Lithium ion secondary battery

Abstract

To provide a lithium ion secondary battery capable of achieving improved battery output and extended service life.SOLUTION: A secondary battery 1 as a lithium ion secondary battery includes an electrode body 10 in which positive and negative electrode sheets 35 are stacked with a separator arranged therebetween. Each of the electrode sheets 35 is formed by applying, to a substrate 36, a mixture paste 37 as an electrode mixture. An opposing surface 50N of a negative electrode mixture layer 32N in an electrode sheet 35N on a negative electrode 4 side is greater in size than an opposing surface 50P of a positive electrode mixture layer 32P in an electrode sheet 35P on a positive electrode 3 side. The negative electrode mixture layer 32N contains greater than or equal to 1,000 ppm and less than or equal to 1,500 ppm of lithium, and the density of the negative electrode mixture layer 32N is set to 1.1 g / cc or greater and 1.4 g / cc or less. The positive electrode mixture layer 32P contains a lithium transition metal oxide as a positive electrode active material. A Li / M ratio of a number of atoms of lithium to a sum of a number of atoms of a transition metal is set to 1.16 or greater and 1.20 or less.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a lithium ion secondary battery. [Background technology]

[0002] Conventionally, some lithium ion secondary batteries have an electrode body formed by stacking positive and negative electrode sheets with a separator between them. Furthermore, each of these electrode sheets is formed by coating an electrode mixture on a substrate that serves as a current collector. Some of these lithium ion secondary batteries have lithium pre-contained in the negative electrode mixture that constitutes the electrode sheet on the negative electrode side, as shown in Patent Documents 1 and 2.

[0003] That is, by increasing the amount of lithium in the positive electrode mixture layer in the electrode sheet on the positive electrode side, the battery output can be improved. However, by adopting such a configuration, lithium ions that should originally move between the positive electrode mixture layer and the negative electrode mixture layer, which are opposite to each other, tend to move to the non-positive region of the negative electrode mixture layer that is not opposite to the positive electrode mixture layer. In this way, the lithium in the positive electrode mixture layer escapes to the non-positive region of the negative electrode mixture layer, and the battery capacity tends to decrease due to repeated charging and discharging. In other words, a problem occurs in which the battery life is shortened.

[0004] In consideration of this, in the above-mentioned conventional example, the non-facing portion of the negative electrode mixture layer is made to contain more lithium than the facing portion of the positive electrode mixture layer, thereby making it difficult for lithium in the positive electrode mixture layer to escape to the non-facing portion of the negative electrode mixture layer, thereby improving the battery life. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-056412 A [Patent Document 2] Japanese Patent Application Publication No. 7-192766 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in applications requiring high levels of battery performance, such as electric vehicles, further improvements in performance are being sought on a daily basis, and therefore further improvements are being sought in the above-mentioned conventional technologies in order to meet the evolving requirements. [Means for solving the problem]

[0007] Various aspects of the lithium ion secondary battery that solves the above problems will be described below. A first aspect is a lithium ion secondary battery including an electrode body in which positive and negative electrode sheets are laminated with a separator therebetween, each of the electrode sheets being formed by coating an electrode mixture on a substrate serving as a current collector, and in which a surface facing a negative electrode mixture layer in the electrode sheet on the negative electrode side is larger than a surface facing a positive electrode mixture layer in the electrode sheet on the positive electrode side, the negative electrode mixture layer preliminarily contains 1000 ppm or more and 1500 ppm or less of lithium, the negative electrode mixture layer has a density of 1.1 g / cc or more and 1.4 g / cc or less, the positive electrode mixture layer contains a lithium transition metal oxide as a positive electrode active material, and the Li / M ratio, which is the ratio of the sum of the numbers of transition metal atoms (M) in the lithium transition metal oxide to the number of lithium atoms (Li), is 1.16 or more and 1.20 or less.

[0008] That is, by setting the Li / M ratio high, the positive electrode mixture layer contains more lithium. This can improve the battery output. In addition, since lithium is present in the negative electrode mixture layer in advance, including the non-positive region that does not face the positive electrode mixture layer, the lithium in the positive electrode mixture layer is less likely to escape to the non-positive region of the negative electrode mixture layer. Furthermore, when the density of the negative electrode mixture layer is low, the electrolyte is more likely to penetrate into the negative electrode mixture layer. This makes it easier for the positive region of the negative electrode mixture layer that faces the positive electrode mixture layer to accept lithium ions that have moved from the positive electrode mixture layer. As a result, the lithium in the positive electrode mixture layer is even less likely to escape to the non-positive region of the negative electrode mixture layer. Therefore, according to the above configuration, the battery output can be effectively improved and the life can be extended.

[0009] Furthermore, the above-mentioned configuration has the advantage that it is not necessary to set different lithium contents for the front and rear regions, which makes it possible to easily manufacture the battery and improve its output and life.

[0010] Aspect 2 is the lithium ion secondary battery according to Aspect 1, wherein the lithium pre-contained in the negative electrode mixture layer is derived from a carboxymethyl cellulose-lithium salt contained in a negative electrode mixture that forms the negative electrode mixture layer by the coating.

[0011] That is, for the negative electrode mixture, for example, carboxymethylcellulose (CMC) can be used as a thickener or dispersant. Therefore, as in the above configuration, by using its lithium salt "CMC-Li" as this "CMC", it is possible to easily form a negative electrode mixture layer that contains lithium in advance.

[0012] Aspect 3 is the lithium ion secondary battery according to aspect 2, wherein the negative electrode mixture contains 0.4 wt % or more and 0.6 wt % or less of the carboxymethyl cellulose-lithium salt. According to the above-mentioned configuration, the amount of lithium contained in the negative electrode mixture layer in advance can be easily adjusted to the preferred range shown in the embodiment 1. Furthermore, in consideration of the thickening effect due to the inclusion of "CMC-Li", the ease of kneading and coating can be ensured. This makes it possible to easily manufacture the battery, improve its output, and extend its life.

[0013] In a fourth aspect, the lithium transition metal oxide contained in the positive electrode mixture layer is LiNi x Co y Mn z O2 [x+y+z=1,0 <x<1,0<y<1,0<z<1] The lithium ion secondary battery according to any one of Aspects 1 to 3, wherein:

[0014] According to the above-mentioned configuration, by setting the Li / M ratio high, the positive electrode mixture layer contains more lithium, and this leads to an improvement in the battery output.

[0015] A fifth aspect is the lithium ion secondary battery according to any one of the first to fourth aspects, in which the negative electrode capacity / positive electrode capacity ratio for the positive and negative electrode sheets is 1.6 or more and 1.8 or less. That is, the electrode sheet usually has a portion at its end region that does not have an electrode mixture layer on the substrate, that is, an uncoated portion where the electrode mixture is not coated. In addition, by setting the negative electrode capacity / positive electrode capacity ratio of the positive and negative electrode sheets constituting the electrode body high, the non-positive region of the negative electrode mixture layer is expanded. In other words, the uncoated portion arranged between the positive region and the non-positive region is separated from the position directly facing the positive electrode mixture layer that is the positive region. Furthermore, by the configuration of aspect 1, lithium is contained in the non-positive region in advance, so that even if the non-positive region is large, lithium in the positive electrode mixture layer is unlikely to move to this non-positive region. Therefore, according to the above configuration, it is possible to suppress the movement of lithium ions from the positive electrode mixture layer toward the uncoated portion on the negative electrode side while improving the battery output and extending the life. This avoids the occurrence of short circuit failure caused by lithium precipitation in the uncoated portion on the negative electrode side, thereby ensuring high safety and reliability.

[0016] Aspect 6 is the lithium ion secondary battery according to any one of Aspects 1 to 5, wherein an edge region of the electrode sheet where the electrode mixture is not applied to the base material is defined as an uncoated portion of the electrode sheet, and the electrode sheet on the negative electrode side has the edge region with a width of the uncoated portion of 300 μm or less.

[0017] That is, in an electrode body in which positive and negative electrode sheets are laminated with a separator sandwiched therebetween, one of a pair of negative electrode composite layers laminated on both sides of a substrate may be an opposing layer having a positive electrode composite layer facing it, and the other may be a non-opposing layer not having a positive electrode composite layer facing it. Furthermore, in this case, the amount of lithium in the opposing layer increases due to charging, and based on the concentration gradient formed in the end region, there is a possibility that lithium ions may move from the opposing layer to the non-opposing layer, bypassing this end region. As a result, the amount of lithium that can be effectively used decreases, and the battery capacity is more likely to decrease due to repeated charging and discharging.

[0018] However, because the non-facing layer already contains lithium in the configuration of embodiment 1, the movement of lithium ions from the facing layer to the non-facing layer, bypassing the end region, is less likely to occur. This makes it possible to suppress the decrease in battery capacity due to repeated charging and discharging, while ensuring high design freedom by narrowing the uncoated portion of the end region as in the above configuration.

[0019] A seventh aspect is the lithium ion secondary battery according to any one of the first to sixth aspects, wherein the separator has a porosity of 50% or more and 60% or less. According to the above-mentioned configuration, the separator can secure the electrolyte retention, and the performance change when the secondary battery is repeatedly charged and discharged, i.e., the cycle characteristics, can be improved, and the separator can have sufficient mechanical strength required. Effect of the Invention

[0020] According to the present invention, it is possible to improve the battery output and extend the battery life. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a perspective view of a secondary battery. [Diagram 2] FIG. 2 is an exploded view of the electrode assembly. [Diagram 3] FIG. 3 is a side view of the secondary battery. [Figure 4] FIG. 4 is an explanatory diagram that shows a schematic diagram of positive and negative electrode sheets facing each other with a separator interposed therebetween. [Diagram 5] FIG. 5 is an explanatory diagram that illustrates a schematic diagram of positive and negative electrode sheets that face each other with a separator sandwiched therebetween in the secondary battery of the reference example. [Figure 6] FIG. 6 is an explanatory diagram that illustrates a schematic diagram of an electrode sheet having a double-sided laminated structure. [Figure 7] FIG. 7 is a table showing the test results of the secondary battery. [Figure 8] FIG. 8 is a graph showing the relationship between the Li / M ratio and the battery output. [Figure 9] FIG. 9 is a graph showing the relationship between the amount of lithium in the negative electrode mixture layer and the degradation rate. [Figure 10] FIG. 10 is a graph showing the relationship between the density of the negative electrode mixture layer and the deterioration rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of a secondary battery will be described with reference to the drawings. (Lithium-ion secondary battery) 1, the secondary battery 1 includes an electrode assembly 10 in which a positive electrode 3, a negative electrode 4, and a separator 5 are integrated, and a case 20 that houses the electrode assembly 10. The secondary battery 1 of this embodiment has a configuration as a lithium ion secondary battery in which the electrode assembly 10 in the case 20 is impregnated with a non-aqueous electrolyte solution (not shown).

[0023] More specifically, in the secondary battery 1 of this embodiment, the positive electrode 3, the negative electrode 4, and the separator 5 are laminated with a sheet-like outer shape. Then, by winding up the laminate of the positive electrode 3, the negative electrode 4, and the separator 5, an electrode body 10 is formed in which the positive and negative electrodes and the separators 5 are alternately arranged in the radial direction with the separator 5 sandwiched between the positive electrode 3 and the negative electrode 4.

[0024] The case 20 of this embodiment includes a case body 21 having a flat, substantially rectangular box shape, and a lid member 22 that closes an open end 21x of the case body 21. The electrode body 10 of this embodiment has a flat outer shape that corresponds to the box shape of the case 20.

[0025] (Electrode sheet and electrode body) More specifically, as shown in FIG. 2, in the secondary battery 1 of this embodiment, the positive electrode 3 and the negative electrode 4 each have a configuration as an electrode sheet 35 including a current collector 31 having a sheet-like outer shape and an electrode mixture layer 32 laminated on this current collector 31.

[0026] Specifically, for the electrode sheet 35P for the positive electrode 3, an electrode mixture containing lithium transition metal oxide as a positive electrode active material, that is, a composite paste 37P as a positive electrode mixture, is applied to a substrate 36P made of aluminum or the like that constitutes the positive electrode current collector 31P. For the electrode sheet 35N for the negative electrode 4, an electrode mixture in the form of a slurry containing a carbon-based material that serves as a negative electrode active material, that is, a composite paste 37N as a negative electrode mixture, is applied to a substrate 36N made of copper or the like that constitutes the negative electrode current collector 31N. Furthermore, each of these composite pastes 37P and 37N contains a binder. In the secondary battery 1 of this embodiment, the composite pastes 37P and 37N are dried to form the corresponding positive electrode composite layer 32P and negative electrode composite layer 32N on the positive and negative electrode sheets 35P and 35N, respectively.

[0027] Furthermore, in the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N are each shaped into a belt-like shape. The electrode body 10 of this embodiment has a configuration as a wound body 10X in which the positive and negative electrode sheets 35P, 35N stacked with the separator 5 sandwiched therebetween are wound around a winding axis 10x extending in the width direction of the belt-like shape (the left-right direction in FIG. 2).

[0028] 2, the separator 5 and each electrode sheet 35 are wound in such a manner that the electrode sheet 35P constituting the positive electrode 3 is wound inward. However, this figure is one example showing the structure of the electrode body 10, and the separator 5 and each electrode sheet 35 may be wound in such a manner that the electrode sheet 35N constituting the negative electrode 4 is wound inward. This determines whether the electrode sheet 35 arranged on the outermost shell of the electrode body 10 is the electrode sheet 35P constituting the positive electrode 3 or the electrode sheet 35N constituting the negative electrode 4.

[0029] 1 to 3, the cover member 22 of the case 20 is provided with a positive electrode terminal 38P and a negative electrode terminal 38N that protrude to the outside of the case 20. Furthermore, each electrode sheet 35 has an uncoated portion 39 where the electrode mixture layer 32 is not formed on the current collector 31. The secondary battery 1 of this embodiment is configured such that, by utilizing these uncoated portions 39, the electrode sheet 35P constituting the positive electrode 3 and the positive electrode terminal 38P are electrically connected, and the electrode sheet 35N constituting the negative electrode 4 and the negative electrode terminal 38N are electrically connected.

[0030] Specifically, the electrode body 10 of this embodiment is housed in the case 20 with its winding axis 10x aligned along the longitudinal direction (left-right direction in FIG. 1) of the cover member 22, which is an elongated, generally rectangular plate. Furthermore, in this state, an uncoated portion 39P of an electrode sheet 35P constituting the positive electrode 3 is connected to a positive electrode terminal 38P via a connecting member 40P. Similarly, an uncoated portion 39N of an electrode sheet 35N constituting the negative electrode 4 is connected to a negative electrode terminal 38N via a connecting member 40N.

[0031] Furthermore, an electrolyte solution 45 is injected into the case 20. That is, the electrolyte solution 45 of the secondary battery 1 having a configuration as a lithium ion secondary battery is one in which a lithium salt serving as a supporting salt is dissolved in an organic solvent. Thus, the secondary battery 1 of this embodiment is configured such that the electrode body 10 sealed in the case 20 is impregnated with the electrolyte solution 45.

[0032] (High output / long life) As shown in FIG. 4, in the secondary battery 1 of this embodiment, when comparing the positive and negative electrode sheets 35P, 35N constituting the electrode body 10, the negative electrode mixture layer 32N on the negative electrode 4 side is larger than the positive electrode mixture layer 32P on the positive electrode 3 side. In detail, when comparing the positive electrode mixture layer 32P and the negative electrode mixture layer 32N facing each other with the separator 5 in between, the opposing surface 50N on the negative electrode mixture layer 32N side is larger than the opposing surface 50P on the positive electrode mixture layer 32P side. For convenience of explanation, the separator 5 is omitted in FIG. 4 and FIG. 5 to be referred to below. The negative electrode mixture layer 32N of this embodiment has a facing region 51 facing the positive electrode mixture layer 32P and a non-facing region 52 not facing the positive electrode mixture layer 32P.

[0033] As described above, the positive electrode mixture layer 32P constituting the electrode sheet 35P on the positive electrode 3 side, that is, the mixture paste 37P as the positive electrode mixture applied to the base material 36P, contains a lithium transition metal oxide as a positive electrode active material.

[0034] Specifically, in the secondary battery 1 of this embodiment, the lithium transition metal oxide used is lithium nickel-cobalt-manganese oxide, abbreviated as "NCM" as shown below.

[0035] LiNi x Co y Mn z O2 [x+y+z=1,0 <x<1,0<y<1,0<z<1] Furthermore, in the secondary battery 1 of this embodiment, the Li / M ratio, which is the ratio of the sum of the number of transition metal atoms (M) in the lithium transition metal oxide contained in the positive electrode mixture layer 32P to the number of lithium atoms (Li), is set to 1.16 or more and 1.20 or less. This Li / M ratio may be abbreviated as "Li / Me ratio". This Li / M ratio is equivalent to the molar ratio in the lithium transition metal oxide. Furthermore, in a general lithium ion secondary battery, this Li / M ratio is set to, for example, about 1.12 to 1.13. That is, in the secondary battery 1 of this embodiment, the Li / M ratio is set higher than usual. And, the secondary battery 1 of this embodiment is configured to contain more lithium in the positive electrode mixture layer 32P.

[0036] In the secondary battery 1 of this embodiment, the negative electrode mixture layer 32N constituting the electrode sheet 35N on the negative electrode 4 side also contains lithium. Specifically, in the secondary battery 1 of this embodiment, the negative electrode mixture layer 32N contains lithium of 1000 ppm or more and 1500 ppm or less before the secondary battery 1 is initially charged. In this case, "ppm" means "parts per million by mass". Furthermore, the density of the negative electrode mixture layer 32N is set to 1.1 g / cc or more and 1.4 g / cc or less. Thus, the secondary battery 1 of this embodiment is configured to improve its output and extend its life.

[0037] More specifically, in the secondary battery 1 of this embodiment, the composite paste 37N serving as the negative electrode composite material, which is applied to the substrate 36N to form the electrode sheet 35N on the negative electrode 4 side, contains carboxymethylcellulose having the functions of a thickener and a dispersant. This carboxymethylcellulose is often abbreviated as "CMC". Furthermore, in the secondary battery 1 of this embodiment, the "CMC" contained in the composite paste 37N is its lithium salt "CMC-Li". In the secondary battery 1 of this embodiment, this "CMC-Li" is obtained by, for example, substituting the cation of carboxymethylcellulose-sodium salt, abbreviated as "CMC-Na", that is, "Na", with "Li". Specifically, in the secondary battery 1 of this embodiment, the composite paste 37N serving as the negative electrode composite material contains 0.4 wt% or more and 0.6 wt% or less of "CMC-Li". In secondary battery 1 of the present embodiment, the amount of lithium contained in negative electrode mixture layer 32N is thereby set to be not less than 1000 ppm and not more than 1500 ppm.

[0038] In the secondary battery 1 of this embodiment, the negative electrode capacity / positive electrode capacity ratio of the positive and negative electrode sheets 35P, 35N constituting the electrode body 10 is set to, for example, 1.6 or more and 1.8 or less. The negative electrode capacity / positive electrode capacity ratio in a typical lithium ion secondary battery is, for example, about 1.2 to 1.3. In the secondary battery 1 of this embodiment, the porosity of the separator 5 is set to, for example, 50% or more and 60% or less.

[0039] (action) The secondary battery 1B of the reference example shown in FIG. 5 contains "NCM" as a positive electrode active material in the positive electrode composite layer 32P, similarly to the secondary battery 1 of the present embodiment. Furthermore, the Li / M ratio is also set to a value higher than normal. Thus, the secondary battery 1B of the reference example also contains more lithium in the positive electrode composite layer 32P.

[0040] However, in secondary battery 1B of this reference example, negative electrode mixture layer 32N does not contain lithium, and the density of negative electrode mixture layer 32N is also greater than 1.4 g / cc.

[0041] That is, by setting the Li / M ratio high, the positive electrode mixture layer 32P contains more lithium. This can improve the battery output. However, by using such a so-called "high Li content positive electrode", lithium ions that should originally move from the positive electrode mixture layer 32P to the positive electrode mixture layer 51 of the negative electrode mixture layer 32N during charging are also likely to move to the non-positive electrode mixture layer 52. As a result, the lithium in the positive electrode mixture layer 32P escapes to the non-positive electrode mixture layer 52 of the negative electrode mixture layer 32N in this way, and the battery capacity is likely to decrease due to repeated charging and discharging.

[0042] In this regard, as shown in FIG. 4, the secondary battery 1 of this embodiment contains lithium in advance in the negative electrode mixture layer 32N, including the non-positive region 52. Therefore, even when a "high Li content positive electrode" is used, the lithium in the positive electrode mixture layer 32P is less likely to escape to the non-positive region 52 on the negative electrode mixture layer 32N side. In addition, the secondary battery 1 of this embodiment has a lower density of the negative electrode mixture layer 32N than the secondary battery 1B of the above reference example, so that the electrolyte 45 is more likely to permeate the negative electrode mixture layer 32N. Furthermore, since the electrolyte 45 has a high permeability to the negative electrode mixture layer 32N, the lithium ions that have moved from the positive electrode mixture layer 32P are more likely to be received by the positive electrode mixture layer 51 of the negative electrode mixture layer 32N that faces the positive electrode mixture layer 32P. As a result, the lithium in the positive electrode mixture layer 32P is more unlikely to escape to the non-positive region 52 on the negative electrode mixture layer 32N side. This enables the secondary battery 1 of this embodiment to have improved battery output and a longer life.

[0043] If the Li / M ratio is too high, the structure of the lithium transition metal oxide "NCM" used in the positive electrode active material may not be maintained. In addition, by increasing the amount of lithium in the negative electrode mixture layer 32N, the lithium concentration gradient between the positive electrode 3 and the negative electrode 4 becomes small. If the density of the negative electrode mixture layer 32N is low, the permeability of the electrolyte 45 increases, and the battery reaction is more likely to proceed. In other words, the deterioration is also more likely to proceed.

[0044] In consideration of this, in the secondary battery 1 of this embodiment, as described above, the Li / M ratio on the positive electrode 3 side is set to 1.16 or more and 1.20 or less. The amount of lithium in the negative electrode mixture layer 32N is set to 1000 ppm or more and 1500 ppm or less. And the density of the negative electrode mixture layer 32N is set to a range of 1.1 g / cc or more and 1.4 g / cc or less.

[0045] In addition, "CMC-Li" in the composite paste 37N as the negative electrode composite material functions as a thickener. Therefore, when the content of "CMC-Li" is increased, the viscosity of the composite paste 37N tends to increase. This makes it difficult to knead the composite paste 37N and to apply the composite paste 37N to the base material 36N.

[0046] In consideration of this, in the secondary battery 1 of this embodiment, the amount of "CMC-Li" contained in the composite paste 37N is set to 0.4 wt% or more and 0.6 wt% or less, as described above. Furthermore, in the secondary battery 1 of this embodiment, when the amount of "CMC-Li" contained in the composite paste 37N is the upper limit value of the preferred range, "0.6 wt%, " the amount of lithium contained in the negative electrode composite layer 32N is the upper limit value of the preferred range, "1500 ppm". Thus, the secondary battery 1 of this embodiment can be easily manufactured and accurately adjusted to the amount of lithium contained in the negative electrode composite layer 32N.

[0047] In addition, the negative electrode capacity / positive electrode capacity ratio of the positive and negative electrode sheets 35P, 35N constituting the electrode body 10 tends to reflect the difference in size between the opposing surface 50N on the negative electrode mixture layer 32N side and the opposing surface 50P on the positive electrode mixture layer 32P side, which face each other with the separator 5 sandwiched therebetween. That is, generally, by setting the negative electrode capacity / positive electrode capacity ratio high, the non-positive facing region 52 of the negative electrode mixture layer 32N is enlarged. In other words, in the electrode sheet 35N on the negative electrode 4 side, the interval between the uncoated portion 39N sandwiching the non-positive facing region 52 and the positive facing region 51 is enlarged. That is, the uncoated portion 39N on the negative electrode 4 side is separated from the position directly facing the positive electrode mixture layer 32P, which is the positive facing region 51. This suppresses the movement of lithium ions from the positive electrode mixture layer 32P toward the uncoated portion 39N on the negative electrode 4 side.

[0048] That is, in the secondary battery 1 of the present embodiment, as described above, the presence of lithium contained in advance in the negative electrode mixture layer 32N makes it difficult for the lithium in the positive electrode mixture layer 32P to escape to the non-positive electrode region 52 of the negative electrode mixture layer 32N. For this reason, even if the non-positive electrode region 52 of the negative electrode mixture layer 32N is enlarged by setting the negative electrode capacity / positive electrode capacity ratio high, the decrease in the battery capacity due to repeated charging and discharging is unlikely to progress.

[0049] By utilizing this, the secondary battery 1 of the present embodiment avoids the deposition of lithium in the uncoated portion 39N on the negative electrode 4 side. This prevents the occurrence of short circuit failures caused by the deposition of lithium, thereby making it possible to ensure high safety and reliability.

[0050] As shown in FIG. 6, in the secondary battery 1 of the present embodiment, in the electrode sheet 35N on the negative electrode 4 side arranged on the outermost shell of the electrode body 10, only one of the negative electrode mixture layers 32N, 32N laminated on both sides of the base material 36N has a positive electrode mixture layer 32P facing it. For convenience of explanation, the electrode sheet 35P and the separator 5 on the positive electrode 3 side are omitted in FIG. 6. That is, in FIG. 6, of the pair of negative electrode mixture layers 32N, 32N, the negative electrode mixture layer 32N arranged on the radial inner side (upper side in FIG. 6) of the electrode body 10 having the configuration as the wound body 10X becomes the facing layer 53 having the facing positive electrode mixture layer 32P. And the negative electrode mixture layer 32N arranged on the radial outer side (lower side in FIG. 6) of the wound body 10X becomes the non-facing layer 54 not having the facing positive electrode mixture layer 32P.

[0051] Furthermore, when lithium is not contained in these negative electrode mixture layers 32N, 32N as in the secondary battery 1B of the above reference example, there is a possibility that migration of lithium ions from the opposing layer 53 toward the non-opposing layer 54, bypassing the end region 35Nx of the electrode sheet 35N, occurs. That is, during charging, the opposing layer 53 receives lithium ions from the opposing positive electrode mixture layer 32P, thereby increasing the amount of lithium in the opposing layer 53. In contrast, the non-opposing layer 54 does not have the positive electrode mixture layer 32P that increases the amount of lithium. Furthermore, the electrolyte 45 is also present in the end region 35Nx of the electrode sheet 35N. Then, based on the concentration gradient formed by this, migration of lithium ions occurs bypassing the end region 35Nx. As a result, the amount of lithium that can be effectively utilized decreases, and the battery capacity is more likely to decrease due to repeated charging and discharging.

[0052] However, in the secondary battery 1 of this embodiment, lithium is already contained in both the facing layer 53 and the non-facing layer 54. Therefore, even if the amount of lithium in the facing layer 53 increases due to charging, the concentration gradient between the facing layer 53 and the non-facing layer 54 formed in the end region 35Nx of the electrode sheet 35N is small. Therefore, in the secondary battery 1 of this embodiment, migration of lithium ions from the facing layer 53 toward the non-facing layer 54, bypassing the end region 35Nx, is unlikely to occur.

[0053] In the secondary battery 1 of this embodiment, the electrode sheet 35N on the negative electrode 4 side has an uncoated portion 39N used for terminal connection in an end region 35Nxa located on one side in the width direction (left side in FIG. 6) of the strip shape wound as the electrode body 10 (see FIG. 2). In addition, the electrode sheet 35N has a cut portion 55 when shaping the electrode sheet 35N into a strip shape in an end region 35Nxb located on the other side in the width direction (right side in FIG. 6). Furthermore, in the electrode sheet 35N of this embodiment, the cut portion 55 is also an uncoated portion 39b in which the negative electrode composite layer 32N is not laminated on the base material 36N. In the electrode sheet 35N of this embodiment, the width W of the uncoated portion 39b that becomes the cut portion 55 is set to 300 μm or less.

[0054] That is, the wider the uncoated portion 39 formed in the end region 35Nx of the electrode sheet 35N, the less likely it is that lithium ions will migrate from the opposing layer 53 to the non-opposing layer 54, bypassing the end region 35Nx. However, in the secondary battery 1 of this embodiment, as described above, regardless of the presence or absence of the uncoated portion 39, lithium ions will migrate from the opposing layer 53 to the non-opposing layer 54, bypassing the end region 35Nx. The secondary battery 1 of this embodiment utilizes this to make the uncoated portion 39b of the end region 35Nxb narrow as described above. This makes it possible to ensure a high degree of freedom in designing the electrode sheet 35N on the negative electrode 4 side.

[0055] Another method for suppressing the migration of lithium ions from the facing layer 53 toward the non-facing layer 54, bypassing the end region 35Nx of the electrode sheet 35N, is to set the porosity of the separator 5 low. That is, by adopting such a configuration, the liquid retention of the electrolyte 45 by the separator 5 is reduced. This reduces the permeability of the lithium ions, making it possible to suppress the migration of lithium ions that have bypassed the end region 35Nx.

[0056] However, if the porosity of the separator 5 is low, the cycle characteristics are likely to deteriorate when charging and discharging are repeated due to a decrease in the electrolyte retention. If the electrolyte retention is ensured by increasing the porosity of the separator 5, the lithium ion permeability is improved, and the migration of lithium ions that bypass the end region 35Nx of the electrode sheet 35N as described above is likely to occur.

[0057] In this regard, in the secondary battery 1 of the present embodiment, as described above, both the facing layer 53 and the non-facing layer 54 contain lithium in advance, so that migration of lithium ions from the facing layer 53 to the non-facing layer 54, bypassing the end region 35Nx, is less likely to occur. This makes it possible to increase the porosity of the separator 5 and improve the cycle characteristics.

[0058] That is, in the secondary battery 1 of this embodiment, the lower limit of the porosity of the separator 5 is set from the viewpoint of improving cycle characteristics. Also, the upper limit of the porosity is set based on the required mechanical strength of the separator 5. Thus, in the secondary battery 1 of this embodiment, the porosity of the separator 5 is set in the range of 50% or more and 60% or less, as described above.

[0059] Next, the effects of this embodiment will be described. (1) The secondary battery 1 as a lithium ion secondary battery includes an electrode body 10 in which positive and negative electrode sheets 35 are laminated with a separator 5 sandwiched therebetween. Each electrode sheet 35 is formed by applying a composite paste 37 as an electrode composite to a substrate 36 serving as a current collector 31. In addition, a facing surface 50N of the negative electrode composite layer 32N in the electrode sheet 35N on the negative electrode 4 side is larger than a facing surface 50P of the positive electrode composite layer 32P in the electrode sheet 35P on the positive electrode 3 side. Furthermore, the negative electrode composite layer 32N contains lithium of 1000 ppm or more and 1500 ppm or less, and the density of the negative electrode composite layer 32N is set to 1.1 g / cc or more and 1.4 g / cc or less. In addition, the positive electrode composite layer 32P contains a lithium transition metal oxide as a positive electrode active material. The Li / M ratio, which is the ratio of the sum of the numbers of transition metal atoms (M) to the number of lithium atoms (Li) in this lithium transition metal oxide, is set to 1.16 or more and 1.20 or less.

[0060] That is, by setting the Li / M ratio high, the positive electrode mixture layer 32P contains more lithium. This can improve the battery output. In addition, since lithium is present in the negative electrode mixture layer 32N in advance, including the non-opposing region 52 that does not face the positive electrode mixture layer 32P, the lithium in the positive electrode mixture layer 32P is less likely to escape to the non-opposing region 52 of the negative electrode mixture layer 32N. Furthermore, when the density of the negative electrode mixture layer 32N is low, the electrolyte 45 is more likely to permeate the negative electrode mixture layer 32N. This makes it easier for the opposing region 51 of the negative electrode mixture layer 32N facing the positive electrode mixture layer 32P to accept lithium ions that have moved from the positive electrode mixture layer 32P. As a result, the lithium in the positive electrode mixture layer 32P is more unlikely to escape to the non-opposing region 52 of the negative electrode mixture layer 32N. Therefore, with the above-mentioned configuration, it is possible to effectively improve the battery output and extend its life.

[0061] Furthermore, the above configuration has the advantage that it is not necessary to set different lithium contents for the front facing region 51 and the non-front facing region 52. This makes it possible to easily manufacture the battery, improve its battery output, and extend its life.

[0062] (2) The lithium contained in advance in negative electrode mixture layer 32N originates from carboxymethyl cellulose-lithium salt contained in mixture paste 37N that forms negative electrode mixture layer 32N by coating substrate 36.

[0063] That is, for the composite paste 37N as the negative electrode composite, for example, carboxymethyl cellulose (CMC) can be used as a thickener or dispersant. Then, as in the above configuration, by using "CMC-Li", which is a lithium salt of "CMC", as this "CMC", it is possible to easily form the negative electrode composite layer 32N that contains lithium in advance.

[0064] (3) The negative electrode mixture paste 37N contains 0.4 wt % or more and 0.6 wt % or less of carboxymethyl cellulose-lithium salt. According to the above-mentioned configuration, the amount of lithium contained in the negative electrode mixture layer 32N in advance can be easily adjusted to the preferable range shown in (1) above. Furthermore, in consideration of the thickening effect due to the inclusion of "CMC-Li", the ease of kneading and coating can be ensured. This makes it possible to easily manufacture the battery, improve its output, and extend its life.

[0065] (4) In the positive electrode mixture layer 32P, as the lithium transition metal oxide, LiNi x Co y Mn z O2 [x+y+z=1,0 <x<1,0<y<1,0<z<1] Includes:

[0066] According to the above configuration, by setting the Li / M ratio high, the positive electrode mixture layer 32P contains more lithium, which can improve the battery output.

[0067] (5) The negative electrode capacity / positive electrode capacity ratio for the positive and negative electrode sheets 35P, 35N is 1.6 or more and 1.8 or less. That is, the electrode sheet 35N has an uncoated portion 39N in its end region 35Nx, which is a portion not having the negative electrode mixture layer 32N on the substrate 36N, that is, where the mixture paste 37N is not coated. In addition, by setting the negative electrode capacity / positive electrode capacity ratio of the positive and negative electrode sheets 35P, 35N constituting the electrode body 10 high, the non-positive region 52 of the negative electrode mixture layer 32N is expanded. In other words, the uncoated portion 39N arranged with the non-positive region 52 sandwiched between the positive electrode mixture layer 32P and the non-positive region 51 is separated from the position facing the positive electrode mixture layer 32P that is the positive region 51. Furthermore, because the non-positive region 52 contains lithium in advance due to the configuration of (1) above, even if the non-positive region 52 is large, lithium in the positive electrode mixture layer 32P is unlikely to move to the non-positive region 52. Therefore, the above configuration can improve the battery output and extend the battery life, while suppressing the movement of lithium ions from the positive electrode composite layer 32P toward the uncoated portion 39N on the negative electrode 4 side. This can prevent the occurrence of a short circuit failure caused by the deposition of lithium in the uncoated portion 39N on the negative electrode 4 side, thereby ensuring high safety and reliability.

[0068] (6) The electrode sheet 35N on the negative electrode 4 side has an end region 35Nx in which the width W of the uncoated portion 39N is 300 μm or less. That is, in the electrode body 10, one of the pair of negative electrode mixture layers 32N, 32N laminated on both sides of the base material 36N may be an opposing layer 53 having the opposing positive electrode mixture layer 32P, and the other may be a non-opposing layer 54 not having the opposing positive electrode mixture layer 32P. Furthermore, in this case, the amount of lithium in the opposing layer 53 increases due to charging, and based on the concentration gradient formed in the end region 35Nx, there is a possibility that lithium ions may move from the opposing layer 53 to the non-opposing layer 54, bypassing the end region 35Nx. This reduces the amount of lithium that can be effectively used, and the battery capacity is more likely to decrease due to repeated charging and discharging.

[0069] However, with the above configuration (1), the non-facing layer 54 also contains lithium in advance, making it difficult for lithium ions to migrate from the facing layer 53 to the non-facing layer 54, bypassing the end region 35Nx. This makes it possible to suppress a decrease in battery capacity due to repeated charging and discharging, while ensuring a high degree of design freedom by narrowing the uncoated portion 39N of the end region 35Nx as in the above configuration.

[0070] (7) The porosity of the separator 5 is 50% or more and 60% or less. According to the above-mentioned configuration, the separator 5 can secure the retention of the electrolyte 45, and the performance change when the secondary battery 1 is repeatedly charged and discharged, that is, the cycle characteristics can be improved. Furthermore, the separator 5 can secure sufficient mechanical strength required for the secondary battery 1.

[0071] In addition, by increasing the retention of the electrolyte solution 45 by the separator 5, the permeability of lithium ions is improved. This makes it easier for lithium ions to migrate from the facing layer 53 to the non-facing layer 54, bypassing the end region 35Nx of the electrode sheet 35N as described above. However, because the non-facing layer 54 contains lithium in advance due to the configuration (1) above, it is difficult for lithium ions to migrate from the facing layer 53 to the non-facing layer 54, bypassing the end region 35Nx. This makes it possible to suppress a decrease in battery capacity due to repeated charging and discharging.

[0072] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0073] In the above embodiment, the lithium contained in advance in the negative electrode mixture layer 32N originates from the carboxymethyl cellulose-lithium salt contained in the mixture paste 37N that forms the negative electrode mixture layer 32N by coating the base material 36. However, the present invention is not limited to this, and the method of containing lithium in the negative electrode mixture layer 32N may be changed as desired.

[0074] The lithium transition metal oxide as the positive electrode active material contained in positive electrode mixture layer 32P is also not necessarily limited to the above-mentioned "NCM" and may be changed arbitrarily. The amount of lithium contained in the negative electrode mixture layer 32N in advance may be changed as desired. The density of the negative electrode mixture layer 32N may also be changed as desired. And the Li / M ratio of the lithium transition metal oxide contained in the positive electrode mixture layer 32P may also be changed as desired. However, it is preferable that each of these values ​​is set within the preferred range shown in the above embodiment.

[0075] The amount of carboxymethyl cellulose-lithium salt contained in the composite paste 37N may be changed as desired. Furthermore, the negative electrode capacity / positive electrode capacity ratio for the positive and negative electrode sheets 35P, 35N may also be changed as desired. And the porosity of the separator 5 may also be changed as desired. However, it is preferable to set each of these values ​​within the preferred ranges shown in the above embodiment.

[0076] In the above embodiment, the electrode sheet 35N has a cut portion 55 in the end region 35xb when the electrode sheet 35N is shaped into a belt-like shape, and the cut portion 55 has a configuration as the uncoated portion 39b. The width W of the uncoated portion 39b is set to 300 μm or less. However, this is not limited to this, and the width W of the uncoated portion 39b may be changed arbitrarily. For example, the width W of the uncoated portion 39b may be "0". The uncoated portion 39b may have an end region 35xb in which the width W is 300 μm or less in a portion other than the cut portion 55.

[0077] Each electrode sheet 35 may have a so-called double-sided laminated structure in which the electrode mixture layer 32 is laminated on both sides of the base material 36, or a so-called single-surface layered structure in which the electrode mixture layer 32 is laminated on only one side of the base material 36.

[0078] In the above embodiment, the electrode body 10 has a configuration as a wound body 10X, but the positive and negative electrode sheets 35P, 35N stacked with the separator 5 sandwiched therebetween do not necessarily have to be wound.

[0079] The terminal shapes of the positive electrode terminal 38P and the negative electrode terminal 38N are not limited to the shapes shown in Fig. 1 and may be changed as desired. The shape of the case 20 that defines the outer shape of the secondary battery 1 is also not necessarily limited to a flat rectangular box shape and may be changed as desired, for example, to a cylindrical shape. EXAMPLES

[0080] Examples will be described below to more specifically explain the configuration and effects of the present invention, but the present invention is not limited to these examples. FIG. 7 is a table showing test results for the secondary battery 1 when the Li / M ratio of the lithium transition metal oxide contained in the positive electrode composite layer 32P, the amount of lithium in the negative electrode composite layer 32N, and the density of the negative electrode composite layer 32N are changed. In this test, the battery output and battery life were evaluated as the battery performance. The deterioration rate of the battery capacity was measured as an index of the battery life. This deterioration rate was measured by measuring the change in battery capacity before and after storage of the target secondary battery 1 for a predetermined period of time under a constant temperature environment.

[0081] In FIG. 7, the unit of battery output is "W". The unit of degradation rate is "% / √day". In other words, the rate of degradation of battery capacity was evaluated as the "decrease rate per square root of the number of days". The smaller the value of "% / √day", the slower the rate of degradation. In other words, this indicates that the target secondary battery 1 has a long life.

[0082] The amount of lithium (ppm) in negative electrode mixture layer 32N was measured as follows. First, the electrode sheet 35N is punched out to a specified area. Next, the test piece is ultrasonically dispersed in pure water to peel off the negative electrode composite layer 32N from the substrate 36N. Furthermore, the dispersed contents of the negative electrode composite layer 32N are dissolved using nitric acid and hydrogen peroxide. Then, after removing the residue using a membrane filter, the lithium amount (ppm) was quantified by performing ICP measurement. Note that "ICP measurement" is an abbreviation for "high frequency inductively coupled plasma spectroscopy." The measurement device used was "Shimadzu Corporation: ICPE-9000."

[0083] The density (g / cc) of negative electrode mixture layer 32N was measured as follows. First, the electrode sheet 35N is punched out to a specified area, and the weight of the test piece (the weight of the negative electrode composite layer 32N and the base material 36N) is measured. Next, the negative electrode composite layer 32N is peeled off, and the weight of the base material 36N portion is measured. Furthermore, the weight of the base material 36N portion is subtracted from the weight of the test piece previously measured to measure the weight of the negative electrode composite layer 32N portion. Then, the weight of the negative electrode composite layer 32N portion is divided by the punched area of ​​the test piece to calculate the "weight per unit area". The unit of this "weight per unit area" is "mg / cm2".

[0084] Also, the thickness of electrode sheet 35 and the thickness of base material 36N were measured using a dot-type thickness meter. Furthermore, the "thickness of negative electrode mixture layer 32N" was measured by subtracting the thickness of base material 36N from the thickness of electrode sheet 35. Then, the density (g / cc) of negative electrode mixture layer 32N was calculated by dividing the "basis weight" by this "thickness of negative electrode mixture layer 32N."

[0085] The porosity (%) of the separator 5 was measured as follows. First, the separator 5 was punched into a rectangular shape and its weight was measured. Note that this weight measurement was performed "N=3", that is, three independent measurements were performed. The theoretical weight was calculated from the specific gravity of the resin material used in the separator 5. The porosity (%) of the separator 5 was calculated as "measured weight (average value of N=3) / theoretical weight×100".

[0086] (Relationship between the amount of lithium in the negative electrode mixture layer and the battery output) 7 and 8, in all of the test results shown in "Example 1" to "Example 13" and "Comparative Example 1" to "Comparative Example 19" in the table, it was confirmed that the higher the Li / M ratio of the lithium transition metal oxide contained in positive electrode mixture layer 32P, the more improved the battery output. This tendency is presumably due to the fact that the amount of lithium in positive electrode mixture layer 32P also increases as the Li / M ratio increases.

[0087] In addition, when the Li / M ratio was the same, no significant difference was observed in the battery output even when the amount of lithium in the negative electrode mixture layer 32N and the density of the negative electrode mixture layer 32N were different. For this reason, Fig. 8 only illustrates an approximate graph α when the amount of lithium in the negative electrode mixture layer 32N was "0 ppm" and the density of the negative electrode mixture layer 32N was "1.2 g / cc", as a trend of the battery output increasing approximately linearly as the Li / M ratio increases.

[0088] (Relationship between negative electrode Li content and degradation rate) Also, as shown in FIG. 7 and FIG. 9, the test results confirmed that the deterioration rate of the battery capacity tends to slow down as the amount of lithium in the negative electrode mixture layer 32N increases. That is, the approximate graph β1 in FIG. 9 shows the case where the Li / M ratio is "1.13", and the approximate graph β2 shows the case where the Li / M ratio is "1.16". Also, in the same figure, the approximate graph β3 shows the case where the Li / M ratio is "1.18", and the approximate graph β2 shows the case where the Li / M ratio is "1.20". The density of the negative electrode mixture layer 32N is "1.2g / cc" in all of these cases. And, each of these approximate graphs β1 to β4 shows that the deterioration rate tends to improve approximately linearly as the amount of lithium in the negative electrode mixture layer 32N increases.

[0089] Specifically, when the Li / M ratio is "1.16" or more, the effect of extending the life due to the presence of lithium in the negative electrode mixture layer 32N in advance is more pronounced. Furthermore, compared to when the amount of lithium in the negative electrode mixture layer 32N is "0 ppm", when the negative electrode mixture layer 32N contains "1000 ppm" or more of lithium in advance, the effect of extending the life is even more pronounced. From the test results, it was confirmed that the values ​​"1.16" and "1000 ppm", which are the lower limits of the preferred ranges shown in the above embodiment, are appropriate for the Li / M ratio and the amount of lithium to be contained in the negative electrode mixture layer 32N in advance, respectively.

[0090] In addition, the approximate curves β3 and β4 for the case where the Li / M ratio is higher show that even when the amount of lithium contained in the negative electrode mixture layer 32N is "600 ppm," the presence of lithium in the negative electrode mixture layer 32N provides a sufficient effect of extending the life of the negative electrode mixture layer 32N. Therefore, it is presumed that the preferable range of the amount of lithium contained in the negative electrode mixture layer 32N can be extended to, for example, a lower limit of "600 ppm" or more.

[0091] (Relationship between density of negative electrode mixture layer and degradation rate) 7 and 10, the test results confirmed that the rate of deterioration of the battery capacity is slower when the density of the negative electrode mixture layer 32N is "1.4 g / cc" or less than when the density is "1.6 g / cc". That is, the approximate graphs γ1 to γ3 in FIG. 10 show the cases where the amount of lithium pre-contained in the negative electrode mixture layer 32N is "0 ppm", "1280 ppm", and "1500 ppm", respectively. The Li / M ratio in the positive electrode mixture layer 32P is "1.20" in all of these cases.

[0092] Furthermore, when comparing the approximate curves γ1 to γ3 when the density of the negative electrode composite layer 32N is equal to or less than "1.4 g / cc", the deterioration rate becomes faster as the density becomes lower. This is presumably because, as described above, the increased permeability of the electrolyte 45 makes the battery reaction more likely to proceed, and as a result, the deterioration also becomes more likely to proceed.

[0093] In addition, in each of these approximate graphs γ1 to γ3, when the density of the negative electrode mixture layer 32N is equal to or greater than "1.1 g / cc", the effect of extending the life becomes more noticeable. From this result, it was confirmed that the density of the negative electrode mixture layer 32N is appropriate to have a lower limit of the preferable range of "1.1 g / cc" and an upper limit of "1.4 g / cc" as shown in the above embodiment.

[0094] The approximate graphs γ2 and γ3 in the case where lithium is present in the negative electrode mixture layer 32N show that a sufficient effect of extending the life can be obtained even when the density of the negative electrode mixture layer 32N is "1.0 g / cc". Therefore, it is presumed that the lower limit of the preferable range of the density of the negative electrode mixture layer 32N can be extended to "1.0 g / cc" or more.

[0095] (verification) Next, based on a comparison of "Example 1" to "Example 13" and "Comparative Example 1" to "Example 19" shown in FIG. 9, the preferred ranges for the Li / M ratio, the amount of lithium in negative electrode composite layer 32N, and the density of negative electrode composite layer 32N will be examined.

[0096] In all of "Example 1" to "Example 3", the Li / M ratio is "1.16" and the density of the negative electrode mixture layer 32N is "1.2 g / cc". Furthermore, the amount of lithium contained in the negative electrode mixture layer 32N is "1000 ppm" in "Example 1", "1280 ppm" in "Example 2", and "1500 ppm" in "Example 3". As a result, in all of "Example 1" to "Example 3", the Li / M ratio, the amount of lithium contained in the negative electrode mixture layer 32N, and the density of the negative electrode mixture layer 32N are all values ​​within the above-mentioned preferred ranges.

[0097] When comparing "Example 1" to "Example 3" with "Comparative Example 1" to "Comparative Example 5" whose Li / M ratio is "1.13", higher battery output is obtained in all of them. Furthermore, the degradation speed of the battery capacity in all of "Example 1" to "Example 3" is almost the same as that in "Comparative Example 1" to "Comparative Example 5".

[0098] Furthermore, these "Example 1" to "Example 3" are compared with "Comparative Example 6" and "Comparative Example 7" in which the Li / M ratio and the density of the negative electrode composite layer 32N are equal, but the amount of lithium contained in the negative electrode composite layer 32N is set to "0 ppm" and "600 ppm", respectively. In this case, for each of "Example 1" to "Example 3", a battery output approximately equivalent to these "Comparative Example 6" and "Comparative Example 7" is obtained. Furthermore, with regard to the deterioration rate of the battery capacity, a lower value is obtained for "Example 1" to "Example 3" than for these "Comparative Example 6" and "Comparative Example 7", indicating an improvement in the deterioration rate.

[0099] In "Example 4" to "Example 6", the Li / M ratio is "1.18". In addition, in "Example 4" to "Example 6", the density of the negative electrode mixture layer 32N is "1.2 g / cc", which is the same as in "Example 1" to "Example 3". Furthermore, the amount of lithium contained in the negative electrode mixture layer 32N is "1000 ppm" in "Example 4", "1280 ppm" in "Example 5", and "1500 ppm" in "Example 6". As a result, in "Example 4" to "Example 6", the Li / M ratio, the amount of lithium contained in the negative electrode mixture layer 32N, and the density of the negative electrode mixture layer 32N are all values ​​within the above-mentioned preferred ranges.

[0100] When comparing "Example 4" to "Example 6" with "Example 1" to "Example 3" having a low Li / M ratio, higher battery output is obtained. Furthermore, "Example 4" to "Example 6" are compared with "Comparative Example 8" and "Comparative Example 9" in which the Li / M ratio and the density of the negative electrode composite layer 32N are equal, but the amount of lithium contained in the negative electrode composite layer 32N is set to "0 ppm" and "600 ppm", respectively. In this case, all of "Example 4" to "Example 6" obtain battery output approximately equivalent to these "Comparative Example 8" and "Comparative Example 9". And, regarding the deterioration rate of the battery capacity, "Example 4" to "Example 6" obtain lower values ​​indicating an improvement in the deterioration rate than these "Comparative Example 8" and "Comparative Example 9".

[0101] In "Example 7", the Li / M ratio is "1.20". In addition, in "Example 7", the density of the negative electrode mixture layer 32N is "1.2 g / cc", which is the same as in "Example 1" to "Example 6". Furthermore, the amount of lithium contained in the negative electrode mixture layer 32N is "1000 ppm", which is the same as in "Example 1" and "Example 4". Thus, in "Example 7", the Li / M ratio, the amount of lithium contained in the negative electrode mixture layer 32N, and the density of the negative electrode mixture layer 32N are each within the above-mentioned preferred ranges.

[0102] When "Example 7" is compared with "Example 1" to "Example 6" having a low Li / M ratio, a higher battery output is obtained. Furthermore, "Example 7" is compared with "Comparative Example 10" to "Comparative Example 14" and "Comparative Example 15" having the same Li / M ratio and the amount of lithium contained in the negative electrode composite layer 32N set to "0 ppm" and "600 ppm", respectively. In this case, "Example 7" obtains a battery output substantially equivalent to those of "Comparative Example 10" to "Comparative Example 14" and "Comparative Example 15". And, regarding the deterioration rate of the battery capacity, "Example 7" obtains a lower value indicating an improvement in the deterioration rate than those of "Comparative Example 10" to "Comparative Example 14" and "Comparative Example 15".

[0103] The Li / M ratios of "Example 8" to "Example 10" are all "1.20", the same as "Example 7". The amount of lithium contained in the negative electrode mixture layer 32N of "Example 8" to "Example 10" is "1280 ppm". Furthermore, the density of the negative electrode mixture layer 32N is "1.1 g / cc" for "Example 8", "1.2 g / cc" for "Example 9", and "1.4 g / cc" for "Example 10". As a result, the Li / M ratios, the amount of lithium contained in the negative electrode mixture layer 32N, and the density of the negative electrode mixture layer 32N of "Example 8" to "Example 10" are all within the above-mentioned preferred ranges.

[0104] These "Example 8" to "Example 10" also obtained battery outputs approximately equivalent to those of "Example 7" having the same Li / M ratio. Furthermore, regarding the rate of deterioration of the battery capacity, these "Example 8" to "Example 10" obtained lower values, which indicate an improved rate of deterioration, than "Example 7" having a smaller amount of lithium in the negative electrode mixture layer 32N.

[0105] The Li / M ratios of "Example 11" to "Example 13" are all "1.20", the same as those of "Example 7" to "Example 10". In addition, the amount of lithium contained in the negative electrode mixture layer 32N of these "Example 11" to "Example 13" is "1500 ppm". Furthermore, the density of the negative electrode mixture layer 32N is "1.1 g / cc" in "Example 11" which is the same as that of "Example 8", "1.2 g / cc" in "Example 12" which is the same as that of "Example 9", and "1.4 g / cc" in "Example 13" which is the same as that of "Example 9". As a result, the Li / M ratios, the amount of lithium contained in the negative electrode mixture layer 32N, and the density of the negative electrode mixture layer 32N of these "Example 11" to "Example 13" are also all values ​​within the above-mentioned preferred ranges.

[0106] These "Example 11" to "Example 13" also have battery outputs substantially equivalent to those of "Example 7" to "Example 10" having the same Li / M ratio. Furthermore, with regard to the rate of deterioration of the battery capacity, these "Example 11" to "Example 13" have lower values, which indicate an improved rate of deterioration, than "Example 7" to "Example 13" having a smaller amount of lithium in the negative electrode composite layer 32N.

[0107] Also, "Example 8" to "Example 10", "Comparative Example 16" and "Comparative Example 17" are compared, in which the Li / M ratio and the amount of lithium in the negative electrode mixture layer 32N are equal to each other. In this case, the deterioration rate of "Example 8" to "Example 10" and "Comparative Example 16" in which the density of the negative electrode mixture layer 32N is "1.4 g / cc" or less is improved compared to "Comparative Example 17" in which the density is "1.6 g / cc". Furthermore, "Example 11" to "Example 13", "Comparative Example 18" and "Comparative Example 19" in which the Li / M ratio and the amount of lithium in the negative electrode mixture layer 32N are equal to each other are compared. Also in this case, the deterioration rate of "Example 11" to "Example 13" and "Comparative Example 18" in which the density of the negative electrode mixture layer 32N is "1.4 g / cc" or less is improved compared to "Comparative Example 19" in which the density is "1.6 g / cc".

[0108] In this way, in all of "Example 1" to "Example 13" in which the Li / M ratio, the amount of lithium contained in the negative electrode mixture layer 32N, and the density of the negative electrode mixture layer 32N are within the above-mentioned preferred ranges, the effects of improving the battery output and extending the lifespan are obtained. Also from this verification result, it was confirmed that the following are appropriate: the negative electrode mixture layer 32N contains lithium of 1000 ppm or more and 1500 ppm or less; the density of the negative electrode mixture layer 32N is 1.1 g / cc or more and 1.4 g / cc or less; and the Li / M ratio of the lithium transition metal oxide contained as the positive electrode active material in the positive electrode mixture layer 32P is 1.16 or more and 1.20 or less. It was confirmed that it is appropriate to combine the above to set the preferred range. [Explanation of symbols]

[0109] 1...Secondary battery (lithium ion secondary battery) 3...Positive electrode 4...Negative electrode 5…Separator 10...Electrode body 31...Current collector 32P…Positive electrode composite layer 32N…Negative electrode composite layer 35...Electrode sheet 35P…Electrode sheet 35N…Electrode sheet 36...Base material 37...Composite paste (electrode composite) 50P…Opposite surface 50N…opposing surface

Claims

1. A lithium ion secondary battery comprising an electrode body in which positive and negative electrode sheets are laminated with a separator sandwiched therebetween, each of the electrode sheets being formed by coating an electrode mixture on a substrate serving as a current collector, and a surface facing a negative electrode mixture layer of the electrode sheet on the negative electrode side being larger than a surface facing a positive electrode mixture layer of the electrode sheet on the positive electrode side, The negative electrode mixture layer contains lithium in advance in a range of 1000 ppm or more and 1500 ppm or less, The density of the negative electrode mixture layer is 1.1 g / cc or more and 1.4 g / cc or less, The positive electrode mixture layer contains a lithium transition metal oxide as a positive electrode active material, and a Li / M ratio, which is a ratio of the sum of the numbers of transition metal atoms (M) in the lithium transition metal oxide to the number of lithium atoms (Li), is 1.16 or more and 1.20 or less.

2. The lithium contained in the negative electrode mixture layer in advance is derived from carboxymethyl cellulose-lithium salt contained in the negative electrode mixture that forms the negative electrode mixture layer by the coating. The lithium ion secondary battery according to claim 1 .

3. 3. The lithium ion secondary battery according to claim 2, wherein the negative electrode mixture contains 0.4 wt % or more and 0.6 wt % or less of the carboxymethyl cellulose-lithium salt.

4. The lithium transition metal oxide contained in the positive electrode mixture layer is L)) ｘ Co ｙ Mn ｚ O ２ [x+y+z=1,0<x<1,0<y<1,0<z<1] The lithium ion secondary battery according to any one of claims 1 to 3.

5. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the negative electrode capacity / positive electrode capacity ratio for the positive and negative electrode sheets is 1.6 or more and 1.8 or less.

6. An end region of the electrode sheet where the electrode mixture is not applied to the base material is defined as an uncoated portion of the electrode sheet, The lithium ion secondary battery according to any one of claims 1 to 3, wherein the electrode sheet on the negative electrode side has an end region in which the width of the uncoated portion is 300 µm or less.

7. The porosity of the separator is 50% or more and 60% or less. The lithium ion secondary battery according to any one of claims 1 to 3.

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