Negative electrode for secondary battery, and secondary battery

Abstract

A negative electrode (12) for a secondary battery is characterized by comprising an elongated negative electrode core (30), and a negative electrode mixture layer (32) disposed on the negative electrode core (30), the negative electrode mixture layer (32) having a first end region (12a) on one end side in the longitudinal direction and a second end region (12b) on the other end side in the longitudinal direction, the first end region (12a) exhibiting a smaller negative electrode plate charging expansion ratio than the second end region (12b), a ratio (E1 / E2) of a negative electrode plate charging expansion ratio (E1) of the first end region (12a) to a negative electrode plate charging expansion ratio (E2) of the second end region (12b) being 0.9 or less, a difference between the negative electrode plate porosity of the second end region (12b) and the negative electrode plate porosity of the first end region (12a) being 3% 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 0.9 or less, and the difference between the negative electrode plate porosity in the second end region and the negative electrode plate porosity in the first end region is 3% 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; FIG. 2 is a plan view showing an example of a negative electrode before winding; and FIG. 3 is a diagram showing an example of a transition of the amount of application of a negative electrode mixture slurry from a first end region to a second end region.

[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 a negative electrode 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 of the negative electrode mixture layer 32 in the longitudinal direction, and a second end region 12b at the other end of the negative electrode mixture layer 32 in the longitudinal direction.

[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] In the negative electrode 12, the first end region 12a has a smaller negative plate swelling rate (E ２ ) the negative electrode plate charge swelling rate (E １ ) ratio (E １ / E ２ The negative electrode plate swelling rate during charging is a value obtained by subtracting 1 from 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. That is, the negative electrode plate swelling rate during charging (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) (or the value expressed as a percentage). The method for measuring the negative electrode plate swelling rate upon charging will be described later.

[0034] In addition, in the negative electrode 12, the negative electrode plate porosity (A ２ ) and the negative electrode plate porosity (A １ ) and the difference (A ２ -A １ The porosity of the negative electrode plate is calculated by the following method.

[0035] The negative electrode 12 is removed from a fully discharged secondary battery 10. Then, a cutter is used to cut out a portion of the negative electrode 12 corresponding to the first end region 12a, which serves as a measurement sample. The pore volume distribution of the measurement sample is then measured using a mercury porosimeter. The porosimeter used is an Autopore V9620 manufactured by Shimadzu Corporation. From the obtained pore volume distribution, a pore distribution with a pore diameter ranging from 0.003 μm to 3.0 μm is extracted, and the cumulative pore volume (Vp) is calculated. The porosity of the negative electrode plate is calculated by dividing the obtained cumulative pore volume Vp by the apparent volume (Va) of the measurement sample, as shown in the following equation (1). Va is calculated from the projected area (S) of the negative electrode portion, which is the measurement sample, and the thickness (T) of the negative electrode portion (Va = S × T). The thickness (T) of the negative electrode portion is measured using a contact-type thickness measuring device. Negative electrode plate porosity (%) = (Vp / Va) x 100 (1)

[0036] A cutter is used to cut out a negative electrode portion corresponding to the second end region 12b from the negative electrode 12, and the cut out portion is used as a measurement sample to measure the negative electrode plate porosity in the same manner as above. The negative electrode plate porosity in the intermediate region between the first end region 12a and the second end region 12b can also be measured in the same manner as above.

[0037] As in this embodiment, (E １ / E ２ ) is 0.90 or less, and (A ２ -A １ By using the negative electrode 12 having an (E ) of 3% or less, the deterioration of high-rate charge-discharge characteristics is suppressed. The reason for the above effect is presumed to be as follows. １ / E ２ ) is 0.90 or less, the first end region 12a, which has a low negative electrode plate swelling rate during charging, is located on the inner periphery of the electrode body 14. Therefore, it is presumed that the pressure concentrated on the inner periphery of the electrode body 14 is alleviated even during high-rate charging. ２ -A １Since the difference in the electrode plate resistance between the first end region 12 a and the second end region 12 b is almost zero, it is presumed that the deposition of metallic lithium during high-rate charging is suppressed. These factors are thought to be linked to the suppression of deterioration in high-rate charge-discharge characteristics.

[0038] (E １ / E ２ ) is preferably 0.80 or less, since even during high-rate charging, the pressure concentrated on the inner circumferential side of the electrode body 14 is further alleviated, and the deterioration of high-rate charge / discharge characteristics is further suppressed. 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.

[0039] 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.

[0040] The charge swelling rate of the negative electrode plate 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 charge swelling rate of the negative electrode plate increase at a constant rate from the first end region 12 a to the second end region 12 b.

[0041] Negative plate charge expansion rate (E １ ) and the negative electrode plate charge swelling rate (E ２ ) is, for example, preferably 10% or more and 35% or less, and more preferably 15% or more and 35% or less.１ ) and the negative electrode plate charge swelling rate (E ２ When the negative electrode plate swelling rate (%) 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 swelling rate during charging is measured as follows.

[0042] 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.

[0043] 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.

[0044] 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 )

[0045] (A ２ -A １ ) is preferably 1% or less in order to further suppress the deterioration of high-rate charge / discharge characteristics. １ ) and the negative electrode plate porosity (A ２ ) are preferably 20% or more and 30% or less, respectively, in order to further suppress the deterioration of high-rate charge-discharge characteristics.

[0046] In addition, the negative electrode plate porosity (A １ ) and the negative electrode plate porosity of the middle region 12c, and the negative electrode plate porosity of the second end region 12b (A ２ The difference between the porosity of the negative electrode plate in the first region 12c and the porosity of the intermediate region 12d is preferably 3% or less, and more preferably 1% or less, in order to further suppress the deterioration of high-rate charge-discharge characteristics, for example.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] The negative electrode active material preferably includes a first Si-containing material and a second Si-containing material having different charge swelling rates. The first Si-containing material has a smaller charge swelling rate than the second Si-containing material. The charge swelling rate of the negative electrode active material is determined as follows. A negative electrode is fabricated using a single active material (e.g., the first Si-containing material or the second Si-containing 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 negative electrode active material.

[0058] The first Si-containing material is preferably a composite particle containing a carbon phase and a silicon phase dispersed within the carbon phase, because it has a low charge swelling rate among Si-containing materials and good charge / discharge cycle characteristics. The second Si-containing material is preferably a composite particle containing a silicon oxide phase and a silicon phase dispersed within the silicon oxide phase, because it has a high charge swelling rate among Si-containing materials and good charge / discharge cycle characteristics.

[0059] In terms of suppressing degradation of high-rate charge / discharge characteristics, the negative electrode mixture layer 32 preferably has a first Si-containing material ratio, where the ratio of the mass of the first Si-containing material to the total mass of the first and second Si-containing materials is defined as the first Si-containing material ratio, and a second Si-containing material ratio, where the ratio of the mass of the second Si-containing material to the total mass of the first and second Si-containing materials is defined as the second Si-containing material ratio. The first Si-containing material ratio in the first end region 12a is preferably greater than the first Si-containing material ratio in the second end region 12b, and the second Si-containing material ratio in the second end region 12b is preferably greater than the second Si-containing 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. Furthermore, because the first Si-containing material and the second Si-containing material are the same type of Si-containing material, the difference in charge / discharge capacity is not significant. Therefore, as will be described later, when forming the negative electrode mixture layer 32, by applying a substantially constant amount of the negative electrode mixture slurry containing the first Si-containing material and the second Si-containing material from the first end region 12 a to the second end region 12 b, it is possible to make the charge / discharge capacity of the negative electrode 12 constant from the first end region 12 a to the second end region 12 b, and also to reduce the difference in density (i.e., the difference in negative electrode plate porosity) between the first end region 12 a and the second end region 12 b.

[0060] The first Si-containing 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 Si-containing 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 Si-containing material ratio decrease at a constant rate from the first end region 12 a to the second end region 12 b and the second Si-containing material ratio increase at a constant rate from the first end region 12 a to the second end region 12 b.

[0061] The ratio of the mass of the first Si-containing material to the total mass of the negative electrode active material in the first end region 12 a is preferably smaller than the mass of the second Si-containing material to the total mass of the negative electrode active material in the second end region 12 b. This makes it easier to make the negative electrode plate charge swelling rate in the first end region 12 a smaller than the negative electrode plate charge swelling rate in the second end region 12 b. As a result, even during high-rate charging, pressure concentrated on the inner periphery of the electrode body 14 is alleviated, which may lead to suppression of deterioration in high-rate charge-discharge characteristics.

[0062] When the first Si-containing material and the second Si-containing material are used as the negative electrode active material, a carbon material such as graphite may be used in combination. The total amount of the first Si-containing material and the second Si-containing material is preferably 50% by mass or less, more preferably 40% by mass or less, based on the total mass of the negative electrode active material, from the viewpoint of suppressing deterioration of high-rate charge / discharge characteristics. The lower limit of the total amount of the first Si-containing material and the second Si-containing material is preferably 6% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, from the viewpoint of increasing the capacity of the battery.

[0063] The negative electrode active material preferably includes first and second graphites having different charge swelling rates. The first graphite has a smaller charge swelling rate than the second graphite. When the first and second graphites are used as the negative electrode active material, a Si-containing material may be used in combination. Furthermore, the first and second Si-containing materials may be used in combination with the first and second graphites.

[0064] The first graphite is preferably artificial graphite, for example, in that it has a low swelling rate upon charging, and the second graphite is preferably natural graphite, for example, in that it has a high swelling rate upon charging.

[0065] In terms of suppressing degradation of high-rate charge / discharge characteristics, the negative electrode mixture layer 32 preferably has a first graphite ratio (the ratio of the mass of the first graphite to the total mass of the first graphite and the second graphite) and a second graphite ratio (the ratio of the mass of the second graphite to the total mass of the first graphite and the second graphite). The first graphite ratio in the first end region 12a is greater than the first graphite ratio in the second end region 12b, and the second graphite ratio in the second end region 12b is greater than the second graphite 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. Furthermore, because the first graphite and the second graphite are the same type of graphite material, the difference in charge / discharge capacity is not significant. Therefore, when forming the negative electrode mixture layer 32, by making the amount of application of the negative electrode mixture slurry containing the first graphite and the second graphite constant from the first end region 12a to the second end region 12b, it is possible to make the charge / discharge capacity of the negative electrode 12 constant from the first end region 12a to the second end region 12b, and also to reduce the density difference (i.e., the difference in negative electrode plate porosity) between the first end region 12a and the second end region 12b.

[0066] The first graphite 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 graphite 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 graphite ratio decrease at a constant rate from the first end region 12 a to the second end region 12 b and the second graphite ratio increase at a constant rate from the first end region 12 a to the second end region 12 b.

[0067] An example of a method for producing the negative electrode mixture layer 32 when using a first Si-containing material and a second Si-containing material having different charge swelling rates will be described below. Note that the following method for producing the negative electrode mixture layer 32 is also applicable when the first graphite material and the second graphite material are used. In that case, the first Si-containing material should be read as the first graphite material, and the second Si-containing material should be read as the second graphite material.

[0068] A first anode mixture slurry containing a first Si-containing material and a binder and a second anode mixture slurry containing a second Si-containing material and a binder are prepared. Preferably, the first anode mixture slurry and the second anode mixture slurry each contain graphite. Using a multi-layer die coater, the first anode mixture slurry and the second anode mixture slurry are applied to the anode core 30 while varying the application amount ratio between them at a predetermined timing. This allows for the formation of an anode mixture layer 32 in which the ratio of the first Si-containing material and the ratio of the second Si-containing material vary from the first end region 12a to the second end region 12b. The resulting anode mixture layer 32 is then preferably dried and compressed.

[0069] FIG. 3 is a diagram showing an example of the change in the coating amount of the negative electrode mixture slurry from the first end region to the second end region. The solid line in FIG. 3 indicates the total amount of the coating amount of the first negative electrode mixture slurry and the coating amount of the second negative electrode mixture slurry, hereinafter referred to as the coating amount of the negative electrode mixture slurry. The dashed line in FIG. 3 indicates the coating amount of the first negative electrode mixture slurry, and the dashed-dotted line in FIG. 3 indicates the coating amount of the second negative electrode mixture slurry. When applying the first negative electrode mixture slurry and the second negative electrode mixture slurry using a multi-layer die coater, the coating amount of the first negative electrode mixture slurry is decreased at a constant rate from the first end region 12 a to the second end region 12 b as shown by the dashed line in FIG. 3 , and the coating amount of the second negative electrode mixture slurry is increased at a constant rate as shown by the dashed line in FIG. 3 , while the negative electrode mixture slurries are applied to the negative electrode core 30. This results in a negative electrode mixture layer 32 in which the ratio of the first Si-containing material decreases at a constant rate from the first end region 12a to the second end region 12b and the ratio of the second Si-containing material increases at a constant rate from the first end region 12a to the second end region 12b. That is, a negative electrode mixture layer 32 in which the negative electrode plate expansion rate increases at a constant rate from the first end region 12a to the second end region 12b is obtained. In this embodiment, when the first negative electrode mixture slurry and the second negative electrode mixture slurry are applied, the application amount of the negative electrode mixture slurry can be constant from the first end region 12a to the second end region 12b, as shown by the solid line in FIG. 3 . In this embodiment, the first Si-containing material and the second Si-containing material are used. However, because these materials are the same type of Si-containing material, the difference in charge / discharge capacity is not significant. Therefore, by keeping the amount of negative electrode mixture slurry applied substantially constant from the first end region 12 a to the second end region 12 b, the charge / discharge capacity of the negative electrode 12 can be made constant from the first end region 12 a to the second end region 12 b. Furthermore, even if the obtained negative electrode mixture layer 32 is compressed, the negative electrode plate porosity of the negative electrode mixture layer 32 can be adjusted to be substantially constant from the first end region 12 a to the second end region 12 b. Note that when graphite and a Si-containing material with different charge swelling rates are used, there is a large difference in charge / discharge capacity between the graphite and the Si-containing material.Therefore, when a first anode mixture slurry containing graphite and a second anode mixture slurry containing a Si-containing material are prepared and applied in the same manner as described above, the charge / discharge capacity of the anode 12 cannot be made constant from the first end region 12 a to the second end region 12 b unless the amount of the anode mixture slurry applied (the total amount of the first anode mixture slurry and the second anode mixture slurry applied) is applied so as to decrease from the first end region 12 a to the second end region 12 b. In this case, when the obtained anode mixture layer 32 is compressed, the anode plate porosity of the anode mixture layer 32 increases from the first end region 12 a to the second end region 12 b.

[0070] 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.

[0071] [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.

[0072] 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.

[0073] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0074] 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.

[0075] [Fabrication of Negative Electrode] As the first Si-containing material, composite particles (hereinafter referred to as SiC-1) containing a carbon phase and silicon particles dispersed within the carbon phase were prepared. Furthermore, as the second Si-containing material, composite particles (hereinafter referred to as SiO) containing a silicon oxide phase and silicon particles dispersed within the silicon oxide phase and having a composition of SiO were prepared. Then, a negative electrode active material obtained by mixing graphite powder and SiC-1 in a mass ratio of 91:9, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a solid content mass ratio of 98:1:1, and a first negative electrode mixture slurry was prepared using water as a dispersion medium. Furthermore, a negative electrode active material obtained by mixing graphite powder and SiO in a mass ratio of 91:9, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a solid content mass ratio of 98:1:1, and a second negative electrode mixture slurry was prepared using water as a dispersion medium. Next, the first negative electrode mixture slurry and the second negative electrode mixture slurry were set in a multilayer die coater, and on 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, the coating amount ratio of the first negative electrode mixture slurry to the second negative electrode mixture slurry was continuously changed from 1:0 to 0:1, so that the charge / discharge capacity of the negative electrode was constant in the longitudinal direction, 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.

[0076] In the negative electrode of Example 1, the only Si-containing material contained in the first end region is SiC-1. That is, the ratio of the first Si-containing material in the first end region is 100% by mass. Furthermore, the only Si-containing material contained in the second end region is SiO. That is, the ratio of the second Si-containing material in the second end region is 100% by mass. The same applies to the following examples.

[0077] In addition, in the negative electrode of Example 1, the ratio of the mass of the Si-containing material to the total mass of the negative electrode active material in the first end region (hereinafter referred to as the Si-containing material addition rate in the first end region) is 9 mass%, and the ratio of the mass of the Si-containing material to the total mass of the negative electrode active material in the second end region (hereinafter referred to as the Si-containing material addition rate in the second end region) is 9 mass%.

[0078] In addition, the negative electrode plate swelling rate during charging of the negative electrode of Example 1 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) was 22.5%, and the negative plate charging swelling rate (E ２ ) is 25%, and (E １ / E ２ ) was 0.90. Furthermore, as a result of measuring the porosity of the negative electrode plate, the porosity of the negative electrode plate in the first end region and the porosity of the negative electrode plate in the second end region were each 20%.

[0079] [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.

[0080] [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.

[0081] [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.

[0082] Example 2 A negative electrode was fabricated in the same manner as in Example 1, except that the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 90:10, and the pressure used to compress the coating was 0.8 times the pressure used in Example 1. In the negative electrode of Example 2, the addition rate of the Si-containing material in the second end region was 10 mass%.

[0083] 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 ) was 22.5%, and the negative plate charging swelling rate (E ２ ) is 26%, and (E １ / E ２ ) was 0.87. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region was 22%, and the porosity of the negative electrode plate in the second end region was 23%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 2.

[0084] 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 SiC-1 were mixed at a mass ratio of 85:15, the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 85:15, and the pressure used when compressing the coating was 1.1 times the pressure used in Example 1. In the negative electrode of Example 3, the Si-containing material addition rate in the first end region and the Si-containing material addition rate in the second end region were each 15 mass%.

[0085] 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 28%, and the negative plate charging swelling rate (E ２ ) is 35%, and (E １ / E ２ ) was 0.80. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region and the second end region was 20%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 3.

[0086] Example 4 A negative electrode was fabricated in the same manner as in Example 1, except that the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 88:12, and the pressure used to compress the coating was 0.85 times the pressure used in Example 1. In the negative electrode of Example 4, the addition rate of the Si-containing material in the second end region was 12 mass%.

[0087] 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 ) was 22.5%, and the negative plate charging swelling rate (E ２ ) is 29%, and (E １ / E ２ ) was 0.78. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region was 20%, and the porosity of the negative electrode plate in the second end region was 23%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 4.

[0088] Example 5 A negative electrode was produced in the same manner as in Example 1, except that the pressure used to compress the coating was set to 0.7 times the pressure used in Example 1.

[0089] 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 ) was 22.5%, and the negative plate charging swelling rate (E ２ ) is 25%, and (E １ / E ２ ) was 0.90. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region and the second end region was 30%, respectively. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 5.

[0090] Example 6 A negative electrode was fabricated in the same manner as in Example 1, except that the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 90:10, and the pressure used to compress the coating was 0.72 times the pressure used in Example 1. In the negative electrode of Example 6, the addition rate of the Si-containing material in the second end region was 10 mass%.

[0091] 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 ) was 22.5%, and the negative plate charging swelling rate (E ２ ) is 26%, and (E １ / E ２ ) was 0.87. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region was 29%, and the porosity of the negative electrode plate in the second end region was 30%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 6.

[0092] Example 7 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 SiC-1 were mixed at a mass ratio of 85:15, the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 85:15, and the pressure used when compressing the coating was 0.85 times the pressure used in Example 1. In the negative electrode of Example 7, the Si-containing material addition rate in the first end region and the Si-containing material addition rate in the second end region were each 15 mass%.

[0093] 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 28%, and the negative plate charging swelling rate (E ２ ) is 35%, and (E １ / E ２ ) was 0.80. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region and the second end region was 30%, respectively. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 7.

[0094] Example 8 A negative electrode was fabricated in the same manner as in Example 1, except that the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 88:12, and the pressure used to compress the coating was 0.8 times the pressure used in Example 1. In the negative electrode of Example 8, the addition rate of the Si-containing material in the second end region was 12 mass%.

[0095] The negative electrode plate swelling rate during charging of the negative electrode of Example 8 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) was 22.5%, and the negative plate charging swelling rate (E ２ ) is 29%, and (E １ / E ２ ) was 0.78. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region was 27%, and the porosity of the negative electrode plate in the second end region was 30%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Example 8.

[0096] Comparative Example 1 A negative electrode was produced in the same manner as in Example 1, except that a negative electrode active material obtained by mixing graphite powder and SiO at a mass ratio of 91:9, a dispersion of styrene butadiene rubber, and sodium carboxymethyl cellulose were mixed at a solid content mass ratio of 98:1:1, and the negative electrode mixture slurry was applied to both surfaces of a negative electrode core using water as a dispersion medium, and the pressure used to compress the coating was set to 0.7 times the pressure used in Example 1.

[0097] The negative electrode plate swelling rate during charging of the negative electrode of Comparative Example 1 was measured, and the negative electrode plate swelling rate during charging of the first end region (E １ ) is 25%, and the negative plate charge swelling rate (E ２ ) is 25%, and (E １ / E ２ ) was 1.00. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region and the second end region was 30%, respectively. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 1.

[0098] 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 SiO were mixed at a mass ratio of 92:8, the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 88:12, and the pressure used when compressing the coating was 0.85 times the pressure used in Example 1. In the negative electrode of Comparative Example 2, the addition rate of the Si-containing material in the first end region was 8 mass%, and the addition rate of the Si-containing material in the second end region was 12 mass%.

[0099] 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 29%, and (E １ / E ２ ) was 0.80. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region was 19%, and the porosity of the negative electrode plate in the second end region was 23%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 2.

[0100] 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 SiO were mixed at a mass ratio of 92:8, the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 88:12, and the pressure used when compressing the coating was 0.8 times the pressure used in Example 1. In the negative electrode of Comparative Example 3, the addition rate of the Si-containing material in the first end region was 8 mass%, and the addition rate of the Si-containing material in the second end region was 12 mass%.

[0101] 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 23%, and the negative plate charging swelling rate (E ２ ) is 29%, and (E １ / E ２ ) was 0.80. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region was 26%, and the porosity of the negative electrode plate in the second end region was 30%. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 3.

[0102] Comparative 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 SiC-2 were mixed at a mass ratio of 91:9, the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 91:9, and the pressure used when compressing the coating was 0.8 times the pressure used in Example 1. SiC-2 is a composite particle containing a carbon phase and silicon particles dispersed within the carbon phase, and is a material with a higher charge swelling rate than SiC-1.

[0103] The negative electrode plate swelling rate during charging of the negative electrode of Comparative Example 4 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. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region and the second end region was 23%, respectively. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 4.

[0104] Comparative Example 5 A negative electrode was produced 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 SiC-2 were mixed at a mass ratio of 91:9, and the second negative electrode mixture slurry used a negative electrode active material in which graphite powder and SiO were mixed at a mass ratio of 91:9.

[0105] The negative electrode plate swelling rate during charging of the negative electrode of Comparative Example 5 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. In addition, the porosity of the negative electrode plate was measured, and the porosity of the negative electrode plate in the first end region and the second end region was 30%, respectively. A cylindrical battery was fabricated in the same manner as in Example 1 using the negative electrode of Comparative Example 5.

[0106] [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

[0107]

[0108] As shown in Table 1, (E １ / E ２ ) is 0.9 or less, and the difference between the negative electrode plate porosity in the second end region and the negative electrode plate porosity in the first end region is 3% or less. １ / E ２ ) exceeded 0.9 or the difference between the negative electrode plate porosity in the second end region and the negative electrode plate porosity in the first end region exceeded 3%. １ / E ２ ) is 0.9 or less, and the difference between the negative electrode plate porosity in the second end region and the negative electrode plate porosity in the first end region is 3% or less, it can be said that the deterioration of high-rate charge-discharge cycle characteristics can be suppressed.

[0109] 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 0.9 or less, and the difference between the negative electrode plate porosity of the second end region and the negative electrode plate porosity of the first end region is 3% or less. １ / E ２ ) is 0.8 or less. Aspect 3: The negative electrode for a secondary battery according to Aspect 1 or 2, wherein the negative electrode plate porosity in the second end region and the negative electrode plate porosity in the first end region are 20% or more and 30% or less, respectively. Aspect 4: The negative electrode for a secondary battery according to Aspect 1 or 2, wherein the negative electrode plate porosity in the first end region is 20% or more and 30% or less, respectively. １ ) and the negative plate charge swelling rate (E ２) are 10% or more and 35% or less, respectively. Configuration 5: The negative electrode for a secondary battery according to any one of Configurations 1 to 4, wherein the negative electrode mixture layer includes a first Si-containing material and a second Si-containing material having different charge swelling rates, the first Si-containing material having a lower charge swelling rate than the second Si-containing material, and wherein, when a first Si-containing material ratio is a ratio of the mass of the first Si-containing material to the total mass of the first Si-containing material and the second Si-containing material, and a second Si-containing material ratio is a ratio of the mass of the second Si-containing material to the total mass of the first Si-containing material and the second Si-containing material, the first Si-containing material ratio in the first end region is greater than the first Si-containing material ratio in the second end region, and the second Si-containing material ratio in the second end region is greater than the second Si-containing material ratio in the first end region. The negative electrode for a secondary battery according to the present invention is characterized in that a ratio of a mass of the first Si-containing material to a total mass of the negative electrode active material in the first end region is smaller than a ratio of a mass of the second Si-containing material to a total mass of the negative electrode active material in the second end region. The negative electrode for a secondary battery according to the present invention is characterized in that the first Si-containing material is a composite particle including a carbon phase and a silicon phase dispersed in the carbon phase, and the second Si-containing material is a composite particle including a silicon oxide phase and a silicon phase dispersed in the silicon oxide phase. Configuration 8: The negative electrode for a secondary battery according to any one of Configurations 1 to 7, wherein the negative electrode mixture layer includes first graphite and second graphite having different charge swelling rates, the first graphite having a smaller charge swelling rate than the second graphite, and wherein, when a first graphite ratio is a ratio of the mass of the first graphite to a total mass of the first graphite and the second graphite, and a second graphite ratio is a ratio of the mass of the second graphite to a total mass of the first graphite and the second graphite, the first graphite ratio in the first end region is larger than the first graphite ratio in the second end region, and the second graphite ratio in the second end region is larger than the second graphite ratio in the first end region. Configuration 9: The negative electrode for a secondary battery according to Configuration 8, wherein the first graphite is artificial graphite, and the second graphite is natural graphite.Configuration 10: The negative plate charge swelling rate of the intermediate region between the first end region and the second end region is equal to or greater than the negative plate charge swelling rate (E) of the first end region. １ ) and the negative plate charge swelling rate (E ２ ) or less. Structure 11: The negative electrode for a secondary battery according to any one of Structures 1 to 10, 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. Structure 12: The negative electrode for a secondary battery according to any one of Structures 1 to 11, wherein a difference between the negative electrode plate porosity of the first end region and the negative electrode plate porosity of an intermediate region between the first end region and the second end region, and a difference between the negative electrode plate porosity of the intermediate region and the negative electrode plate porosity of the second end region, are each 3% or less. Structure 13: A secondary battery comprising an electrode assembly in which the negative electrode for a secondary battery according to any one of Structures 1 to 12 and a positive electrode are wound with a separator interposed therebetween, wherein the negative electrode for a secondary battery is provided such that the first end region is located closer to the inner periphery of the electrode assembly than the second end region.

[0110] REFERENCE SIGNS LIST 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 body, 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 0.9 or less, and a difference between the negative electrode plate porosity of the second end region and the negative electrode plate porosity of the first end region is 3% 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 0.8 or less.

3. A negative electrode for a secondary battery according to claim 1 or 2, wherein the negative electrode plate porosity in the second end region and the negative electrode plate porosity in the first end region are 20% or more and 30% or less, respectively.

4. The negative electrode plate charging swelling rate (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 ratios of the Cr, Cu, and Cu content to the total content of the negative electrode are 10% or more and 35% or less, respectively.

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

6. A negative electrode for a secondary battery as described in claim 5, wherein the ratio of the mass of the first Si-containing material to the total mass of the negative electrode active material in the first end region is smaller than the ratio of the mass of the second Si-containing material to the total mass of the negative electrode active material in the second end region.

7. The negative electrode for a secondary battery according to claim 5, wherein the first Si-containing material is a composite particle including a carbon phase and a silicon phase dispersed within the carbon phase, and the second Si-containing material is a composite particle including a silicon oxide phase and a silicon phase dispersed within the silicon oxide phase.

8. The negative electrode for a secondary battery according to claim 1 or 2, wherein the negative electrode mixture layer comprises first graphite and second graphite having different swelling rates upon charging, the first graphite having a smaller swelling rate upon charging than the second graphite, and wherein, when the ratio of the mass of the first graphite to the total mass of the first graphite and the second graphite is defined as a first graphite ratio and the ratio of the mass of the second graphite to the total mass of the first graphite and the second graphite is defined as a second graphite ratio, the first graphite ratio in the first end region is greater than the first graphite ratio in the second end region, and the second graphite ratio in the second end region is greater than the second graphite ratio in the first end region.

9. The negative electrode for a secondary battery according to claim 8, wherein the first graphite is artificial graphite and the second graphite is natural graphite.

10. 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.

11. 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.

12. A negative electrode for a secondary battery according to claim 1 or 2, wherein the difference between the negative plate porosity in the first end region and the negative plate porosity in the intermediate region between the first end region and the second end region, and the difference between the negative plate porosity in the intermediate region and the negative plate porosity in the second end region are each 3% or less.

13. 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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