Secondary battery negative electrode and secondary battery

Abstract

A secondary battery negative electrode (12) is characterized by: comprising a long negative electrode core (30), and a negative electrode mixture layer (32) disposed on the negative electrode core (30); including a first end region (12a) on one end side in the longitudinal direction of the negative electrode mixture layer (32), and a second end region (12b) on the other end side in the longitudinal direction of the negative electrode mixture layer (32); the first end region (12a) having a negative electrode plate charge swelling rate smaller than that of the second end region (12b); and the ratio (E1 / E2) of a negative electrode plate charge swelling rate (E1) of the first end region (12a) to a negative electrode plate charge swelling rate (E2) of the second end region (12b) being 0.80 or less.

Description

Negative electrode for secondary battery and secondary battery

[0001] The present disclosure relates to a negative electrode for a secondary battery and a secondary battery.

[0002] Conventionally, secondary batteries equipped with a wound electrode assembly in which long positive and negative electrodes are wound with a separator interposed therebetween have been widely used. In the wound electrode assembly, when the electrodes expand due to charging of the battery, pressure concentrates more on the inner periphery of the electrode assembly than on the outer periphery, resulting in uneven pressure distribution in the radial direction of the electrode assembly.

[0003] For example, Patent Document 1 discloses a negative electrode constituting a wound electrode assembly, the negative electrode including a first active material and a second negative electrode active material having a larger expansion coefficient during charging than the first active material, and further discloses that, when the ratio of the mass of the second negative electrode active material to the total mass of the first negative electrode active material and the second negative electrode active material is defined as the second negative electrode active material ratio, the ratio of the second negative electrode active material on the inner end side of the winding is smaller than the ratio of the second negative electrode active material on the outer end side of the winding. Patent Document 1 also discloses that a negative electrode having the above configuration can relieve pressure applied near the inner end side of the electrode assembly and suppress the occurrence of internal short circuits near the inner end side of the electrode assembly.

[0004] International Publication No. 2022 / 024712

[0005] However, with conventional technology, it is difficult to alleviate the pressure concentrated on the inner periphery of the electrode body and to equalize the pressure distribution in the radial direction of the electrode body during high-rate charging. As a result, metallic lithium is deposited on the inner periphery of the electrode body during high-rate charge-discharge cycles, resulting in a problem of reduced cycle performance.

[0006] Therefore, an object of the present disclosure is to provide a negative electrode for a secondary battery and a secondary battery that can suppress the deterioration of high-rate charge / discharge characteristics.

[0007] The negative electrode for a secondary battery according to the present disclosure comprises a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and has a first end region at one end in the longitudinal direction of the negative electrode mixture layer and a second end region at the other end in the longitudinal direction of the negative electrode mixture layer, the first end region having a negative electrode plate swelling rate that is smaller than that of the second end region, and the negative electrode plate swelling rate (E ２ The negative plate charge swelling rate (E １ ) ratio (E １ / E ２ ) is 0.80 or less.

[0008] The secondary battery according to the present disclosure comprises an electrode body in which the negative electrode for the secondary battery and the positive electrode are wound with a separator interposed therebetween, and the negative electrode for the secondary battery is characterized in that the first end region is positioned closer to the inner periphery of the electrode body than the second end region.

[0009] According to the present disclosure, it is possible to provide a negative electrode for a secondary battery and a secondary battery capable of suppressing deterioration in high-rate charge / discharge characteristics.

[0010] 1 is a cross-sectional view of a secondary battery according to an embodiment of the present invention;

[0011] Hereinafter, an example of an embodiment of a negative electrode for a secondary battery according to the present disclosure and a secondary battery using the negative electrode will be described with reference to the drawings. Note that the negative electrode and secondary battery according to the present disclosure are not limited to the embodiment described below.

[0012] Fig. 1 is a cross-sectional view of a secondary battery according to an embodiment. The secondary battery 10 shown in Fig. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, an electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical case body 16 with a bottom and a sealing body 17 that closes the opening of the case body 16. Examples of the battery case 15 include a cylindrical or rectangular metal case, a resin case (so-called pouch-type) formed by laminating a resin sheet, and the like.

[0013] The electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0014] 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 include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0015] Furthermore, examples of the solid electrolyte that can be used include solid or gel-like polymer electrolytes, inorganic solid electrolytes, and the like. 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. For example, a polymer material that absorbs a non-aqueous solvent and gels is used as the matrix polymer. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. For example, the inorganic solid electrolyte can be a material known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, and the like). While the above-exemplified electrolytes are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may be an aqueous electrolyte.

[0016] The case body 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports the sealing body 17. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and supports the sealing body 17 on its upper surface.

[0017] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and all components except for the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. If the internal pressure of the secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 may deform and rupture, 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. If the internal pressure further increases, the upper valve body 26 may rupture, and gas may be discharged from the opening of the cap 27.

[0018] In the secondary battery 10 shown in Fig. 1, a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the case body 16. The positive electrode lead 20 is connected by welding or the like to the underside of a filter 23, which is the bottom plate of the sealing body 17, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner bottom surface of the case body 16, and the case body 16 serves as the negative electrode terminal.

[0019] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the secondary battery 10 will be further described below.

[0020] The positive electrode 11 includes a long positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal such as aluminum, an aluminum alloy, stainless steel, or titanium that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on its surface.

[0021] The positive electrode mixture layer contains, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer may be provided on only one side of the positive electrode core, or on both sides. The positive electrode mixture layer is produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it. N-methyl-2-pyrrolidone (NMP), for example, is used as the dispersion medium for the positive electrode mixture slurry. A protective layer containing inorganic particles and a binder may be disposed between the positive electrode core and the positive electrode mixture layer, or on the positive electrode mixture layer.

[0022] The positive electrode active material uses a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn. Examples of metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. Examples of suitable composite oxides include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al. One type of lithium transition metal composite oxide may be used alone, or multiple types may be used in combination.

[0023] The lithium transition metal composite oxide has, for example, a layered rock salt structure. Examples of the layered rock salt structure include a layered rock salt structure belonging to the space group R-3m and a layered rock salt structure belonging to the space group C2 / m. Among these, a layered rock salt structure belonging to the space group R-3m is preferred from the viewpoints of high capacity and stability of the crystal structure. The content of the positive electrode active material is, for example, 90% by mass or more and 99% by mass or less with respect to the mass of the positive electrode mixture layer. From the viewpoint of increasing the capacity of the battery, the density of the positive electrode mixture layer is preferably 3.3 g / cc or more, and, for example, 3.3 cc or more and 3.8 g / cc or less.

[0024] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. One type of conductive agent may be used alone, or multiple types may be used in combination. The content of the conductive agent is, for example, 0.1% by mass or more and 5% by mass or less relative to the mass of the positive electrode mixture layer.

[0025] Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer, styrene butadiene copolymer (SBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is, for example, 0.1% to 5% of the mass of the positive electrode mixture layer.

[0026] 2 is a plan view showing an example of a negative electrode before winding. The negative electrode 12 has a long negative electrode core 30 and a negative electrode mixture layer 32 disposed on the negative electrode core 30. For the negative electrode core 30, a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film having such a metal disposed on its surface can be used.

[0027] In the example shown in Fig. 2 , the negative electrode 12 has exposed portions 30a and 30b at one end 33a and the other end 33b in the electrode plate longitudinal direction, where the negative electrode core 30 is exposed. The electrode plate longitudinal direction of the negative electrode 12 is the winding direction of the negative electrode 12. In Fig. 2 , the one end 33a of the negative electrode 12 in the electrode plate longitudinal direction is the winding start end of the negative electrode 12, and the other end 33b of the negative electrode 12 in the electrode plate longitudinal direction is the winding end end of the negative electrode 12. In other words, the exposed portion 30a on the winding start end side of the negative electrode 12 is located on the innermost side of the electrode body 14, and the exposed portion 30b on the winding end side of the negative electrode 12 is located on the outermost side of the electrode body 14.

[0028] A negative electrode lead (not shown) is connected to the exposed portion 30b on the winding end side of the negative electrode 12. The negative electrode lead may be connected to both the exposed portions 30a and 30b, or to either one of the exposed portions 30a and 30b.

[0029] The negative electrode mixture layer 32 contains an active material and a binder, and is provided in an area excluding the exposed portions 30a and 30b on one or both surfaces of the negative electrode core 30. A protective layer containing inorganic particles and a binder may be disposed between the negative electrode core 30 and the negative electrode mixture layer 32, or on the negative electrode mixture layer 32.

[0030] As shown in FIG. 2 , the negative electrode 12 has a first end region 12a at one end in the longitudinal direction of the negative electrode mixture layer 32, and a second end region 12b at the other end in the longitudinal direction of the negative electrode mixture layer 32. The first end region 12a has a smaller negative electrode plate charge swelling rate than the second end region 12b. The negative electrode plate charge swelling rate is the ratio of the thickness of the negative electrode 12 in the secondary battery 10 in a charged state to the thickness of the negative electrode 12 in the secondary battery 10 in a discharged state minus 1. That is, the negative electrode plate charge swelling rate (E １ ) is the thickness (T ｄ１ ) of the negative electrode 12 at the first end region 12 a in the secondary battery 10 in a charged state relative to the thickness (T ｃ１ ) ratio (T ｃ１ / T ｄ１ ) minus 1 (T ｃ１ / T ｄ１-1) (or the value expressed as a percentage). The negative electrode plate charging swelling rate (E ２ ) is the thickness (T ｄ２ ) of the negative electrode 12 at the second end region 12b in the secondary battery 10 in a charged state relative to the thickness (T ｃ２ ) ratio (T ｃ２ / T ｄ２ ) minus 1 (T ｃ２ / T ｄ２ -1) value (or the value expressed as a percentage). The method for measuring the negative electrode plate charge swelling rate will be described later.

[0031] The first end region 12a is located at the winding start end of the negative electrode 12, and the second end region 12b is located at the winding end end of the negative electrode 12. In other words, when the negative electrode 12 is wound, the first end region 12a is located closer to the inner periphery of the electrode body 14 than the second end region 12b.

[0032] The length L1 of the first end region 12a is 5% of the length L of the negative electrode mixture layer 32. However, if 5% of the length L of the negative electrode mixture layer 32 is less than 6 cm, the length L1 of the first end region 12a is 6 cm. The length L1 of the first end region 12a is the length from one end to the other end of the first end region 12a in the longitudinal direction of the negative electrode mixture layer 32. Similarly, the length L2 of the second end region 12b is 5% of the length L of the negative electrode mixture layer 32. If 5% of the length L of the negative electrode mixture layer 32 is less than 6 cm, the length L2 of the second end region 12b is 6 cm. The length L2 of the second end region 12b is the length from one end to the other end of the second end region 12b in the longitudinal direction of the negative electrode mixture layer 32.

[0033] Negative plate charging expansion rate (E ２ ) the negative electrode plate charge swelling rate (E １ ) ratio (E １ / E ２ ) is sufficient if it is 0.80 or less, and more preferably 0.60 or less. １ / E ２By using a negative electrode 12 having a (E) of 0.80 or less, for example, the first end region 12a, which has a sufficiently low negative plate swelling rate during charging, is disposed on the inner periphery of the electrode body 14. This reduces the pressure concentrated on the inner periphery of the electrode body 14, even during high-rate charging, reducing the maximum radial pressure generated in the electrode body 14. It is also presumed that the maximum pressure occurs at or near the radial middle of the electrode body 14. As a result, even during high-rate charging, the radial pressure distribution of the electrode body 14 is uniform, which is presumed to lead to suppression of deterioration in high-rate charge / discharge characteristics. １ / E ２ The lower limit of the ratio (R) is preferably 0.40 or more from the viewpoint of ease of manufacturing the negative electrode.

[0034] The negative electrode plate charge swelling rate of the intermediate region 12c between the first end region 12a and the second end region 12b is the negative electrode plate charge swelling rate (E １ ) and the negative electrode plate charge swelling rate (E ２ By setting the negative electrode plate charge swelling rate of the intermediate region 12c within the above range, for example, even during high-rate charging, the pressure distribution in the radial direction of the electrode body 14 is made more uniform, and deterioration of the high-rate charge / discharge characteristics is further suppressed.

[0035] The negative electrode plate swelling rate may increase at a constant rate from the first end region 12 a to the second end region 12 b, or the rate of increase may vary from the first end region 12 a to the second end region 12 b. However, even during high-rate charging, the radial pressure distribution of the electrode body 14 is more uniform, and deterioration of high-rate charge / discharge characteristics is more suppressed. Therefore, it is preferable that the negative electrode plate swelling rate increase at a constant rate from the first end region 12 a to the second end region 12 b.

[0036] The negative electrode plate charge swelling ratio of the second end region 12b is preferably 45% or less, and more preferably 15% to 40%. When the negative electrode plate charge swelling ratio of the second end region 12b satisfies the above range, the radial pressure distribution of the electrode body 14 becomes more uniform even during high-rate charging, which may lead to a deterioration in high-rate charge / discharge characteristics. The negative electrode plate charge swelling ratio is measured as follows.

[0037] After charging the secondary battery 10 to an SOC of 100%, the negative electrode 12 is removed from the charged secondary battery 10 in an inert gas atmosphere, and the thickness of the negative electrode 12 is measured in a region from one longitudinal end to the other longitudinal end of the negative electrode mixture layer 32. The thickness of the negative electrode 12 is measured at 20 equally spaced points along the longitudinal direction of the negative electrode mixture layer 32. The thickness of the negative electrode 12 measured at one longitudinal end of the negative electrode mixture layer 32 is then used as the thickness (T ｃ１ ), and the thickness of the negative electrode 12 measured at the other longitudinal end of the negative electrode mixture layer 32 was defined as the thickness (T ｃ２ The thickness of the negative electrode 12 in the intermediate region of the charged state is the thickness of the negative electrode 12 excluding the thicknesses of the negative electrode 12 at one end and the other end in the longitudinal direction of the negative electrode mixture layer 32 among the 20 points measured at equal intervals as described above.

[0038] Next, the negative electrode 12 is removed from the secondary battery 10 in a fully discharged state, and the thickness of the negative electrode 12 is measured in a region from one longitudinal end to the other longitudinal end of the negative electrode mixture layer 32. The thickness of the negative electrode 12 is measured at 20 equally spaced points along the longitudinal direction of the negative electrode mixture layer 32. The thickness of the negative electrode 12 measured at one longitudinal end of the negative electrode mixture layer 32 is then calculated as the thickness (T ｄ１ ), and the thickness of the negative electrode 12 measured at the other longitudinal end of the negative electrode mixture layer 32 was defined as the thickness (T ｄ２ The thickness of the negative electrode 12 in the intermediate region of the discharged state is the thickness of the negative electrode 12 excluding the thicknesses of the negative electrode 12 at one end and the other end in the longitudinal direction of the negative electrode mixture layer 32 among the 20 points measured at equal intervals.

[0039] The thickness (T ｃ１ ), the thickness (T ｄ１ ) to (T ｃ１ / T ｄ１ −1) was calculated, and the calculated value was used as the negative electrode plate charging swelling rate (E １ ) The calculated thickness (T ｃ２), the thickness of the negative electrode 12 in the second end region 12b in the discharged state (T ｄ２ ) to (T ｃ２ / T ｄ２ -1) was calculated, and the calculated value was used as the negative electrode plate charging swelling rate (E ２ )

[0040] The negative electrode active material preferably includes a first active material and a second active material having different charge swelling rates. The first active material has a smaller charge swelling rate than the second active material. The charge swelling rate of the active material is determined as follows. A negative electrode is fabricated using a single active material (i.e., the first active material or the second active material) as the negative electrode active material, and the charge swelling rate of the negative electrode plate is measured in the same manner as described above. The measured charge swelling rate of the negative electrode plate is defined as the charge swelling rate of the active material.

[0041] In the negative electrode mixture layer 32, the ratio of the mass of the first active material to the total mass of the first and second active materials is defined as the first active material ratio, and the ratio of the mass of the second active material to the total mass of the first and second active materials is defined as the second active material ratio. The first active material ratio in the first end region 12a is preferably greater than the first active material ratio in the second end region 12b, and the second active material ratio in the second end region 12b is preferably greater than the second active material ratio in the first end region 12a. This allows the negative electrode plate charge swelling rate in the first end region 12a to be smaller than the negative electrode plate charge swelling rate in the second end region 12b. This reduces pressure concentrated on the inner periphery of the electrode body 14, thereby suppressing deterioration of high-rate charge / discharge characteristics. Note that methods for making the negative electrode plate charge swelling rate in the first end region 12a smaller than the negative electrode plate charge swelling rate in the second end region 12b are not limited to the above, and may also be possible, for example, by using a larger amount of active material with a smaller particle size in the first end region 12a or by reducing the content of binder in the first end region 12a.

[0042] The first active material ratio may decrease at a constant rate from the first end region 12 a to the second end region 12 b, or the rate of decrease may vary from the first end region 12 a to the second end region 12 b. The second active material ratio may increase at a constant rate from the first end region 12 a to the second end region 12 b, or the rate of increase may vary from the first end region 12 a to the second end region 12 b. However, in terms of making the radial pressure distribution of the electrode body 14 more uniform and further suppressing deterioration of the high-rate charge / discharge characteristics even during high-rate charging, it is preferable that the first active material ratio decrease at a constant rate from the first end region 12 a to the second end region 12 b and the second active material ratio increase at a constant rate from the first end region 12 a to the second end region 12 b.

[0043] The negative electrode mixture layer 32 is fabricated, for example, as follows: A first negative electrode mixture slurry containing a negative electrode active material and a binder and a second negative electrode mixture slurry containing a negative electrode active material and a binder, the first negative electrode mixture slurry having a smaller first negative electrode active material ratio and a larger second negative electrode mixture slurry ratio than the first negative electrode mixture slurry, are prepared. A multi-layer die coater is used to coat the first negative electrode mixture slurry and the second negative electrode mixture slurry on the negative electrode core 30 while changing the coating amount ratio between the first negative electrode mixture slurry and the second negative electrode mixture slurry at a predetermined timing, thereby forming the negative electrode mixture layer 32 in which the first negative electrode active material ratio and the second negative electrode active material ratio change from the first end region 12 a to the second end region 12 b. For example, by using a multi-layer die coater to apply the first anode mixture slurry to the second anode mixture slurry from the first end region 12a to the second end region 12b while decreasing the application amount ratio of the first anode mixture slurry to the second anode mixture slurry, an anode mixture layer 32 is obtained in which the first active material ratio decreases at a constant rate from the first end region 12a to the second end region 12b and the second active material ratio increases at a constant rate from the first end region 12a to the second end region 12b. That is, an anode mixture layer 32 is obtained in which the anode plate expansion rate increases at a constant rate from the first end region 12a to the second end region 12b. Note that the obtained anode mixture layer 32 is preferably compressed after drying.

[0044] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Examples of carbon materials that function as the negative electrode active material include graphite, such as natural graphite, artificial graphite, and mixtures thereof. The negative electrode active material may include elements that alloy with Li, such as Si and Sn, or materials containing such elements. Among these, Si-containing materials are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. The content of the negative electrode active material is, for example, 90% by mass or more and 99.5% by mass or less, based on the mass of the negative electrode mixture layer 32.

[0045] From the viewpoint of charge swelling rate, it is preferable that the first active material is graphite and the second active material is a Si-containing material. For example, in terms of suppressing deterioration of high-rate charge / discharge characteristics, the content of the Si-containing material as the second active material is preferably 50 mass% or less, and more preferably 40 mass% or less, relative to the total mass of the first active material and the second active material in the negative electrode mixture layer 32. For example, in terms of increasing the capacity of the battery, the lower limit of the content of the Si-containing material as the second active material is preferably 6 mass% or more, more preferably 8 mass% or more, and even more preferably 10 mass% or more.

[0046] Examples of the Si-containing material include Si, Si alloys, and Si compounds. The Si-containing material may also be a composite particle containing an ion-conducting phase and a silicon phase (silicon particles in one respect) dispersed within the ion-conducting phase. Examples of the ion-conducting phase include a silicate phase, a carbon phase, and a silicon oxide phase.

[0047] The carbon phase may be composed of, for example, amorphous carbon. Examples of amorphous carbon constituting the carbon layer include hard carbon, soft carbon, and other amorphous carbon. Amorphous carbon has an average interplanar spacing d of (002) planes measured by, for example, X-ray diffraction. ００２ The carbon material has a particle size of more than 0.34 nm.

[0048] The main component of the silicon oxide phase (for example, 95% by mass or more and 100% by mass or less) may be silicon dioxide. The composition of the composite particles containing the silicon oxide phase and the silicon phase dispersed therein is generally SiO ｘ It can be expressed as: SiO ｘ is a material in which silicon particles are amorphous SiO ２ The oxygen content ratio x to silicon is preferably, for example, 0.5≦x<2.0, and more preferably 0.8≦x≦1.5.

[0049] The silicate phase may satisfy the following conditions (1) and / or (2): (1) The silicate phase contains at least one element selected from the group consisting of alkali metal elements and Group 2 elements (Group 2 elements of the long periodic table). (2) The silicate phase contains element L. The element L is at least one element selected from the group consisting of B, Al, Zr, Nb, Ta, V, lanthanoids, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W. Lanthanoids is a collective term for 15 elements ranging from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71.

[0050] Regarding the above condition (1), examples of alkali metal elements include lithium (Li), potassium (K), and sodium (Na). Examples of Group 2 elements include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The inclusion of an alkali metal element and / or a Group 2 element may reduce the irreversible capacity of the silicate phase. A silicate phase containing lithium (hereinafter, sometimes referred to as a "lithium silicate phase") is preferable in terms of, for example, a small irreversible capacity and a high initial charge / discharge efficiency.

[0051] The lithium silicate phase may be an oxide phase containing Li, Si, and O, and may contain other elements. The atomic ratio of O to Si in the lithium silicate phase, O / Si, is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase, Li / Si, is, for example, greater than 0 and less than 4.

[0052] The lithium silicate phase has the formula: Li ２ｚ SiO （２＋ｚ） The lithium silicate phase may contain or be composed of a lithium silicate phase represented by (0<z<2). Preferably, z satisfies the relationship 0<z<1, and z=1 / 2 (i.e., Li ２ Si ２ O ５ ) is more preferred.

[0053] The Si-containing material may also include composite particles containing an ion-conducting phase and a silicon phase dispersed within the ion-conducting phase, and a coating layer covering at least a portion of the surface of the composite particles.

[0054] The coating layer present on the surface of the composite particle may include, for example, a conductive layer. Forming a conductive layer on the surface of the composite particle may increase the conductivity of the Si-containing material. A conductive material containing carbon is preferred as the conductive material constituting the conductive layer. Examples of conductive materials containing carbon include conductive carbon materials. Examples of conductive carbon materials include carbon black, graphite, and amorphous carbon (amorphous carbon) with low crystallinity. Amorphous carbon is preferred because it has a strong buffering effect on the silicon phase, which changes in volume during charging and discharging. The amorphous carbon may be either easily graphitized carbon (soft carbon) or difficult-to-graphitize carbon (hard carbon). Examples of carbon black include acetylene black and ketjen black. The thickness of the conductive layer may be, for example, in the range of 1 to 200 nm. The thickness of the conductive layer can be measured by observing the cross section of the Si-containing material using a SEM or TEM (transmission electron microscope).

[0055] Examples of the binder contained in the negative electrode mixture layer 32 include the same binders as those in the positive electrode 11. One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is, for example, 0.1 mass % or more and 5 mass % or less with respect to the mass of the negative electrode mixture layer 32. The negative electrode mixture layer 32 may also contain a conductive agent.

[0056] [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. The separator 13 may have, for example, a multi-layer structure including a thermoplastic resin layer such as polyolefin and a cellulose fiber layer, a two-layer structure of polyethylene (PE) / polypropylene (PP), or a three-layer structure of PE / PP / PE.

[0057] A filler layer containing an inorganic filler may be disposed 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 containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. 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. In addition, a highly heat-resistant resin layer (heat-resistant layer) such as an aramid resin may be disposed on the surface of the separator 13. The separator 13 may have, for example, a substrate made of a porous sheet and a filler layer or heat-resistant layer disposed on the substrate.

[0058] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0059] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, lithium nickel oxide (LiNi) containing cobalt and aluminum was used. ０．８８ Co ０．０９ Al ０．０３ O ２) was used. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solids mass ratio of 98:1:1, and N-methylpyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. The slurry was applied to both sides of a positive electrode core made of a long aluminum foil with a thickness of 15 μm, and the coating was dried and compressed to form a positive electrode mixture layer on both sides of the positive electrode core. An exposed core portion was formed in the center in the longitudinal direction of the positive electrode core, and a positive electrode lead was joined to the exposed portion.

[0060] [Fabrication of Negative Electrode] A negative electrode active material obtained by mixing graphite powder and a Si-containing material in a mass ratio of 94:6, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose in a solid content mass ratio of 98:1:1 was mixed, and water was used as a dispersion medium to prepare a first negative electrode mixture slurry. A negative electrode active material obtained by mixing graphite powder and a Si-containing material in a mass ratio of 88:12, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose in a solid content mass ratio of 98:1:1 was mixed, and water was used as a dispersion medium to prepare a second negative electrode mixture slurry. Next, the first negative electrode mixture slurry and the second negative electrode mixture slurry were set in a multilayer die coater, and were applied to both sides of a negative electrode core made of a long copper foil with a thickness of 8 μm, from a position corresponding to the first end region to a position corresponding to the second end region, while continuously changing the application amount ratio of the first negative electrode mixture slurry to the second negative electrode mixture slurry from 1:0 to 0:1, and then the coating film was dried and compressed to obtain a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. In addition, a core exposed portion was formed at the longitudinal end of the negative electrode core, and a negative electrode lead was joined to the core exposed portion.

[0061] In the negative electrode of Example 1, the negative electrode plate swelling rate during charging was measured, and the negative electrode plate swelling rate during charging in the first end region (E １ ) is 21%, and the negative plate charging swelling rate (E ２ ) is 27%, and (E １ / E ２ ) was 0.78.

[0062] [Fabrication of Electrode Assembly] The positive electrode, the negative electrode, and a polyethylene separator were spirally wound around a cylindrical winding core member, and stop tapes were attached to both axial ends of the outermost peripheral surface to obtain a wound electrode assembly. At this time, the negative electrode was positioned so that the first end region of the negative electrode was located closer to the inner periphery of the electrode assembly (toward the winding core) than the second end region. After forming the wound structure of the electrode assembly, the winding core member was removed to obtain a wound electrode assembly with a cavity formed in the winding core portion.

[0063] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:3 (25°C), and LiPF ６ was dissolved in a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte solution.

[0064] [Fabrication of Cylindrical Battery] After placing insulating plates above and below the electrode assembly, the negative electrode lead was welded to the inner bottom surface of a cylindrical outer can with a bottom, and the positive electrode lead was welded to the internal terminal plate of a sealing member, and the electrode assembly was housed in the outer can. Thereafter, a nonaqueous electrolyte solution was injected into the outer can under reduced pressure, and the opening of the outer can was sealed with a sealing member via a gasket, thereby obtaining a cylindrical battery.

[0065] Example 2 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 95:5, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 87:13. The negative electrode plate swelling rate during charging of the negative electrode of Example 2 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 20%, and the negative plate charging swelling rate (E ２ ) is 28%, and (E １ / E ２ ) was 0.71. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 2.

[0066] Example 3 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 96:4, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 86:14. The negative electrode plate swelling rate during charging of the negative electrode of Example 3 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 18%, and the negative plate charging swelling rate (E ２ ) is 29%, and (E １ / E ２ ) was 0.62. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 3.

[0067] Example 4 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 97:3, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 85:15. The negative electrode plate swelling rate during charging of the negative electrode of Example 4 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 17%, and the negative plate charging swelling rate (E ２ ) is 30%, and (E １ / E ２ ) was 0.57. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 4.

[0068] Example 5 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 98:2, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 84:16. The negative electrode plate swelling rate during charging of the negative electrode of Example 5 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 16%, and the negative plate charging swelling rate (E ２ ) is 31%, and (E １ / E ２ ) was 0.52. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 5.

[0069] Example 6 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 99:1, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 83:17. The negative electrode plate swelling rate during charging of the negative electrode of Example 6 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 15%, and the negative plate charge swelling rate (E ２ ) is 32%, and (E １ / E ２ ) was 0.47. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 6.

[0070] Example 7 A negative electrode was fabricated in the same manner as in Example 1, except that in the first negative electrode mixture slurry, graphite powder was used as the negative electrode active material, and in the second negative electrode mixture slurry, a negative electrode active material obtained by mixing graphite powder and a Si-containing material in a mass ratio of 82:18 was used. The negative electrode plate swelling rate during charging of the negative electrode of Example 7 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 14%, and the negative plate charging swelling rate (E ２ ) is 33%, and (E １ / E ２ ) was 0.42. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 7.

[0071] Comparative Example 1 A negative electrode was fabricated in the same manner as in Example 1, except that a negative electrode active material obtained by mixing graphite powder and a Si-containing material in a mass ratio of 91:9, a dispersion of styrene butadiene rubber, and sodium carboxymethyl cellulose were mixed in a solids mass ratio of 98:1:1, and the negative electrode mixture slurry was applied to both sides of a negative electrode core using water as a dispersion medium. The negative electrode plate charge swelling rate of the negative electrode of Comparative Example 1 was measured and found to be 24%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 1.

[0072] Comparative Example 2 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 92:8, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 90:10. The negative electrode plate swelling rate during charging of the negative electrode of Comparative Example 2 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 23%, and the negative plate charging swelling rate (E ２ ) is 25%, and (E １ / E ２ ) was 0.92. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 2.

[0073] Comparative Example 3 A negative electrode was fabricated in the same manner as in Example 1, except that the first negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 93:7, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and a Si-containing material were mixed at a mass ratio of 89:11. The negative electrode plate swelling rate during charging of the negative electrode of Comparative Example 3 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 22%, and the negative plate charging swelling rate (E ２ ) is 26%, and (E １ / E ２ ) was 0.85. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 3.

[0074] [High-rate charge-discharge cycle test] Each battery of the example and comparative example was charged at a constant current of 0.8 C in a temperature environment of 25°C until the battery voltage reached 4.2 V. Then, the battery was discharged at a constant current of 0.8 C until the battery voltage reached 2.5 V. This charge-discharge cycle was repeated 200 times. The capacity retention rate of each battery of the example and comparative example in the high-rate charge-discharge cycle was calculated using the following formula, and the results are summarized in Table 1. Capacity retention rate = (discharge capacity at 200th cycle / discharge capacity at 1st cycle) x 100

[0075]

[0076] As shown in Table 1, (E １ / E２ In all of Examples 1 to 7, in which a negative electrode having a (E １ / E ２ The capacity retention rate in the high-rate charge-discharge cycle was higher than that of Comparative Examples 1 to 3, which used negative electrodes with an E １ / E ２ It can be said that the use of a negative electrode having an E ) of 0.8 can suppress the deterioration of high-rate charge-discharge cycle characteristics. １ / E ２ In Examples 4 to 7, in which the value of β is 0.6 or less, the deterioration of the high-rate charge-discharge cycle characteristics could be further suppressed.

[0077] The present disclosure will be further described by the following embodiments. Configuration 1: A negative electrode for a secondary battery comprising a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the negative electrode mixture layer having a first end region at one end in the longitudinal direction thereof and a second end region at the other end in the longitudinal direction thereof, the first end region having a negative electrode plate swelling rate smaller than that of the second end region, and the second end region having a negative electrode plate swelling rate (E ２ The negative plate charge swelling rate (E １ ) ratio (E １ / E ２ ) is 0.80 or less. １ / E ２ ) is 0.40 or more. １ / E ２ ) is 0.60 or less. １ ) and the negative plate charge swelling rate (E ２) is smaller than the negative electrode for secondary batteries according to any one of configurations 1 to 3. Configuration 5: The negative electrode for secondary batteries according to any one of configurations 1 to 4, wherein the negative electrode plate swelling rate during charging increases at a constant rate from the first end region to the second end region. Configuration 6: The negative electrode for secondary batteries according to any one of configurations 1 to 4, wherein the negative electrode plate swelling rate during charging of the second end region (E ２ The negative electrode for a secondary battery according to any one of Configurations 1 to 6, wherein the anode mixture layer includes a first active material and a second active material having different charge swelling rates, the first active material having a smaller charge swelling rate than the second active material, and wherein, when a first active material ratio is a ratio of the mass of the first active material to a total mass of the first active material and the second active material and a second active material ratio is a ratio of the mass of the second active material to a total mass of the first active material and the second active material, the first active material ratio in the first end region is larger than the first active material ratio in the second end region, and the second active material ratio in the second end region is larger than the second active material ratio in the first end region. Configuration 8: The negative electrode for a secondary battery according to Configuration 7, wherein the ratio of the first active material decreases at a constant rate from the first end region to the second end region, and the ratio of the second active material increases at a constant rate from the first end region to the second end region.Configuration 9: The negative electrode for a secondary battery according to Configuration 7 or 8, wherein the first active material is graphite and the second active material is a Si-containing material.Configuration 10: The negative electrode for a secondary battery according to Configuration 9, wherein the content of the Si-containing material in the negative electrode mixture layer is 50 mass% or less with respect to the total mass of the first active material and the second active material in the negative electrode mixture layer.Configuration 11: A secondary battery comprising an electrode body in which the negative electrode for a secondary battery according to any one of Configurations 1 to 10 and a positive electrode are wound with a separator interposed therebetween, wherein the negative electrode for a secondary battery is provided so that the first end region is located closer to the inner periphery of the electrode body than the second end region.

[0078] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 12a First end region, 12b Second end region, 12c Intermediate region, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding portion, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Negative electrode core, 30a, 30b Exposed portion, 32 Negative electrode mixture layer, 33a One end, 33b Other end.

Claims

1. A negative electrode for a secondary battery comprising a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the negative electrode having a first end region at one end in the longitudinal direction of the negative electrode mixture layer and a second end region at the other end in the longitudinal direction of the negative electrode mixture layer, the first end region having a smaller negative electrode plate swelling rate during charging than the second end region, and the second end region having a smaller negative electrode plate swelling rate during charging (E ２ The negative plate charge swelling rate (E １ ) ratio (E １ / E ２ ) is 0.80 or less.

2. The above (E １ / E ２ 2. The negative electrode for a secondary battery according to claim 1, wherein the value of (a) is 0.40 or more.

3. The above (E １ / E ２ 3. The negative electrode for a secondary battery according to claim 1, wherein the value of (a) is 0.60 or less.

4. The negative electrode plate charge swelling rate of the intermediate region between the first end region and the second end region is the negative electrode plate charge swelling rate of the first end region (E １ ) and the negative plate charge swelling rate (E ２ 3. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode has a surface area of ​​100 nm or less.

5. The negative electrode for a secondary battery according to claim 1 or 2, wherein the charge swelling rate of the negative electrode plate increases at a constant rate from the first end region to the second end region.

6. The negative electrode plate charging swelling rate (E ２ 3. The negative electrode for a secondary battery according to claim 1, wherein the ratio of the total mass of the negative electrode to the total mass of the secondary battery is 45% or less.

7. The negative electrode for a secondary battery according to claim 1 or 2, wherein the negative electrode mixture layer comprises a first active material and a second active material having different charge swelling rates, the first active material having a smaller charge swelling rate than the second active material, and wherein, when a first active material ratio is a ratio of the mass of the first active material to the total mass of the first active material and the second active material, and a second active material ratio is a ratio of the mass of the second active material to the total mass of the first active material and the second active material, the first active material ratio in the first end region is larger than the first active material ratio in the second end region, and the second active material ratio in the second end region is larger than the second active material ratio in the first end region.

8. A negative electrode for a secondary battery as described in claim 7, wherein the first active material ratio decreases at a constant rate from the first end region to the second end region, and the second active material ratio increases at a constant rate from the first end region to the second end region.

9. The negative electrode for a secondary battery according to claim 7, wherein the first active material is graphite and the second active material is a Si-containing material.

10. The negative electrode for a secondary battery according to claim 9, wherein the content of the Si-containing material in the negative electrode mixture layer is 50 mass % or less relative to the total mass of the first active material and the second active material in the negative electrode mixture layer.

11. A secondary battery comprising an electrode body in which the negative electrode and positive electrode for the secondary battery according to claim 1 or 2 are wound with a separator interposed therebetween, wherein the negative electrode for the secondary battery is arranged so that the first end region is located closer to the inner periphery of the electrode body than the second end region.

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