JP5733550B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery with improved capacity.

  A lithium ion secondary battery includes a positive electrode and a negative electrode, and an electrolyte interposed between the two electrodes. The lithium ions in the electrolyte are charged and discharged by moving between the electrodes. As an active material that reversibly occludes and releases lithium ions in the positive electrode, lithium-containing transition metal oxides are mainly used. Patent documents 1 and 2 are mentioned as technical literature about a cathode material.

JP 2008-84766 A JP 2005-285545 A

In recent years, with the expansion of use of lithium ion secondary batteries, further performance improvement has been demanded. For example, it has been reported that by using a positive electrode active material to which NiO is added, high-temperature storage stability and output characteristics in a charged state can be improved (Patent Documents 1 and 2). However, in such a battery, the amount of Li per unit mass decreases due to the addition of NiO, and a sufficient capacity may not be obtained.
An object of the present invention is to provide a lithium ion secondary battery that includes a positive electrode containing NiO and can exhibit a higher capacity. Another object is to provide a method for producing such a lithium ion secondary battery.

The present inventors, as a cathode active material, focused on solid solution _{(LiMO 2} -Li ₂ MnO ₃₎ of the LiMO ₂ and _Li 2 MnO _3. In a battery using such a positive electrode active material, the upper limit voltage during use is set to a value (for example, about 4.5 to 4.8 V) higher than a normal value (typically about 4.1 to 4.3 V). By doing so, the capacity can be increased. However, when such a battery is initially charged in such a high voltage range, a significant amount of Li may be lost as an irreversible capacity. The present inventor _has, LiMO ₂ -Li not only the addition of NiO into 2 MnO ₃ based positive active material, by performing a predetermined processing, volume by volume reduction and the above-described irreversible capacity generated by NiO using The present invention has been completed by finding that the reduction is sufficiently reduced and a higher capacity lithium ion secondary battery can be realized.

According to the present invention, a lithium ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. Its positive electrode includes a solid solution of LiMO ₂ and _Li 2 MnO ₃ and NiO as the positive electrode active material. According to such a lithium ion secondary battery, since the use of the LiMO ₂ -Li ₂ MnO ₃ based positive electrode active material was a solid solution of NiO, even set an upper limit voltage higher than normal, the positive electrode characteristics during the initial charge Since the resulting decrease in capacity can be reduced, a higher battery capacity can be realized.
In one aspect | mode, the quantity of NiO contained in the said positive electrode active material is 3-13 mass%. According to the lithium ion secondary battery having such a configuration, capacity reduction in a voltage range higher than a normal upper limit voltage value can be more highly reduced during initial charging.

According to the present invention, a method for manufacturing a lithium ion secondary battery is also provided. The manufacturing method is
(A) preparing a positive electrode active material by subjecting a mixture of a solid solution of LiMO ₂ and Li ₂ MnO ₃ and NiO to a solid solution treatment; and
(B) constructing a lithium ion secondary battery using a positive electrode containing the positive electrode active material;
It is characterized by.
According to such a manufacturing method, even when charging to a voltage value higher than a normal upper limit voltage value at the time of initial charging, a reduction in capacity is suppressed, and a lithium ion secondary battery that can exhibit a higher capacity can be realized.

  In one aspect of the lithium ion secondary battery disclosed herein, the amount of NiO to be dissolved in the intermediate is 3 to 13% by mass of the positive electrode active material. According to such a manufacturing method, the capacity reduction as described above is further reduced, and a lithium ion secondary battery having a higher capacity can be realized.

The content disclosed in this specification includes:
(C) preparing a positive electrode active material by heating a mixture of a solid solution of LiMO ₂ and Li ₂ MnO ₃ and NiO at 500 to 800 ° C .; and
(D) constructing a lithium ion secondary battery using a positive electrode containing the positive electrode active material;
A method for manufacturing a lithium ion secondary battery is included. According to such a manufacturing _method, it is possible to perform the solid solution treatment to a mixture of LiMO ₂ -Li ₂ MnO ₃ solid solution and NiO suitably.

  As described above, a battery that can be used up to an upper limit voltage higher than usual and has a higher capacity is suitable as a power source used in a vehicle. Therefore, according to the present invention, there is provided a vehicle including any lithium ion secondary battery disclosed herein or a lithium ion secondary battery manufactured by any method disclosed herein. In particular, a vehicle (for example, an automobile) including such a lithium ion secondary battery as a power source (typically, a power source of a hybrid vehicle or an electric vehicle) is preferable.

It is a perspective view which shows typically the external shape of the lithium ion secondary battery which concerns on one Embodiment. It is the II-II sectional view taken on the line in FIG. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery of this invention. It is a perspective view which shows typically the shape of the coin cell produced in the Example.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The lithium ion secondary battery disclosed here contains one or more solid solutions of LiMO ₂ , Li ₂ MnO ₃ and NiO as a positive electrode active material. Each of these oxides indicates the composition of the phase constituting the solid solution crystal, and the starting materials used for the formation of the solid solution may be the same or different. The solid solution is obtained by incorporating NiO into a positive electrode active material crystal in which two phases of LiMO ₂ and Li ₂ MnO ₃ coexist (that is, LiMO ₂ -Li ₂ MnO ₃ in which NiO is dissolved). As a positive electrode active material). In the present specification, the solid solution refers to a material in which the raw materials are not simply mixed, but subjected to a solid solution treatment after mixing, and the crystal structure of the solid solution may not be uniform, There may be a partial deviation in the distribution of the constituent elements. Further, after the solid solution treatment, a part of NiO may exist outside the crystal (for example, the crystal surface).

LiMO ₂ has a layered rock salt type crystal structure. M represents a transition metal ion, and may be one or more selected from, for example, Ni, Co, Mn, V, Ti, Cu, Zn, Mo, Fe, and Zr. In addition to these transition metals, LiMO ₂ is one or two selected from non-transition metals or metalloids (for example, Al, Si, Mg, Ca, etc.) within the range that the layered rock salt crystal structure is not impaired. May be included. Specific examples of the _{LiMO 2, LiNi x Co y Mn} z O 2 (x + y + z = 1), LiNi x Al y O 2 (x + y = 1), LiCo x Al y O 2 (x + y = 1), LiMn x Al y And O ₂ (x + y = 1). A particularly preferable example is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ . Note that the concept of LiMO ₂ herein, shall not be included _Li 2 MnO ₃ below.

Li ₂ MnO ₃ has a layered rock salt type crystal structure similar to LiMO ₂ . Li ₂ MnO ₃ can also be expressed as LiLi _1/3 Mn _2/3 O ₂ and can also be understood as a compound in which M in LiMO ₂ is Li _1/3 Mn _2/3 . That is, the above composition formula LiLi _1/3 Mn _2/3 O ₂ is 25% Li in Li ₂ MnO ₃ (Li corresponding to Li _1/3 in LiLi _1/3 Mn _2/3 O ₂ ) is In the crystal, not in the interlayer but in the same manner as M in LiMO ₂ , it is located at the octahedral site. The amount of Li ₂ MnO ₃ contained in the solid solution is preferably about 0.1 mol to 5 mol (for example, 0.5 mol to 4 mol) with respect to 1 mol of LiMO ₂ . If the amount of _Li 2 MnO ₃ for LiMO ₂ amount is too large, the capacity reduction of the time of initial charging becomes too large. If the amount of Li ₂ MnO ₃ is too small, a sufficient capacity may not be obtained.

NiO is incorporated into a part of the layered rock salt type crystal structure formed from LiMO ₂ and Li ₂ MnO ₃ (typically an octahedral structure) by solid solution. The amount of NiO contained in the solid solution is preferably about 0.08 mol to 0.45 mol (for example, 0.1 mol to 0.4 mol) with respect to 1 mol of Li ₂ MnO ₃ . In one aspect, for example, the solid solution is formed so that NiO is about 3 to 13% by mass of the total amount of the positive electrode active material. Such an embodiment is suitable when LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as LiMO ₂ . If the solid solution amount of NiO is too large, the amount of Li is relatively small and a sufficient capacity may not be obtained. If the amount of NiO dissolved is too small, the effect of suppressing the capacity reduction during the initial charge may not be sufficiently obtained.

The method for producing the solid solution is not particularly limited as long as a layered rock salt type crystal structure can be constructed, and a conventionally known method (for example, a solgel method, a coprecipitation method, a flux method, a sintering method, etc.) is appropriately employed. be able to. The formation of the solid solution may be performed at once, or may be performed in multiple stages.
As the solid solution as the positive electrode active material disclosed herein, for example, a solid solution (intermediate) of LiMO ₂ and Li ₂ MnO ₃ is prepared, and the solid solution treatment is performed on the mixture of the intermediate and NiO. Can be manufactured. According to this manufacturing method, after a layered rock salt type crystal skeleton is constructed from LiMO ₂ and Li ₂ MnO ₃ , NiO can be efficiently incorporated into the crystal.

Examples of the intermediate include salts (acetate, alkoxide, chloride salt, etc.) of each metal (ie, Li, one or more M, Mn) contained in the LiMO ₂ phase and the Li ₂ MnO ₃ phase. , Each metal element is weighed so as to have a desired molar ratio, dissolved or dispersed in an appropriate solvent (which may be a mixed solvent), and then subjected to treatment such as solvent removal if necessary, and then 200 to 200- It can form by baking at about 1100 degreeC (for example, 200-1000 degreeC) grade. The calcination may be performed at once, or may be performed in multiple stages at different temperature settings. For example, after the preliminary calcination is performed at about 200 to 700 ° C., typically after pulverization and mixing, the main calcination can be performed at about 600 to 1100 ° C.
The solid solution treatment method is not particularly limited. For example, a mixture of the intermediate and NiO weighed so as to have a desired mass ratio or molar ratio is dissolved in an appropriate solvent (which may be a mixed solvent). Alternatively, after dispersion, if necessary, treatment such as solvent removal may be performed, followed by heating at about 500 to 800 ° C. NiO having a purity of about 90% or more can be used without particular limitation.
As said solvent, water, alcohols, such as ethanol, organic solvents, such as hexane, or the mixed solvent containing these 2 or more types can be used, for example.

  In the step (A), if the firing temperature is too high, Li in the active material may evaporate. If the firing temperature is too low, it may be difficult to achieve a sufficient solid solution. In the step (B), if the firing temperature is too high, the surface area may become too small. If the firing temperature is too low, the solid solution becomes incomplete, and a sufficient capacity reduction suppressing effect may not be obtained during initial charging. In any case, the firing time can be, for example, about 1 to 5 hours. These firing steps can be performed in the air.

  According to the present invention, there is provided a lithium ion secondary battery comprising a positive electrode having any of the positive electrode active materials disclosed herein. An embodiment of such a lithium ion secondary battery will be described in detail by taking as an example a lithium ion secondary battery 100 (FIG. 1) having a configuration in which an electrode body and a non-aqueous electrolyte are accommodated in a rectangular battery case. The technology disclosed herein is not limited to such an embodiment. That is, the shape of the lithium ion secondary battery disclosed herein is not particularly limited, and the battery case, electrode body, and the like can be appropriately selected in material, shape, size, and the like according to the application and capacity. . For example, the battery case may have a rectangular parallelepiped shape, a flat shape, a cylindrical shape, or the like. In addition, in the following drawings, the same code | symbol is attached | subjected to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  As shown in FIGS. 1 and 2, the lithium ion secondary battery 100 includes a wound electrode body 20 and a flat box-shaped battery case 10 corresponding to the shape of the electrode body 20 together with an electrolyte (not shown). It can be constructed by being housed inside the opening 12 and closing the opening 12 of the case 10 with a lid 14. The lid body 14 is provided with a positive terminal 38 and a negative terminal 48 for external connection so that a part of the terminals protrudes to the surface side of the lid body 14.

  The electrode body 20 includes a positive electrode sheet 30 in which a positive electrode active material layer 34 is formed on the surface of a long sheet-like positive electrode current collector 32, and a negative electrode active material layer on the surface of a long sheet-like negative electrode current collector 42. The negative electrode sheet 40 on which the electrode 44 is formed is rolled up with two long sheet-like separators 50, and the obtained wound body is crushed from the side surface and ablated to form a flat shape. ing.

  The positive electrode sheet 30 is formed such that the positive electrode active material layer 34 is not provided (or removed) at one end portion along the longitudinal direction, and the positive electrode current collector 32 is exposed. Similarly, the negative electrode sheet 40 to be wound is not provided with (or removed from) the negative electrode active material layer 44 at one end along the longitudinal direction so that the negative electrode current collector 42 is exposed. Is formed. Then, the positive electrode terminal 38 is joined to the exposed end portion of the positive electrode current collector 32, and the negative electrode terminal 48 is joined to the exposed end portion of the negative electrode current collector 42, respectively. The positive electrode sheet 30 or the negative electrode sheet 40 is electrically connected. The positive and negative terminals 38 and 48 and the positive and negative current collectors 32 and 42 can be joined by, for example, ultrasonic welding, resistance welding, or the like.

  The positive electrode sheet 30 is, for example, a paste or slurry composition in which any of the positive electrode active materials disclosed herein is dispersed in an appropriate solvent together with a conductive material, a binder (binder), and the like as necessary. (Positive electrode mixture) can be preferably prepared by applying the positive electrode current collector 32 to the positive electrode current collector 32 and drying the composition.

  As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. A conductive material can be used alone or in combination of two or more. The amount of the conductive material contained in the positive electrode mixture may be appropriately selected according to the type and amount of the positive electrode active material.

As the binder, for example, a water-soluble polymer that dissolves in water, a polymer that disperses in water, a polymer that dissolves in a non-aqueous solvent (organic solvent), and the like can be appropriately selected and used. Moreover, only 1 type may be used independently and 2 or more types may be used in combination.
Examples of the water-soluble polymer include carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP), and polyvinyl alcohol (PVA). It is done.
Examples of the water-dispersible polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetra. Fluorine resin such as fluoroethylene copolymer (ETFE), vinyl acetate copolymer, styrene butadiene block copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), rubbers such as gum arabic, etc. It is done.
Examples of the polymer dissolved in the non-aqueous solvent (organic solvent) include, for example, polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer. (PEO-PPO) and the like.
What is necessary is just to select the addition amount of a binder suitably according to the kind and quantity of a positive electrode active material.

  For the positive electrode current collector 32, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector 32 may vary depending on the shape of the lithium ion secondary battery, and is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. . In the present embodiment, a sheet-like aluminum positive electrode current collector 32 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In such an embodiment, for example, an aluminum sheet having a thickness of about 10 μm to 30 μm can be preferably used.

  The negative electrode sheet 40 is made of, for example, a paste or slurry composition (negative electrode mixture) in which a negative electrode active material is dispersed in a suitable solvent together with a binder (binder) as necessary. It can preferably be prepared by applying and drying the composition.

  As the negative electrode active material, one type or two or more types of materials conventionally used in lithium ion secondary batteries can be used without any particular limitation. For example, a carbon particle is mentioned as a suitable negative electrode active material. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Any carbon material of a so-called graphitic material (graphite), non-graphitizable carbon material (hard carbon), easily graphitized carbon material (soft carbon), or a combination of these materials is preferably used. obtain. Among these, graphite particles such as natural graphite can be preferably used.

  As the binder, the same positive electrode as that described above can be used alone or in combination of two or more. Although it does not specifically limit, the usage-amount of the binder with respect to 100 mass parts of negative electrode active materials can be made into the range of 0.1-10 mass parts, for example.

  As the negative electrode current collector 42, a conductive member made of a metal having good conductivity is preferably used. For example, copper or an alloy containing copper as a main component can be used. In addition, the shape of the negative electrode current collector 42 may vary depending on the shape of the lithium ion secondary battery and the like, and thus is not particularly limited, and may be various forms such as a rod shape, a plate shape, a sheet shape, a foil shape, and a mesh shape. possible. In the present embodiment, a sheet-like copper negative electrode current collector 42 is used, and can be preferably used for the lithium ion secondary battery 100 including the wound electrode body 20. In this embodiment, for example, a copper sheet having a thickness of about 6 μm to 30 μm can be preferably used.

The nonaqueous electrolytic solution contains a supporting salt in a nonaqueous solvent (organic solvent). As the supporting salt, a lithium salt used as a supporting salt in a general lithium ion secondary battery can be appropriately selected and used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiCF ₃ SO _{3 and the} like. These supporting salts can be used alone or in combination of two or more. A particularly preferred example is LiPF ₆ . The non-aqueous electrolyte is preferably prepared, for example, so that the concentration of the supporting salt is within a range of 0.7 to 1.3 mol / L.

  As said non-aqueous solvent, the organic solvent used for a general lithium ion secondary battery can be selected suitably, and can be used. Examples of particularly preferred non-aqueous solvents include carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and propylene carbonate (PC). The These organic solvents can be used alone or in combination of two or more. For example, a mixed solvent of EC and DEC can be preferably used.

  The separator 50 is a layer interposed between the positive electrode sheet 30 and the negative electrode sheet 40, and typically has a sheet shape, and the positive electrode active material layer 34 of the positive electrode sheet 30 and the negative electrode active material layer of the negative electrode sheet 40. 44 to be in contact with each other. Then, prevention of short circuit due to the contact between the electrode active material layers 34 and 44 in the positive electrode sheet 30 and the negative electrode sheet 40, and the conduction path between the electrodes (conductive path) by impregnating the electrolyte in the pores of the separator 50. ). As this separator 50, a conventionally well-known thing can be especially used without a restriction | limiting. For example, a porous sheet made of resin (a microporous resin sheet) can be preferably used. A porous polyolefin resin sheet such as polyethylene (PE), polypropylene (PP), and polystyrene is preferred. In particular, a PE sheet, a PP sheet, a multilayer structure sheet in which a PE layer and a PP layer are laminated, and the like can be suitably used. The thickness of the separator is preferably set within a range of approximately 10 μm to 40 μm, for example.

In practicing the present invention, by a solid solution of NiO in LiMO ₂ -Li ₂ MnO ₃ based positive electrode material, it is not necessary to elucidate the mechanism of reduction capacity at the initial charge is reduced, the following It is possible.

When NiO is added, high-temperature storage stability, output characteristics and the like can be improved, but the battery capacity can be reduced by decreasing the amount of lithium per unit mass. _Further, when the initial charge LiMO ₂ -Li ₂ MnO ₃ type lithium ion secondary battery, the voltage is low stage between the terminals, mainly apart Li of interlayer is removed, the said voltage is above 4.5V, Li ₂ Li at the octahedral site of MnO ₃ phase begins to desorb. As the octahedral site Li is desorbed, O that forms the apex of the octahedron is released out of the crystal for charge compensation, and oxygen holes are generated in the crystal structure. In this way, since octahedral sites surrounded by O are reduced, a part of the detached Li cannot be returned to the crystal during discharge, resulting in an irreversible capacity, which also reduces the capacity of the battery. Invite.

On the other hand, in the NiO LiMO ₂ -Li ₂ MnO ₃ type lithium ion secondary battery which is a solid solution, NiO is incorporated in the crystal structure (octahedral structure), since ^{the Ni 2+} is present in the crystal, Li ₂ When Li is desorbed from the octahedral site of the MnO ₃ phase, charge compensation is performed by changing the valence of Ni ²⁺ , for example, as represented by the reaction formula: NiO + xO → NiO _{1 + x} ; This prevents O from being released during initial charging, and maintains an octahedral site capable of occluding Li, thereby suppressing the occurrence of irreversible capacity. That is, at least a part of the capacity reduction due to NiO is offset by the use of Li ₂ MnO ₃ and the capacity increase effect due to the high upper limit voltage setting and the irreversible capacity reduction effect due to the solid solution NiO. Here, NiO is not solid solution in LiMO ₂ -Li ₂ MnO ₃ based positive electrode material, simply are mixed, since no ^{Ni 2+} is incorporated in the crystal, the charge compensation mechanism as described above Does not work.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Example 1>
Lithium acetate, cobalt acetate, nickel acetate and manganese acetate, which were precisely weighed so that the molar ratio Li: Ni: Co: Mn was 9: 1: 1: 4, were added to pure water together with glycolic acid and stirred and dissolved. After removing water by evaporating at 80 ° C., it was baked (pre-baked) at 500 ° C. This was pulverized and mixed, and then fired at 800 ° C. (main firing). As the positive electrode active material according to this example, the composition formula was LiNi _1/3 Co _1/3 Mn _1/3 O ₂ : Li ₂ MnO. _The compound M which is ₃ (molar ratio 1: 1) was obtained. Compound M and NiO were pulverized and mixed so that the mass ratio was 90:10 to obtain a positive electrode active material of this example.
This positive electrode active material and carbon black (conductive material) were mixed so that the mass ratio was 80:15. N-methyl-2-pyrrolidone (NMP) in which PVDF was dissolved was added thereto to obtain a slurry-like positive electrode mixture. This slurry was applied to an aluminum foil having a thickness of 10 μm to obtain a positive electrode sheet.
The positive electrode sheet was punched into a circle having a diameter of 16 mm to obtain a test positive electrode. As shown in FIG. 4, this positive electrode 61, a lithium negative electrode 62 (a metal lithium foil having a diameter of 19 mm and a thickness of 0.15 mm), and an electrolytic solution (1M LiPF ₆ solution (volume ratio of 3: 7 EC / DMC mixed) The separator 63 impregnated with the solvent)) (circular porous polyethylene sheet with a diameter of 22 mm) is assembled in a stainless steel container 65 (counter electrode terminal), sealed with a gasket 64 and a lid 66 (working electrode terminal), and 20 mm in diameter. A 2032 type coin cell 60 (a half cell for evaluation) having a thickness of 3.2 mm was constructed.
<Example 2>
The compound M and NiO obtained in Example 1 were pulverized and mixed so that the mass ratio M: NiO was 95: 5, and fired at 600 ° C. to obtain the positive electrode active material of this example. A 2032 type coin cell was constructed in the same manner as in Example 1 except that this positive electrode active material was used.
<Example 3>
A 2032 type coin cell was constructed in the same manner as in Example 2 except that M: NiO was changed to 90:10.
<Example 4>
A 2032 type coin cell was constructed in the same manner as in Example 2 except that M: NiO was 85:15.
<Example 5>
A 2032 type coin cell was constructed in the same manner as in Example 2 except that M: NiO was changed to 80:20.
<Example 6>
A 2032 type coin cell was constructed in the same manner as in Example 1 except that only the compound M obtained in Example 1 was used as the positive electrode active material.

[Initial discharge capacity measurement]
Each battery cell was charged at a rate of 0.1 C (1 C is a current value that can be fully charged and discharged in 1 hour) until the voltage between both terminals reached 4.8 V. Next, the battery was discharged at a rate of 1 C until the voltage between both terminals became 2.5 V, and the capacity at that time was measured as the initial discharge capacity (mAh / g). The measurement results are shown in Table 1 together with the amount of NiO used in each example.

As shown in Table _1, LiMO ₂ -Li 2 MnO ₃ as compared with Example 1 of the battery made by using a mixture of solid solution and _NiO, Example 2 comprising a solid solution and a LiMO ₂ -Li 2 MnO ₃ solid solution and NiO The batteries of ˜5 had a capacity of 10 to 35 mAh / g after the initial charge. Among them, the batteries of Examples 2 and 3 showed higher capacity than the battery of Example 6 not using NiO even though NiO was used.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Vehicle 20 Winding electrode body 30 Positive electrode sheet 32 Positive electrode current collector 34 Positive electrode active material layer 38 Positive electrode terminal 40 Negative electrode sheet 42 Negative electrode current collector 44 Negative electrode active material layer 48 Negative electrode terminal 50 Separator 60 2032 type coin cell 100 Lithium ion secondary battery

Claims (6)

A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The positive electrode is a solid solution of LiMO ₂ and _Li 2 MnO ₃ and NiO, the amount of NiO contained in the solid solution is 0.08 mol to 0.45 mol per 1 mol of _Li 2 MnO ₃ look including a solid solution as a positive electrode active material,
Wherein said LiMO ₂ and _Li 2 MnO ₃ is a compound both having a layered rock salt type crystal structure, the element M in the LiMO ₂ as essential constituent elements capable of forming LiMO ₂ of layered rock-salt type crystal structure Lithium ion dioxide containing one or more transition metal elements and other one or more non-transition metal elements or metalloid elements as the other optional constituent elements or not containing the optional constituent elements Next battery.   The lithium ion secondary battery according to claim 1, wherein the positive electrode active material contains 3 to 13 mass% of NiO. A method for producing a lithium ion secondary battery, comprising:
The amount of NiO that an solid solution contained in the solid solution of LiMO ₂ and _Li 2 MnO ₃ and NiO is subjected to solid solution treatment in a mixture of solid solution and NiO with (A) LiMO ₂ and _Li 2 MnO ₃ is 1 Preparing a positive electrode active material comprising a solid solution of 0.08 mol to 0.45 mol with respect to mol of Li ₂ MnO ₃ , wherein both LiMO ₂ and Li ₂ MnO ₃ have a layered rock salt type crystal structure; a compound having the element M in the LiMO ₂ encompasses one or more transition metal elements as an essential constituent element capable of forming a LiMO ₂ of layered rock-salt type crystal structure, any element other than it Including one or two or more non-transition metal elements or metalloid elements or not including the optional constituent elements ; and
(B) constructing a lithium ion secondary battery using a positive electrode containing the positive electrode active material;
A method for producing a lithium ion secondary battery.   The method for producing a lithium ion secondary battery according to claim 3, wherein the mixture is heated at 500 to 800 ° C. as the solid solution treatment.   The method for producing a lithium ion secondary battery according to claim 3 or 4, wherein the amount of NiO contained in the positive electrode active material is 3 to 13 mass% of the total amount of the positive electrode active material.   A vehicle comprising the lithium ion secondary battery according to claim 1 or 2 or the lithium ion secondary battery produced by the method according to any one of claims 3 to 5.

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