Battery

Abstract

The invention relates to the field of battery materials, and discloses a battery which comprises a shell, a roll core and electrolyte, the electrolyte comprises an organic solvent and a lithium salt, the organic solvent comprises chain carbonate with the mass ratio of a in the electrolyte, and a is greater than or equal to 50% and less than or equal to 90%; the roll core is a cylindrical roll core, the roll core comprises a negative plate, and a negative active material in the negative plate comprises a silicon-based material; when the battery is in a 100% SOC state, the ratio of the diameter of the roll core to the inner diameter of the shell is K1; when the battery is in a 0% SOC state, the ratio of the diameter of the roll core to the inner diameter of the shell is K0; and 0 < K1-K0 < = 2.5%. According to the invention, through mutual cooperation between the chain carbonate and the values of K1-K0, the fast charging performance of the battery can be obviously improved, and the cycle life of the battery can be obviously prolonged.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and particularly to a battery. Background Art

[0002] Silicon anode materials have an ultra-high theoretical specific capacity (4200 mAh / g), and have become an important anode active material for improving the energy density of lithium batteries. In order to improve the energy density of the battery, silicon anodes can be used. However, due to its special alloying lithium intercalation mechanism, the silicon anode expands greatly during charging (up to about 300% at most). Its high volume expansion makes the anode polarization increase, the kinetic performance decline, and the fast charging performance decline during the charge and discharge process; moreover, the repeated expansion and contraction of silicon particles will also cause the active material particles to break and pulverize, resulting in material failure and affecting the cycle performance; the silicon anode is also not conducive to maintaining the integrity of the SEI film, resulting in continuous side reactions at the anode interface, consuming the electrolyte, not only reducing the first Coulomb efficiency, but also affecting the cycle life of the battery.

[0003] At the same time, according to the different structures of the battery casing, lithium-ion power batteries can be divided into soft-pack batteries, square batteries, and cylindrical batteries. Due to the advantages of low cost and high energy density, large cylindrical batteries have become a key research direction. For large cylindrical batteries, in order to ensure the effective use of space, the outer diameter of the battery cell is usually set to be equivalent to the inner diameter of the casing. However, due to the use of a silicon anode, the expansion of the battery cell will increase. Therefore, there is extrusion between the battery cell and the casing after the battery cell expands. The space between the battery cell and the casing is too small, which is not conducive to the infiltration of the electrolyte and the transmission of lithium ions, resulting in the occurrence of lithium deposition, ultimately affecting the fast charging performance and cycle life of the battery. Summary of the Invention

[0004] The present invention provides a long-cycle silicon-doped cylindrical battery, aiming to solve the problems of poor fast charging performance and cycle life of the battery.

[0005] A battery provided by the present invention includes a casing, a wound core, and an electrolyte;

[0006] The electrolyte contains an organic solvent and a lithium salt, and the organic solvent includes a chain carbonate with a mass fraction of a in the electrolyte, 50% ≤ a ≤ 90%;

[0007] The wound core is a cylindrical wound core, and the wound core includes a negative electrode sheet. The negative electrode active material in the negative electrode sheet includes a silicon-based material; when the battery is in a 100% SOC state, the ratio of the diameter of the wound core to the inner diameter of the casing is K1; when the battery is in a 0% SOC state, the ratio of the diameter of the wound core to the inner diameter of the casing is K0;

[0008] 0 < K1 - K0 ≤ 2.5%.

[0009] Preferably, 99% ≤ K1 ≤ 100%;

[0010] and / or, 97.5% ≤ K0 < 99%;

[0011] and / or, 60% ≤ a ≤ 80%;

[0012] and / or, 0 < (K1 - K0) / a ≤ 0.05, preferably, 0 < (K1 - K0) / a ≤ 0.04.

[0013] The organic solvent includes one or a combination of two or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, diethyl carbonate, ethyl formate, ethyl acetate, ethyl propionate, and propyl propionate;

[0014] and / or, the lithium salt includes one or a combination of two or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, and lithium bis(trifluoromethylsulfonyl)imide;

[0015] and / or, the electrolyte further includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes one or a combination of two or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, succinonitrile, adiponitrile, ethylene sulfate, dimethyl sulfite, and silane coupling agent.

[0016] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer on one or both surfaces of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a graphite material and a silicon material. The mass ratio of silicon element in the silicon material in the negative electrode active material is b, 0.1% ≤ b ≤ 10%, preferably, 0.1% ≤ b ≤ 5%.

[0017] Preferably, the silicon material includes silicon-carbon material and / or silicon-oxygen material.

[0018] The ratio of Dv50 of the graphite material to Dv50 of the silicon material is c, 1.3 ≤ c ≤ 2.6;

[0019] Preferably, the Dv50 of the graphite material is 10 - 16 μm, and / or, the Dv50 of the silicon material is 6.0 - 10.0 μm.

[0020] A bottom coating is further provided between the negative electrode current collector and the negative electrode active layer;

[0021] Preferably, the thickness of the negative electrode current collector is 4.5 - 6 μm, and the thickness of the bottom coating is 0.5 - 2.0 μm;

[0022] Preferably, the negative electrode current collector is a copper foil;

[0023] Preferably, the bottom coating layer includes a conductive agent and a binder.

[0024] The negative electrode active layer further includes a binder, a conductive agent, and a thickening agent; the mass ratio of the negative electrode active material in the negative electrode active layer is 94-98.5 wt%, the mass ratio of the conductive agent in the negative electrode active layer is 0.5-2 wt%, the mass ratio of the binder in the negative electrode active layer is 0.5-3 wt%, and the mass ratio of the thickening agent in the negative electrode active layer is 0.5-1 wt%;

[0025] Preferably, the conductive agent includes carbon nanotubes, and the mass ratio of the carbon nanotubes in the negative electrode active layer is 0.5-1 wt%; more preferably, the carbon nanotubes are single-walled carbon nanotubes, the diameter of the single-walled carbon nanotubes < 3 nm, and the length is 1800-7200 nm; more preferably, the aspect ratio of the single-walled carbon nanotubes is 1200-3000.

[0026] The single-sided areal density of the negative electrode sheet is 6-8 mg / cm 2 ;

[0027] and / or, the tap density of the negative electrode sheet is 1.4-1.8 g / cm 3 ; preferably, along the width direction of the negative electrode sheet, the negative electrode sheet includes an edge region and a middle region, the width of the edge region is 0-20 mm, and the tap density of the middle region of the negative electrode sheet is 1.4-1.65 g / cm 3 The tap density of the edge region of the negative electrode sheet is 1.65-1.8 g / cm 3 ; the battery in the present invention is a cylindrical battery, the negative electrode sheet in the cylindrical battery includes a long side and a short side, the length of the short side is the width of the negative electrode sheet, and the negative electrode sheet of the battery is wound along the long side direction; the region 0-20 mm away from the long side edge of the negative electrode sheet is the edge region, the width of the edge region is the same as the width direction of the negative electrode sheet, it can be understood that the maximum width of the edge region is 20 mm, and the region outside the edge region is the middle region.

[0028] Preferably, the surface of the active material layer of the negative electrode sheet has recesses, the minimum vertical distance D from the recesses to the edge of the negative electrode sheet is 10-20 mm, the depth of the recesses is 3 μm-40 μm, the width is 50 μm-500 μm, and the distance L between adjacent two recesses is 400 μm-5000 μm.

[0029] The separator includes a base film and a ceramic layer coated on one or both sides of the base film. Preferably, the thickness of the base film is 5-9 μm, and the thickness of the ceramic layer on one side is 1-4 μm;

[0030] and / or, the effective welding area of the tab extending from the battery is d mm 2 , 33 ≤ d / b ≤ 15000.

[0031] 500 ≤ d ≤ 1500;

[0032] and / or, 50 ≤ d / b ≤ 15000.

[0033] The technical solution of the present invention has the following advantages:

[0034] A battery provided by the present invention includes a housing, a wound core and an electrolyte; the electrolyte contains an organic solvent and a lithium salt, and the organic solvent includes a chain carbonate with a mass ratio of a in the electrolyte, 50% ≤ a ≤ 90%; when the battery is in a 100% SOC state, the ratio of the diameter of the wound core to the inner diameter of the housing is K1; when the battery is in a 0% SOC state, the ratio of the diameter of the wound core to the inner diameter of the housing is K0; 0 < K1 - K0 ≤ 2.5%. By using a chain carbonate within a specific content range as the organic solvent in the electrolyte, the present invention can effectively achieve a better effect of wetting the electrode sheet; at the same time, the value range of K1 - K0 is set to ≤ 2.5%, which can leave an expansion space for the battery core and avoid extrusion between the battery core and the housing after the battery core expands, improving the wetting of the electrolyte and the transmission effect of lithium ions; therefore, through the mutual cooperation between the chain carbonate and the value of K1 - K0, the fast charging performance and cycle life of the battery are significantly improved.

[0035] The additional aspects and detailed advantages of the embodiments of the present invention will be partially described and shown in the subsequent description, or will be explained through the implementation of the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1 It is a schematic structural diagram of the negative electrode sheet in the present invention.

[0038] Among them, the reference numerals are explained as follows:

[0039] 1 - negative electrode sheet, 2 - recess. Detailed implementation manners

[0040] The following embodiments are provided to better further understand the present invention. They are not limited to the best embodiment described above, and do not limit the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other prior arts falls within the protection scope of the present invention.

[0041] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0042] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0043] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0044] The present invention provides a battery, including a housing, a wound core, and an electrolyte; the electrolyte contains an organic solvent and a lithium salt, and the organic solvent includes a chain carbonate with a mass ratio of a in the electrolyte, 50% ≤ a ≤ 90%; the wound core is a cylindrical wound core, and the wound core includes a negative electrode sheet, and the negative electrode active material in the negative electrode sheet includes a silicon-based material; when the battery is in a 100% SOC state, the ratio of the diameter of the wound core to the inner diameter of the housing is K1; when the battery is in a 0% SOC state, the ratio of the diameter of the wound core to the inner diameter of the housing is K0; 0 < K1 - K0 ≤ 2.5%.

[0045] For a battery, doping with silicon can effectively improve the energy density of the battery. However, due to the limitations of volume expansion and low conductivity of silicon materials, the cycle performance and fast charging performance of the battery are poor. Especially for cylindrical batteries with a wound core, the structure of the internal wound core is tight, and after the battery core expands, there will be a problem of extrusion between the battery core and the shell. If the space inside the shell is too small, it will affect the infiltration of the electrolyte and the transmission of lithium ions, further affecting the cycle performance and fast charging performance of the battery. In the present invention, K1 - K0 can characterize the volume expansion change rate of the battery from 0% SOC to 100% SOC. Controlling K1 - K0 within 2.5% can avoid relatively large expansion, prevent the electrode sheets from being subjected to large extrusion forces after expansion, making the contact between the electrode sheets of the battery core closer, reducing the pores between the electrode sheets of the battery core, affecting the infiltration of the electrolyte and the transmission of lithium ions, and thus affecting the fast charging performance and cycle performance of the battery. At the same time, the present invention uses an electrolyte containing chain carbonate with a specific content of 50% ≤ a ≤ 90%. Compared with cyclic organic solvents, it has a lower viscosity and better electrochemical stability. Among them, a cannot be too large. When it is too large, the SEI film is unstable, which will cause continuous decomposition of the electrolyte, consume more lithium ions, and reduce the cycle life of the battery. The mass ratio a of the chain carbonate in the electrolyte cannot be too low. When it is too low, the viscosity of the electrolyte will be relatively high, which will affect the fluidity and wettability of the electrolyte, is not conducive to the transmission of lithium ions, increases the internal polarization of the battery, and affects the fast charging performance and cycle performance of the battery. Preferably, 60% ≤ a ≤ 80%. The use of chain carbonate in the present invention can effectively reduce the viscosity of the electrolyte, improve the fluidity, wettability and kinetic performance of the electrolyte, and cooperate with the internal wound core with a tightly structured volume expansion change rate within 2.5%. Through the above-mentioned chain carbonate, it effectively promotes the infiltration of the electrolyte inside the wound core, further facilitates the transmission of lithium ions, reduces the internal polarization of the battery, and comprehensively improves the cycle life and fast charging performance of the battery.

[0046] As an example, the mass ratio a of the chain carbonate in the electrolyte can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or within the range composed of any two of the above values; the value of K1 - K0 can be 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or within the range composed of any two of the above values.

[0047] It should be noted that the above-mentioned wound core diameter and the inner diameter of the shell can be obtained through CT non-destructive testing; and under the 100% SOC state, there is no direct extrusion between the wound core and the shell.

[0048] In the present invention, 0 < (K1 - K0) / a ≤ 0.05. The value of (K1 - K0) / a cannot be too large. When it is too large, it indicates that the battery cell has relatively large expansion during charge and discharge. After expansion, the electrode sheets are subject to large extrusion forces. The expansion brought by the negative active material will make the contact between the electrode sheets of the battery cell closer, and the pores between the electrode sheets of the battery cell are small, which is not conducive to the infiltration of the electrolyte and the transmission of lithium ions, thereby affecting the fast charging performance and cycle performance of the battery; or, it indicates that the content of the chain carbonate is relatively small, its viscosity is relatively high, and there are problems that are not conducive to the infiltration of the electrolyte and the transmission of lithium ions, thereby affecting the fast charging performance and cycle performance of the battery. By comprehensively controlling the volume expansion change rate (K1 - K0) from 0% SOC to 100% SOC and the content a of the chain carbonate in the present invention, such that 0 < (K1 - K0) / a ≤ 0.05, good fast charging performance and cycle performance of the battery can be obtained; preferably, 0 < (K1 - K0) / a ≤ 0.04 can further improve the fast charging performance and cycle performance of the battery;

[0049] As an example, (K1 - K0) / a can be 0.0001, 0.001, 0.01, 0.02, 0.03, 0.04, 0.05 or within the range composed of any two of the above values.

[0050] In an optional embodiment, 97.5% ≤ K0 < 99%; when K0 is within the above range, the wound core can be smoothly placed into the cylindrical shell for assembly, without being unable to be placed due to the wound core being too large, nor will the internal space utilization rate of the shell be insufficient due to the wound core being too small, reducing the energy density of the battery;

[0051] As an example, K0 can be 97.50%, 98.00%, 98.50%, 98.99% or within the range composed of any two of the above values.

[0052] In an optional embodiment, 99% ≤ K1 ≤ 100%; when winding the electrode sheet and the separator to obtain the wound core, by adjusting the magnitude of the winding tension, the change of K1 can be controlled; specifically, when the winding tension becomes smaller, K1 becomes larger, and when the winding tension becomes larger, K1 becomes smaller; when K1 is within the above range, the battery can occupy a larger space within the shell after being fully charged, without insufficient space utilization, nor will there be extrusion between the wound core and the cylindrical shell due to excessive volume expansion after being fully charged, ensuring that the internal voids of the wound core can meet the requirements of electrolyte infiltration, ensuring the infiltration of the electrolyte and the transmission effect of lithium ions, thereby improving the fast charging performance and cycle performance of the battery;

[0053] As an example, K1 can be 99.0%, 99.2%, 99.4%, 99.6%, 99.8%, 100% or within the range composed of any two of the above values.

[0054] In the present invention, the types of other organic solvents other than chain carbonates are not particularly limited, and they can be selected from other types of organic solvents commonly used in the art. In an alternative embodiment, the organic solvents include, but are not limited to, ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), diethyl carbonate (DMC), ethyl formate, ethyl acetate (EA), ethyl propionate (EP), and propyl propionate (PP), or a combination of two or more thereof. Among them, ethyl methyl carbonate (EMC), diethyl carbonate (DMC), dimethyl carbonate (DEC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC) are all chain carbonates.

[0055] The types of lithium salts in the electrolyte are not particularly limited, and they can be selected from lithium salts commonly used in the art. In an alternative embodiment, the lithium salts include, but are not limited to, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)phosphate (LiDFOP), and lithium bis(trifluoromethylsulfonyl)imide, or a combination of two or more thereof.

[0056] In an alternative embodiment, the electrolyte further includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes at least one or a combination of two or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinonitrile (SN), adiponitrile (AND), ethylene sulfate (ES), dimethyl sulfite (DMS), and silane coupling agent;

[0057] Since the negative electrode of the present invention is doped with a silicon-based material, the surface of the silicon particles has a high reaction activity and will continuously react with the electrolyte to consume active lithium, and the silicon particles have a large volume expansion during charge and discharge, which is likely to damage the negative electrode interface. The above problems will cause the SEI on the negative electrode surface to not be stable, but will be continuously damaged and react with the electrolyte again to form a new SEI, which is likely to cause the electrolyte to be depleted and the active lithium to be lost quickly, which is not conducive to the long-term cycling performance of the battery. When the above negative electrode film-forming additive is contained in the electrolyte, a relatively complete and stable SEI can be formed on the surface of the silicon-doped negative electrode, thereby improving the stability of the negative electrode interface and being conducive to improving the long-term cycling performance of the negative electrode.

[0058] In an alternative embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer on one or both surfaces of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a graphite material and a silicon material. The mass ratio b of silicon element in the silicon material in the negative electrode active material is 0.1% to 10%. Among them, b cannot be too low, otherwise it will affect the energy density of the battery; at the same time, b cannot be too high, otherwise it will affect the negative electrode polarization, and further affect the kinetic performance and interface stability, thus affecting the fast charging performance. In the present invention, by controlling the mass ratio b of the silicon material in the negative electrode active material to be 0.1 to 10%, preferably 0.1 to 5%, the lithium ion energy density and fast charging performance are ensured;

[0059] As an example, the mass ratio b of the silicon material in the negative electrode active material is 0.1%, 0.5%, 1%, 3%, 5%, 7%, 9%, 10% or within the range composed of any two of the above values.

[0060] In an alternative embodiment, the ratio of Dv50 of the graphite material to Dv50 of the silicon material is c, and 1.3 ≤ c ≤ 2.6. Further comprehensively controlling the range value of c can achieve the size matching between the particles of the graphite material and the particles of the silicon material, forming a good co-insertion environment, that is, the silicon material can effectively fill the voids between the particles of the graphite material, thereby improving the space utilization rate and the compaction density. At the same time, during charging, the voids between the particles of the graphite material can provide a buffer space for the expansion of silicon, thereby reducing the overall expansion of the negative electrode sheet during the charge-discharge cycle, being beneficial to maintaining the integrity of the negative electrode interface, and further improving the battery cycle life;

[0061] As an example, c can be 1.3, 1.5, 1.8, 2, 2.3, 2.6 or within the range composed of any two of the above values.

[0062] In an alternative embodiment, a relatively small particle size is beneficial to improving the kinetic performance of the material. The Dv50 of the graphite material in the present invention is preferably 10 to 16 μm, and the Dv50 of the silicon material is preferably 6.0 to 10.0 μm. By the mutual cooperation of the graphite material and the silicon material with smaller sizes, the effect of improving the fast charging performance is achieved.

[0063] As an example, the Dv50 of the graphite material can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or within the range composed of any two of the above values; the Dv50 of the silicon material can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or within the range composed of any two of the above values.

[0064] In an optional embodiment, a primer layer is further provided between the negative electrode collector and the negative electrode active layer; when the silicon content in the negative electrode active layer of the present invention is increased, the adhesion of the negative electrode active layer will be affected. The present invention can effectively improve the adhesion between the negative electrode active layer and the negative electrode collector at a higher silicon content by providing a primer layer on the negative electrode collector copper foil, thereby avoiding the negative electrode active layer from being peeled off from the current collector due to uneven force and extrusion deformation caused by the expansion of the pole piece and the winding core during the cycle, thereby effectively improving the cycle performance of the battery.

[0065] In an optional embodiment, the thickness of the negative electrode current collector is 4.5-6 μm, and the thickness of the primer layer is 0.5-2.0 μm; this thickness can achieve a good bonding effect, and at the same time, the energy density will not be affected due to excessive thickness;

[0066] As an example, the thickness of the primer layer can be 0.5 μm, 1 μm, 1.5 μm, 2.0 μm or within the range of any two of the above values; the thickness of the negative electrode collector can be 4.5 μm, 5 μm, 5.5 μm, 6 μm or within the range of any two of the above values.

[0067] In an optional embodiment, the negative electrode current collector is copper foil; and / or the primer layer includes a conductive agent and a binder.

[0068] The binder in the primer layer may include a combination of one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylonitrile, polyacrylamide, polyvinylidene fluoride, etc., and the conductive agent in the primer layer may include a combination of one or more of conductive carbon black, graphene and carbon nanotubes.

[0069] In an optional embodiment, the negative electrode active layer also includes a binder, a conductive agent and a thickener; the mass proportion of the negative electrode active material in the negative electrode active layer is 94-98.5wt%, the mass proportion of the conductive agent in the negative electrode active layer is 0.5-2wt%, the mass proportion of the binder in the negative electrode active layer is 0.5-3wt%, and the mass proportion of the thickener in the negative electrode active layer is 0.5-1wt%. The present invention increases the proportion of negative electrode active materials as much as possible, which can increase the surface capacity of the negative electrode sheet, thereby increasing the energy density of the battery; by cooperating with a specific content of binder, the problem of insufficient flexibility of the negative electrode sheet causing the sheet to break or demold during the winding process is overcome, and at the same time, the bonding performance of the graphite material and the silicon material is improved, and the powdering and peeling caused by the expansion of the negative electrode during the cycle is avoided, thereby improving the cycle performance; by cooperating with a specific content of conductive agent, the connection performance of the conductive network between the graphite material and the silicon material is improved, and the situation of blocking the electron path due to the large expansion of the negative electrode during the cycle is reduced, and the surface resistance is reduced, thereby improving the fast charging performance and cycle performance of the battery.

[0070] The conductive agent in the negative electrode sheet of the present invention is not particularly limited, and it may be selected from the conductive agents commonly used in the art, including but not limited to at least one selected from conductive carbon black (SP), acetylene black, Ketjen black, graphite conductive agents (KS-6, KS-15, S-O, SEG-6), conductive carbon fibers (VGCG), carbon nanotubes (CNT), and graphene. Preferably, the conductive agent is carbon nanotubes; carbon nanotubes have better electron conductivity. Among them, single-walled carbon nanotubes have better dispersion stability and higher electron conductivity, and can maintain a more uniform dispersion in the slurry without agglomeration; moreover, due to the poorer conductivity of silicon particles themselves, in the present invention, single-walled carbon nanotubes can uniformly coat the surfaces of graphite and silicon particles, forming a three-dimensional conductive network between the particles, which can effectively improve the conductivity of the negative electrode sheet, thereby reducing the polarization of the electrode sheet during charging at high currents and high rates, and enhancing the fast charging performance; therefore, the conductive agent in the negative electrode active layer of the present invention contains carbon nanotubes, and the carbon nanotubes are preferably single-walled carbon nanotubes.

[0071] In an alternative embodiment, the mass ratio of carbon nanotubes in the negative electrode active layer of the present invention is 0.5-1 wt%; if the content of carbon nanotubes is too low, the purpose of improving the conductivity cannot be achieved, and if the content of carbon nanotubes is too high, the improvement of conductivity is not obvious and it will affect performance such as energy density; preferably, the diameter of the single-walled carbon nanotubes in the negative electrode active layer is <3 nm, and the length is 1800-7200 nm; more preferably, the aspect ratio of the single-walled carbon nanotubes is 1200-3000.

[0072] As an example, the mass ratio of carbon nanotubes in the negative electrode active layer is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%; the length of the single-walled carbon nanotubes is 1800 nm, 2000 nm, 2500 nm, 3000 nm, 3500 nm, 4000 nm, 4500 nm, 5000 nm, 5500 nm, 6000 nm, 6500 nm, 7000 nm, 7200 nm or within the range composed of any two of the above values; the aspect ratio of the single-walled carbon nanotubes is 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000 or within the range composed of any two of the above values.

[0073] The present invention does not particularly limit the binder in the negative electrode active layer, and it can be selected from the binders commonly used in the art, including but not limited to one or more of aqueous binders such as styrene-butadiene rubber (SBR), polyacrylic acid (salt), polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polymethacrylate, alginic acid (salt), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).

[0074] The present invention does not particularly limit the thickener in the negative electrode active layer, and it can be selected from the thickeners commonly used in the art, including but not limited to one or a combination of CMC (carboxymethyl cellulose), CMCLi (lithium carboxymethyl cellulose), and CMCNa (sodium carboxymethyl cellulose).

[0075] In an optional embodiment, the single-sided surface density of the negative electrode sheet is 6-8 mg / cm 2 . If the surface density is too large, it will be difficult for the electrolyte to infiltrate into the negative electrode sheet after the electrode sheet is wound, resulting in excessive negative electrode polarization and lithium deposition during charging; if the surface density is too low, the energy density of the battery will be too low. Through surface density control, the present invention takes into account both the energy density and kinetic performance of the battery;

[0076] As an example, the single-sided surface density of the negative electrode sheet is 6 mg / cm 2 , 6.5 mg / cm 2 , 7 mg / cm 2 , 7.5 mg / cm 2 , 8 mg / cm 2 or within the range formed by any two of the above values.

[0077] In an optional embodiment, the compaction density of the negative electrode sheet is 1.4-1.8 g / cm 3 . If the compaction density is too large, there will be too few internal voids after the electrode sheet is wound, resulting in the inability of the electrolyte to infiltrate; if the compaction density is too low, the particle contact is poor or the energy density of the battery is too low. Through compaction density control, the present invention enables the negative electrode active material particles to maintain effective physical contact and form a good conductive network, which is beneficial to improving the fast charging performance of the battery at high rates;

[0078] As an example, the compaction density of the negative electrode sheet is 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 or within the range formed by any two of the above values.

[0079] In an alternative embodiment, along the width direction of the negative electrode sheet, the negative electrode sheet includes an edge region and a middle region. The width of the edge region is 0 to 20 mm, that is, the edge region is the region within 0 to 20 mm from the long-edge of the negative electrode sheet, and the other regions are the middle region. The compaction density of the middle region of the negative electrode sheet is 1.4 to 1.65 g / cm 3 , and the compaction density of the edge region of the negative electrode sheet is 1.65 to 1.8 g / cm 3 . In the present invention, the compaction density of the middle region of the negative electrode sheet is relatively low, which can make the internal voids of the wound core relatively more, facilitating the penetration and infiltration of the electrolyte into the interior, thereby enhancing the infiltration of lithium ions inside the wound core. The compaction density of the edge region of the electrode sheet is relatively high, which can make the infiltration of the electrolyte in the edge region into the negative electrode relatively slower, thereby delaying the lithium deposition in the edge region of the negative electrode during fast charging.

[0080] In an alternative embodiment, the surface of the active material layer of the negative electrode sheet contains recesses, as Figure 1 shown. The minimum vertical distance D from the recess to the edge of the negative electrode sheet is 10 to 20 mm, the depth of the recess is 3 μm to 40 μm, the width is 50 μm to 500 μm, and the spacing L between two adjacent recesses is 400 μm to 5000 μm; the recessed parts with appropriate size and spacing can increase the specific surface area of the negative electrode, promote the faster infiltration of the electrolyte into the negative electrode interior, facilitate the rapid diffusion and transmission of lithium ions to the bottom paste of the negative electrode, reduce the polarization difference from the surface layer to the bottom layer of the negative electrode, thereby improving the fast charging performance and cycling performance of the negative electrode;

[0081] As an example, the minimum vertical distance D from the recess to the edge of the electrode sheet is 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm or within the range composed of any two of the above values; the depth of the recess is 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or within the range composed of any two of the above values; the width of the recess is 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm or within the range composed of any two of the above values; the spacing L of the recesses is 400 μm, 800 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, 3000 μm, 3500 μm, 4000 μm, 4500 μm, 5000 μm or within the range composed of any two of the above values.

[0082] The shape of the recess is not limited, and any shape can achieve the purpose of the present invention. It can be a circular or polygonal structure, or a linear structure.

[0083] In an alternative embodiment, the separator comprises a base film and a ceramic layer coated on one or both sides of the base film. Coating the surface of the base film with the ceramic layer can enhance the thermal stability of the separator. When the battery is fast-charged, the internal temperature rises relatively high. The separator coated with ceramic is not prone to heat shrinkage or wrinkling, thereby improving the safety of the battery interior under high-temperature conditions and high-rate charging. Due to the presence of the ceramic layer, the separator can be free of coating glue, effectively reducing the thickness of the separator and thus increasing the energy density of the battery. Preferably, the thickness of the base film is 5-9 μm, and the thickness of the single-sided ceramic layer is 1-4 μm;

[0084] As an example, the thickness of the base film can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or within the range composed of any two of the above values; the thickness of the single-sided ceramic layer can be 1 μm, 2 μm, 3 μm, 4 μm or within the range composed of any two of the above values.

[0085] The cylindrical battery of the present invention can be prepared by conventional processes. For example: a negative electrode sheet, a positive electrode sheet and a separator are wound together to form a cylindrical core, the core is placed in a battery case, and then the tabs of the positive electrode sheet and the negative electrode sheet are welded to the case structure members, and then the case structure members are fixed by welding, and after liquid injection, formation and sorting, the finished product is obtained.

[0086] Among them, the effective welding area between the tab extending from the core and the structure member (such as a current collector plate) is the effective welding area d of the tab extending from the battery, with the unit of mm 2 。

[0087] In an alternative embodiment, the present invention can make the design of the effective welding area of the cylindrical battery more compatible with the battery energy density by comprehensively controlling 50 ≤ d / b ≤ 15000; among them, the ratio of the effective welding area of the cylindrical battery to the proportion of silicon material d / b cannot be too small. When it is too small, insufficient overcurrent inside the battery will cause excessive temperature rise of the battery, affecting the safety performance and cycle life of the battery; at the same time, the ratio of the effective welding area of the cylindrical battery to the proportion of silicon material d / b should not be too large. An overly large effective welding area may lead to an increase in the non-uniformity during the charge and discharge process of the battery, affecting the service life and cycle performance of the battery. The present invention can make the design of the effective welding area of the cylindrical battery more compatible with the battery energy density by comprehensively controlling the range value of d / b; that is, when the silicon doping amount increases, the energy density of the cylindrical battery increases. At this time, the welding area between the tab and the structure member is increased, thereby enhancing the overcurrent capacity of the battery, and further improving the fast-charging ability and cycle performance of the battery; at the same time, when the effective welding area is too large, the present invention adopts an optimized electrolyte formulation, so that the electrolyte can be timely replenished to the surface of the electrode plate, reducing battery polarization and enhancing the cycle life of the battery.

[0088] As an example, d / b can be 50, 100, 500, 1000, 3000, 5000, 8000, 10000, 13000, 15000, or within the range formed by any two of the above values.

[0089] In an alternative embodiment, by further controlling 100 ≤ d / b ≤ 15000, a battery with better fast charging performance can be obtained.

[0090] In an alternative embodiment, 500 ≤ d ≤ 1500. In the present invention, the effective welding area should not be too small, as this will affect the fast charging performance; at the same time, the effective welding area should not be too large either. When it is too large, in order to increase the effective welding area, the tab size or quantity usually needs to be increased, which will lead to an increase in the volume and weight of the battery, and is not conducive to the lightweight and miniaturization of the battery.

[0091] As an example, d can be 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, or within the range formed by any two of the above values.

[0092] The positive electrode plate in the present invention includes a positive electrode current collector and a positive electrode active layer coated on one or both surfaces of the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder.

[0093] In an alternative embodiment, the mass ratio of the positive electrode active material in the positive electrode active layer is 95 - 99 wt%, the mass ratio of the conductive agent in the positive electrode active layer is 0.5 - 2.5 wt%, and the mass ratio of the binder in the positive electrode active layer is 0.5 - 2.5 wt%. By obtaining a relatively high proportion of the positive electrode active material, the areal capacity of the positive electrode plate can be improved, thereby improving the energy density of the battery; by cooperating with a specific content of the binder, the problem of powder falling caused by insufficient particle adhesion in the positive electrode plate can be overcome, and the cycle performance can be improved. By cooperating with a specific content of the conductive agent, the electronic conductivity of the electrode plate can be increased, the surface resistance can be reduced, and further the fast charging performance and cycle performance of the battery can be improved.

[0094] The present invention does not particularly limit the conductive agent in the positive electrode plate, and it can be selected from the conductive agents commonly used in the art, including but not limited to at least one selected from conductive carbon black (SP), acetylene black, Ketjen black, graphite conductive agents (KS-6, KS-15, S-O, SEG-6), conductive carbon fibers (VGCG), carbon nanotubes (CNT), and graphene.

[0095] The binder in the positive electrode sheet of the present invention is not particularly limited, and it may be selected from binders commonly used in the art, including but not limited to polyvinylidene fluoride (PVDF), copolymer of polyvinylidene fluoride - hexafluoropropylene (PVDF-HFP), hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or one or more of them.

[0096] In an alternative embodiment, the positive electrode active material of the present invention includes a ternary material, and the chemical formula of the ternary material is Li e Ni x Co y Mn z A k O2, where 0.9 ≤ e ≤ 1.1, 0.8 ≤ x ≤ 0.95, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ k ≤ 0.05, and A is a doping element. Preferably, the doping element includes one or more of Al, Mg, Ti, Y, B, P, Zr. Preferably, 0.9 ≤ x ≤ 0.95.

[0097] The preparation process of the positive electrode sheet in the present invention is not specifically limited, and it can be prepared by using conventional preparation methods in the art.

[0098] For the long-cycle silicon-doped cylindrical battery in the present invention, its cut-off voltage ≤ 4.25V, and it can achieve fast charging performance of the battery at high voltage. The outer shell of the long-cycle silicon-doped cylindrical battery is a hard shell, generally an aluminum shell or a steel shell, which can improve the structural strength and inhibit the expansion of the wound core.

[0099] The following further describes the present invention in detail with specific examples, and these examples should not be construed as limiting the scope of protection required by the present invention. In all examples and comparative examples of the present invention, the unit wt% represents mass percentage content.

[0100] Example 1

[0101] A cylindrical battery is prepared as follows:

[0102] (1) Prepare the positive electrode sheet

[0103] Mix 97 wt% of the positive electrode active material (the single crystal accounts for 20%, the polycrystal accounts for 80%, and the chemical formula of the single crystal is LiNi 0.9 Co 0.04 Mn 0.04 Al 0.02 O2, and the chemical formula of the polycrystal is LiNi 0.92 Co 0.02 Mn 0.04 Al 0.02O2), 1.4 wt% binder PVDF, 0.8 wt% conductive agent SP, and 0.8 wt% carbon nanotubes were mixed according to the mass ratio, and a uniformly dispersed mixture was obtained by high-speed stirring. Then, NMP was used as the solvent to make the positive electrode active material slurry, and the solid content in the slurry was 70 wt%.

[0104] The slurry was evenly coated on the positive electrode current collector aluminum foil to form a wet film, and then a single-sided positive electrode was obtained after baking. A double-sided positive electrode was coated in the same way and then obtained the positive electrode sheet after baking, rolling, and slitting.

[0105] (2) Preparation of the negative electrode sheet

[0106] 97% negative electrode active material, 0.5% thickener CMCLi, 1.5% binder SBR, and 1% conductive agent (0.5% carbon nanotubes + 0.5% SP) were mixed, as shown in Table 1. A uniformly dispersed mixture was obtained by high-speed stirring, and water was used as the solvent to make the surface layer negative electrode slurry. The solid content in the negative electrode slurry was 50 wt%. The negative electrode active material included graphite material and silicon-carbon material, and the mass ratio b of silicon element in the silicon-carbon material in the negative electrode active material was 5%. The Dv50 of the graphite material was 13 μm, the Dv50 of the silicon-carbon material was 8 μm, and the ratio c of Dv50 of the graphite material to Dv50 of the silicon-carbon material was 1.625. The carbon nanotubes were single-walled carbon nanotubes, with a diameter of about 2 nm, a length of about 5000 nm, and an aspect ratio of about 2500.

[0107] During coating, a bottom coating with a thickness of 1 μm should be first coated on a copper foil with a thickness of 5 μm. The composition of the bottom coating was binder SBR, conductive agent carbon nanotubes, and conductive agent SP with a mass ratio of 1.5:0.5:0.5. After drying, the negative electrode slurry was evenly sprayed on the bottom coating to form a wet film, and then a single-sided negative electrode was obtained after baking. After coating both sides in the same way, it was baked, rolled, punched to form a concave part, and slit to obtain the negative electrode sheet 1. When rolling, the area 15 mm away from the edge of the electrode sheet was the edge area, and the rest was the middle area. After rolling, the compaction density in the middle area was 1.5 g / cm 3 and the compaction density in the edge area was 1.7 g / cm 3 ; The single-sided surface density of the negative electrode sheet was 7 mg / cm 2 .

[0108] The coated negative electrode sheet 1 was placed in a laser drilling machine, and the surface of the negative electrode was etched with high-energy laser. By controlling the power of the laser and the etching time, the width of the punched hole or linear groove could be adjusted to form the concave part 2. The minimum vertical distance D from the concave part 2 to the edge of the negative electrode sheet was 15 mm. The depth of the concave part was 20 μm and the width was 200 μm, and the distance L between adjacent two concave parts was 2000 μm.

[0109] (3) Preparation of electrolyte

[0110] Select LiPF6 as the lithium salt. The organic solvent includes EC and chain carbonate. Add 5% of the negative electrode film-forming additive to form an electrolyte with a LiPF6 concentration of 1 mol / L. The mass ratio of the chain carbonate in the electrolyte is a. The types of the chain carbonate and the negative electrode film-forming additive are shown in Table 1.

[0111] (4) The separator is a commercial separator, which includes a base film and ceramic layers provided on both sides of the base film. The thickness of the base film is 7 μm, and the thickness of the single-sided ceramic layer is 3 μm.

[0112] (5) Preparation of the battery

[0113] Wind the negative electrode sheet, separator, and positive electrode sheet prepared in the above steps by winding to form a core with an effective welding area A of 700 mm 2 and then make a cylindrical battery with the ratio K0 of the core diameter to the inner diameter of the shell after shelling, welding, encapsulation, electrolyte injection, formation, and sorting. When the battery is in the 100% SOC state, the ratio of the core diameter to the inner diameter of the shell is K1, as shown in Table 1 below.

[0114] Table 1

[0115]

[0116] Example 2

[0117] A cylindrical battery, which is different from Example 1-1 in that the surface density of the negative electrode sheet, the compaction density of the negative electrode sheet, the concave part, the thickness of the negative electrode current collector, and the thickness of the negative electrode bottom coating are different, as shown in Table 2 below.

[0118] Table 2

[0119]

[0120]

[0121] In this example, other conditions are the same as those in Example 1-1.

[0122] Example 3

[0123] A long-cycle silicon-doped cylindrical battery, which is different from Example 1-1 in that the particle size Dv50 of the graphite material and the silicon-carbon material in the negative electrode active material and the ratio c of the particle size Dv50, the tube diameter, length, and length-to-diameter ratio of the single-walled carbon nanotubes, and the thickness of the base film and the single-sided ceramic layer in the separator are different, as shown in Table 3 below.

[0124] Table 3

[0125]

[0126] In this embodiment, other conditions are the same as those in Embodiment 1-1.

[0127] Embodiment 4

[0128] A long-cycle silicon-doped cylindrical battery, which is different from Embodiment 1-1 in that the mass ratio b of the silicon-carbon material in the negative electrode active material, the ratios of the negative electrode active material, thickener, binder and conductive agent in the negative electrode active layer, and the effective welding area d mm of the battery 2 , and the value of d / b are different, as shown in Table 4 below.

[0129] Table 4

[0130]

[0131] In this embodiment, other conditions are the same as those in Embodiment 1-1.

[0132] Experimental Example

[0133] The lithium-ion batteries obtained in the examples and comparative examples were respectively subjected to cycle performance tests and short-circuit safety tests, and the test results are shown in the table.

[0134] 1. Cycle performance test:

[0135] At 25°C, in the charge-discharge window of 4.2V to 2.5V, 1C / 1C charge-discharge cycles were carried out. The test process was as follows: First, charge at a constant current of 1C to 4.2V, then charge at a constant voltage until the cut-off current was 0.05C, and finally discharge at a constant current of 1C to 2.5V, and so on for cyclic testing. The number of times when the ratio of the discharge capacity to the first discharge capacity (capacity retention rate) reached 80% was recorded in Table 1.

[0136] 2. DCR growth:

[0137] DCR test method: At 25°C, the battery was left standing for 30 min at 50% SOC, the terminal voltage V1 was recorded, it was discharged at a current of 3C for 10 s, and the terminal voltage V2 was recorded. DCR = (V1 - V2) / current;

[0138] The ratio of the DCR value of the battery at 50% SOC at the end of the cycle to the DCR value in the initial state was recorded, which was the DCR growth rate.

[0139] 3. Fast charging window confirmation:

[0140] At room temperature, the battery cells nC (n = 1, 2, 3, 4, 5) are charged to 4.2V and then charged at a constant voltage, with the cut-off current being 0.05C, and left standing for 30 minutes; discharged at 1C to 2.5V and left standing for 30 minutes; such charge and discharge cycles are repeated 20 times. Finally, after the battery cells are fully charged, the test is ended and the cells are dissected to observe whether lithium plating occurs at the edge of the negative electrode.

[0141] Record the maximum rate at which the battery does not experience lithium plating, which is the fast charging window of the battery.

[0142] The data obtained from the above examples and comparative examples are shown in Table 5 - 8 below.

[0143] Table 5

[0144]

[0145]

[0146] Table 6

[0147] 25°C Cycle Life / cycles DCR Increase / % Fast Charging Window / °C Example 2-1 912 24.2 5.2 Example 2-2 905 25.7 5.1 Example 2-3 881 27.1 4.9 Example 2-4 869 30.0 4.6 Example 2-5 620 69.1 0.9 Example 2-6 614 72.0 0.6 Example 2-7 873 28.5 4.8 Example 2-8 861 31.3 4.5 Example 2-9 852 32.9 4.4 Example 2-10 802 38.7 3.8 Example 2-11 793 40.2 3.7

[0148] Table 7

[0149] 25°C Cycle Life / cycles DCR Increase / % Fast Charging Window / °C Example 3-1 836 34.2 4.3 Example 3-2 824 35.8 4.1 Example 3-3 813 37.3 4.0 Example 3-4 708 53.2 2.4 Example 3-5 675 59.0 1.8 Example 3-6 831 34.4 4.2 Example 3-7 785 46.5 3.2 Example 3-8 819 37.1 4.1

[0150] Table 8

[0151] 25°C Cycle Life / cycles DCR Increase / % Fast Charging Window / °C Example 4-1 901 24.3 4.9 Example 4-2 933 22.9 5.3 Example 4-3 632 66.2 1.2 Example 4-4 897 24.4 4.8 Example 4-5 619 70.6 0.7 Example 4-6 886 24.8 4.5 Example 4-7 895 24.5 4.7

[0152] From the comparison of the data of the examples and comparative examples in Tables 1 - 4, it can be seen that when K1 - K0 is controlled within 2.5%, relatively large swelling can be avoided, and it can be avoided that after swelling, the large extrusion force on the electrode sheet makes the contact between the electrode sheets of the battery cell closer, reducing the pores between the electrode sheets of the battery cell, affecting the infiltration of the electrolyte and the transmission of lithium ions, and further affecting the fast charging performance and cycle performance of the battery; using an electrolyte containing a chain carbonate with a specific content of 50% ≤ a ≤ 90% can effectively reduce the viscosity of the electrolyte, improve the fluidity, wettability and kinetic performance of the electrolyte, and cooperate with the internal winding core with a volume expansion rate of less than 2.5% and a tight structure to effectively promote the infiltration of the electrolyte inside the winding core, further facilitating the transmission of lithium ions, reducing the internal polarization of the battery, and comprehensively improving the cycle life and fast charging performance of the battery.

[0153] Obviously, the above examples are merely illustrations given for clarity and are not limitations on the implementation methods. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. And the obvious changes or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. A battery, comprising a housing, a wound core, and an electrolyte; characterized in that, the electrolyte contains an organic solvent and a lithium salt, and the organic solvent includes a chain carbonate having a mass ratio of a in the electrolyte, 50% ≤ a ≤ 90%; the wound core is a cylindrical wound core, the wound core includes a negative electrode sheet, and the negative electrode active material in the negative electrode sheet includes a silicon-based material; when the battery is in a 100% SOC state, the ratio of the diameter of the wound core to the inner diameter of the housing is K1; when the battery is in a 0% SOC state, the ratio of the diameter of the wound core to the inner diameter of the housing is K0; 0 < K1 - K0 ≤ 2.5%.

2. The battery according to claim 1, characterized in that, 99％≤K1≤100％； and / or, 97.5% ≤ K0 < 99%; and / or, 60% ≤ a ≤ 80%; and / or, 0 < (K1 - K0) / a ≤ 0.05, preferably, 0 < (K1 - K0) / a ≤ 0.

04.

3. The battery according to claim 1 or 2, characterized in that, The organic solvent includes one or a combination of two or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, diethyl carbonate, ethyl formate, ethyl acetate, ethyl propionate, and propyl propionate; and / or, the lithium salt includes one or a combination of two or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium difluoro(dioxalato)borate, and lithium bis(trifluoromethylsulfonyl)imide; and / or, the electrolyte further includes a negative electrode film-forming additive, and the negative electrode film-forming additive includes one or a combination of two or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, ethylene sulfate, dimethyl sulfite, and silane coupling agent.

4. The battery according to any one of claims 1-3, characterized in that, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer on one or both surfaces of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes a graphite material and a silicon material, and the mass ratio of silicon element in the silicon material in the negative electrode active material is b, 0.1% ≤ b ≤ 10%, preferably, 0.1% ≤ b ≤ 5%.

5. The battery according to claim 4, characterized in that, The ratio of Dv50 of the graphite material to Dv50 of the silicon material is c, 1.3 ≤ c ≤ 2.6; Preferably, the Dv50 of the graphite material is 10-16 μm, and / or, the Dv50 of the silicon material is 6.0-10.0 μm.

6. The battery according to claim 4, characterized in that, A bottom coating is further provided between the negative electrode current collector and the negative electrode active layer; Preferably, the thickness of the negative electrode current collector is 4.5-6 μm, and the thickness of the bottom coating is 0.5-2.0 μm; Preferably, the negative electrode current collector is a copper foil; Preferably, the bottom coating includes a conductive agent and a binder.

7. The battery according to claim 6, characterized in that, The negative electrode active layer further includes a binder, a conductive agent, and a thickening agent; the mass ratio of the negative electrode active material in the negative electrode active layer is 94 to 98.5 wt%, the mass ratio of the conductive agent in the negative electrode active layer is 0.5 to 2 wt%, the mass ratio of the binder in the negative electrode active layer is 0.5 to 3 wt%, and the mass ratio of the thickening agent in the negative electrode active layer is 0.5 to 1 wt%. Preferably, the conductive agent includes carbon nanotubes, and the mass ratio of the carbon nanotubes in the negative electrode active layer is 0.5 to 1 wt%; more preferably, the carbon nanotubes are single-walled carbon nanotubes, the diameter of the single-walled carbon nanotubes is <3 nm, and the length is 1800 to 7200 nm; more preferably, the aspect ratio of the single-walled carbon nanotubes is 1200 to 3000.

8. The battery according to claim 4, characterized in that, The single-sided areal density of the negative electrode sheet is 6 to 8 mg / cm 2 ; And / or, the compaction density of the negative electrode sheet is 1.4 to 1.8 g / cm 3 ; Preferably, along the width direction of the negative electrode sheet, the negative electrode sheet includes an edge region and a middle region, the width of the edge region is 0 to 20 mm, and the compaction density of the middle region of the negative electrode sheet is 1.4 to 1.65 g / cm 3 , and the compaction density of the edge region of the negative electrode sheet is 1.65 to 1.8 g / cm 3 ; Preferably, the surface of the active material layer of the negative electrode sheet has recesses, the minimum vertical distance D from the recesses to the edge of the negative electrode sheet is 10 to 20 mm, the depth of the recesses is 3 μm to 40 μm, the width is 50 μm to 500 μm, and the distance L between two adjacent recesses is 400 μm to 5000 μm.

9. The battery according to any one of claims 1-7, characterized in that, The separator in the wound core includes a base film and a ceramic layer coated on one or both sides of the base film. Preferably, the thickness of the base film is 5 to 9 μm, and the thickness of the ceramic layer on one side is 1 to 4 μm. And / or, the effective welding area of the tab extending from the battery is d mm 2 , 50 ≤ d / b ≤ 15000.

10. The battery according to claim 9, characterized in that, 500≤d≤1500； and / or, 100 ≤ d / b ≤ 15000.

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