Battery

Abstract

A battery. The battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The electrolyte comprises ethyl butyrate, the mass proportion of the ethyl butyrate is denoted as A% based on the total mass of the electrolyte, the redundant width of the separator is denoted as B mm, and A and B satisfy: A≥10B. When the mass proportion A of the ethyl butyrate is 5-70%, then the redundant width B of the separator is 0.5-2.5 mm. By adjusting the relationship between the mass proportion A of the ethyl butyrate in the electrolyte and the redundant width B of the separator, the battery has the advantages of a good cycling performance and reduced lithium evolution.

Description

A battery TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of lithium batteries, and in particular to a battery. BACKGROUND

[0002] With the rapid development of technology, people's dependence on electronic devices is increasing, and the demand for battery technology is becoming more and more urgent. Lithium batteries have become the mainstream battery technology in the current electronic device field due to their high energy density, long cycle life and environmental friendliness. At the same time, with the acceleration of the pace of life, fast charging technology has emerged as the times require, providing people with more convenient and efficient charging experience. However, in the pursuit of fast charging, the battery is more likely to lithiumize and the cycle life is quickly attenuated. SUMMARY

[0003] The purpose of the present disclosure is to overcome the above-mentioned problems existing in the prior art, and to provide a battery, by regulating the relationship between the mass percentage A of ethyl butyrate in the electrolyte and the redundancy width B of the separator, when A≥10B, and when A and B take values within a certain range, the risk of lithiumization of the battery during fast charging can be reduced, and the cycle performance of the battery during fast charging can be improved.

[0004] In order to achieve the above-mentioned purpose, the present disclosure provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises ethyl butyrate, and the mass percentage of the ethyl butyrate in the total mass of the electrolyte is denoted as A%; the redundancy width of the separator is denoted as B mm;

[0005] A and B satisfy: A≥10B;

[0006] The mass percentage A of the ethyl butyrate is 5%-70%;

[0007] The redundancy width B of the separator is 0.5mm-3.5mm.

[0008] In some embodiments, the battery comprises a positive electrode sheet, a separator and a negative electrode sheet which are sequentially stacked and wound; the positive electrode sheet comprises a first flat area and a first circular arc area; at least part of the first circular arc area is provided with a plurality of first recesses; the depth of the first recesses is less than the thickness of the positive electrode sheet.

[0009] In some embodiments, the negative electrode sheet comprises a second flat area and a second circular arc area; at least part of the second circular arc area is provided with a plurality of second recesses; the depth of the second recesses is less than the thickness of the negative electrode sheet.

[0010] The present disclosure has the following beneficial effects by adopting the above technical solutions:

[0011] (1) The battery provided in this disclosure can reduce the risk of lithium plating during fast charging and improve the cycle performance of the battery during fast charging by adjusting the mass ratio A of ethyl butyrate in the electrolyte and the redundancy B of the separator to satisfy A≥10B and the values ​​of A and B within a specific range.

[0012] (2) In the wound lithium-ion battery provided in this disclosure, during fast charging, the battery expands significantly due to the intensified side reactions in the electrolyte, causing compression in the arc-shaped area, which may lead to insufficient electrolyte in the arc-shaped area. Providing a recess in the arc-shaped area can reduce the problem of lithium deposition in the arc-shaped area and improve the cycle performance of the battery.

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description

[0014] Figure 1 shows a schematic diagram of the redundant diaphragm structure in the electrode.

[0015] Figure 2 shows a partial structural diagram of a wound battery.

[0016] Figure 3 shows a schematic diagram of the structure of the positive electrode, in which the first flat region and the first arc region are cyclically distributed, and all the arc regions are perforated.

[0017] Figure 4 shows a schematic diagram of the structure of the first flat region and the first arc region in the positive electrode, with the arc region partially perforated.

[0018] Figure 5 shows a schematic diagram of the structure of the negative electrode sheet, in which the second flat region and the second arc region are cyclically distributed, and all arc regions are perforated.

[0019] Figure 6 shows a schematic diagram of the structure of the negative electrode, in which the second flat region and the second arc region are cyclically distributed, and the arc region is partially perforated.

[0020] Figure 7 shows a schematic cross-sectional view of the holes drilled in the positive and negative electrode plates.

[0021] Figure 8 shows a schematic diagram of the overhang width in the electrode. Detailed Implementation

[0022] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure.

[0023] Unless otherwise defined, all scientific and technical terms used in the present disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure pertains.

[0024] The present disclosure provides a battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises ethyl butyrate, the mass percentage of the ethyl butyrate in the total mass of the electrolyte is denoted as A%; the width of the separator is denoted as B mm;

[0025] A and B satisfy: A≥10B;

[0026] The mass percentage A of the ethyl butyrate is 5%-70%;

[0027] The width B of the separator is 0.5mm-3.5mm.

[0028] It should be noted that in the battery, in the width direction of the battery, the negative electrode sheet exceeds the width of the positive electrode sheet, and the size of the separator exceeds the negative electrode sheet. The "excess width of the separator" refers to the width of the separator exceeding the negative electrode sheet in the width direction of the battery. As shown in FIG. 1, in the width direction of the battery (X-axis direction), the excess width B of the separator refers to the width of the separator 2 exceeding the negative electrode sheet 3.

[0029] In some embodiments, the mass percentage A of the ethyl butyrate is 5%-70%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or any point value in the range consisting of any two of the above point values, preferably 10%-50%.

[0030] In some embodiments, the width B of the separator is 0.5mm-3.5mm, for example, it can be 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 2.8mm, 3mm, 3.2mm, 3.5mm or any point value in the range consisting of any two of the above point values, preferably 0.5mm-2mm.

[0031] When the battery is rapidly charged, heat is generated inside the battery due to the obstruction of lithium ion migration, which causes a series of side reactions such as electrolyte reaction decomposition and gas production, thereby increasing the instability and safety risk of the battery. Moreover, when the battery is rapidly charged, the problem of insufficient electrolyte in the arc region of the electrode sheet and the wound battery is prone to occur, which affects the fast charging performance of the battery, and also easily leads to lithium precipitation in the arc region of the battery.

[0032] Ethyl butyrate (EB, chemical structure is ) has good kinetics while the interface stability is good. Adding EB to the electrolyte, because EB has good kinetics and good redox stability itself, the electrode-electrolyte interface stability is good, which can meet the rapid shuttle of lithium ions between the positive and negative electrodes, realize fast charging, reduce battery heat production and electrolyte side reactions; and the reaction activity of EB with the interface is low, reducing the interface side reactions and lithium precipitation. Adjusting the separator redundancy to be within a suitable range can avoid too much electrolyte existing in the separator redundancy, causing insufficient electrolyte in the electrode and the arc area, affecting the fast charging performance of the battery and the lithium precipitation in the arc area; it can also avoid too small separator redundancy causing the battery to be easily short-circuited and the cycle capacity to decay faster; when the separator redundancy is within the range of 0.5mm-3.5mm, the electrolyte existing in the area outside the electrode can be reduced, ensuring more electrolyte existing in the electrode and the arc area, effectively solving the problem of insufficient electrolyte in the electrode and the arc area, and reducing the problem of lithium precipitation in the electrode and the arc area.

[0033] The present disclosure also adjusts the mass ratio A of ethyl butyrate and the separator redundancy B to satisfy A≥10B. The larger the separator redundancy is, the higher the content of EB in the electrolyte is, which can ensure that a large amount of electrolyte exists in the electrode and the arc area, and when relatively more electrolyte exists in the separator redundancy, the overall kinetics of the electrolyte needs to be higher, and the content of EB needs to be higher, thereby synergistically ensuring the fast charging kinetics of the electrolyte itself and excellent film forming performance, and the size of the separator redundancy and the mass ratio of EB can be matched, thereby further improving the fast charging performance of the battery and reducing lithium precipitation. If A<10B, when the separator redundancy is within a suitable range, the content of EB added to the electrolyte is less, which cannot effectively improve the kinetic performance of the electrolyte, and the effects of improving the fast charging performance of the battery and reducing lithium precipitation are limited; or when the content of EB added to the electrolyte is within a suitable range, the separator redundancy is too large, and relatively more electrolyte exists in the separator redundancy, causing insufficient electrolyte in the electrode and the arc area, affecting the fast charging performance of the battery and the lithium precipitation in the arc area.

[0034] In some embodiments, A and B satisfy: 50B≥A≥15B. Further, when the mass ratio A of ethyl butyrate and the separator redundancy B satisfies A≥10B, adjusting the relationship between the two to satisfy the more optimal range of 50B≥A≥15B, when the content of EB in the electrolyte is within a suitable range, the separator redundancy is smaller, which can ensure that more electrolyte exists in the electrode and the arc area, and is more conducive to improving the fast charging performance of the battery and reducing lithium precipitation; or when the separator redundancy is within a suitable range, the content of EB in the electrode liquid is higher, which can further improve the kinetic performance of the electrolyte, improve the fast charging performance of the battery, reduce battery heat production and electrolyte side reactions.

[0035] In some embodiments, in the width direction of the battery, the width of the negative electrode tab beyond the positive electrode tab is 0.5mm-3mm, preferably 1mm-2mm. As shown in FIG. 8, in the width direction of the battery (X-axis direction), the width of the negative electrode tab beyond the positive electrode tab is the Overhang width (abbreviated as OH width), and the design of the negative electrode tab being slightly larger than the positive electrode tab can prevent edge lithium precipitation. When the mass ratio A of ethyl butyrate and the redundancy width B of the separator satisfy A≥10B, and the OH width is adjusted to be within the above range, in combination with the high kinetic EB solvent, the lithium precipitation caused by small OH and local lack of negative electrode can be reduced, thereby improving the cycle and safety performance of the battery. If the OH width is too large, it is easy to cause the redundancy width of the separator to be too small, which can cause the battery to easily short circuit, the cycle capacity to decay faster, and the cycle performance to deteriorate. If the OH width is too small, it is easy to cause the redundancy width of the separator to be too large, which can cause the electrolyte to be insufficient in the tab and arc region, affect the fast charging performance of the battery, and cause lithium precipitation in the arc region.

[0036] In some embodiments, the electrolyte further comprises fluoroethylene carbonate (FEC). Preferably, the mass ratio of the fluoroethylene carbonate is 1%-20% based on the total mass of the electrolyte, for example, it can be 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20% or any point value within the range of two point values. When the mass ratio A of ethyl butyrate and the redundancy width B of the separator satisfy the above values and relationship, the interface stability of the SEI film (Solid Electrolyte Interphase) or CEI film (Cathode Electrolyte Interface) formed on the electrode-electrolyte interface is limited, and the combination of EB and FEC in the electrolyte can further improve the interface stability. FEC can form a stable passivation film (such as SEI film) on the surface of the electrode, which has reaction inertness and further inhibits the side reaction of EB at the interface, which helps to reduce the side reaction between the electrode material and the electrolyte, thereby improving the cycle stability of the battery, thereby reducing the interface side reaction and reducing lithium precipitation.

[0037] In some embodiments, the electrolyte further comprises a sulfonic acid additive. Preferably, the mass fraction of the sulfonic acid additive in the total mass of the electrolyte is 0.5%-5%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any point value in the range consisting of any two of the above point values. When the mass fraction A of ethyl butyrate and the redundancy width B of the separator satisfy the above values and relationship, the interface stability of the SEI film or CEI film formed on the electrode-electrolyte interface is limited, and further adjustment of the combination of EB and the sulfonic acid additive in the electrolyte can exchange lithium ions on the surface of the electrode material with the sulfonic acid additive to form a more stable interface layer, reduce the side reaction between the electrode and the electrolyte, and further improve the cycle stability of the battery, reduce the interface side reaction and reduce lithium precipitation.

[0038] In some embodiments, the sulfonic acid additive comprises at least one of 1,3-propane sulfone, 1-propylene-1,3-sulfonic acid lactone, 5-methylthiophene 2,2-dioxide, 1,3-propylene sulfonic acid lactone, 2,4-butane sulfone, 1,4-butane sulfonic acid lactone and derivatives thereof, and more preferably 1,3-propane sulfone. "Derivative" refers to the addition of other substituent groups to the original structure of the sulfonic acid additive, and the original structure remains unchanged.

[0039] Further, when the mass fraction A of ethyl butyrate and the redundancy width B of the separator satisfy the above values and relationship, further adjustment of the combination of EB, FEC and the sulfonic acid additive in the electrolyte can form a better SEI film at the interface, better inhibit the side reaction of EB at the interface, and thus EB, FEC and the sulfonic acid additive synergistically improve the interface, reduce the interface side reaction and lithium precipitation, and better improve the cycle performance of the battery.

[0040] In some embodiments, the electrolyte further comprises a nitrile compound. Preferably, the mass fraction of the nitrile compound in the total mass of the electrolyte is 2%-6%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6% or any point value in the range consisting of any two of the above point values. When the mass fraction A of ethyl butyrate and the redundancy width B of the separator satisfy the above values and relationship, the battery is prone to a series of side reactions such as electrolyte reaction decomposition and gas production due to the obstruction of lithium ion migration and the generation of more heat inside the battery during fast charging. Adjustment of the combination of EB and the nitrile additive in the electrolyte can reduce the decomposition rate of the electrolyte at high temperature due to the good thermal stability of the nitrile additive, thereby improving the stability of the high kinetic electrolyte and the fast charging performance of the battery, reducing the interface side reaction and reducing lithium precipitation.

[0041] In some embodiments, the nitrile compounds include one or more of 1,3,5-hexanetricarbonitrile (HTCN), adiponitrile (AND), succinonitrile (SN), ethylene glycol bis(propionitrile) ether (DENE), tris(3-cyanopropyl)phosphate (PCN), pentanediolonitrile, heptanediolnitrile, octanediolnitrile, glycerol tricarbonitrile, ethoxy pentafluorophosphazene, 1,4-dicyano-2-butene, and 1,3,6-hexanetricarbonitrile.

[0042] In some embodiments, the battery includes a positive electrode sheet, a separator, and a negative electrode sheet which are sequentially stacked and arranged in a roll shape; the positive electrode sheet includes a first flat area and a first arc area; at least part of the first arc area is provided with a plurality of first recesses; the depth of the first recesses is less than the thickness of the positive electrode sheet.

[0043] In some embodiments, the negative electrode sheet includes a second flat area and a second arc area; at least part of the second arc area is provided with a plurality of second recesses; the depth of the second recesses is less than the thickness of the negative electrode sheet.

[0044] When the mass ratio A of ethyl butyrate and the redundancy width B of the separator satisfy the above values and relationship, although the problem of insufficient electrolyte in the electrode sheet and the arc area can be improved to some extent, the electrolyte decomposition by-products produced during fast charging may react with the electrode material, consume the lithium embedded in the electrode, reduce the available lithium amount of the battery, and thus the room temperature cycle performance of the battery is not greatly improved. By providing recesses (or referred to as punching the arc area) in at least part of the arc area of the positive electrode sheet and / or the negative electrode sheet, the electrolyte can exist and be uniformly distributed in the electrode sheet inside the arc area, which is beneficial to the electrolyte wetting in the arc area and reduces the lithium precipitation caused by the broken bridge of lithium ions. The electrolyte with EB has better kinetic performance, and the punching of the arc area not only ensures that the electrolyte with high kinetic performance exists more in the electrode sheet area, but also realizes the further improvement of the lithium ion conduction kinetics in the arc area, improves the conduction efficiency of the electrolyte in the electrode sheet, thereby synergistically meeting the demand of fast shuttling of lithium ions between the positive and negative electrodes, and better realizing the improvement of the battery fast charging performance; and EB further suppresses the lithium precipitation phenomenon through its interface stability, and cooperates with the punching of the arc area to reduce the interface side reaction and lithium precipitation, and improves the cycle stability of the battery.

[0045] In some embodiments, as shown in FIG. 2, the winding core of the winding lithium ion battery is formed by winding the positive electrode sheet 1, the separator 2 and the negative electrode sheet 3 arranged in sequence. When the positive electrode sheet 1, the separator 2 and the negative electrode sheet 3 are wound to form the winding core structure, different regions will exhibit two states: curved state and uncurved state, and the positive electrode sheet 1 and the negative electrode sheet 3 will have curved regions and uncurved regions correspondingly. In the present disclosure, the "arc region" can be a part of the curved region of the positive electrode sheet 1 and the negative electrode sheet 3, and the part contains the inflection point of the curved region, and the "arc region" can also be the entire curved region of the positive electrode sheet 1 and the negative electrode sheet 3, and the inflection point of the curved region is the intersection of the center line of the winding core and the curved region. The "flat region" can be the entire uncurved region of the positive electrode sheet 1 and the negative electrode sheet 3.

[0046] In some embodiments, as shown in FIG. 2, FIG. 3 and FIG. 5, the positive electrode sheet 1 includes a positive electrode current collector 11 and a positive electrode active material layer 12 arranged on both sides of the positive electrode current collector. The positive electrode sheet 1 is cyclically and intermittently distributed with the first flat region 13 and the first arc region 14 along the winding direction. The negative electrode sheet 3 includes a negative electrode current collector 31 and a negative electrode active material layer 32 arranged on both sides of the negative electrode current collector. The negative electrode sheet 3 is cyclically and intermittently distributed with the second flat region 33 and the second arc region 34 along the winding direction.

[0047] In some embodiments, as shown in FIG. 3, FIG. 4 and FIG. 7. At least part or all of the first arc region 13 is provided with a plurality of first recesses 131, and the depth of the first recess 131 is less than the thickness of the positive electrode sheet 1. The first recess does not penetrate the positive electrode sheet, avoiding the penetration of the electrode sheet to cause the leakage of electrolyte and affect the performance and safety of the battery.

[0048] In some embodiments, as shown in FIG. 5, FIG. 6 and FIG. 7. At least part or all of the second arc region 34 is provided with a plurality of second recesses 331, and the depth of the second recess 331 is less than the thickness of the negative electrode sheet 3. The positive electrode sheet 1, the negative electrode sheet 3 and the separator 2 are wound along the Y-axis direction (the length direction of the electrode sheet) to form the winding core as shown in FIG. 2. The second recess does not penetrate the negative electrode sheet, avoiding the penetration of the electrode sheet to cause the leakage of electrolyte and affect the electrochemical performance and safety of the battery.

[0049] In some embodiments, the first recess and the second recess are usually realized by physical or chemical methods during the preparation process of the electrode sheet, for example, using laser, electron beam or other high-energy particle beam to punch holes. The shape of the first recess and the second recess can be V-shaped groove, trapezoidal groove, rectangular groove, circular groove or elliptical groove.

[0050] In some embodiments, the distance between two adjacent first recesses is 0.5 mm to 2 mm (for example, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, or any point value within the range defined by any two of the above point values), the width of the first recess is 50 μm to 200 μm (for example, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, or any point value within the range defined by any two of the above point values), and the depth of the first recess is 5 μm to 30 μm (for example, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 30 μm, or any point value within the range defined by any two of the above point values).

[0051] In some embodiments, the distance between two adjacent second recesses is 0.5 mm to 2 mm (for example, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, or any point value within the range defined by any two of the above point values), the width of the second recess is 50 μm to 200 μm (for example, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, or any point value within the range defined by any two of the above point values), and the depth of the second recess is 5 μm to 30 μm (for example, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 30 μm, or any point value within the range defined by any two of the above point values).

[0052] The "distance between two adjacent recesses" can be explained as follows, taking the shape of the first recess as a circular recess as an example. In two adjacent closest first recesses, the distance between the centers of the two circular recesses. When the first recess is not a regular shape, the distance between the centers of the circumscribed circles of the two first recesses in the two adjacent closest first recesses. The "width of the recess" can be explained as the maximum straight-line distance between the two inner side edges in the recess in a direction parallel to the pole piece. The "depth of the recess" can be explained as the maximum distance between the bottom of the recess and the outer surface of the active material layer in the thickness direction of the pole piece.

[0053] When the distance, width, and depth of the first recess in the positive pole piece and the distance, width, and depth of the second recess in the negative pole piece satisfy the above conditions, the charge and discharge performance and the rate capability of the battery can be significantly improved.

[0054] In some embodiments, in the width direction of the battery, the width of the separator is greater than the width of the negative pole piece, and the width of the negative pole piece is greater than the width of the positive pole piece.

[0055] Preferably, the width of the positive electrode sheet is 20mm-200mm, and / or the thickness of the positive electrode sheet is 20μm-150μm. Preferably, the width of the negative electrode sheet is 20mm-200mm, and / or the thickness of the negative electrode sheet is 20μm-150μm; preferably, the width of the separator is 20mm-250mm. The length of the positive electrode sheet and the negative electrode sheet is not limited, and can be adjusted according to the design requirements of the battery. The width and thickness of the positive electrode sheet and the negative electrode sheet are not limited to the above ranges, and can be adjusted according to the design requirements of the battery.

[0056] In some embodiments, the electrolyte further comprises a carbonate solvent and / or a carboxylic acid ester solvent, such as a combination of one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), dimethyl carbonate (DMC), ethyl formate (EF), ethyl acetate (EA), and ethyl propionate (EP).

[0057] In some embodiments, the electrolyte further comprises an electrolyte lithium salt. Preferably, the electrolyte lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethylsulfonylimide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), and lithium difluoro(oxalato)borate (LiDFOP). The electrolyte lithium salt improves the ionic conduction performance of the electrolyte, promotes the rapid transport of lithium ions in the battery, and improves the charge-discharge efficiency of the battery.

[0058] In some embodiments, the separator comprises a base film, a ceramic layer disposed on at least one side surface of the base film, and a glue coating layer disposed on the ceramic layer away from the surface of the base film. The ceramic layer and the glue coating layer on the surface of the separator can improve the safety, electrochemical performance, and cycle stability of the lithium ion battery.

[0059] In some embodiments, the thickness of the base film is 3μm-10μm, preferably 4μm-8μm. The thickness of the ceramic layer is 1μm-5μm. The thickness of the glue coating layer is 50nm-5μm. When the thicknesses of the base film, the ceramic layer, and the glue coating layer are within the above ranges, the relationship between the energy density of the battery and the overall thickness and effect of the separator can be balanced, i.e., the mechanical stability and safety of the separator are improved, and the battery has a relatively high energy density.

[0060] In some embodiments, the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises lithium cobaltate and / or a ternary material with a chemical formula of Li a Ni x Coy Mn z M k O2, wherein 0.9≤a≤1.1, 0.5≤x≤0.95, 0<y≤0.2, 0<z≤0.3, 0≤k≤0.05, M is a doping element, and the doping element includes at least one of Al, Mg, Ti, Zr, B, P, W and Y. The lithium cobaltate and / or the ternary material has a layered structure, which provides a shorter ion diffusion path, is beneficial to the rapid diffusion and intercalation / deintercalation process of lithium ions inside the positive active material, and thus improves the charge and discharge rate of the battery. However, the electrical conductivity of the ternary material is low, and the diffusion speed of lithium ions inside the ternary material is slow, which is not conducive to improving the fast-charging performance of the battery. When the mass ratio A of ethyl butyrate and the redundancy width B of the separator meet the above values and relationships, the combination of the ternary material and the high-kinetic-performance electrolyte and the redundancy width range provided by the present disclosure can make the electrolyte exist more in the positive electrode sheet, that is, improve the electrolyte wettability of the ternary material in the positive electrode sheet, improve the migration rate of lithium ions in the positive electrode sheet, and thus improve the fast-charging performance and cycle performance of the battery, and also improve the energy density of the battery.

[0061] In some embodiments, the negative electrode sheet includes a negative active material, and the negative active material includes a carbon-based material and optionally a silicon-based material. Preferably, the mass ratio of the silicon-based material in the negative active material is 0-30%, for example, the mass ratio of the silicon-based material is 0, 5%, 10%, 15%, 20%, 25%, 30% or any point value in the range of two point values, and preferably 5%-25%. The silicon-based material has a higher specific capacity than the carbon-based material, and increasing the mass ratio of the silicon-based material can improve the overall capacity and energy density of the battery. The silicon-based material will undergo a large volume expansion during the charging and discharging process, which will squeeze the electrode sheet and the arc region, easily leading to a lack of electrolyte in the electrode sheet and the arc region, and also affecting the cycle stability of the battery. When the mass ratio A of ethyl butyrate and the redundancy width B of the separator meet the above values and relationships, adjusting the mass ratio of the silicon-based material to meet the above conditions, and combining the silicon-based material with the high-kinetic-performance electrolyte provided by the present disclosure can reduce the problem of the silicon-based material expanding too much and squeezing the electrode sheet, leading to a lack of electrolyte in the electrode sheet and the arc region, and also make the electrolyte exist more in the negative electrode sheet and the arc region, effectively solving the problem of a lack of electrolyte in the electrode sheet and the arc region, reducing the problem of lithium precipitation in the electrode sheet and the arc region, and also improving the energy density of the battery.

[0062] In some embodiments, the carbon-based material includes artificial graphite and / or natural graphite. Artificial graphite and natural graphite have good cycle stability, can prolong the cycle life of the battery, and improve the service life of the battery.

[0063] In some embodiments, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, nano-silicon and silicon alloy.

[0064] The technical solutions in the embodiments of the present disclosure will be described clearly and completely below in conjunction with the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative work are within the protection scope of the present disclosure.

[0065] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0066] The present disclosure will be described in detail below in conjunction with specific examples, which are used for understanding rather than limiting the present disclosure.

[0067] The batteries of the examples and comparative examples were prepared according to the following preparation method, and the specific differences are shown in Tables 1-2.

[0068] (1) Preparation of positive electrode sheet

[0069] The positive electrode active material lithium cobaltate (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) was added, and stirring was performed under the action of a vacuum stirrer until the mixed system became a homogeneous flowable positive electrode active paste; the positive electrode active paste was uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil was dried, then rolled, and cut to obtain the desired positive electrode sheet.

[0070] (2) Preparation of negative electrode sheet

[0071] The negative electrode active material artificial graphite, sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, deionized water was added, and a negative electrode active paste was obtained under the action of a vacuum stirrer; the negative electrode active paste was uniformly coated on both surfaces of a copper foil; the coated copper foil was air-dried at room temperature, then transferred to a 80°C oven for drying for 10 h, and then cold-pressed and cut to obtain the negative electrode sheet.

[0072] (3) Preparation of electrolyte

[0073] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the solvent EC / PC / EB / DEC was mixed uniformly according to a mass ratio of 15:15:A:70-A. Then 12wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte was rapidly added, and the specific substances and amounts are shown in Table 1. Subsequently, 2wt% of HTCN and 1wt% of ADN based on the total mass of the electrolyte were added, and 10% FEC and 3% PS were added. After stirring uniformly, the desired electrolyte was obtained after passing the moisture and free acid tests.

[0074] 4) Preparation of lithium ion battery

[0075] After the positive electrode sheet of step (1), the negative electrode sheet of step (2) and the separator were stacked in the order of positive electrode sheet, separator and negative electrode sheet, the cell was obtained by winding. The cell was placed in an outer packaging aluminum foil, and the electrolyte of step (3) was injected into the outer packaging. After vacuum packaging, standing, formation, shaping, sorting and other processes, the separator redundancy width was B, and the OH width was 1.5 mm. The other specific features are shown in Table 1. The lithium ion battery was obtained. The charge and discharge range of the battery of the present disclosure is 3.0-4.5V.

[0076] The lithium ion batteries obtained in the examples and comparative examples were respectively tested for 60℃ storage performance and 25℃ fast charging performance.

[0077] (1) Round arc lithium precipitation test

[0078] The batteries in Table 1 were subjected to charge and discharge cycles at a rate of 2C within the charge and discharge cut-off voltage range at 25℃. After 50T cycles, the batteries were fully charged in a dry room and disassembled. The negative electrode sheet was obtained by disassembly, and whether lithium was precipitated in the round arc area of the sheet crease was observed. The degree of lithium precipitation was divided into four grades: no lithium precipitation, slight lithium precipitation, lithium precipitation and severe lithium precipitation. No lithium precipitation means that no gray or silver lithium is produced in the round arc area of the sheet crease; slight lithium precipitation means that lithium precipitation appears in the form of lines near the edge, head and tail of the sheet, crease, round arc area and tab, showing gray; lithium precipitation means that the lithium precipitation area spreads to the center of the negative electrode sheet on the basis of slight lithium precipitation, also showing gray; severe lithium precipitation means that a large area of lithium precipitation appears on the sheet, and the area of lithium precipitation accounts for more than one-third of the area of the sheet.

[0079] (2) 25℃ cycle performance test

[0080] The battery is charged and discharged at 25℃ in the range of charge-discharge cut-off voltage at a rate of 2C, the discharge capacity of the first week is counted as x1 mAh, and the discharge capacity of the Nth cycle is counted as y1 mAh; the capacity of the Nth week is divided by the capacity of the first week to obtain the cycle capacity retention rate R2 of the Nth week = y1 / x1, and the cycle number of the battery when the cycle capacity retention rate R2 is 80% is recorded. The 25-degree fast-charging cycle performance and the interface whether lithium is precipitated can represent the fast-charging performance of the battery, and the higher the 25-degree fast-charging cycle number is, the better the fast-charging performance is.

[0081] In the example group 1 and the comparative example group 1-4, the mass ratio A of ethyl butyrate and the width B of the separator are changed, and the specific different characteristics are shown in Table 1. In the example group 1-5, the electrolyte solvent EC / PC / EB is mixed uniformly according to the mass ratio of 12.5:12.5:75; in the comparative example 4, no EB is added, and an equivalent amount of propyl butyrate is used to replace EB.

[0082] Table 1

[0083] As can be seen from Table 1, by adjusting the relationship between the mass ratio A of ethyl butyrate in the electrolyte and the width B of the separator, the cycle performance of the battery can be improved and the lithium precipitation can be reduced.

[0084] The example group 2 is carried out with reference to the example 1-1, and the difference is that the recesses are arranged in the circular arc area of the positive electrode sheet and the negative electrode sheet by laser drilling. In the example group 2-1, the example group 2-2, the example group 2-3 and the example group 2-4, the recesses are arranged in the entire area of the circular arc area, and in the example group 2-5, the recesses are arranged only in the middle third of the circular arc area of the positive electrode sheet and the negative electrode sheet. The spacing between the recesses, the width of the recesses and the depth of the recesses are shown in Table 2. The example group 3 is carried out with reference to the example group 2-1, and the difference is that only the width of OH is changed, and the specific difference is shown in Table 2.

[0085] Table 2

[0086] As can be seen from Table 2, the recesses arranged in at least part of the circular arc area of the positive electrode sheet and the negative electrode sheet improve the cycle performance of the battery. The more the holes (the smaller the distance between the recesses), the larger the holes (the width of the recesses multiplied by the depth), and the better the normal temperature cycle performance, but the loss of the energy density of the battery will be caused.

[0087] Example group 4

[0088] The example group 4 is carried out with reference to the example 1-1, and the difference is that the amount of PS added in the electrolyte is changed.

[0089] In the example group 4-1, the content of PS is 0.5wt%;

[0090] In Example 4-2, the content of PS is 5wt%.

[0091] Example 5 group

[0092] Refer to Example 2-1, except that the type of positive active material is changed:

[0093] In Example 5-1, an equivalent amount of ternary material (chemical formula LiNi 0.5 Co 0.2 Mn 0.3 O2) replaces lithium cobaltate, and the voltage range is 3-4.35V;

[0094] In Example 5-2, an equivalent amount of ternary material (chemical formula LiNi 0.5 Co 0.2 Mn 0.3 O2) and lithium cobaltate are mixed in a mass ratio of 1:1 to replace lithium cobaltate, and the voltage range is 3-4.35V.

[0095] Example 6 group

[0096] Refer to Example 2-1, except that the type of negative active material is changed:

[0097] In Example 6-1, artificial graphite and silicon-carbon are mixed to replace artificial graphite, and the mass ratio of silicon-carbon is 5%;

[0098] In Example 6-2, artificial graphite and silicon-carbon are mixed to replace artificial graphite, and the mass ratio of silicon-carbon is 10%.

[0099] The test data of Example 4 group-Example 6 group are shown in Table 3.

[0100] Table 3

[0101] As can be seen from Table 3, in Example 4 group, the content of sulfonic acid additive is related to the cycle performance of the battery. When the amount of sulfonic acid additive is less, the internal resistance of the battery is lower, and the room temperature cycle performance is better, but the high temperature storage will be worse. In Example 5 group, the addition of ternary material in the positive electrode sheet can improve the energy density of the battery. With the increase of the content of ternary material, the energy density of the battery increases, but the cycle performance of the battery decreases slightly. Overall, the addition of ternary material in the positive electrode can improve the electrochemical performance of the battery. In Example 6 group, the addition of silicon-carbon in the negative electrode sheet reduces the problem of lithium precipitation in the sheet and the arc area. In addition, with the increase of the content of silicon-carbon, the energy density of the battery increases, but the cycle performance of the battery decreases slightly. Overall, the addition of silicon-carbon in the negative electrode can improve the electrochemical performance of the battery.

[0102] It should be noted that, as used in this document, the terms "comprises" or "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element. Furthermore, it should be noted that the methods and apparatus of the present embodiments are not limited to the order of execution of the steps recited as the order of execution can vary depending on the implementation. For example, the described methods can be executed in an order different than that described, and / or various steps can be added, omitted, or combined, and / or various steps can be executed at substantially the same time, etc. Also, features described with respect to certain examples can be combined in other examples.

[0103] The foregoing is merely illustrative of the principles of this disclosure and various modifications can be made by those skilled in the art without departing from the scope and spirit of the disclosure.

Claims

1. A battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte includes ethyl butyrate, and the mass percentage of ethyl butyrate based on the total mass of the electrolyte is denoted as A%; the separator width is denoted as B mm; A and B satisfy: A≥10B; The mass percentage of ethyl butyrate A is 5%-70%; The diaphragm width B is 0.5mm-3.5mm.

2. The battery according to claim 1, characterized in that, A and B satisfy: 50B≥A≥15B; Preferably, the mass percentage A of ethyl butyrate is 10%-50%; Preferably, the diaphragm width B is 0.5mm-2mm.

3. The battery according to claim 1 or 2, characterized in that, In the width direction of the battery, the negative electrode extends beyond the positive electrode by 0.5mm to 3mm, preferably 1mm to 2mm.

4. The battery according to any one of claims 1-3, characterized in that, The electrolyte also includes fluoroethylene carbonate; Preferably, the mass percentage of the fluoroethylene carbonate is 1%-20% based on the total mass of the electrolyte.

5. The battery according to any one of claims 1-4, characterized in that, The electrolyte also includes sulfonic acid additives; Preferably, the sulfonic acid additive accounts for 0.5%-5% of the total mass of the electrolyte.

6. The battery according to claim 5, characterized in that, The sulfonic acid additives include at least one of 1,3-propanesulfonyl lactone, 1-propene-1,3-sulfonyl lactone, 5-methyloxathiapentane 2,2-dioxide, 1,3-propenesulfonyl lactone, 2,4-butanesulfonyl lactone, 1,4-butanesulfonyl lactone and their derivatives, more preferably 1,3-propanesulfonyl lactone.

7. The battery according to any one of claims 1-6, characterized in that, The electrolyte also includes nitrile compounds; Preferably, the nitrile compound accounts for 2%-6% of the total mass of the electrolyte.

8. The battery according to claim 7, characterized in that, The nitrile compounds include one or more of 1,3,5-hexanetrionitrile, adiponitrile, succinic anhydride, ethylene glycol bis(propionitrile) ether, tri(3-cyanopropyl) phosphate, glutaronitrile, heptacyanide, octanoic anhydride, glycerol trionitrile, ethoxypentafluorophosphazene, 1,4-dicyano-2-butene, and 1,3,6-hexanetrionitrile.

9. The battery according to any one of claims 1-8, characterized in that, The battery includes a positive electrode sheet, a separator, and a negative electrode sheet that are sequentially stacked and wound together; the positive electrode sheet includes a first flat region and a first arc region; wherein, at least a portion of the first arc region is provided with a plurality of first recesses; the depth of the first recesses is less than the thickness of the positive electrode sheet.

10. The battery according to claim 9, characterized in that, The distance between two adjacent first recesses is 0.5mm-2mm; And / or, the width of the first recess is 50μm-200μm; And / or, the depth of the first recess is 5μm-30μm.

11. The battery according to any one of claims 1-10, characterized in that, The battery includes a positive electrode sheet, a separator, and a negative electrode sheet that are sequentially stacked and wound together; the negative electrode sheet includes a second flat region and a second arc region; wherein, at least a portion of the second arc region is provided with a plurality of second recesses; the depth of the second recesses is less than the thickness of the negative electrode sheet.

12. The battery according to claim 11, characterized in that, The distance between two adjacent second recesses is 0.5mm-2mm; And / or, the width of the second recess is 50μm-200μm; And / or, the depth of the second recess is 5μm-30μm.

13. The battery according to any one of claims 1-12, characterized in that, In the width direction of the battery, the width of the separator is greater than the width of the negative electrode, and the width of the negative electrode is greater than the width of the positive electrode. Preferably, the width of the positive electrode sheet is 20mm-200mm, and / or the thickness of the positive electrode sheet is 20μm-150μm; Preferably, the width of the negative electrode sheet is 20mm-200mm, and / or the thickness of the negative electrode sheet is 20μm-150μm; Preferably, the width of the diaphragm is 20mm-250mm.

14. The battery according to any one of claims 1-13, characterized in that, The positive electrode sheet includes a positive electrode active material, which includes lithium cobalt oxide and / or a ternary material, wherein the chemical formula of the ternary material is Li. a Ni x Co y Mn z M k O2, wherein 0.9≤a≤1.1, 0.5≤x≤0.95, 0<y≤0.2, 0<z≤0.3, 0≤k≤0.05, and M includes at least one of Al, Mg, Ti, Zr, B, P, W and Y.

15. The battery according to any one of claims 1-14, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes a carbon-based material and optionally a silicon-based material; Preferably, the silicon-based material accounts for 0-30% of the mass of the negative electrode active material; Preferably, the silicon-based material includes at least one of silicon-carbon, silicon-oxygen, nano-silicon, and silicon alloy.

Images