JP2018133190A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which can achieve high-level good balance between output characteristics at a low temperature in a low state-of-charge condition and the capability of suppressing the rise in temperature in the state of being overcharged.SOLUTION: A lithium ion secondary battery herein disclosed comprises: a laminate arranged by laminating positive and negative electrodes and separators as an electrode body; and a nonaqueous electrolyte. The positive electrode has a positive electrode active material layer including a positive electrode active material. The positive electrode active material includes lithium (Li), and a metal element (M) other than lithium. The ratio (Li/M) of the lithium element to the metal element other than lithium included in the positive electrode active material of the positive electrode of an interior layer portion of the laminate is larger than the ratio (Li/M) of the lithium element to the metal element other than lithium included in the positive electrode active material of the positive electrode of an exterior layer portion of the laminate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries are lighter and have a higher energy density than existing batteries, and have recently been used as so-called portable power sources for vehicles and personal computers and power sources for driving vehicles. Lithium-ion secondary batteries are expected to become increasingly popular as high-output power sources for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). Yes.

  Lithium ion secondary batteries are required to have higher performance with the spread of the lithium ion secondary batteries, and various developments have been made for higher performance. For example, Patent Document 1 discloses that a lithium-containing compound containing a lithium element and one or more transition metal elements is used as a positive electrode active material used for a positive electrode of a lithium ion secondary battery. And in patent document 1, in order to obtain a favorable battery characteristic, in the said lithium containing compound, the molar ratio (lithium element / total transition metal element) of a lithium element and all the transition metal elements was made larger than 1.05, And it is described to make it smaller than 1.25.

JP 2013-037774 A

When an overcharge occurs in a lithium ion secondary battery, a rapid temperature rise can occur, and it is desired that the temperature rise during the overcharge is highly suppressed. In addition, it is desired that the output of the lithium ion secondary battery be high even in a low temperature and low charge environment where output is difficult to output.
As a result of intensive studies by the present inventor, as described in Patent Document 1, a positive electrode active material having a large molar ratio of lithium element to all transition metal elements (lithium element / all transition metal elements) is used as a lithium ion secondary battery. When used, the temperature rise during overcharge can be suppressed, but the output at low temperature and low charge is low, while the molar ratio of lithium element to all transition metal elements (lithium element / total transition metal element) is It has been found that when a small positive electrode active material is used for a lithium ion secondary battery, the output at low temperature and low charge is high, but the degree of suppression of temperature rise at overcharge is small. Moreover, in order to suppress the temperature rise at the time of overcharge, a method of arranging a member having a large heat capacity inside the electrode body of the lithium ion secondary battery can be considered. I found that the output was low.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion secondary battery having a good balance between output characteristics at low temperature and low charge and temperature rise suppression during overcharge.

The lithium ion secondary battery disclosed herein includes a laminated body in which a positive electrode, a negative electrode, and a separator are laminated as an electrode body, and a nonaqueous electrolyte. The positive electrode includes a positive electrode active material layer containing a positive electrode active material. The positive electrode active material contains lithium (Li) and a metal element (M) other than lithium. Lithium element ratio (Li / M) to metal elements other than lithium contained in the positive electrode active material of the positive electrode in the inner layer portion of the laminate is lithium contained in the positive electrode active material of the positive electrode in the outer layer portion of the laminate. It is larger than the ratio of lithium element to other metal elements (Li / M).
According to such a configuration, the positive electrode active material having a high ratio of lithium element to metal element other than lithium, which has a high effect of suppressing temperature rise during overcharge, is formed in the inner layer portion of the electrode body (laminated body) that is easily trapped. A positive electrode active material having a low ratio of lithium element to metal elements other than lithium, which is excellent in output characteristics at low temperature and low charge, can be contained in the positive electrode of the outer layer portion of the electrode body (laminate). It can be included. Therefore, it is possible to provide a lithium ion secondary battery with a high balance between output characteristics at low temperature and low charge and temperature rise suppression during overcharge.

It is sectional drawing which shows typically the internal structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the electrode body (laminated electrode body) of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the electrode body (winding electrode body) of the modification of the lithium ion secondary battery which concerns on one Embodiment of this invention. It is a figure which shows typically the cross section of the direction perpendicular | vertical to the winding axis | shaft of the winding electrode body of the modification of the lithium ion secondary battery which concerns on one Embodiment of this invention. Lithium ion secondary battery (X) using a positive electrode active material having an Li / M ratio of 1.05 for both the inner layer portion and the outer layer portion of the electrode body, and a Li / M ratio of 1 for both the inner layer portion and the outer layer portion of the electrode body It is a graph which shows about the time-dependent change of the temperature of a lithium ion secondary battery at the time of making it overcharge intentionally about the lithium ion secondary battery (Y) using the positive electrode active material which is .20. A lithium ion secondary battery (A) using a positive electrode active material having a Li / M ratio of 1.05 for both the inner layer portion and the outer layer portion of the electrode body in both the inner layer portion and the outer layer portion of the electrode body, and the inner layer portion of the electrode body A lithium-ion secondary battery (B) using a positive electrode active material having a Li / M ratio of 1.15 and a positive electrode active material having a Li / M ratio of 1.05 for the outer layer of the electrode body; Intended for a lithium ion secondary battery (C) using a positive electrode active material having an Li / M ratio of 1.20 for an inner layer portion and a positive electrode active material having a Li / M ratio of 1.05 for an outer layer portion of an electrode body. 5 is a graph showing a change with time in the temperature of a lithium ion secondary battery when overcharge is caused in an automatic manner. A lithium ion secondary battery (1) using a positive electrode active material having a Li / M ratio of 1.05 for both the inner layer portion and the outer layer portion of the electrode body for both the inner layer portion and the outer layer portion of the electrode body, and the inner layer portion of the electrode body Lithium ion secondary battery (2) in which the Li / M ratio of the positive electrode active material is larger than the Li / M ratio of the positive electrode active material in the outer layer part of the electrode body, and the temperature rise during overcharge at the center part of the electrode body It is a graph which shows the output at the time of low temperature and low charge about the lithium ion secondary battery (3) which has arrange | positioned the member with a large heat capacity so that the grade of suppression may become high.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a general configuration and manufacturing process of a lithium ion secondary battery that does not characterize the present invention) are as follows. Therefore, it can be grasped as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Moreover, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

In the present specification, the “secondary battery” refers to a general power storage device that can be repeatedly charged and discharged, and is a term including a so-called storage battery such as a lithium ion secondary battery and a power storage element such as an electric double layer capacitor.
Hereinafter, the present invention will be described in detail by taking a flat rectangular lithium ion secondary battery as an example, but the present invention is not intended to be limited to those described in the embodiment.

  A lithium ion secondary battery 100 shown in FIG. 1 is constructed by accommodating a flat electrode body 20A and a nonaqueous electrolyte (not shown) in a flat rectangular battery case (that is, an exterior container) 30. This is a sealed lithium ion secondary battery 100. The battery case 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin safety valve 36 set so as to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. Yes. In addition, the battery case 30 is provided with an inlet (not shown) for injecting a nonaqueous electrolyte. The positive terminal 42 is electrically connected to the positive current collector 42a. The negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a. As the material of the battery case 30, for example, a light metal material having good thermal conductivity such as aluminum is used.

The non-aqueous electrolyte can be the same as that of a conventional lithium ion secondary battery, and typically, an organic solvent (non-aqueous solvent) containing a supporting salt can be used.
As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, lactones and the like used in electrolytes of general lithium ion secondary batteries are used without particular limitation. Can do. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), Examples thereof include monofluoromethyl difluoromethyl carbonate (F-DMC) and trifluorodimethyl carbonate (TFDMC). Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate.
As the supporting salt, for example, a lithium salt such as LiPF ₆ , LiBF ₄ , LiClO ₄ (preferably LiPF ₆ ) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

  In addition, the non-aqueous electrolyte is, for example, a gas generating agent such as biphenyl (BP) or cyclohexylbenzene (CHB); Various additives such as a film forming agent such as vinylene carbonate (VC); a dispersant; a thickener may be included.

  As shown in FIG. 2, the electrode body 20A is a laminated body in which a plurality of positive electrode sheets 50A and a plurality of negative electrode sheets 60A are laminated with a separator 70A interposed therebetween. That is, in this embodiment, the electrode body 20A is a stacked electrode body. In FIG. 2, the description of a part of the laminated structure is omitted, and FIG. 2 does not represent the actual number of laminated layers of the positive electrode sheet 50A, the negative electrode sheet 60A, and the separator 70A. The number of laminations of the positive electrode sheet 50A, the negative electrode sheet 60A, and the separator 70A may be the same as the number of laminations of the laminated electrode body used in the conventional lithium ion secondary battery.

  The positive electrode sheet 50A has a configuration in which a positive electrode active material layer 54A containing a positive electrode active material is formed on one or both surfaces (here, both surfaces) of a sheet-like positive electrode current collector 52A. The negative electrode sheet 60A has a configuration in which a negative electrode active material layer 64A containing a negative electrode active material is formed on one or both surfaces (here, both surfaces) of a sheet-like negative electrode current collector 62A. In the left-right direction in FIG. 1 (the direction parallel to the longitudinal direction of the bottom surface and the top surface in the normal use state of the lithium ion secondary battery 100), the positive electrode active material layer non-formed portion 52Aa is formed at one end of the electrode body 20A. (That is, the portion where the positive electrode current collector 52A is exposed without forming the positive electrode active material layer 54A), and the negative electrode active material layer non-formation portion 62Aa (that is, the negative electrode active material layer 64A is formed at the other end) The portion where the negative electrode current collector 62A is exposed is formed), and the positive electrode active material layer non-formed portion 52Aa and the negative electrode active material layer non-formed portion 62Aa are respectively formed in the positive electrode current collector plate 42a and the negative electrode current collector plate. 44a is joined.

Examples of the positive electrode current collector 52A constituting the positive electrode sheet 50A include an aluminum foil.
The positive electrode active material included in the positive electrode active material layer 54A contains lithium (Li) and a metal element (M) other than lithium. The positive electrode active material is, for example, a compound represented by the general formula: Li _x MO ₂ (x preferably satisfies 1 ≦ x <1.25). M is, for example, one or more metals selected from the group consisting of Mn, Co, Ni, Al, Fe, Mg, Ti, Cu, Zn, Ga, In, Sn, La, Ta, Ce, etc. Transition metal). The positive electrode active material may further contain a nonmetallic element such as P, Si, or F. Specific examples of the positive electrode active material include Li _x Ni _1/3 Co _1/3 Mn _1/3 O ₂ (1 ≦ x <1.25), Li _x NiO ₂ (1 ≦ x <1.25), Li _x CoO ₂ (1 ≦ x <1.25), Li _x FeO ₂ (1 ≦ x <1.25), Li _x Mn ₂ O ₄ (1 ≦ x <1.25) and the like.
The positive electrode active material layer 54A may include components other than the active material, such as a conductive material and a binder. As the conductive material, for example, carbon black such as acetylene black (AB) and other (eg, graphite) carbon materials can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) can be used.

  Examples of the negative electrode current collector 62A constituting the negative electrode sheet 60A include copper foil. As the negative electrode active material contained in the negative electrode active material layer 64A, for example, a carbon material such as graphite, hard carbon, or soft carbon can be used. The negative electrode active material layer 64A can include components other than the active material, such as a binder and a thickener. As the binder, for example, styrene butadiene rubber (SBR) can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

  Examples of the separator 70A include a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat resistant layer (HRL) may be provided on the surface of the separator 70A.

In the present embodiment, the laminate constituting the electrode body 20A is a ratio of a lithium element to a metal element other than lithium contained in the positive electrode active material of the positive electrode sheet 50A of the inner layer portion 22A (hereinafter also referred to as “Li / M ratio”). However, the ratio of the lithium element to the metal element other than lithium contained in the positive electrode active material of the positive electrode sheet 50A of the outer layer portion 24A of the laminate (Li / M) is larger.
Specifically, for example, as the inner layer portion 22A, the central portion in the stacking direction of the stacked body and 15% to 30% of the total number of layers (total number of the positive electrode sheet 50A, the negative electrode sheet 60A, and the separator sheet 70A) In the portion corresponding to the number of layers (number of sheets), the Li / M ratio of the positive electrode active material of the positive electrode sheet 50A is set to be more than 1.15 and less than 1.25 (particularly 1.18 to 1.22). Then, as the outer layer portion 24A, the Li / M ratio of the positive electrode active material of the remaining positive electrode sheet 50A is set to 1.0 or more and 1.15 or less (particularly 1.0 or more and 1.10 or less).
As an example, the inner layer portion 22A has a Li / M ratio of the positive electrode active material of the positive electrode sheet 50A in the central portion in the stacking direction of the stacked body and corresponding to 20% of the total number of layers. , 1.20. Then, as the outer layer portion 24A, in each of the remaining portions, that is, each side end portion in the stacking direction of the stacked body and corresponding to 40% of the total number of layers, the positive electrode active of the positive electrode sheet 50A. The Li / M ratio of the material is 1.05.

As described above, the lithium ion secondary battery 100 according to the present embodiment can be configured.
Next, a modification of this embodiment will be described. In the above example, a stacked electrode body is used as the electrode body. However, the present modification is different in that a wound electrode body is used as the electrode body. Therefore, since the configuration of the lithium ion secondary battery other than using the wound electrode body and the material constituting the electrode body are the same as those in the above example, these descriptions are omitted, and only the wound electrode body is used. explain.

As shown in FIG. 3, the electrode body (rolled electrode body) 20B of the present modification is a positive electrode active material layer along the longitudinal direction on one or both surfaces (here, both surfaces) of a long positive electrode current collector 52B. The positive electrode sheet 50B in which 54B is formed and the negative electrode sheet 60B in which the negative electrode active material layer 64B is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62B are 2 It has a form in which the sheet is overlapped via a long separator sheet 70B and wound in the longitudinal direction.
The electrode body 20B has a flat shape, and in the flat portion, the positive electrode 50B and the negative electrode 60B are disposed between the separator 70B in the direction perpendicular to the winding axis direction (the sheet width direction orthogonal to the longitudinal direction). (In particular, at the starting point of winding, the positive electrode 50B or the negative electrode 60B may overlap two consecutively).
Thus, the electrode body 20B forms a laminate having the positive electrode 50B layer, the negative electrode 60B layer, and the separator 70B layer. A positive electrode active material layer non-formed part 52Ba and a negative electrode active material layer non-formed part 62Ba are formed so as to protrude outward from both ends in the winding axis direction of the electrode body 20B.

In the present modification, as shown in FIG. 4, the stacked body constituting the electrode body 20B has an inner layer portion 22B and an outer layer portion 24B in a direction perpendicular to the flat surface and the winding axis of the electrode body 20B ( For convenience of reference, FIG. 4 schematically shows a roll of a stack of the positive electrode 50B, the negative electrode 60B, and the separator 70B. The positive electrode 50B, the negative electrode 60B, and the separator 70B are not depicted separately. Also, it does not indicate the actual number of stacked layers of the positive electrode 50B, the negative electrode 60B, and the separator 70B). And ratio (Li / M) of the lithium element with respect to metal elements other than lithium contained in the positive electrode active material of the positive electrode sheet 50B of the inner layer part 22B is included in the positive electrode active material of the positive electrode sheet 50B of the outer layer part 24B of the laminate. The ratio of the lithium element to the metal element other than lithium (Li / M) is larger.
Specifically, for example, the inner layer portion 22B is a central portion in the stacking direction of the stacked body and a layer of 15% to 30% of the total number of layers (total number of positive electrode 50B layers, negative electrode 60B layers, separator 60B layers). In the portion corresponding to the number, the Li / M ratio of the positive electrode active material of the positive electrode 50B is set to be more than 1.15 and less than 1.25 (particularly 1.18 or more and 1.22 or less). Then, as the outer layer portion 24B, the Li / M ratio of the positive electrode active material of the remaining positive electrode 50B layer is set to 1.0 or more and 1.15 or less (particularly 1.0 or more and 1.10 or less).
More specifically, for example, as the inner layer portion 22B, the positive portion of the positive electrode 50B layer in the central portion (that is, the inner peripheral portion) in the stacking direction of the stacked body and corresponding to 20% of the total number of layers. The Li / M ratio of the active material is set to 1.20. Then, as the outer layer portion 24B, the remaining portion, that is, the outer peripheral portion of the laminate, and the portion corresponding to 80% of the total number of layers, the Li / M ratio of the positive electrode active material of the positive electrode 50B layer To 1.05.

  FIG. 5 shows a lithium ion secondary battery (X) using a positive electrode active material having a Li / M ratio of 1.05 for both the inner layer portion (inner peripheral portion) and outer layer portion (outer peripheral portion) of the wound electrode body. The lithium ion secondary battery (Y) using a positive electrode active material having a Li / M ratio of 1.20 for both the inner layer portion (inner peripheral portion) and the outer layer portion (outer peripheral portion) of the wound electrode body is intentionally 2 is a graph showing a change over time in the temperature of a lithium ion secondary battery when overcharge is caused in the battery. As shown in FIG. 5, in the lithium ion secondary battery using the positive electrode active material in which the Li / M ratio is 1.05 in both the inner layer portion and the outer layer portion of the electrode body, a rapid temperature rise is observed. In the lithium ion secondary battery using the positive electrode active material in which the Li / M ratio is 1.20 in both the inner layer portion and the outer layer portion of the body, the temperature rise is suppressed.

  FIG. 6 shows a lithium ion secondary battery using a positive electrode active material having a Li / M ratio of 1.05 for both the positive electrode of the inner layer portion (inner peripheral portion) and the positive electrode of the outer layer portion (outer peripheral portion) of the wound electrode body. A positive electrode active material having a Li / M ratio of 1.15 is used for the positive electrode of (A) and the inner layer portion (the number of layers is 20% of the total number of layers) of the wound electrode body. A lithium ion secondary battery (B) using a positive electrode active material having a Li / M ratio of 1.05 for the positive electrode of the outer layer portion (the number of layers is 80% of the total number of layers); A positive electrode active material having a Li / M ratio of 1.20 was used for the positive electrode of the inner layer portion (the number of layers was 20% of the total number of layers) of the rotating electrode body, and the outer layer portion (layers) of the wound electrode body was The number is the number of layers corresponding to 80% of the total number of layers), and the lithium ion secondary battery (C) using a positive electrode active material having a Li / M ratio of 1.05 is used for the positive electrode. When the manner to cause overcharging is a graph showing the change with time of the temperature of the lithium ion secondary battery. As shown in FIG. 6, the Li / M ratio of the positive electrode active material in the inner layer portion of the electrode body (laminate) is made larger than the Li / M ratio of the positive electrode active material in the outer layer portion of the electrode body (laminate). It can be seen that the degree of suppression of temperature rise during overcharge increases.

  FIG. 7 shows a lithium ion secondary battery (1) using a positive electrode active material having a Li / M ratio of 1.05 for both the inner layer portion (inner peripheral portion) and outer layer portion (outer peripheral portion) of the wound electrode body. As in the lithium ion secondary battery (B), the Li / M ratio of the positive electrode active material in the inner layer portion of the wound electrode body is set to be higher than the Li / M ratio of the positive electrode active material in the outer layer portion of the wound electrode body. A large lithium ion secondary battery (2) and a lithium ion secondary battery (3) in which a member having a large heat capacity is arranged at the center of the wound electrode body so as to increase the degree of suppression of temperature rise during overcharging. Is a graph showing the output at low temperature and low charge. In the graph, the output at low temperature and low charge of the lithium ion secondary battery (1) using the positive electrode active material in which the Li / M ratio is 1.05 in both the inner layer portion and the outer layer portion of the wound electrode body is 1 As shown, the outputs of the other lithium ion secondary batteries (2) and (3) are shown as relative ratios. According to the study by the present inventor, the smaller the Li / M ratio of the positive electrode active material used, the higher the output of the lithium ion secondary battery at low temperature and low charge. In FIG. 7, by comparing the lithium ion secondary batteries (1) and (2), the Li / M ratio of the positive electrode active material in the inner layer portion of the electrode body (laminated body) is determined as the outer layer portion of the electrode body (laminated body). It can be seen that even when the Li / M ratio of the positive electrode active material is made larger, the output at low temperature and low charge is not greatly impaired. In addition, there is a method in which a member having a large heat capacity is arranged at the center of the electrode body so that the degree of suppression of temperature rise during overcharging is increased. However, the comparison between the lithium ion secondary batteries (2) and (3) shows that the Li / M ratio of the positive electrode active material in the inner layer part of the electrode body (laminated body) is the positive electrode in the outer layer part of the electrode body (laminated body). Even by a method of making the ratio larger than the Li / M ratio of the active material, it is possible to suppress the temperature rise during overcharge, and the degree of suppression of the temperature rise during overcharge is high at the center of the electrode body. It can be seen that the output characteristics are superior to the method of disposing a member having a large heat capacity.

  As described above, in the lithium ion secondary battery 100 according to the present embodiment, a positive electrode active material having a high Li / M ratio that has a high effect of suppressing a temperature rise during overcharge is easily deposited in an electrode body (laminated body). A positive electrode active material having a small Li / M ratio, which is included in the positive electrodes 50A and 50B of the inner layer portions 22A and 22B of 20A and 20B, and is excellent in output characteristics at low temperature and low charge, is formed into an electrode body (laminated body) 20A, The outer layers 24A and 24B of the 20B are included in the positive electrodes 50A and 50B. Therefore, according to the lithium ion secondary battery 100 according to the present embodiment, it is possible to provide a lithium ion secondary battery with high balance between output characteristics at low temperature and low charge and temperature rise suppression performance at overcharge. .

  The lithium ion secondary battery 100 configured as described above can be used for various applications. Suitable applications include driving power sources mounted on vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). The lithium ion secondary battery 100 can also be used in the form of a battery pack typically formed by connecting a plurality of lithium ion secondary batteries 100 in series and / or in parallel.

  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.

20A, 20B Electrode bodies 22A, 22B Inner layer portions 24A, 24B Outer layer portion 30 Battery case 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plates 50A, 50B Positive electrode sheet (positive electrode)
52A, 52B Positive electrode current collectors 52Aa, 52Ba Positive electrode active material layer non-formed portions 54A, 54B Positive electrode active material layers 60A, 60B Negative electrode sheet (negative electrode)
62A, 62B Negative electrode current collectors 62Aa, 62Ba Negative electrode active material layer non-formed portions 64A, 64B Negative electrode active material layers 70A, 70B Separator sheets (separators)
100 Lithium ion secondary battery

Claims (1)

A laminate in which a positive electrode, a negative electrode, and a separator are laminated as an electrode body;
A non-aqueous electrolyte,
A lithium ion secondary battery comprising:
The positive electrode includes a positive electrode active material layer containing a positive electrode active material,
The positive electrode active material contains lithium (Li) and a metal element (M) other than lithium,
Lithium element ratio (Li / M) to metal elements other than lithium contained in the positive electrode active material of the positive electrode in the inner layer portion of the laminate is lithium contained in the positive electrode active material of the positive electrode in the outer layer portion of the laminate. It is characterized by being larger than the ratio of lithium element to other metal elements (Li / M),
Lithium ion secondary battery.

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