, the negative electrode active material layer 15 is formed on only one side of the outermost layer current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21.

Further, in the bipolar secondary battery 10b shown in FIG. 3, a positive electrode current collector plate (positive electrode tab) 25 is arranged so as to be adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a battery exterior. It is derived from the laminated film 29. On the other hand, the negative electrode current collector plate (negative electrode tab) 27 is arranged so as to be adjacent to the outermost layer current collector 11b on the negative electrode side, and is similarly extended and led out from the laminated film 29.

The number of times the cell cell layer 19 is laminated is adjusted according to the desired voltage. Further, in the bipolar type secondary battery 10b, the number of times the cell cell layer 19 is laminated may be reduced as long as a sufficient output can be secured even if the thickness of the battery is made as thin as possible. Even in the bipolar secondary battery 10b, in order to prevent external impact and environmental deterioration during use, the power generation element 21 is vacuum-sealed in the laminated film 29 which is the battery exterior, and the positive electrode current collector plate 25 and the negative electrode current collector are collected. It is preferable to have a structure in which the electric plate 27 is taken out from the laminated film 29.

The main components of the all-solid-state battery will be described below.

[Current collector]
The current collector has a function of mediating the movement of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. There are no particular restrictions on the materials that make up the current collector. As a constituent material of the current collector, for example, a metal or a resin having conductivity can be adopted.

Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, and the like may be used. Further, the foil may be a metal surface coated with aluminum. Of these, aluminum, stainless steel, copper, and nickel are preferable from the viewpoints of electron conductivity, battery operating potential, adhesion of the negative electrode active material by sputtering to the current collector, and the like.

Further, as the latter resin having conductivity, a resin in which a conductive filler is added to a non-conductive polymer material as needed can be mentioned.

Examples of the non-conductive polymer material include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), and polyimide. (PI), Polyethyleneimide (PAI), Polyethylene (PA), Polytetrafluoroethylene (PTFE), Styrene-butadiene rubber (SBR), Polyacrylonitrile (PAN), Polymethylacrylate (PMA), Polymethylmethacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), polystyrene (PS) and the like. Such non-conductive polymer materials can have excellent potential resistance or solvent resistance.

A conductive filler may be added to the above-mentioned conductive polymer material or non-conductive polymer material as needed. In particular, when the resin used as the base material of the current collector is composed of only a non-conductive polymer, a conductive filler is inevitably indispensable in order to impart conductivity to the resin.

The conductive filler can be used without particular limitation as long as it is a conductive substance. For example, materials having excellent conductivity, potential resistance, or lithium ion blocking property include metals and conductive carbon. The metal is not particularly limited, and includes at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or at least one of these metals. It preferably contains an alloy or metal oxide. Further, the conductive carbon is not particularly limited. Preferably, it is selected from the group consisting of acetylene black, vulcan (registered trademark), black pearl (registered trademark), carbon nanofiber, Ketjen black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It contains at least one species.

The amount of the conductive filler added is not particularly limited as long as it can impart sufficient conductivity to the current collector, and is generally 5 to 80% by mass with respect to 100% by mass of the total mass of the current collector. Is.

The current collector may have a single-layer structure made of a single material, or may have a laminated structure in which layers made of these materials are appropriately combined. From the viewpoint of reducing the weight of the current collector, it is preferable to include a conductive resin layer made of at least a conductive resin. Further, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided as a part of the current collector.

[Positive electrode active material layer]
The positive electrode active material layer contains a positive electrode active material. In the battery of the present embodiment, the positive electrode active material includes the predetermined positive electrode active material of the present invention.

Positive electrode active material according to the present invention contains at least carbon and sulfur, in the Raman spectrum, the peaks present in 980 ~ 1000 cm ^-1 of the main peak existing on the 1430 ~ 1450 cm ^-1 Raman shift relative to height A It is a positive electrode active material for a lithium ion secondary battery having a height B ratio B / A of 0.3 or more.

The positive electrode active material of the present invention preferably contains carbon and sulfur as main constituent elements. Preferably, the total mass ratio of carbon and sulfur is 90% by mass or more, more preferably 95% by mass or more, still more preferably 96% by mass or more, and even more preferably 97% by mass or more. Within the above range, a high energy density can be obtained. In addition, since it is possible to suppress a decrease in the redox activity of sulfur due to the inclusion of elements other than carbon and sulfur, high rate characteristics can be obtained.

Further, the positive electrode active material of the present invention preferably has a sulfur mass ratio of 65% by mass or more, preferably 67% by mass or more, and preferably 70% by mass or more. Within the above range, a high energy density can be obtained. In addition, since it is possible to suppress a decrease in the redox activity of sulfur due to the inclusion of elements other than carbon and sulfur, high rate characteristics can be obtained.

The composition ratio (atomic ratio) of carbon and sulfur is not particularly limited, but it is preferably 1 ≦ S / C (atomic ratio) ≦ 1.5. When the S / C (atomic ratio) is 1 or more, the capacity per mass of the active material is high, which is preferable. Further, when it is 1.5 or less, the polysulfide bond (-S-S-S-) is relatively small, so that the rate characteristics and the cycle durability can be improved, which is preferable.

The mass ratio of carbon and sulfur in the positive electrode active material can be obtained by the method described in Examples. In addition, the atomic ratio of carbon and sulfur can be obtained from the mass ratio.

The positive electrode active material of the present invention, in the Raman spectrum, the ratio B / A of the height B of the peaks present in 980 ~ 1000 cm ^-1 of the main peak to the height A present 1430 ~ 1450 cm ^-1 Raman shift 0 .3 or more. If the B / A is less than 0.3, the rate characteristics become insufficient. B / A is preferably 0.48 or more, and more preferably 0.61 or more. Within the above range, the effect of the present invention can be further improved. The upper limit of B / A is not particularly limited, but is, for example, 1 or less.

The B / A ratio of the positive electrode active material can be obtained by the method described in the examples.

The shape of the positive electrode active material is not particularly limited, and examples thereof include a particle shape (spherical shape, a fibrous shape), a thin film shape, and the like. When the positive electrode active material has a particle shape, its average particle size is not particularly limited.

The method for preparing the positive electrode active material of the present invention containing carbon and sulfur and having a predetermined Raman spectrum is not particularly limited. For example, a method of synthesizing polycarbon sulfide by electrolytic reduction polymerization of carbon disulfide and heat-treating the synthesized polycarbon sulfide can be mentioned.

(Synthesis of polycarbon sulfide)
The electrolytic reduction polymerization of carbon disulfide (CS ₂ _{) can be carried out, for example, by using a solution obtained by dissolving CS 2 or} a supporting electrolyte in a solvent and mixing them. It is considered that when a voltage is applied to the solution using an electrode such as platinum, CS ₂ is reduced to generate CS carbene (: CS), which initiates polymerization.

_{The concentration of CS 2} in the solution is not particularly limited, but it is desirable that the concentration is close to saturation within the range in which _{CS 2} can be dissolved, depending on the combination of the solvent and supporting electrolyte used.

The supporting electrolyte is not particularly limited, but for example, tetrabutylammonium perchlorate or the like can be used. The concentration of the supporting electrolyte in the solution is not particularly limited, but is preferably 0.05 to 0.5 M, and more preferably 0.1 to 0.3 M. Within the above range, the polymerization reaction can proceed favorably.

As the solvent, for example, acetonitrile, N, N-dimethylformamide, hexamethylphosphoric acid triamide, N-methylpyrrolidone, tetrahydrofuran, ethyl acetate, acetone, dimethyl sulfoxide, propylene carbonate and the like can be used.

The applied voltage is not particularly limited, but is preferably 3 to 6 V, and more preferably 4 to 5 V. When the voltage is 3 V or higher, the polymerization can proceed favorably. When the voltage is 6 V or less, the electrolytic efficiency is unlikely to decrease due to gas generation, so that the polymerization can proceed favorably.

The reaction time of electrolytic reduction polymerization is not particularly limited and can be adjusted as appropriate.

(Heat treatment of synthesized polycarbon sulfide)
The synthesized polycarbon sulfide is preferably heat-treated. This makes it possible to remove low molecular weight components and increase the proportion of active sulfur.

The heat treatment is preferably carried out under reduced pressure or under an inert gas atmosphere. When the operation is carried out in an inert gas atmosphere, the dew point is preferably −30 ° C. or lower, and more preferably the dew point is −40 ° C. or lower. By doing so, the synthesized polycarbon sulfide can be sufficiently dehydrated. This makes it possible to prevent deterioration of the solid electrolyte in the positive electrode mixture due to the reaction between the solid electrolyte and water when the positive electrode mixture is produced.

The heat treatment temperature is preferably 80 to 250 ° C, still more preferably 80 to 200 ° C, and even more preferably 130 to 200 ° C. If the temperature is 80 ° C. or higher, the structure is likely to change to an electrochemically active sulfur-rich structure, which is preferable. Further, when the temperature is 250 ° C. or lower, thermal decomposition of polycarbon sulfide is unlikely to occur, which is preferable.

The heat treatment time is preferably 0.5 to 12 hours, more preferably 2 to 8 hours, and even more preferably 4 to 8 hours. If it is 0.5 hours or more, the effect of heat treatment (structural change and dehydration) can be sufficiently obtained. If it is 12 hours or less, the effect according to the heat treatment time can be obtained, which is preferable.

The positive electrode active material layer contains carbon and sulfur, and may contain a positive electrode active material (other positive electrode active material) other than the positive electrode active material of the present invention having a predetermined Raman spectrum.

As other positive electrode active material, for example, elemental sulfur (S), lithium sulfide (Li 2 _S), particles or a thin film of the organic sulfur compounds other than polysulfide carbon or inorganic sulfur compound and the like, redox sulfur A substance capable of releasing lithium ions during charging and occluding lithium ions during discharging can be used by utilizing the reaction.

Further, as another positive electrode active material, a positive electrode active material containing no sulfur may be contained. Examples of the sulfur-free positive electrode active material include layered rock salt type active materials _{such as LiCoO 2} , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , and Li (Ni-Mn-Co) O ₂ _{, LiMn 2} O ₄ , LiNi _0. Examples thereof include spinel-type active materials such as ₅ Mn _1.5 O ₄ , olivine-type active materials such as _{LiFePO 4} and LiMnPO ₄ , and Si-containing active materials such as _{Li 2} FeSiO ₄ and Li ₂ _{MnSiO 4.} Examples of the oxide active material other than the above include Li ₄ Ti ₅ O ₁₂ .

At this time, the content of the positive electrode active material of the present invention with respect to the total amount of the positive electrode active material is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. It is more preferably 95% by mass or more, and particularly preferably 100% by mass.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, preferably in the range of 50 to 90% by mass, for example. More preferred.

The positive electrode active material layer preferably further contains a solid electrolyte. Since the positive electrode active material layer contains a solid electrolyte, the ionic conductivity of the positive electrode active material layer can be improved. Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes, and sulfide solid electrolytes are preferable.

Examples of the sulfide solid electrolyte include LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ S-P ₂ O ₅ , LiI-Li ₃ PO _4- P ₂ S ₅ , Li ₂ S-P ₂ S ₅ , LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _4, Li ₃ PS ₄ , Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -Li I, Li ₂ S-P ₂ S _5- Li ₂ O, Li ₂ S-P ₂ S ₅ _{-Li 2} O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS _2- LiI, Li ₂ S-SiS _2- LiBr, Li ₂ S-SiS ₂ -LiCl, Li ₂ S-SiS _2- B ₂ S _3- LiI, Li ₂ S-SiS _2- P ₂ S _5- LiI, Li ₂ _{SB 2} S ₃ , Li ₂ _{SP 2} S _5- Z _m S _n (where m and n are positive numbers and Z is one of Ge, Zn or Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ _{-Li 3} PO ₄ , Examples thereof include Li ₂ S-SiS ₂ _{-Li x} MO _y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga and In). .. The description of "Li ₂ SP ₂ S ₅ " means a sulfide solid electrolyte made by using a raw material composition containing _{Li 2} S and P ₂ S _{5, and the same applies to other descriptions.}

The sulfide solid electrolyte may have, for example, a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. .. Examples of the sulfide solid electrolyte having a Li ₃ PS ₄ _{skeleton include LiI-Li 3} PS ₄ , LiI-LiBr-Li ₃ PS _{4, and} Li ₃ PS ₄ . Further, examples of the sulfide solid electrolyte having a Li ₄ P ₂ S ₇ skeleton include a Li-PS-based solid electrolyte called LPS (for example, Li ₇ P ₃ S ₁₁ ). Further, as the sulfide solid electrolyte, for example, _{LGPS represented by Li (4-x)} Ge _(1-x) P _x S ₄ (x satisfies 0 <x <1) may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing a P element, and the sulfide solid electrolyte is more preferably a material containing Li ₂ SP ₂ S ₅ as a main component. Further, the sulfide solid electrolyte may contain halogens (F, Cl, Br, I).

When the sulfide solid electrolyte is a Li ₂ SP ₂ S ₅ system, the ratio of Li ₂ S and P ₂ S ₅ is a molar ratio of Li ₂ S: P ₂ S ₅ = 50: 50 to 100. It is preferably in the range of: 0, and in particular, Li ₂ S: P ₂ S ₅ = 60: 40 to 80:20.

Further, the sulfide solid electrolyte may be sulfide glass, crystallized sulfide glass, or a crystalline material obtained by the solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (ball mill or the like) on the raw material composition. Further, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature equal to or higher than the crystallization temperature. The ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 ° C.) ^{is preferably 1 × 10 -5} S / cm or more ^{, for example, 1 × 10 -4} S / cm. It is more preferably cm or more. The value of the ionic conductivity of the solid electrolyte can be measured by the AC impedance method.

Examples of the oxide solid electrolyte include compounds having a NASICON type structure and the like. As an example of a compound having a NASICON type structure, a compound _{(LAGP) represented by the general formula Li 1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 2), a general formula Li _{1 + x} Al _x Ti ₂ Examples thereof include a compound (LATP) represented by _−x (PO ₄ ) _{3 (0 ≦ x ≦ 2).} Further, as another example of the oxide solid electrolyte, LiLaTIO (for example, Li _0.34 La _0.51 TiO ₃ ), LiPON (for example, Li _2.9 PO _3.3 N _0.46 ), LiLaZrO (for example, Li LaZrO). , Li ₇ La ₃ Zr ₂ O ₁₂ ) and the like.

Examples of the shape of the solid electrolyte include a particle shape such as a true spherical shape and an elliptical spherical shape, and a thin film shape. When the solid electrolyte has a particle shape, its average particle size (D ₅₀ ) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and further preferably 10 μm or less. On the other hand, the average particle size (D ₅₀ ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

The content of the solid electrolyte in the positive electrode active material layer is, for example, preferably in the range of 1 to 60% by mass, and more preferably in the range of 10 to 50% by mass.

The positive electrode active material layer may further contain at least one of a conductive auxiliary agent and a binder in addition to the positive electrode active material and the solid electrolyte described above.

Examples of the conductive auxiliary agent include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-grown carbon fibers). (VGCF), polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, rayon-based carbon fiber, activated carbon fiber, etc.), carbon nanotube (CNT), carbon black (specifically, acetylene black, Ketjen black (registered trademark)) , Furness black, channel black, thermal lamp black, etc.), but is not limited to these. Further, a particulate ceramic material or a resin material coated with the above metal material by plating or the like can also be used as a conductive auxiliary agent. Among these conductive auxiliaries, from the viewpoint of electrical stability, it is preferable to contain at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, and aluminum, stainless steel. It is more preferable to contain at least one selected from the group consisting of silver, gold, and carbon, and it is further preferable to contain at least one carbon. Only one kind of these conductive auxiliaries may be used alone, or two or more kinds thereof may be used in combination.

The shape of the conductive auxiliary agent is preferably particulate or fibrous. When the conductive auxiliary agent is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, columnar, indefinite, flint, and spindle. It doesn't matter.

The average particle size (primary particle size) when the conductive auxiliary agent is in the form of particles is not particularly limited, but is preferably 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery. In the present specification, the “particle size of the conductive auxiliary agent” means the maximum distance L among the distances between any two points on the contour line of the conductive auxiliary agent. As the value of the "average particle size of the conductive auxiliary agent", the particle size of the particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of is adopted.

When the positive electrode active material layer contains a conductive auxiliary agent, the content of the conductive auxiliary agent in the positive electrode active material layer is not particularly limited, but is preferably 0 to 10% by mass with respect to the total mass of the positive electrode active material layer. , More preferably 2 to 8% by mass, and even more preferably 4 to 7% by mass. Within such a range, a stronger electron conduction path can be formed in the positive electrode active material layer, which can effectively contribute to the improvement of battery characteristics.

On the other hand, the binder is not particularly limited, and is, for example, polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including a compound in which a hydrogen atom is replaced with another halogen element), polyethylene, polypropylene, polymethyl. Penten, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene -Polypolymers such as butadiene-styrene block copolymer and its hydrogen additive, styrene-isoprene-styrene block copolymer and its hydrogen additive, tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetra Fluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyfluoropolymer Fluororesin such as vinyl (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluoropolymer) Rubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride -Perfluoromethyl Vinyl Ether-Tetrafluoroethylene Fluororesin (VDF-PFMVE-TFE Fluororubber), Vinylidene Fluoride-Chlorotrifluoroethylene Fluororesin (VDF-CTFE Fluororesin), etc. , Epoxy resin and the like. Of these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

The thickness of the positive electrode active material layer varies depending on the configuration of the target all-solid-state battery, but is preferably in the range of 0.1 to 1000 μm, for example.

The method for producing the positive electrode active material layer is not particularly limited. Conventionally known methods can be referred to as appropriate.

[Negative electrode active material layer]
The negative electrode active material layer contains a negative electrode active material. The type of the negative electrode active material is not particularly limited, and examples thereof include a carbon material, a metal oxide, and a metal active material. Examples of the carbon material include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon and the like. Examples of the metal oxide include Nb ₂ O ₅ and Li ₄ Ti ₅ O ₁₂ . Further, a silicon-based negative electrode active material or a tin-based negative electrode active material may be used. Here, silicon and tin belong to Group 14 elements and are known to be negative electrode active materials that can greatly improve the capacity of a non-aqueous electrolyte secondary battery. Since these simple substances can occlude and release a large number of charge carriers (lithium ions, etc.) per unit volume (mass), they are high-capacity negative electrode active materials. Here, it is preferable to use Si alone as the silicon-based negative electrode active material. Similarly, it is also preferable to use a silicon oxide such as _{SiO x} (0.3 ≦ x ≦ 1.6) disproportionated into two phases, a Si phase and a silicon oxide phase. At this time, the range of x is more preferably 0.5 ≦ x ≦ 1.5, and even more preferably 0.7 ≦ x ≦ 1.2. Further, a silicon-containing alloy (silicon-containing alloy-based negative electrode active material) may be used. On the other hand, examples of the negative electrode active material containing a tin element (tin-based negative negative active material) include Sn alone, tin alloys (Cu—Sn alloy, Co—Sn alloy), amorphous tin oxide, tin silicon oxide and the like. _{Of these, SnB 0.4} P _0.6 O _3.1 is exemplified as the amorphous tin oxide. _{Further, SnSiO 3} is exemplified as the tin silicon oxide. Further, as the negative electrode active material, a metal containing lithium may be used. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples thereof include metallic lithium and lithium-containing alloys. Examples of the lithium-containing alloy include alloys of Li and at least one of In, Al, Si and Sn. In some cases, two or more kinds of negative electrode active materials may be used in combination. Needless to say, a negative electrode active material other than the above may be used. The present invention exerts a particularly excellent effect when the expansion and contraction of the negative electrode active material during charging and discharging is large. From such a viewpoint and a high capacity, the negative electrode active material preferably contains metallic lithium, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and particularly preferably contains metallic lithium. Further, from the viewpoint of obtaining a battery having a high energy density, it is preferable to use an all-solid-state battery having metallic lithium as a negative electrode active material.

Examples of the shape of the negative electrode active material include a particle shape (spherical shape, fibrous shape), a thin film shape, and the like. When the negative electrode active material has a particle shape, its average particle size (D ₅₀ ) is preferably in the range of, for example, 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, and further preferably in the range of 100 nm. It is in the range of ~ 20 μm, and particularly preferably in the range of 1 to 20 μm. In the present specification, the value of the average particle size (D ₅₀ ) of the active material can be measured by the laser diffraction / scattering method.

The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is, for example, in the range of 0 to 100% by mass, preferably in the range of 0 to 99% by mass, and is preferably 50. More preferably, it is in the range of ~ 90% by mass.

The negative electrode active material layer may further contain a solid electrolyte, a conductive auxiliary agent and / or a binder as well as the positive electrode active material layer.

[Solid electrolyte layer]
The solid electrolyte layer is a layer interposed between the positive electrode active material layer and the negative electrode active material layer, and contains a solid electrolyte (usually as a main component). Since the specific form of the solid electrolyte contained in the solid electrolyte layer is the same as that described above, detailed description thereof will be omitted here.

The content of the solid electrolyte in the solid electrolyte layer is preferably in the range of, for example, 10 to 100% by mass, and more preferably in the range of 50 to 100% by mass, based on the total mass of the solid electrolyte layer. It is preferably in the range of 90 to 100% by mass, and more preferably in the range of 90 to 100% by mass.

The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte. Since the specific form of the binder that can be contained in the solid electrolyte layer is the same as that described above, detailed description thereof will be omitted here.

The thickness of the solid electrolyte layer varies depending on the configuration of the target all-solid-state battery, but is preferably in the range of 0.1 to 1000 μm, and more preferably in the range of 0.1 to 300 μm. preferable.

[Positive current collector plate and negative electrode current collector plate]
The material constituting the current collector plates (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a secondary battery can be used. As the constituent material of the current collector plate, for example, metal materials such as aluminum, carbon-coated aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. The same material may be used or different materials may be used for the positive electrode current collector plate 25 and the negative electrode current collector plate 27.

[Positive lead and negative electrode lead]
Further, although not shown, the current collector 11 and the current collector plates (25, 27) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode leads, materials used in known lithium ion secondary batteries can be similarly adopted. The part taken out from the exterior is heat-shrinkable with heat-resistant insulation so that it does not come into contact with peripheral devices or wiring and leak electricity, affecting the product (for example, automobile parts, especially electronic devices). It is preferable to cover with a tube or the like.

[Battery exterior]
As the battery exterior, a known metal can case can be used, or a bag-shaped case using a laminated film 29 containing aluminum, which can cover the power generation element as shown in FIG. 2, can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but the laminate film is not limited thereto. A laminated film is desirable from the viewpoint of high output and excellent cooling performance, and can be suitably used for batteries for large devices for EVs and HEVs. Further, since the group pressure applied to the power generation element from the outside can be easily adjusted, a laminated film containing aluminum is more preferable for the exterior body.

The all-solid-state lithium-ion secondary battery of this embodiment has an excellent output characteristic at a high rate because it has a configuration in which a plurality of single battery layers are connected in series. Therefore, the all-solid-state lithium-ion secondary battery of this embodiment is suitably used as a power source for driving EVs and HEVs.

FIG. 4 is a perspective view showing the appearance of a laminated all-solid-state lithium ion secondary battery according to an embodiment of the present invention.

As shown in FIG. 4, the flat laminated secondary battery 50 has a rectangular flat shape, and positive electrode tabs 58 and negative electrode tabs 59 for extracting electric power are pulled out from both side portions thereof. There is. The power generation element 57 is wrapped by the battery exterior (laminate film 52) of the laminated secondary battery 50, and the periphery thereof is heat-sealed. The power generation element 57 pulls out the positive electrode tab 58 and the negative electrode tab 59 to the outside. It is sealed in a closed state. Here, the power generation element 57 corresponds to the power generation element 21 of the laminated secondary battery 10a shown in FIG. 2 described above. The power generation element 57 is formed by stacking a plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15.

The all-solid-state battery of this embodiment is not limited to a flat shape. The wound all-solid-state battery may have a cylindrical shape, or may be deformed into a rectangular flat shape. There are no particular restrictions. The cylindrical shape is not particularly limited, for example, a laminated film may be used for the exterior body, or a conventional cylindrical can (metal can) may be used. Preferably, the power generation element is exteriorized with an aluminum laminate film. By this form, weight reduction can be achieved.

Further, the extraction of

tabs

58 and 59 shown in FIG. 4 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of each and taken out from each side. It is not limited to. Further, in the winding type all-solid-state battery, the terminal may be formed by using, for example, a cylindrical can (metal can) instead of the tab.

Although the embodiment of the present invention has been described above by taking an all-solid-state battery as an example, the positive electrode active material of the present invention can be applied to a lithium ion secondary battery other than the all-solid-state battery without limitation.

[Battery set]
An assembled battery is formed by connecting a plurality of batteries. More specifically, it is composed of serialization, parallelization, or both by using at least two or more. By connecting in series or in parallel, the capacitance and voltage can be adjusted freely.

It is also possible to form a small assembled battery that can be attached and detached by connecting multiple batteries in series or in parallel. Then, by connecting a plurality of small detachable batteries in series or in parallel, a large capacity and a large capacity suitable for a vehicle driving power source or an auxiliary power source that require a high volume energy density and a high volume output density. It is also possible to form an assembled battery having an output. How many batteries are connected to make an assembled battery, and how many stages of small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the vehicle (electric vehicle) to be installed. It may be decided according to the output.

[vehicle]
The all-solid-state battery according to this embodiment has a high energy density per volume. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles are required to have higher capacity and larger size than those used for electric and portable electronic devices. Therefore, the all-solid-state battery according to the present embodiment can be suitably used as a power source for a vehicle, for example, a vehicle drive power source or an auxiliary power source.

Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on the vehicle. In the present invention, since a high-capacity battery having excellent output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage and an electric vehicle having a long one-charge mileage can be configured by mounting such a battery. In addition to hybrid vehicles, fuel cell vehicles, electric vehicles (all four-wheeled vehicles (passenger cars, trucks, commercial vehicles such as buses, light vehicles, etc.)) , Including two-wheeled vehicles (motorcycles) and three-wheeled vehicles), it is possible to make an automobile with a long mileage. However, the application is not limited to automobiles, and can be applied to various power sources of other vehicles, for example, moving objects such as trains, and power supplies for mounting such as uninterruptible power supplies. It is also possible to use it as.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the technical scope of the present invention is not limited to the following examples.

[Example 1]
<Raw materials and reagents used>
In the following examples and comparative examples, the following materials were used.

・ Reagent for polycarbon sulfide synthesis Carbon disulfide (Fujifilm Wako Pure Chemical Industries, Ltd. special grade)
Dimethyl sulfoxide (special grade manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.)
Tetrabutylammonium perchlorate (manufactured by Tokyo Chemical Industry Co., Ltd.)
Methanol (special grade manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.)
-Conductive aid Ketjen Black (registered trademark) (manufactured by Lion, EC600JD)
・ Negative electrode material Lithium foil (manufactured by Niraco, thickness 0.20 mm)
Indium foil (manufactured by Niraco, thickness 0.30 mm)
・ Solid electrolyte material Lithium sulfide (Mitsuwa Chemical Co., Ltd., Li ₂ S)
Phosphorus pentasulfide (Aldrich _Corp., P _{2 S} 5).

1. 1. Preparation of positive electrode active material <Synthesis of polycarbon sulfide>
15 mL of carbon disulfide and 5.14 g of tetrabutylammonium perchlorate were sufficiently mixed and dissolved in 60 mL of dimethyl sulfoxide by stirring at room temperature. A platinum anode and a cathode were placed in this mixed solution, and a voltage of 4.5 V was applied between the cathode and the anode with a constant voltage power source to perform electrolysis for 72 hours. The red-black-brown product produced in the mixed solution and on the surface of the platinum plate by electrolysis was collected by filtration, thoroughly washed with methanol, and dried at 80 ° C. with a constant temperature dryer to obtain powdered polycarbon sulfide.

<Heat treatment of polycarbon sulfide>
The synthesized polycarbon sulfide was heat-treated at 200 ° C. for 6 hours under a reduced pressure of 5 Pa or less in an argon atmosphere having a dew point of −76 ° C. or lower. The ratio of the height B of the peak at around 980 ~ 1000 cm ^-1 to the height A of the main peak around 1430 ~ 1450 cm ^-1 of Raman shift in the Raman spectrum of the polysulfide carbon after heat treatment (B / A) is 0. It was 61.

<Analysis method of polycarbon sulfide>
The combustion infrared absorption method (HORIBA, Ltd. carbon sulfur analyzer EMIA-Expert) was used to quantify sulfur and carbon contained in polycarbon sulfide.

A Raman spectrophotometer (Laser Raman spectrophotometer NRS-5600 manufactured by Nippon Spectroscopy Co., Ltd.) was used for the Raman spectrum of polycarbon sulfide. The excitation wavelength was 532 nm, and data in the range of ^{Raman shift 2000 to 200 cm -1 was acquired.}

Background Raman spectrum subtracts a straight line method, was determined and the height A of the main peak existing on the 1430 ~ 1450 cm ^-1 Raman shift, the peaks present in 980 ~ 1000 cm ^-1 height B and, respectively.

2. Preparation of solid electrolyte and positive electrode mixture <Production of solid electrolyte>
In an argon glove box with a dew point of -76 ° C or lower, lithium sulfide (Li ₂ S) and diphosphorus sulfide (P ₂ S ₅ ) were mixed in a molar ratio of Li ₂ S: P ₂ S ₅ = 75: 25, for a total of 1.8 g. Weighed in a Menou mortar for 15 minutes and 162 g of 4 mm diameter zirconia balls in a zirconia pot with a capacity of 80 ml, and put it in a planetary ball mill (Fritsch, Premium line P-7) at 470 rpm. To prepare a solid electrolyte.

<Preparation of positive electrode mixture>
Next, in a glove box having an argon atmosphere with a dew point of −76 ° C. or lower, 0.100 g of polycarbon sulfide obtained by synthesizing and heat-treating 40 g of zirconia balls having a diameter of 5 mm and the above-mentioned solid electrolyte prepared above. 0.080 g and 0.020 g of Ketjen Black (registered trademark) were placed in a zirconia container having a capacity of 45 ml and treated with a planetary ball mill (Fritsch, Premium line P-7) at 370 rpm for 6 hours. A powder of the positive electrode mixture was obtained.

3. 3. Manufacture of all-solid-state lithium-ion battery <Battery manufacture>
The battery was prepared in a glove box having an argon atmosphere with a dew point of −76 ° C. or lower in which the solid electrolyte was prepared.

A SUS cylindrical convex punch (10 mm diameter) is inserted into one side of a McCall cylindrical tube jig (tube inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and the solid prepared above from the upper side of the cylindrical tube jig. 80 mg of electrolyte was added. After that, another SUS cylindrical convex punch is inserted to sandwich the solid electrolyte, and the solid electrolyte layer having a diameter of 10 mm and a thickness of about 0.6 mm is formed into a cylinder by pressing with a hydraulic press at a pressure of 75 MPa for 3 minutes. Formed in a tube jig. Next, the cylindrical convex punch inserted from the upper side is once pulled out, 7.5 mg of the positive electrode mixture is put on one side of the solid electrolyte layer in the cylindrical tube, and the cylindrical convex punch (also serves as the positive electrode current collector) is again inserted from the upper side. ) Was inserted and pressed at a pressure of 300 MPa for 3 minutes to form a positive electrode active material layer (positive electrode mixture layer) having a diameter of 10 mm and a thickness of about 0.06 mm on one side surface of the solid electrolyte layer. Next, the lower cylindrical convex punch (which also serves as the negative electrode current collector) is extracted, and the lithium foil punched to a diameter of 8 mm and the indium foil punched to a diameter of 9 mm are used as the negative electrode so that the lithium foil is on the negative electrode current collector side. A cylindrical convex punch was inserted again from the lower side of the cylindrical tube jig, and pressed at a pressure of 75 MPa for 3 minutes to form a lithium-indium negative electrode.

As described above, an all-solid-state lithium-ion battery in which a negative electrode current collector, a lithium-indium negative electrode, a solid electrolyte layer, a polycarbon sulfide positive electrode active material layer, and a positive electrode current collector are laminated was produced.

[Example 2]
The synthesized polycarbon sulfide was heat-treated at 130 ° C. for 4 hours under a reduced pressure of 5 Pa or less in an argon atmosphere having a dew point of −76 ° C. or lower. The ratio of the height B of the peak at around 980 ~ 1000 cm ^-1 of the main peak in the vicinity of 1430 ~ 1450 cm ^-1 Raman shift relative to the height A from the Raman spectra of polysulfides carbon after heat treatment (B / A) is 0. It was 48.

Batteries were produced using the same materials, compositions, and procedures as in Example 1 except for the above.

[Example 3]
The synthesized polycarbon sulfide was heat-treated at 130 ° C. for 4 hours under atmospheric pressure in an argon atmosphere with a dew point of −76 ° C. or lower. The ratio of the height B of the peak at around 980 ~ 1000 cm ^-1 to the height A of the main peak around 1430 ~ 1450 cm ^-1 of Raman shift in the Raman spectrum of the polysulfide carbon after heat treatment (B / A) is 0. It was 30.

[Comparative Example 1]
The synthesized polycarbon sulfide was heat-treated at 70 ° C. for 4 hours under a reduced pressure of 5 Pa or less in an argon atmosphere having a dew point of −76 ° C. or lower. The ratio of the height B of the peak of 980 ~ 1000 cm around ^-1 from the Raman spectra of the main peak around 1430 ~ 1450 cm ^-1 Raman shift relative to the height A (B / A) was 0.11.

[Comparative Example 2]
The synthesized polycarbon sulfide was heat-treated at 70 ° C. for 4 hours in a state where the pressure was reduced to 5 Pa or less in a nitrogen atmosphere having a purity of 99.9% or more. The ratio of the height B of the peak at around 980 ~ 1000 cm ^-1 to the height A of the main peak around 1430 ~ 1450 cm ^-1 of Raman shift in the Raman spectrum (B / A) was 0.07.

[Comparative Example 3]
The synthesized polycarbon sulfide was heat-treated at 70 ° C. for 4 hours in atmospheric pressure air having a dew point of −40 ° C. or lower. Although the Raman spectrum main peak around 1430 ~ 1450 cm ^-1 Raman shift was seen, it was not possible to detect the peak in the vicinity of 980 ~ 1000 cm ^-1.

<Rate characteristic evaluation method>
The evaluation of the batteries produced in Examples 1 to 3 and Comparative Examples 1 to 3 was carried out in a constant temperature and constant temperature bath set at 25 ° C. using a charge / discharge test device (HJ-SD8 manufactured by Hokuto Denko Co., Ltd.).

After installing the battery in the constant temperature bath and keeping the cell temperature constant, as cell conditioning, ^{constant current discharge is performed at a current density of 0.1 mA / cm 2 to} a cell voltage of 0.6 V, followed by the same current density. The 2.0 V constant current constant voltage charge was set to a ^{cutoff current of 0.01 mA / cm 2.} The capacity value (mAh / g) per polycarbon sulfide mass was determined from the charge / discharge capacity value obtained after repeating this conditioning charge / discharge cycle 10 times and the mass value of polycarbon sulfide contained in the positive electrode.

Similarly, the rate characteristics were charged at 25 ° C. with a cutoff current of 0.01C at a constant current of 0.2C-2.0V, and then discharged at a constant current of 0.6V with a cutoff voltage at each predetermined discharge rate. It was evaluated by the discharge capacity value obtained at times.

FIG. 5 shows the Raman spectrum of the positive electrode active material prepared in Examples 1, 3 and Comparative Example 1, and FIG. 6 shows the rate characteristics of the batteries prepared in each Example and Comparative Example. In FIG. 6, the discharge rate characteristic (%) shows the ratio (%) of the discharge capacities of 0.1C, 0.2C, 0.5C, and 1C to the 0.05C discharge capacity. Table 1 shows the B / A of the Raman spectrum of the positive electrode active material prepared in each Example and Comparative Example, the mass ratio of carbon and sulfur, the total mass ratio of carbon and hydrogen, and the rate characteristics of the battery. .. In Table 1, the discharge rate characteristic (%) shows the value (%) of the 1C discharge capacity with respect to the 0.05C discharge capacity.

From the results shown in Table 1 and FIGS. 5 and 6, the lithium ion secondary batteries of Examples 1 to 3 using the positive electrode active material having a predetermined Raman spectrum according to the present invention are compared with the batteries of Comparative Examples 1 to 3. It was found that the discharge capacity was maintained at a high rate even under high rate conditions.

10a, 50 stacked secondary batteries,
10b bipolar secondary battery,
11 Current collector,
11'Positive current collector,
11'' Negative electrode current collector,
11a Outermost layer current collector on the positive electrode side,
11b Outermost layer current collector on the negative electrode side,
13 Positive electrode active material layer,
15 Negative electrode active material layer,
17 Electrolyte layer,
19 Single battery layer,
21,57 Power generation elements,
23 Bipolar electrode,
25 Positive electrode current collector plate (positive electrode tab),
27 Negative electrode current collector plate (negative electrode tab),
29, 52 Laminated film,
31 Seal part,
58 Positive tab,
59 Negative electrode tab.

Claims

Containing at least carbon and sulfur, in the Raman spectrum, the ratio B / A of the height B of the peaks present in 980 ~ 1000 cm -1 of the main peak existing on the 1430 ~ 1450 cm -1 Raman shift relative to height A Positive electrode active material for lithium ion secondary batteries, which is 0.3 or more.
The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the total mass ratio of carbon and sulfur is 90% by mass or more.
The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the mass ratio of sulfur is 65% by mass or more.
The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the B / A is 0.48 or more.
A lithium ion secondary battery containing a positive electrode containing the positive electrode active material according to any one of claims 1 to 4, a negative electrode containing a negative electrode active material, and an electrolyte.
The lithium ion secondary battery according to claim 5, which is an all-solid-state battery having metallic lithium as a negative electrode active material.