Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) comprises an electrode body (14) that has a positive electrode (11) and a negative electrode (12), and a non-aqueous electrolyte, said non-aqueous electrolyte secondary battery (10) being characterized in that: the positive electrode (11) has a positive electrode collector (30) and a positive electrode mixture layer (32) which is provided on the positive electrode collector (30); the negative electrode (12) has a negative electrode collector (40) and a negative electrode mixture layer (42) which is provided on the negative electrode collector (40); the positive electrode mixture layer (32) contains a positive electrode active material; the positive electrode active material has first and second peaks in a volume-based particle size distribution curve; the negative electrode mixture layer (42) contains a negative electrode active material; the negative electrode active material contains at least a silicon-containing material; and the discharge capacity per 1.0 g of the negative electrode mixture layer (42) is not less than 0.60Ah.

Description

Non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Conventionally, a known non-aqueous electrolyte secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an outer can that houses the electrode assembly, in which the positive electrode has a positive electrode mixture layer disposed on a positive electrode current collector, and the negative electrode has a negative electrode mixture layer disposed on a negative electrode current collector.

[0003] Furthermore, in recent years, from the viewpoint of increasing the capacity of non-aqueous electrolyte secondary batteries, the use of a silicon-containing material capable of occluding more lithium ions per unit mass than carbon materials such as graphite has been considered as the negative electrode active material contained in the negative electrode mixture layer (see, for example, Patent Document 1).

[0004] International Publication No. 2019 / 151016

[0005] However, silicon-containing materials undergo larger volume changes (expansion and contraction) due to lithium ion absorption than carbon materials. Therefore, in nonaqueous electrolyte secondary batteries using silicon-containing materials in the negative electrode mixture layer, the expansion and contraction of the negative electrode mixture layer due to charge and discharge may result in uneven distribution of the electrolyte within the electrode body. As a result, repeated charge and discharge may result in a decrease in battery capacity. Therefore, it is not easy to achieve both high capacity and improved charge and discharge cycle characteristics in nonaqueous electrolyte secondary batteries.

[0006] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure is a nonaqueous electrolyte secondary battery including an electrode assembly having a positive electrode and a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector, the positive electrode mixture layer containing a positive electrode active material, the positive electrode active material having a first peak and a second peak in a volume-based particle size distribution curve, the negative electrode mixture layer containing a negative electrode active material, and the negative electrode active material containing at least a silicon-containing material, and the discharge capacity per 1.0 g of the negative electrode mixture layer is 0.60 Ah or more.

[0007] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, it is possible to achieve both an increase in capacity and improvement in charge-discharge cycle characteristics of the nonaqueous electrolyte secondary battery.

[0008] 1 is a schematic view showing an example of the structure of a negative electrode mixture layer;

[0009] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and variations described below are included within the scope of the present disclosure.

[0010] In the following, a cylindrical battery in which a wound electrode assembly is housed in a cylindrical outer can with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the outer can of the battery is not limited to a cylindrical outer can. The secondary battery according to the present disclosure may be, for example, a prismatic battery with a prismatic outer can, a coin battery with a coin-shaped outer can, or a pouch-type battery with an outer can made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, and may be a stacked type in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0011] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte, and an outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is a cylindrical metal container with a bottom and an open axial end, and the opening of the outer can 16 is closed by a sealing member 17. For ease of explanation, the sealing member 17 side of the battery will be referred to as the "top" and the bottom side of the outer can 16 will be referred to as the "bottom."

[0012] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length and width directions. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11. The electrode assembly 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0013] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes through a through hole in the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0014] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a groove 22 formed on its side surface that protrudes inward and supports the sealing body 17. The groove 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the groove 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0015] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0016] The positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte that constitute the electrode assembly 14 will be described in detail below, with the positive electrode 11 and the negative electrode 12 being particularly described below.

[0017] [Positive Electrode] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 32 disposed on the positive electrode current collector 30. The positive electrode current collector 30 can be a foil of a metal such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on its surface. The positive electrode mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder.

[0018] The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode current collector 30, drying the coating, and then compressing it to form a positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0019] The positive electrode mixture layer 32 contains particulate lithium-containing composite oxide as a positive electrode active material. The lithium-containing composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. Specifically, the lithium-containing composite oxide has a composition formula of, for example, Li ｙ Ni ｘ M （１－ｘ） O ２－δ(wherein 0.5≦x≦1, 0<y≦1.2, 0≦δ≦0.05, and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Si, Nb, Zr, Mo, Zn, and B).

[0020] In the above composition formula, M preferably contains at least one element selected from the group consisting of Co, Mn, Al, and Fe. In the above composition formula, the value of y, which indicates the composition ratio of lithium, increases or decreases with charge and discharge. Examples of suitable lithium-containing composite oxides include lithium-containing composite oxides containing Ni, Co, and Mn, and lithium-containing composite oxides containing Ni, Co, and Al.

[0021] The content of Ni in the lithium-containing composite oxide is preferably 50 mol% or more relative to the total number of moles of metal elements excluding Li. By increasing the content of Ni, the battery capacity can be improved. The content of Ni may be 60 mol% or more, 70 mol% or more, or 80 mol% or more relative to the total number of moles of metal elements excluding Li. The upper limit of the content of Ni is, for example, 98 mol% relative to the total number of moles of metal elements excluding Li.

[0022] The content of Co in the lithium-containing composite oxide is, for example, 0 mol % or more and 20 mol % or less with respect to the total number of moles of metal elements excluding Li, and Co is an optional component. In other words, the lithium-containing composite oxide does not need to contain Co. By containing Co, the lithium-containing composite oxide can improve the heat resistance of the battery.

[0023] The content of Mn in the lithium-containing composite oxide is, for example, 0 mol % or more and 50 mol % or less with respect to the total number of moles of metal elements excluding Li, and Mn is an optional component. In other words, the lithium-containing composite oxide does not need to contain Mn. By containing Mn, the lithium-containing composite oxide can stabilize its crystal structure.

[0024] The content of Al in the lithium-containing composite oxide is, for example, 0 mol % or more and 20 mol % or less with respect to the total number of moles of metal elements excluding Li, and Al is an optional component. In other words, the lithium-containing composite oxide does not need to contain Al. By containing Al, the lithium-containing composite oxide can stabilize its crystal structure.

[0025] The content of the elements constituting the lithium-containing composite oxide can be measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0026] Here, the positive electrode active material has a first peak and a second peak in a volume-based particle size distribution curve (hereinafter simply referred to as a "particle size distribution curve"), that is, the positive electrode active material includes a first positive electrode active material group whose peak position on the particle size distribution curve is the same as the peak position of the first peak, and a second positive electrode active material group whose peak position on the particle size distribution curve is the same as the peak position of the second peak.

[0027] The particle size distribution curve of the positive electrode active material can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac-Bell Co., Ltd.) with water as the dispersion medium. The peak of the particle size distribution curve is the peak of a volume-based particle size distribution graph with the horizontal axis representing particle diameter [μm] and the vertical axis representing frequency [%], and the position of the apex of the peak of the particle size distribution curve is the particle diameter at the maximum value of the peak.

[0028] The particle size distribution curve of the positive electrode active material has a first peak and a second peak, which improves the diffusibility of the non-aqueous electrolyte in the positive electrode mixture layer 32 and achieves a uniform distribution of the non-aqueous electrolyte in the positive electrode mixture layer 32. Although the detailed mechanism is not clear, it is presumed that the particle size distribution curve of the positive electrode active material has a first peak and a second peak, which reduces the curvature of the voids (pores) formed in the positive electrode mixture layer 32 through which the non-aqueous electrolyte passes, thereby ensuring a flow path for the non-aqueous electrolyte.

[0029] As will be described in more detail below, the negative electrode mixture layer 42 of this embodiment contains a predetermined amount of silicon-containing material, and the discharge capacity per 1.0 g of the negative electrode mixture layer 42 is 0.60 Ah or more. Silicon-containing materials can absorb more lithium ions per unit mass than carbon materials such as graphite, thereby achieving high capacity. However, silicon-containing materials undergo large volume changes during charge and discharge. As a result, the expansion and contraction of the negative electrode mixture layer 42 during charge and discharge may result in non-uniform distribution of the non-aqueous electrolyte within the electrode assembly 14. In particular, the positive electrode mixture layer 32 is compressed due to the expansion of the negative electrode mixture layer 42, which tends to result in non-uniform distribution of the non-aqueous electrolyte within the positive electrode mixture layer 32. Non-uniform distribution of the non-aqueous electrolyte within the positive electrode mixture layer 32 may result in uneven charge and discharge reactions within the electrode assembly 14, leading to deterioration of charge and discharge cycle characteristics.

[0030] Therefore, as described above, even when a predetermined amount of silicon-containing material is used in the negative electrode mixture layer 42 and the discharge capacity per 1.0 g of the negative electrode mixture layer 42 is 0.60 Ah or more, by using a positive electrode active material whose particle size distribution curve has a first peak and a second peak in the positive electrode mixture layer 32, it is possible to improve the diffusibility of the nonaqueous electrolyte in the positive electrode mixture layer 32. As a result, it is possible to achieve both a high capacity and improved charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery.

[0031] In the particle size distribution curve of the positive electrode active material, the first peak is preferably located at a position of 0.5 μm or more and less than 5.0 μm, and more preferably at a position of 2.0 μm or more and 4.5 μm or less. The second peak is preferably located at a position of 10.0 μm or more and 20.0 μm or less, and more preferably at a position of 12.0 μm or more and 18.0 μm or less. When the first peak is located at a position of 0.5 μm or more and 5 μm or less, and the second peak is located at a position of 10 μm or more and 20 μm or less, it becomes easier to form a flow path for the nonaqueous electrolyte in the positive electrode mixture layer 32, and the diffusibility of the nonaqueous electrolyte in the positive electrode mixture layer 32 can be further improved. As a result, the charge / discharge cycle characteristics can be further improved.

[0032] The positive electrode active material includes, for example, a first lithium-containing composite oxide having a volume-based median diameter (D50) of 0.5 μm or more and less than 5.0 μm, and a second lithium-containing composite oxide having a volume-based D50 of 10.0 μm or more and 20.0 μm or less. Here, D50 refers to the particle size at which the cumulative frequency is 50% from the smallest particle size in the volume-based particle size distribution, and is also called the median diameter.

[0033] The first lithium-containing composite oxide and the second lithium-containing composite oxide are composed of at least one of single particles and secondary particles formed by agglomeration of a plurality of single particles. Note that a single particle is a primary particle having no grain boundary therein. Furthermore, a secondary particle is formed by agglomeration of, for example, 2 to 1000 single particles.

[0034] Here, the first lithium-containing composite oxide may be composed of single particles, and the second lithium-containing composite oxide may be composed of secondary particles. When the first lithium-containing composite oxide is composed of single particles and the second lithium-containing composite oxide is composed of secondary particles, it becomes easy to form a flow path in the nonaqueous electrolyte in the positive electrode mixture layer 32. Note that both the first lithium-containing composite oxide and the second lithium-containing composite oxide may be composed of single particles, or both may be composed of secondary particles.

[0035] The mass ratio of the first lithium-containing composite oxide to the total mass of the positive electrode active material is, for example, 20 mass% or more and 80 mass% or less. Also, the mass ratio of the second lithium-containing composite oxide to the total mass of the positive electrode active material is, for example, 20 mass% or more and 80 mass% or less.

[0036] The positive electrode active material may contain a lithium-containing composite oxide other than the first lithium-containing composite oxide and the second lithium-containing composite oxide (hereinafter referred to as a "third lithium-containing composite oxide"). Examples of the third lithium-containing composite oxide include a lithium-containing composite oxide having a volume-based D50 of 5.0 μm or more and less than 10.0 μm, and a lithium-containing composite oxide having a volume-based D50 of more than 20.0 μm.

[0037] When the positive electrode active material includes a third lithium-containing composite oxide, the positive electrode active material may have a third peak in addition to the first and second peaks in its particle size distribution curve. When the positive electrode active material includes a third lithium-containing composite oxide, the positive electrode active material preferably contains the first lithium-containing composite oxide and the second lithium-containing composite oxide as its main components. More specifically, the sum of the masses of the first lithium-containing composite oxide and the second lithium-containing composite oxide relative to the total mass of the positive electrode active material is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0038] The positive electrode active material, which is one example of the embodiment, can be produced by the following method: Note that the production method described here is only an example, and the method for producing the positive electrode active material is not limited to this method.

[0039] The manufacturing process of the positive electrode active material includes, for example, a synthesis step of obtaining a metal composite oxide, a washing step of washing the fired product with water and dehydrating it to obtain a cake-like composition, and a drying step of drying the cake-like composition to obtain a powder-like composition.

[0040] In the synthesis step, for example, a metal oxide containing predetermined amounts of Ni and M (M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Si, Nb, Zr, Mo, Zn, and B) is mixed with a Li compound to obtain a metal composite oxide.

[0041] The metal oxide can be obtained, for example, by adding dropwise an alkaline solution such as sodium hydroxide to a stirred solution of a metal salt containing Ni and M, adjusting the pH to the alkaline side (for example, 8.5 or more and 12.5 or less), thereby precipitating (co-precipitating) a composite hydroxide containing Ni and M, and then heat-treating the composite hydroxide. The heat treatment temperature is not particularly limited, but is, for example, in the range of 250°C or more and 600°C or less.

[0042] Here, the particle size of the final lithium-containing composite oxide can be adjusted by the particle size of the composite hydroxide, which is the precursor. The particle size of the composite hydroxide tends to be smaller as the pH during synthesis increases. The particle size of the composite hydroxide can also be controlled by adjusting the amount of metal salt solution added; for example, the particle size tends to be larger as the amount of solution increases.

[0043] Examples of Li compounds include Li ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ Examples of the metal oxide include O, LiH, and LiF. The mixing ratio of the metal oxide and the Li compound affects the particle size of the lithium-containing composite oxide. The mixing ratio of the metal oxide and the Li compound is, for example, preferably such that the molar ratio of the total amount of metal elements in the metal oxide to Li is in the range of 1:0.8 or more and 1:1.2 or less, and more preferably 1:1.0 or more and 1:1.1 or less.

[0044] The synthesis step includes a calcination step in which the obtained mixture is calcined. The calcination step is performed, for example, under an oxygen atmosphere. The calcination conditions may include a temperature increase rate of more than 1.0°C / min and less than 5.5°C / min from 450°C to 680°C, and a maximum temperature of 700°C to 850°C. The temperature increase rate from over 680°C to the maximum temperature may be, for example, 0.1°C / min to 3.5°C / min. The maximum temperature may be maintained for 1 hour to 30 hours. This calcination step may be a multi-stage calcination, and multiple first and second temperature increase rates may be set for each temperature range as long as they are within the above-specified range. The particle size of the lithium-containing composite oxide can be adjusted by adjusting the calcination conditions. For example, the particle size of the lithium-containing composite oxide can be increased by increasing the maximum temperature.

[0045] In the washing step, the metal composite oxide obtained in the synthesis step is washed with water and dehydrated to obtain a cake-like composition. By washing with water, unreacted lithium compounds added in the synthesis step and impurities other than lithium compounds can be removed. For example, 300 g to 5000 g of lithium-containing composite oxide are added per liter of water during the water washing step. The water washing step may be repeated multiple times. Dehydration after the water washing step may be performed using, for example, a filter press. Furthermore, Ca compounds, Sr compounds, Fe compounds, Cu compounds, Zr compounds, Mg compounds, Si compounds, Cr compounds, Ti compounds, S compounds, fluorides, etc. may be added to the cake-like composition obtained in the washing step.

[0046] In the drying step, the cake-like composition obtained in the washing step is dried to obtain a powdery composition. The drying step may be performed under a vacuum atmosphere. The drying conditions are, for example, 150°C or higher and 400°C or lower for 0.5 hours or longer and 15 hours or shorter.

[0047] As described above, the positive electrode mixture layer 32 contains a conductive agent and a binder in addition to the positive electrode active material. Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, graphene, and other carbon materials. The content of the conductive agent in the positive electrode mixture layer 32 is, for example, 0.5 mass % or more and 5 mass % or less with respect to the total mass of the positive electrode mixture layer 32.

[0048] Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, etc. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), etc. The content of the binder in the positive electrode mixture layer 32 is, for example, 0.5 mass % or more and 5 mass % or less with respect to the total mass of the positive electrode mixture layer 32.

[0049] Here, the basis weight of the positive electrode mixture layer 32 is 250 g / m ２ or more, and２ or more. In general, increasing the basis weight of the positive electrode mixture layer 32 can increase the capacity of the battery. However, increasing the basis weight of the positive electrode mixture layer 32 tends to reduce the diffusibility of the non-aqueous electrolyte in the positive electrode mixture layer 32, resulting in a decrease in charge-discharge cycle characteristics. In particular, when the negative electrode mixture layer 42 contains a silicon-containing material, the decrease in charge-discharge cycle characteristics is significant.

[0050] In this embodiment, as described above, the particle size distribution curve of the positive electrode active material has a first peak and a second peak. This improves the diffusibility of the non-aqueous electrolyte in the positive electrode mixture layer 32, and realizes a uniform distribution of the non-aqueous electrolyte in the positive electrode mixture layer 32. In other words, when a positive electrode active material having a particle size distribution curve with a first peak and a second peak is used, the diffusibility of the non-aqueous electrolyte in the positive electrode mixture layer 32 is ensured even if the basis weight of the positive electrode mixture layer 32 is increased. As a result, it is possible to achieve a high capacity battery while ensuring charge / discharge cycle characteristics. The upper limit of the basis weight of the positive electrode mixture layer 32 is, for example, 400 g / m ２ The basis weight of the positive electrode mixture layer 32 means the weight per unit area of ​​the positive electrode mixture layer 32 formed on the surface of the positive electrode current collector 30.

[0051] [Negative Electrode] The negative electrode 12 has a negative electrode current collector 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode current collector 40. The negative electrode mixture layer 42 is preferably formed on both sides of the negative electrode current collector 40. The negative electrode current collector 40 can be a foil of a metal such as copper or a copper alloy that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface layer. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0052] The anode mixture layer 42 includes, for example, a anode active material and a binder. The thickness of the anode mixture layer 42 is, for example, 50 μm or more and 300 μm or less. The anode 12 can be produced, for example, by applying an anode mixture slurry including the anode active material, the binder, etc. to the surface of the anode current collector 40, drying the coating, and then rolling the coating to form the anode mixture layer 42 on both sides of the anode current collector 40.

[0053] The negative electrode mixture layer 42 has a discharge capacity per 1.0 g of the negative electrode mixture layer 42 of 0.60 Ah or more, preferably 0.70 Ah or more, and more preferably 0.80 Ah or more. By achieving a discharge capacity per 1.0 g of the negative electrode mixture layer 42 of 0.60 Ah or more, a high capacity battery can be achieved. The discharge capacity per 1.0 g of the negative electrode mixture layer 42 can be adjusted, for example, by adjusting the mass ratio of silicon contained in the negative electrode active material. For example, the discharge capacity per 1.0 g of the negative electrode mixture layer 42 can be increased by increasing the mass ratio of silicon contained in the negative electrode active material. The upper limit of the discharge capacity per 1.0 g of the negative electrode mixture layer 42 is not particularly limited, but is, for example, 1.5 Ah. The discharge capacity per 1.0 g of the negative electrode mixture layer 42 can be determined by the method described in the Examples.

[0054] 2 is a schematic diagram showing an example of the structure of the negative electrode mixture layer 42. As shown in FIG. 2, the negative electrode mixture layer 42 preferably contains a carbon material such as graphite 50 and a silicon-containing material 60. As described above, the silicon-containing material 60 can occlude more lithium ions per unit mass than carbon materials such as graphite 50. Therefore, by using the silicon-containing material 60 as the negative electrode active material, a high capacity battery can be achieved.

[0055] The carbon material contained in the negative electrode mixture layer 42 is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Among these, it is preferable to use at least artificial graphite such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, or amorphous graphite, or a mixture thereof. The volume-based D50 of the carbon material is, for example, 1 μm or more and 30 μm or less, and preferably 5 μm or more and 25 μm or less.

[0056] The silicon-containing material 60 contained in the negative electrode mixture layer 42 may be any material containing silicon. Examples include silicon alloys, silicon compounds, and composite materials containing silicon. Among these, composite materials containing silicon are preferred. The volume-based median diameter (D50) of the composite material is generally smaller than the volume-based median diameter (D50) of the carbon material. The volume-based median diameter (D50) of the composite material is, for example, 1 μm or more and 15 μm or less. Note that one type of silicon-containing material 60 may be used alone, or two or more types may be used in combination.

[0057] A suitable silicon-containing material 60 is a composite particle including an ion-conducting phase 61 and a silicon phase 62 dispersed in the ion-conducting phase 61. The silicon phase 62 is formed by dispersing silicon elements in the form of fine particles. The composite particle may also have a conductive layer formed thereon that covers a portion of the surface of the ion-conducting phase 61. The conductive layer is made of a material that is more conductive than the ion-conducting phase 61 and forms a good conductive path in the negative electrode mixture layer 42. The conductive layer contains, for example, conductive carbon and covers 30% to 70% of the surface area of ​​the ion-conducting phase 61. The coverage of the conductive layer can be calculated, for example, using X-ray photoelectron spectroscopy (XPS).

[0058] The ion-conducting phase 61 is a continuous phase composed of an aggregate of particles finer than the silicon phase 62. The ion-conducting phase 61 is, for example, at least one selected from the group consisting of a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase. Note that the ion-conducting phase 61 preferably contains a carbon phase in order to suppress volumetric changes of the negative electrode active material during charge and discharge and to increase charge and discharge efficiency.

[0059] The silicate phase preferably contains at least one element selected from lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium, for example, from the viewpoint of high lithium ion conductivity, etc. Among these, a silicate phase containing lithium (hereinafter sometimes referred to as a lithium silicate phase) is preferred, for example, from the viewpoint of high lithium ion conductivity, etc.

[0060] The lithium silicate phase can be, for example, a compound of the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). From the viewpoints of stability, ease of preparation, lithium ion conductivity, and the like, z preferably satisfies the relationship 0<z<1, and more preferably z=1 / 2.

[0061] Another example of a suitable silicon-containing material 60 has a sea-island structure in which fine silicon phases 62 are uniformly dispersed in an amorphous silicon oxide phase, and is generally represented by the general formula SiO ｘ (0<x≦2). The main component of the silicon oxide may be silicon dioxide. The content ratio (x) of oxygen element to silicon element is, for example, 0.5≦x<2.0, preferably 0.8≦x≦1.5.

[0062] Another example of a suitable silicon-containing material 60 is a composite particle having a sea-island structure in which fine silicon phases 62 are substantially uniformly dispersed in a carbon phase. The carbon phase is preferably an amorphous carbon phase. The carbon phase may contain a crystalline phase component, but preferably contains a larger amount of amorphous phase components. The amorphous carbon phase is, for example, composed of a carbon material having an average interplanar spacing of (002) planes of greater than 0.34 nm as measured by X-ray diffraction. The amorphous carbon phase is, for example, composed of amorphous carbon particles. Note that when the silicon-containing material 60 is a composite particle having a sea-island structure in which fine silicon phases 62 are substantially uniformly dispersed in a carbon phase, the total mass of elemental silicon contained in the silicon-containing material 60 may be equal to the mass of the silicon phases 62.

[0063] The mass ratio of the silicon phase 62 to the total mass of the silicon-containing material 60 is preferably 30 mass% or more. In this case, the discharge capacity is increased, and the battery is likely to have high output. Furthermore, the mass ratio of the silicon phase 62 to the total mass of the silicon-containing material 60 is preferably 60 mass% or less. In this case, the volume change of the negative electrode mixture layer 42 during charge and discharge can be reduced, the expansion and contraction of the electrode body 14 during charge and discharge can be suppressed, and the battery is likely to have excellent durability. Therefore, the mass ratio of the silicon phase 62 to the total mass of the silicon-containing material 60 is preferably 30 mass% or more and 60 mass% or less.

[0064] The crystallite size of the silicon phase 62 constituting the composite particle is, for example, 10 nm or more and 30 nm or less. The crystallite size of the silicon phase 62 is calculated by the Scherrer equation from the half-width of the analysis peak assigned to the Si(111) plane in the X-ray diffraction pattern of the silicon phase 62.

[0065] The ratio of the total mass of elemental silicon contained in the silicon-containing material 60 to the mass of the negative electrode mixture layer 42 is preferably 12 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more. By setting the ratio of the total mass of elemental silicon contained in the silicon-containing material 60 to the mass of the negative electrode mixture layer 42 to be 12 mass% or more, it becomes easy to achieve a discharge capacity of 0.60 Ah or more per 1.0 g of the negative electrode mixture layer 42, thereby realizing a high capacity battery.

[0066] Furthermore, the ratio of the total mass of silicon contained in the silicon-containing material 60 to the mass of the negative electrode mixture layer 42 is preferably 50 mass% or less, more preferably 45 mass% or less, and even more preferably 40 mass% or less. If the ratio of the total mass of silicon contained in the silicon-containing material 60 to the mass of the negative electrode mixture layer 42 exceeds 50 mass%, the volume change of the negative electrode mixture layer 42 during charge and discharge may become excessively large, and the diffusibility of the non-aqueous electrolyte within the electrode body 14 may be reduced. Therefore, the ratio of the total mass of silicon contained in the silicon-containing material 60 to the mass of the negative electrode mixture layer 42 is preferably 12 mass% or more and 50 mass% or less, more preferably 15 mass% or more and 45 mass% or less, and even more preferably 20 mass% or more and 40 mass% or less. The mass of the silicon may be approximately the same as the mass of the silicon phase 62. That is, the ratio of the mass of the silicon phase 62 to the mass of the negative electrode mixture layer 42 may be 12 mass % or more and 50 mass % or less.

[0067] The total mass of silicon contained in the silicon-containing material 60 can be measured using ICP (Inductively Coupled Plasma). ICP is a type of optical emission spectroscopy. When plasma energy is applied to an analytical sample from the outside, the contained component elements (atoms) are excited. In ICP, emission lines (spectral lines) emitted when the excited atoms return to a lower energy level are measured, and the content of the component elements (atoms) is measured based on the measured emission lines.

[0068] As described above, the negative electrode mixture layer 42 contains a binder in addition to the negative electrode active material. Examples of binders contained in the negative electrode mixture layer 42 include fluorine-containing resins such as styrene butadiene rubber (SBR), nitrile-butadiene rubber (NBR), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF), as well as polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. Among these, SBR and NBR are preferred, with SBR being particularly preferred. These may be used alone or in combination of two or more. The content of the binder in the negative electrode mixture layer 42 is, for example, 0.5% by mass or more and 5% by mass or less, relative to the mass of the negative electrode mixture layer 42.

[0069] The negative electrode mixture layer 42 may further contain a thickener. Examples of thickeners include carboxymethyl cellulose (CMC) or a salt thereof (CMC-Na, etc.), polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyethylene oxide (PEO), and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more. The content of the thickener in the negative electrode mixture layer 42 is, for example, 0.5% by mass or more and 10% by mass or less, relative to the mass of the negative electrode mixture layer 42.

[0070] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0071] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0072] [Non-aqueous electrolyte] The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0073] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0074] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0075] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0076] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２ Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0077] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0078] Examples of unsaturated cyclic carbonates include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0079] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0080] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0081] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0082] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0083] Example 1 Preparation of Lithium-Containing Composite Oxide A [Ni ０．９０ Co ０．０５ Al ０．０５ ](OH) ２The composite hydroxide represented by the formula (1) was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. At this time, the pH and the amount of the metal salt solution were adjusted so that the D50 of the lithium-containing composite oxide finally obtained would be 4.0 µm. Next, lithium hydroxide monohydrate (LiOH·H ) was added to the composite hydroxide so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1:1.03. ２ O) was mixed to obtain a mixture. Then, this mixture was heated from room temperature to 650°C at a temperature increase rate of 2.0°C / min in an oxygen stream with an oxygen concentration of 95%, and fired, and then heated from 650°C to 740°C at a temperature increase rate of 0.5°C / min, and fired again. The fired product was then crushed, washed with water, dried, and extracted with LiNi. ０．９０ Co ０．０５ Al ０．０５ O ２ Thus, a lithium-containing composite oxide A consisting of single particles represented by the formula:

[0084] [Preparation of Lithium-Containing Composite Oxide B] [Ni ０．９０ Co ０．０５ Al ０．０５ ](OH) ２ The composite hydroxide represented by the formula (1) was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. At this time, the pH and the amount of the metal salt solution were adjusted so that the D50 of the lithium-containing composite oxide finally obtained would be 16.0 µm. Next, lithium hydroxide monohydrate (LiOH·H ) was added to the composite hydroxide so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1:1.03. ２ O) was mixed to obtain a mixture. Then, this mixture was heated from room temperature to 650°C at a temperature increase rate of 2.0°C / min in an oxygen stream with an oxygen concentration of 95%, and fired, and then heated from 650°C to 740°C at a temperature increase rate of 0.5°C / min, and fired again. The fired product was then crushed, washed with water, dried, and extracted with LiNi. ０．９０ Co ０．０５ Al ０．０５ O ２ A lithium-containing composite oxide B consisting of secondary particles represented by the formula:

[0085] [Preparation of Positive Electrode] A mixture of the lithium-containing composite oxide A and the lithium-containing composite oxide B described above in a mass ratio of 30:70 was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed in a solid content mass ratio of 95:3:2, and a positive electrode mixture slurry was prepared using N-methyl-2-pyrrolidone (NMP) as a dispersion medium. The positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and after drying the coating, the coating was rolled using a roller and cut to a predetermined electrode size, to obtain a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector. At this time, the basis weight of the positive electrode mixture layer was 350 g / m ２ It was.

[0086] Furthermore, when the volume-based particle size distribution curve of the above-mentioned positive electrode active material was measured using a laser diffraction particle size distribution measuring device (MT3000II, manufactured by Microtrac-Bell Co., Ltd.) with water as a dispersion medium, a first peak appeared at a position of 4.0 μm and a second peak appeared at a position of 16.0 μm.

[0087] [Preparation of silicon-containing material] Coal pitch (MCP250, manufactured by JFE Chemical Corporation) as a carbon raw material and raw silicon (3N, average particle size 10 μm) were mixed in a mass ratio of 66:33, and the mixture was pulverized and micronized using a planetary ball mill (P-5, manufactured by Fritsch). Next, the micronized powder mixture was fired in an inert atmosphere to carbonize the carbon source and obtain a sintered product in which a silicon phase was dispersed within an amorphous carbon phase. Thereafter, the sintered product was pulverized using a jet mill to obtain silicon-containing particles as a silicon-containing material having a D50 of 10 μm. The ratio of the total mass of the silicon phase to the total mass of the silicon-containing material was 50% by mass.

[0088] [Preparation of Negative Electrode] A mixture of graphite and the silicon-containing material described above in a 50:50 mass ratio was used as the negative electrode active material. The negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a solid content mass ratio of 98:1:1, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and the coating was dried. The coating was then rolled using a roller and cut to a predetermined electrode size to obtain a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode current collector. The ratio of the total mass of silicon contained in the silicon-containing material to the mass of the prepared negative electrode mixture layer was 25% by mass.

[0089] [Preparation of non-aqueous electrolyte (electrolyte solution)] LiPF ６ The electrolyte solution was prepared by adding LiPF (lithium salt). ６ The concentration of was 1.0 mol / L. As the non-aqueous solvent, a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of EC:EMC=3:7 was used.

[0090] [Preparation of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] An aluminum lead was attached to a portion of the positive electrode, and a nickel lead was attached to a portion of the negative electrode. The positive and negative electrodes were spirally wound with a polyolefin separator between them to prepare a wound electrode assembly. Insulating plates were placed on the top and bottom of the electrode assembly, and the electrode assembly was housed in an outer can. The negative electrode lead was welded to the bottom of a cylindrical outer can with a bottom, and the positive electrode lead was welded to a sealing member. An electrolyte was poured into the outer can, and the opening of the outer can was sealed with a sealing member via a gasket to prepare a non-aqueous electrolyte secondary battery as a test cell.

[0091] [Evaluation of Discharge Capacity per 1.0 g of Negative Electrode Mixture Layer] The prepared test cell was disassembled, and the removed negative electrode was placed opposite to lithium as a positive electrode. Then, discharge was performed from a state in which the negative electrode was 5 mV higher than lithium to a state in which the negative electrode was 1 V higher than lithium. The negative electrode discharge utilization rate (Ah / g), defined as the discharge capacity per 1.0 g of the negative electrode mix layer, was calculated based on the charge released during the discharge.

[0092] [Evaluation of Initial Discharge Capacity and Charge / Discharge Cycle Characteristics] The prepared test cell was charged at a constant current of 0.3 C in a temperature environment of 25°C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 C. Thereafter, the cell was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V, and the discharge capacity at this time was taken as the initial discharge capacity. This charge / discharge cycle was counted as one cycle, and 100 cycles were repeated. The initial discharge capacity and the discharge capacity at the 100th cycle were determined, and the capacity retention rate was calculated using the following formula: Capacity retention rate (%) = Discharge capacity at the 100th cycle / Initial discharge capacity × 100

[0093] Example 2 A test cell was prepared and evaluated in the same manner as in Example 1, except that a mixture of graphite and a silicon-containing material in a mass ratio of 60:40 was used in the preparation of the negative electrode. The ratio of the total mass of silicon contained in the silicon-containing material to the mass of the prepared negative electrode mixture layer was 20 mass%.

[0094] Example 3 A test cell was prepared and evaluated in the same manner as in Example 1, except that a mixture of graphite and a silicon-containing material in a mass ratio of 70:30 was used in the preparation of the negative electrode. The ratio of the total mass of silicon contained in the silicon-containing material to the mass of the prepared negative electrode mixture layer was 15 mass%.

[0095] Example 4: The basis weight of the positive electrode mixture layer was 250 g / m ２ A test cell was prepared in the same manner as in Example 1 except for the above, and evaluation was carried out.

[0096] Example 5: The basis weight of the positive electrode mixture layer was 240 g / m ２ A test cell was prepared in the same manner as in Example 1 except for the above, and evaluation was carried out.

[0097] <Comparative Example 1> A test cell was produced and evaluated in the same manner as in Example 1, except that only the following lithium-containing composite oxide C was used as a positive electrode active material in the production of a positive electrode, and a mixture of graphite and a silicon-containing material in a mass ratio of 92:8 was used in the production of a negative electrode.

[0098] The volumetric particle size distribution curve of the prepared positive electrode active material was measured using a laser diffraction particle size distribution analyzer (MT3000II, manufactured by Microtrac-Bell Corporation) with water as a dispersion medium, and a peak appeared only at the position of 12.0 μm. The basis weight of the positive electrode mixture layer was 350 g / m ２ The ratio of the total mass of silicon contained in the silicon-containing material to the mass of the produced negative electrode mixture layer was 4 mass %.

[0099] [Preparation of Lithium-Containing Composite Oxide C] [Ni ０．９０ Co ０．０５ Al ０．０５ ](OH) ２ The composite hydroxide represented by the formula (1) was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. At this time, the pH and the amount of the metal salt solution were adjusted so that the D50 of the lithium-containing composite oxide finally obtained would be 12.0 µm. Next, lithium hydroxide monohydrate (LiOH·H ) was added to the composite hydroxide so that the molar ratio of Li to the total amount of Ni, Co, and Al was 1:1.03. ２ O) was mixed to obtain a mixture. Then, this mixture was heated from room temperature to 650°C at a temperature increase rate of 2.0°C / min in an oxygen stream with an oxygen concentration of 95%, and fired, and then heated from 650°C to 740°C at a temperature increase rate of 0.5°C / min, and fired again. The fired product was then crushed, washed with water, dried, and extracted with LiNi. ０．９０ Co ０．０５ Al ０．０５ O ２ A lithium-containing composite oxide C consisting of secondary particles represented by the formula:

[0100] Comparative Example 2 A test cell was produced and evaluated in the same manner as in Example 1, except that only the lithium-containing composite oxide C was used as the positive electrode active material in the production of the positive electrode. ２ It was.

[0101] Comparative Example 3 A test cell was prepared and evaluated in the same manner as in Example 1, except that a mixture of graphite and a silicon-containing material in a mass ratio of 92:8 was used in the preparation of the negative electrode.２ It was.

[0102] The initial discharge capacities and capacity retention rates of the test cells of Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1. Table 1 also shows the discharge capacities per 1.0 g of the negative electrode mixture layer. The initial discharge capacities of the test cells of Examples 1 to 5 and Comparative Examples 1 to 3 shown in Table 1 are expressed relative to the initial discharge capacity of the test cell of Comparative Example 1, which is set to 100. A larger value of the initial discharge capacity indicates a higher capacity.

[0103]

[0104] As shown in Table 1, the test cells of the examples have improved initial discharge capacities and capacity retention rates compared to the test cells of the comparative examples. In other words, by using a predetermined amount of silicon-containing material in the negative electrode active material, setting the discharge capacity per 1.0 g of the negative electrode mixture layer to 0.60 Ah or more, and using a positive electrode active material whose particle size distribution curve has the first peak and the second peak, it is possible to achieve both a high capacity and improved charge-discharge cycle characteristics of the nonaqueous electrolyte secondary battery.

[0105] On the other hand, the test cell of Comparative Example 2, which uses a silicon-containing material in the negative electrode mixture layer and a positive electrode active material with a particle size distribution curve having only one peak while achieving a discharge capacity of 0.60 Ah or more per 1.0 g of the negative electrode mixture layer, has an improved initial discharge capacity but a reduced capacity retention rate compared to the test cell of Comparative Example 1. This is presumably because, although increasing the silicon-containing material in the negative electrode mixture layer can achieve a high capacity, the large volume change in the negative electrode mixture layer reduces the diffusibility of the non-aqueous electrolyte in the positive electrode mixture layer. In other words, unless a positive electrode active material with a particle size distribution curve having a first peak and a second peak is used, it is difficult to improve the charge-discharge cycle characteristics.

[0106] Furthermore, the test cell of Comparative Example 3, which used a positive electrode active material whose particle size distribution curve had a first peak and a second peak but had a discharge capacity per 1.0 g of the negative electrode mixture layer of less than 0.60 Ah, showed a slight improvement in initial discharge capacity but no improvement in capacity retention rate compared to the test cell of Comparative Example 1. This indicates that the use of a positive electrode active material whose particle size distribution curve had a first peak and a second peak while setting the discharge capacity per 1.0 g of the negative electrode mixture layer to 0.60 Ah or more resulted in a specific improvement in charge-discharge cycle characteristics.

[0107] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including an electrode assembly having a positive electrode and a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector, the positive electrode mixture layer contains a positive electrode active material, the positive electrode active material has a first peak and a second peak in a volume-based particle size distribution curve, the negative electrode mixture layer contains a negative electrode active material, and the negative electrode active material contains at least a silicon-containing material, and the non-aqueous electrolyte secondary battery has a discharge capacity of 0.60 Ah or more per 1.0 g of the negative electrode mixture layer. The positive electrode mixture layer has a basis weight of 250 g / m. ２ Above, 400g / m ２The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 12 mass% or more. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 12 mass% or more. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 50 mass% or less. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 40 mass% or less. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the silicon-containing material includes an ion-conducting phase and a silicon phase dispersed in the ion-conducting phase. The nonaqueous electrolyte secondary battery of claim 7, wherein the ion-conducting phase is at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The nonaqueous electrolyte secondary battery of claim 7 or 8, wherein the ratio of the total mass of the silicon phase to the total mass of the silicon-containing material is 30% by mass or more and 60% by mass or less.

[0108] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 32 Positive electrode mixture layer, 40 Negative electrode current collector, 42 Negative electrode mixture layer

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly having a positive electrode and a negative electrode; and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode mixture layer provided on the negative electrode current collector, the positive electrode mixture layer contains a positive electrode active material, the positive electrode active material has a first peak and a second peak in a volume-based particle size distribution curve, the negative electrode mixture layer contains a negative electrode active material, and the negative electrode active material contains at least a silicon-containing material, and the negative electrode mixture layer has a discharge capacity of 0.60 Ah or more per 1.0 g.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the apex of the first peak is located at a position equal to or greater than 0.5 μm and less than 5.0 μm, and the position of the second peak is located at a position equal to or greater than 10.0 μm and less than 20.0 μm.

3. The basis weight of the positive electrode mixture layer is 250 g / m ２ Above, 400g / m ２ 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein:

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 12 mass % or more.

5. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 50 mass % or less.

6. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein a ratio of the total mass of elemental silicon contained in the silicon-containing material to the mass of the negative electrode mixture layer is 40 mass % or less.

7. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the silicon-containing material includes an ion-conducting phase and a silicon phase dispersed in the ion-conducting phase.

8. The nonaqueous electrolyte secondary battery according to claim 7, wherein the ion-conducting phase is at least one selected from the group consisting of a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase.

9. The nonaqueous electrolyte secondary battery according to claim 7, wherein a ratio of a total mass of the silicon phase to a total mass of the silicon-containing material is 30 mass % or more and 60 mass % or less.

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