A battery

Abstract

The application relates to the technical field of batteries, in particular to a battery. The battery comprises an electrode assembly formed by laminating and winding a positive electrode sheet, a diaphragm and a negative electrode sheet, and an electrolyte containing a nitrile additive. The electrode assembly comprises a flat area and a circular arc area. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer. The positive electrode active layer comprises a cobalt-containing positive electrode material and an oxide electrolyte. The mass content of Al in the cobalt-containing positive electrode material is M, in ppm. The positive electrode active layer is provided with a groove on at least part of the circular arc area. In the winding direction of the positive electrode sheet, the groove comprises a bottom wall and first and second inclined walls connected to the two ends of the bottom wall respectively. The ratio of the average CB value of the circular arc area comprising the groove to that of the flat area is A, and 4900<=M / A<=13700. The content of the nitrile additive in the electrolyte is 0.5%-8%. The battery of the application improves the serious lithium precipitation of the negative electrode and improves the cycle stability and safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] Wound lithium-ion batteries are widely used due to their high energy density. However, at the curved corners of the winding, lithium plating on the negative electrode is prone to occur due to mechanical stress concentration, uneven current density distribution, and extended effective ion transport paths, leading to battery capacity decay and safety risks. To alleviate this problem, existing technologies typically use laser drilling or laser surface scanning in the curved area. However, this technology not only increases manufacturing costs and process cycles, but the grooves formed by laser surface scanning in the curved area are mostly rectangular grooves. The right-angle structure at the groove edge easily becomes a stress concentration point. During battery winding and long-term cycling, the local stress at the right angle of the rectangular groove is amplified sharply, easily leading to problems such as powder shedding from the positive electrode active layer. In addition, although setting grooves on the surface of the positive electrode can alleviate the lithium plating problem of the negative electrode in the curved area to some extent, this also leads to a deeper degree of lithium delithiation of the positive electrode active material at the groove during charging, resulting in lattice distortion and particle breakage, exposing new active surfaces, exacerbating side reactions with the electrolyte, and also accelerating battery failure. Therefore, providing a technical solution that can simultaneously improve lithium plating at the arc of the negative electrode and the high specific capacity of the positive electrode in a wound lithium-ion battery is of great significance for improving battery cycle life and safety. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to propose a battery that, while using arc thinning technology to suppress lithium plating on the negative electrode in the arc region, effectively prevents overcharging damage to the positive electrode in the corresponding region by systematically matching the stability of the positive electrode, the dynamic characteristics of the negative electrode and the CB value distribution, thereby improving the cycle stability and safety of the wound lithium-ion battery.

[0004] To address the issue of a low CB value (area capacity ratio) between the positive and negative electrodes located in the arc region, related technologies often employ lasers to locally thin the positive active layer in this region. However, the grooves formed by laser scanning are mostly rectangular, and the right-angled structure at the groove edges easily becomes stress concentration points. During battery winding and long-term cycling, the local stress amplifies sharply, easily causing problems such as powder shedding from the surface positive active layer, which can then puncture the separator and lead to safety hazards such as short circuits. On the other hand, while locally thinning the positive active layer in the arc region can increase the CB value (area capacity ratio) of the negative to positive electrodes in that area, it can suppress lithium plating on the negative electrode to some extent. However, this also introduces new problems: after thinning the positive active layer in the arc region, the CB value in the arc region is often higher than that in the flat region, resulting in differences in electrochemical behavior between the arc and flat regions. During charging, lithium ions are extracted from the positive electrode and embedded in the negative electrode. Because the CB value is larger in the arc-shaped region, the negative electrode surface capacity in this area has a larger margin relative to the positive electrode surface capacity, meaning the positive electrode capacity is relatively smaller. In the electrochemical system, to ensure that the arc-shaped region and the flat region can pass the same amount of charge, the actual required delithiation depth of the positive electrode in this region is forced to increase, resulting in a higher specific capacity than in the normal region. Excessive delithiation causes lattice contraction in the positive electrode active material, generating significant internal stress. This, in turn, induces microcracks or even breakage within the particles of the positive electrode active material, exposing new active surfaces and exacerbating side reactions with the electrolyte, thus accelerating battery failure. Therefore, while simple thinning technology significantly reduces the risk of lithium plating on the negative electrode, it also carries the risk of positive electrode overload and does not systematically solve the problem of localized failure in wound batteries.

[0005] Based on this, the inventors of this invention have optimized the shape of the groove by designing the sidewalls of the groove as a slope. Simultaneously, improvements have been made in three aspects: CB value design, positive electrode formulation, and electrolyte additives. This avoids severe lithium plating in the negative electrode and overload in the positive electrode, achieving a systematic solution to the localized failure problem of wound lithium-ion batteries. Firstly, the groove with sloped walls eliminates the stress concentration effect caused by the right angle of the rectangular groove in the prior art. The inclined groove walls can better adapt to the differentiated stress fields on the inner and outer sides of the electrode during winding, distributing the stress evenly over a wider area and greatly reducing the risk of microcrack initiation and propagation in the positive electrode active layer due to stress. Furthermore, the positive electrode active layer uses cobalt-based positive electrode materials doped with Al, combined with an inactive oxide electrolyte. The Al element in the cobalt-based positive electrode material can stabilize the oxygen framework through Al-O bonds, suppress harmful phase transitions, and buffer local stress, thus alleviating the problems of particle breakage and structural collapse of cobalt-based positive electrode materials after deep delithiation. At the same time, the oxide electrolyte is incorporated into the positive electrode active layer. The oxide electrolyte has high ionic conductivity and good mechanical strength. After being incorporated into the positive electrode active layer, some oxide electrolyte particles adhere to the surface of the cobalt-based positive electrode material or fill the gaps between active particles, constructing a three-dimensional ion transport network between the particles of the positive electrode active material, reducing interfacial impedance, and making the lithium ion insertion and extraction process inside and at the interface of the positive electrode active material more uniform. Meanwhile, as a rigid or semi-rigid framework material, the oxide electrolyte can play a mechanical buffering role, dispersing and alleviating the volume change stress of the cobalt-based positive electrode material during cycling, and reducing the generation and propagation of microcracks in the particles. The Al content (M value) in cobalt-containing cathode materials reflects the cathode material's ability to resist lattice distortion and mechanical stress. By limiting the ratio of M value to A value (the ratio of CB value in the arc region containing the groove and the straight region) within a certain range, it can be ensured that the increased delithiation driving force of the cathode sheet in the arc region due to the groove design matches the structural strength of the cathode active material itself. This not only improves the lithium plating problem in the arc region negative electrode but also avoids particle cracks in the cathode active material at the groove due to deep delithiation, thus improving structural stability. Finally, nitrile additives are further introduced into the electrolyte. When cracks continue to form, the exposed fresh interface reacts with the nitrile additives, promptly building a stable protective film at the new interface. This hinders direct contact between the electrolyte and the cathode active material, reduces electrolyte side reactions, and further improves the cycle stability and safety of the battery.

[0006] Based on this, the present invention proposes the following technical solution: This invention provides a battery comprising an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode, which are stacked and wound together. The electrode assembly includes a flat region and arcuate regions located at both ends of the flat region. The positive electrode includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector. The positive active layer includes a cobalt-containing positive electrode material and an oxide electrolyte. Based on the total mass of the cobalt-containing positive electrode material, the mass content of Al element is M in ppm, and the chemical formula of the oxide electrolyte is Li. a La b Nb c D d O6F, wherein 1.5≤a≤2.01, 0.33≤b≤0.5, 1.9≤c≤2, 0≤d≤0.1, and D includes at least one of Al, S, Bi, Gd, Nd, Eu, Y, Yb, Ho, Zr, Ti, Ce, Hf, Ta, and W; the surface of the positive electrode active layer located in at least a portion of the arcuate region includes grooves along the winding direction of the positive electrode sheet, the grooves including a first inclined wall, a bottom wall, and a second inclined wall, the first inclined wall and the second inclined wall being respectively connected to the two ends of the bottom wall; the ratio of the average CB value of the arcuate region including the grooves to the average CB value of the straight region is A, and A and M satisfy: 4900≤M / A≤13700; the electrolyte includes nitrile additives, and the content of the nitrile additives is 0.5%-8% based on the total mass of the electrolyte.

[0007] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: (1) The positive electrode active layer includes an aluminum-doped cobalt-containing positive electrode material and an oxide electrolyte. A groove with a first inclined wall and a second inclined wall is provided on the surface of the positive electrode active layer located in at least a part of the arc region. The ratio of M value (Al element content) to A value (the ratio of CB value of the arc region containing the groove and the straight region) is limited to the above range. This not only alleviates the lithium plating problem of the negative electrode at the arc, but also eliminates the stress concentration effect caused by the right angle of the rectangular groove in the prior art. It also ensures that the increased delithiation driving force of the positive electrode in this region matches the structural strength of the positive electrode active material itself, improves the resistance of cobalt-based positive electrode materials to lattice distortion and mechanical stress, alleviates the cracks on the surface of the active particles caused by the increased delithiation degree of the positive electrode active material due to the relatively reduced positive electrode capacity at the groove, and inhibits crack generation and further propagation. This achieves both the improvement of positive electrode structural stability and the suppression of lithium plating at the negative electrode at the arc.

[0008] (2) In this invention, nitrile additives are further introduced into the electrolyte. When microcracks inevitably occur on the surface of the cobalt cathode material during cycling, the nitrile additives can quickly form a film at the fresh interface to prevent the electrolyte and the cathode active material from further contacting and aggravating the side reaction of the electrolyte, thereby further avoiding local battery failure.

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the 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. Attached Figure Description

[0010] Figure 1 The diagram shown is a schematic diagram of the arc region in one embodiment of the present invention.

[0011] Figure 2 The figure shown is a cross-sectional schematic diagram of the positive electrode sheet along the thickness direction in one embodiment of the present invention.

[0012] Figure 3 The image shown is a schematic diagram of the surface of the positive electrode sheet in one embodiment of the present invention.

[0013] Figure 4 The image shown is a schematic diagram of the surface of the positive electrode sheet in one embodiment of the present invention.

[0014] Figure 5 The above is a schematic diagram of the structure of an electrode assembly in one embodiment of the present invention.

[0015] Figure 6 The diagram shown is a schematic representation of the groove structure in one embodiment of the present invention.

[0016] Reference numerals: 1. Positive electrode sheet; 2. Separator; 3. Negative electrode sheet; 10. Positive current collector; 11. Positive active layer; 12. Groove; 121. First inclined wall; 122. Second inclined wall; 123. Bottom wall. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of the present invention. 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 the invention.

[0018] The present invention provides a battery comprising an electrode assembly and an electrolyte. The electrode assembly comprises a positive electrode, a separator, and a negative electrode stacked and wound together. The electrode assembly includes a flat region and arcuate regions located at both ends of the flat region.

[0019] In this invention, the positive electrode sheet includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector; the positive active layer includes a cobalt-containing positive electrode material and an oxide electrolyte, wherein the mass content of Al element is M (in ppm) based on the total mass of the cobalt-containing positive electrode material, and the chemical formula of the oxide electrolyte is Li. a La b Nb c D d O6F, where 1.5≤a≤2.01 (e.g., 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.01, or any two of the above values), 0.33≤b≤0.5 (e.g., 0.33, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, or any two of the above values), 1.9≤c≤2 (e.g., ... The d is 1.9, 1.92, 1.94, 1.96, 1.98, 2 or any two of the above values), 0 ≤ d ≤ 0.1 (e.g., 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1 or any two of the above values), and D includes at least one of Al, S, Bi, Gd, Nd, Eu, Y, Yb, Ho, Zr, Ti, Ce, Hf, Ta and W.

[0020] In this invention, the positive electrode active layer has grooves formed on at least a portion of the arcuate regions. Along the winding direction of the positive electrode sheet, the grooves include a first inclined wall, a bottom wall, and a second inclined wall, with the first and second inclined walls respectively connected to both ends of the bottom wall. The term "at least a portion" means that the grooves can be formed in multiple arcuate regions, or in the first few arcuate regions starting from the beginning of the positive electrode sheet winding, depending on the battery design requirements. Furthermore, the grooves can cover the arcuate regions and extend into the flat regions, or they can partially cover the arcuate regions.

[0021] In one embodiment, the positive electrode active layer, at least partially located on the positive electrode current collector side surface of the arc region, includes the groove.

[0022] In one embodiment, the positive electrode active layer, which is at least partially located on both sides of the positive electrode current collector in the arc region, includes the groove.

[0023] like Figure 1 The diagram shown is a schematic representation of the arc-shaped region in one embodiment of the present invention, which includes a positive electrode 1, a separator 2, and a negative electrode 3. The positive electrode 1 located in the arc-shaped region includes a groove 12. Figure 2The diagram shown is a cross-sectional view of the positive electrode sheet along its thickness direction in one embodiment of the present invention. The positive electrode sheet 1 includes a positive current collector 10 and a positive active layer 11 located on both sides of the positive current collector 10. The positive active layer 11 includes a groove 12, and the groove 12 includes a bottom wall 123 and a first inclined wall 121 and a second inclined wall 122 respectively connecting the two ends of the bottom wall 123. Figure 3 The diagram shown is a schematic representation of the surface of a positive electrode sheet in one embodiment of the present invention. All positive electrode sheets located in the arc region include the groove 12. Figure 4 The diagram shown is a schematic representation of the surface of a positive electrode sheet in one embodiment of the present invention. The positive electrode sheet, partially located in the arc region, includes the groove 12. Figure 5 The above is a schematic diagram of the structure of an electrode assembly in one embodiment of the present invention. The electrode assembly is formed by winding a positive electrode 1, a separator 2 and a negative electrode 3 stacked together. At least one side surface of the positive electrode 1, which is at least partially located in the arc region, includes a groove 12.

[0024] In this invention, the ratio of the average CB value of the arc region including the groove to the average CB value of the straight region is A, and A and M satisfy: 4900≤M / A≤13700, for example, 4900, 5000, 5100, 5200, 5400, 5600, 5800, 6000, 6500, 7000, 7500, 8000, 9000, 10000, 11000, 12000, 13000, 13700 or within any two of the above values.

[0025] In this invention, the CB value has a conventional meaning in the art, referring to the balance ratio of the positive and negative electrode capacities, that is, the excess ratio of the negative electrode capacity relative to the positive electrode capacity. Its calculation formula is: CB value = negative electrode active layer capacity / positive electrode active layer capacity; where the areal capacity of the positive electrode active layer is in mAh / cm². 2 The areal capacity of the negative electrode active layer is measured in mAh / cm². 2 The unit of CB value is 1.

[0026] It is understood that the average CB value of the arc region including the groove refers to the ratio of the areal capacity of the negative electrode active layer located in the arc region to the areal capacity of the positive electrode active layer located in the arc region containing the groove per unit area; the average CB value of the flat region refers to the ratio of the areal capacity of the negative electrode active layer located in the flat region to the areal capacity of the positive electrode active layer per unit area.

[0027] In this invention, the electrolyte includes nitrile additives, and the content of the nitrile additives is 0.5%-8% based on the total mass of the electrolyte, for example, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, or within any two of the above values.

[0028] In this invention, the nitrile additives include at least one of benzonitrile, succinic anionyl (SN), fluorobenzonitrile, adiponitrile (ADN), 1,3,6-hexanetrionitrile (HTCN), glyceryl trionitrile, 1,4-dicyano-2-butene, and ethylene glycol bis(propionitrile) ether.

[0029] By creating grooves with first and second inclined walls on the positive electrode active layer of at least a portion of the arc-shaped region of the wound battery, the thickness of the local active layer is reduced, which can increase the average CB value (i.e., A value) of this region. This results in a relatively higher capacity of the negative electrode sheet located in this arc, alleviating the lithium plating problem of the negative electrode sheet in the arc-shaped region. However, after thinning the positive electrode active layer in the arc-shaped region, the CB value of the arc-shaped region with grooves is often higher than that of the flat region. This causes a difference in electrochemical behavior between the arc-shaped and flat regions. During charging, lithium ions are extracted from the positive electrode and inserted into the negative electrode. Since the CB value of the arc-shaped region with grooves is larger, it means that the negative electrode surface capacity in this region has a larger margin relative to the positive electrode surface capacity, i.e., the positive electrode capacity is relatively smaller. In the electrochemical system, in order to ensure that the arc-shaped region and the flat region can pass the same amount of electricity, the actual lithium extraction depth required by the positive electrode in this region is forced to increase, resulting in its positive electrode specific capacity being higher than that of the normal region. Excessive delithiation can cause lattice contraction in the positive electrode active material, generating significant internal stress. This can induce microcracks or even breakage within the particles of the positive electrode active material, exposing new active surfaces and exacerbating side reactions with the electrolyte, thus accelerating battery failure. Therefore, while simple thinning techniques significantly reduce the risk of lithium plating in the negative electrode, they also carry the risk of overloading the positive electrode.

[0030] Therefore, it is necessary to optimize the cathode material and improve its stability to resist side reactions caused by deep delithiation. This involves incorporating Al (content M) into the cobalt-containing cathode material in the active layer and introducing an oxide electrolyte with high ionic conductivity. On one hand, Al can form high-strength Al-O bonds to stabilize the oxygen framework, suppressing irreversible phase transitions in the cobalt-containing cathode material and buffering local stresses. This improves the structural stability of the cobalt-containing cathode material under deep delithiation conditions at the groove, and suppresses the exposure of new interfaces caused by particle breakage. On the other hand, the oxide electrolyte has high ionic conductivity and good mechanical strength. After incorporating it into the active layer, some oxide electrolyte particles adhere to the surface of the cobalt-containing cathode material or fill the gaps between active particles, constructing a three-dimensional ion transport network between the particles of the active material. This reduces interfacial impedance and makes the lithium-ion insertion / extraction process within and at the interface of the active material more uniform. Simultaneously, as a rigid or semi-rigid framework material, the oxide electrolyte can act as a mechanical buffer, dispersing and alleviating the volume change stress of the cobalt-containing cathode material during cycling, and reducing the generation and propagation of microcracks in the particles. Meanwhile, to ensure that the increased delithiation driving force after setting the groove matches the structural strength of the cathode material itself, the relationship between A and M is further adjusted to achieve a balance between the magnitude of the delithiation driving force and the stability of the cathode. When M / A is too low (e.g., <4900), M is too small and / or A is too large, which means that the structural stability of the cobalt-containing cathode material is insufficient under high delithiation driving force, and the risk of cracking of the cathode active material increases. Although the risk of lithium plating in the arc region with grooves is reduced, the overload of the cathode is aggravated, and the side reactions between the cathode and the electrolyte are aggravated, which is not conducive to improving the cycle stability of the battery. When M / A is too high (e.g., >13700), M is too large and / or A is too small. Although the structure of the cobalt-containing cathode material is stable, the excessive Al will reduce the specific capacity and electronic conductivity of the cathode active material, thereby damaging the energy density and rate performance of the battery. At the same time, if A is too low, it cannot significantly improve the lithium plating problem of the arc region anode sheet.

[0031] In actual cycling processes, long-term mechanical fatigue will inevitably lead to microcracks. Introducing nitrile additives containing cyano groups into the electrolyte allows for the rapid formation of a new protective film when fresh, highly active surfaces are exposed by cracks. This prevents direct contact between the electrolyte and the highly active material, reducing electrolyte side reactions. Nitrile additives can synergistically enhance the interface repair capability (M / A) to further improve cathode stability. Conversely, if only nitrile additives are used and the M / A is too low, the structure of the cathode active material will collapse rapidly, resulting in numerous cracks. The nitrile additives will also be quickly depleted, making it difficult to sustain their interface repair capability.

[0032] In this invention, the values ​​of a, b, c, and d can be determined by conventional testing methods in the art, for example, by the following method: take about 0.1g of oxide electrolyte as a sample, add 10mL of hydrochloric acid, digest on a hot plate at 350℃ for 10min, cool, and then make up to 100ml. After diluting 10 times, take a portion of the solution and analyze it with an ICP spectrometer. After obtaining the corresponding test parameters, a, b, c, and d can be obtained by formula conversion.

[0033] In this invention, the mass content of the nitrile additive in the electrolyte can be obtained by conventional testing methods in the art, such as by gas chromatography or gas chromatography coupled with mass spectrometry.

[0034] In this invention, A is 1.01-1.1, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.08, 1.1 or within the range of any two of the above values.

[0035] Limiting A within the aforementioned range ensures that the groove arrangement effectively improves the average CB value of the arc region, mitigating the lithium plating problem in the arc region negative electrode, while also preventing the risk of positive electrode overload. When A is too small (e.g., <1.01), the groove arrangement has no significant effect on improving the average CB value of the arc region, which is detrimental to improving the lithium plating problem in the arc region negative electrode. When A is too large (e.g., >1.1), it will lead to excessively low local capacity of the positive electrode, causing excessive delithiation of the positive electrode active material, resulting in lattice distortion and irreversible phase transition, which is detrimental to improving the structural stability of the positive electrode.

[0036] In this invention, M is 5000ppm-15000ppm, for example, 5000ppm, 5200ppm, 5400ppm, 5600ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm, 12000ppm, 13000ppm, 14000ppm, 15000ppm, or within any two of the above values.

[0037] Al doping can effectively stabilize the crystal structure of cobalt-containing cathode materials and suppress harmful phase transitions (such as suppressing the H2→H3 phase transition in high-nickel materials and suppressing high-voltage phase transitions in lithium cobalt oxide). When M is too low (e.g., <5000ppm), cobalt-containing cathode materials cannot maintain the structural stability of the crystal under high disengagement power, which is not conducive to further improvement of battery cycle stability; when M is too high (e.g., >15000ppm), excessive Al is not conducive to further improvement of battery energy density and ionic conductivity.

[0038] In this invention, the oxide electrolyte comprises secondary particles, wherein the median particle size Dv50 of the secondary particles is 0.2 μm-1.5 μm, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, or falls within any two of the above values. The particle size Dv90 is 1 μm-8 μm, for example, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or falls within any two of the above values.

[0039] In this invention, at least a portion of the surface of the oxide electrolyte includes a carbon coating layer distributed in a dotted pattern. The term "at least a portion" means that the area of ​​the carbon coating layer projected onto the surface of the oxide electrolyte can be 100% or less than 100%.

[0040] It is understood that the volume distribution particle sizes Dv50 and Dv90 have conventional meanings in the art, referring to the particle size that, when arranged from smallest to largest, accumulates to 50% of the total volume, is Dv50, and the particle size that, when accumulated to 90% of the total volume, is Dv90.

[0041] Adjusting the median particle size Dv50 and particle size Dv90 of the secondary particles in the oxide electrolyte within the aforementioned range can ensure efficient lithium-ion transport and reduce electrolyte side reactions. For example, when the median particle size Dv50 or particle size Dv90 of the secondary particles is too large, the transport path of lithium ions in the oxide electrolyte increases, and the contact area between the oxide electrolyte and the positive electrode active material decreases, making it difficult to effectively adhere to its surface. This is not conducive to further improving lithium-ion transport efficiency and resisting structural collapse of the positive electrode active material during deep delithiation. When the median particle size Dv50 or particle size Dv90 of the secondary particles is too small, the specific surface area of ​​the oxide electrolyte increases, the effective contact area with the electrolyte increases, and electrolyte side reactions such as transition metal dissolution are aggravated, which is not conducive to further improving the stability of the positive electrode.

[0042] In this invention, the average CB value of the arc region including the groove and the average CB value of the flat region can be obtained by conventional testing methods in the art, such as by half-cell testing, including the following steps: (1) Discharge: Discharge the battery with a small current (such as 0.1C or 0.2C) to the cutoff voltage to ensure that the battery is in an empty state; (2) Battery disassembly and electrode sampling: Soak and rinse the taken positive and negative electrodes in dimethyl carbonate (DMC) or diethyl carbonate (DEC) solution to remove residual lithium salts (such as LiPF6) on the surface, repeat 2-3 times, and then place them in a petri dish to air dry or vacuum dry; (3) Use a punching machine to punch several small round pieces on the positive electrode (flat region and arc region containing groove) and the negative electrode (flat region and arc region). ;Weigh the surface density of the current collector (aluminum foil or copper foil), which can be obtained by scraping off the coating or using blank foil. Weigh the total weight of the punched electrode. Coating weight = total electrode weight - current collector weight of the corresponding area. Surface density = coating weight / disc area. (4) Half-cell electrode preparation: The cleaned and dried positive and negative electrode discs are directly used as the working electrodes of the coin cell. The negative half-cell uses the negative electrode as the working electrode and the lithium sheet as the counter electrode / reference electrode. The positive half-cell uses the positive electrode as the working electrode and the lithium sheet as the counter electrode / reference electrode. (5) Substitute the average values ​​of multiple tests into the formula: CB = negative electrode surface density × negative electrode average charging capacity / (positive electrode surface density × positive electrode average discharging capacity negative electrode) to obtain the average CB value of the flat area and the average CB value of the arc area with grooves.

[0043] In this invention, the mass content of Al in the cobalt-containing positive electrode active material can be obtained by conventional testing methods in the art: for example, discharging the battery to 0% SOC (e.g., discharging the battery to 3V), disassembling and removing the positive electrode sheet, soaking it in dimethyl carbonate (DMC) solvent for 12 hours, then rinsing it with DMC solvent to remove the lithium salt attached to the positive electrode sheet, calcining the positive electrode sheet in air at 450 degrees for 2-4 hours, scraping the cobalt-containing positive electrode material off the positive electrode sheet with a ceramic knife, and testing it with an inductively coupled plasma optical emission spectrometer (ICP-OES) to obtain the mass content of Al in the cobalt-containing positive electrode material.

[0044] In this invention, the median particle size Dv50 and particle size Dv90 of the secondary particles of the oxide electrolyte can be obtained by conventional testing methods in the art, such as by a laser particle size analyzer.

[0045] In this invention, the first inclined wall and the bottom wall form a first included angle α1, 90°<α1≤150°, for example 91°, 95°, 100°, 105°, 110°, 115°, 120°, 130°, 140°, 150° or within any two of the above values.

[0046] In this invention, a second included angle α2 is formed between the second inclined wall and the bottom wall, where 90° < α2 ≤ 150°, for example, 91°, 95°, 100°, 105°, 110°, 115°, 120°, 130°, 140°, 150° or within any two of the above values.

[0047] In one embodiment, 95°≤α1≤125°.

[0048] In one embodiment, 95°≤α2≤125°.

[0049] In this invention, the slope of the first inclined wall is k1, and |k1| is 0.55-20, for example, 0.55, 0.6, 0.8, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20 or within any two of the above values.

[0050] In this invention, the slope of the second inclined wall is k2, and |k2| is 0.55-20, for example, 0.55, 0.6, 0.8, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20 or within any two of the above values.

[0051] In one embodiment, |k1| is 1-12.

[0052] In one embodiment, |k2| is 1-12.

[0053] When α1, α2, k1, and k2 are adjusted within the above range, the groove shape and the positive electrode load in the groove region can be adjusted, the average CB value of the arc region can be increased, and the lithium plating problem of the negative electrode in the arc region can be improved. When α1 and / or α2 are close to 90° (or, |k1| and / or |k2| > 20), the first and / or second inclined walls are nearly perpendicular to the bottom wall, which easily leads to stress concentration at the edge of the groove. When the battery expands in volume during charging and discharging, the top edge of the first / second inclined wall is sharp, posing a risk of puncturing the separator, which is not conducive to improving battery safety performance. When α1 and / or α2 are greater than 135° (or, |k1| and / or |k2| < 0.55), the first and / or second inclined walls are too gentle. In order to achieve a certain groove depth, the projection size of the first and / or second inclined walls of the groove in the positive electrode winding direction increases, which aggravates the positive electrode overload and the side reaction between the positive electrode and the electrolyte, which is not conducive to improving the battery cycle stability. Conversely, if a certain groove depth cannot be achieved, it is not conducive to improving the arc lithium plating.

[0054] In this invention, the groove can be obtained in a manner conventional in the art, for example, by controlling the coating amount of the positive electrode active slurry in a portion of the arc region. To achieve precise control of the groove's geometric parameters (e.g., k1, k2, h, and L), this can be achieved by adjusting coating process parameters, such as controlling the local coating amount through a coating valve assembly and / or adjusting the rheological parameters (including viscosity and thixotropy) of the coating slurry and / or optimizing the coating speed.

[0055] In this invention, k1 and k2 can be obtained by conventional testing methods in the art, for example, by the following method: discharging the battery to 0% SOC, disassembling and removing the positive electrode sheet, obtaining the contour line of the first inclined wall in the scanning electron microscope image of the cross-section of the positive electrode sheet along the length direction of the positive electrode sheet, sampling the contour line at equal intervals with a fixed spacing of 30 μm along the length direction of the positive electrode sheet, and obtaining a series of sampling points in sequence; taking two adjacent sampling points as endpoints, forming a series of continuous equivalent line segments, calculating the slope of each equivalent line segment, and recording the arithmetic mean of the slopes of all equivalent line segments as the slope k1.

[0056] In this invention, α1 and α2 can be obtained by conventional testing methods in the art, for example, by discharging the battery to 0% SOC, disassembling and removing the positive electrode, obtaining the contour lines of the first inclined wall and the bottom wall in the scanning electron microscope image of the cross-section of the positive electrode along the length direction of the positive electrode, and drawing intersecting straight lines along the contour lines, and measuring the size of the angle formed, which is recorded as α1. The testing method for α2 is the same as that for α1.

[0057] In this invention, along the winding direction of the positive electrode sheet, the size of the orthographic projection of the first inclined wall on the surface of the positive electrode active layer is L1, where L1 is 0.1μm-10μm, for example, 0.1μm, 0.3μm, 0.5μm, 0.6μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 8μm, 10μm, or within any two of the above values.

[0058] In this invention, along the winding direction of the positive electrode sheet, the size of the orthographic projection of the second inclined wall on the surface of the positive electrode active layer is L3, where L3 is 0.1μm-10μm, for example, 0.1μm, 0.3μm, 0.5μm, 0.6μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 8μm, 10μm, or within any two of the above values.

[0059] In this invention, along the winding direction of the positive electrode sheet, the size of the orthographic projection of the bottom wall onto the surface of the positive electrode active layer is L2, which is 1mm-10mm, for example, 1mm, 1.5mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or within any two of the above values.

[0060] In this invention, along the winding direction of the positive electrode sheet, the size of the orthogonal projection of the groove on the surface of the positive electrode active layer is L, which is 5mm-20mm, for example, 5mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm or within any two of the above values.

[0061] The grooves must have sufficient dimensions in the positive electrode winding direction to ensure that the groove size can cover the arc area. When L is too low (e.g., <5mm), the lithium plating problem of the negative electrode in the arc area cannot be effectively improved. When L is too large (e.g., >20mm), the capacity loss of the positive electrode is large, the CB value in this area is too large, the positive electrode overload is aggravated, and the side reactions between the positive electrode and the electrolyte increase, which is not conducive to improving the cycle stability of the battery.

[0062] In this invention, the depth of the groove is h, which is 2μm-20μm, for example, 2μm, 3μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, or within any two of the above values. The depth of the groove has a conventional meaning in the art, referring to the vertical distance from the end of the first inclined wall and / or the second inclined wall away from the bottom wall to the bottom wall.

[0063] When h is too low (e.g., <2μm), the lithium plating problem of the negative electrode in the arc region cannot be effectively improved, which is not conducive to improving the cycle stability of the battery; when h is too large (e.g., >20μm), the excessive setting of the groove will lead to excessive loss of positive electrode active material, local capacity imbalance of the positive electrode, excessive increase of CB value in the arc region, and aggravation of positive electrode overload, which is not conducive to further improvement of battery cycle stability.

[0064] like Figure 6 The diagram shows a schematic of the groove structure in one embodiment of the present invention. The first included angle formed by the first inclined wall 121 and the bottom wall 123 is α1, and the second included angle formed by the second inclined wall 122 and the bottom wall 123 is α2. The depth of the groove 12 in the thickness direction of the positive electrode sheet is h. In the winding direction of the positive electrode sheet, the dimensions of the orthographic projections of the first inclined wall 121, the second inclined wall 122, the bottom wall 123 and the groove 12 on the surface of the positive electrode active layer 11 are L1, L3, L2 and L, respectively.

[0065] In this invention, L2 and L can be obtained by conventional testing methods in the art, such as the following method: discharge the battery to 0% SOC, disassemble and remove the positive electrode, and measure L using a height gauge; obtain the outlines of the first inclined wall, the second inclined wall and the bottom wall in the scanning electron microscope image of the cross section of the positive electrode perpendicular to the width direction of the positive electrode, and measure the length of the bottom wall outline using image analysis software, which is L2.

[0066] In this invention, h can be obtained by conventional testing methods in the art, for example by discharging the battery to 0% SOC, disassembling and removing the positive electrode, obtaining the outline of the first inclined wall and the bottom wall in the scanning electron microscope image of the cross section of the positive electrode perpendicular to the width direction of the positive electrode, and drawing a vertical line of the bottom wall from the highest point of the first inclined wall and measuring the length of the vertical line, which is h.

[0067] In this invention, the positive electrode sheet further includes a non-groove region adjacent to the groove. The areal density of the positive electrode active layer located in the groove region is ρ1, and the areal density of the positive electrode active layer located in the non-groove region is ρ2. ρ1 and ρ2 satisfy the following: ρ1 / ρ2 is 60%-90%, for example, 60%, 62%, 64%, 66%, 68%, 70%, 75%, 80%, 85%, 90%, or within any two of the above values.

[0068] When ρ1 / ρ2 is too large (e.g., >90%), the average CB value at the arc is not sufficiently improved, which is not conducive to further improvement of lithium plating on the negative electrode in the arc region; when ρ1 / ρ2 is too small (e.g., <60%), the local capacity loss of the positive electrode is large, and the average CB value at the arc increases too much, leading to overload of the positive electrode and aggravation of electrolyte side reactions, which is not conducive to improving battery cycle performance.

[0069] In this invention, the positive electrode sheet further includes a non-groove region adjacent to the groove. The compaction density of the positive electrode active layer located in the groove is g1, and the compaction density of the positive electrode active layer located in the non-groove region is g2. g1 and g2 satisfy the following: g1 / g2 is 60%-98%, for example, 60%, 62%, 64%, 66%, 68%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or within any two of the above values.

[0070] When g1 / g2 is too large (e.g., >98%), the improvement in the average CB value at the arc is insufficient, which is not conducive to further improvement of lithium plating on the negative electrode in the arc region; when g1 / g2 is too small (e.g., <60%), the local capacity loss of the positive electrode is large, and the average CB value at the arc increases too much, leading to overload of the positive electrode and aggravation of electrolyte side reactions, which is not conducive to improving battery cycle performance.

[0071] like Figure 3-4The diagram shown is a schematic representation of the surface of a positive electrode sheet in one embodiment of the present invention. The positive electrode sheet includes the groove 12 and a non-groove area 14 disposed adjacent to the groove 12.

[0072] In this invention, g1 and ρ1 can be obtained by conventional testing methods in the art. For example, after discharging the battery to 0% SOC, the positive electrode sheet is disassembled and removed. After soaking in DMC solvent for 12 hours, it is rinsed with DMC solvent to remove the lithium salt adhering to the positive electrode sheet. Then, the residue on the surface of the positive electrode sheet is washed off with deionized water and dried. At least 20 sites are selected on the positive electrode sheet located in the groove, and the thickness of the positive electrode sheet at each site is measured using a micrometer. The average value is taken as the average thickness of the positive electrode sheet including the groove (in μm). The positive electrode sheet including the groove is punched into a disc with a diameter of 44.3 mm using a punching die. Ten discs are taken, and the mass of each disc is weighed. The average value m (in mg) is taken. The areal density ρ1 is calculated as ρ1 = (m - m1) × 100 / 1540.25, where m1 is the mass of the positive current collector in the disc (in mg), and the areal density is in mg / cm³. 2 The compaction density is calculated using the areal density ρ1 and the average thickness of the positive electrode sheet including the groove, as follows: Compaction density g1 of the positive electrode active layer located in the groove = ρ1 × 20 / (Average thickness of the positive electrode sheet including the groove - Thickness of the positive electrode current collector), where the unit of the thickness of the positive electrode current collector is μm. The tests for g2 and ρ2 can be performed using the same methods as for g1 and ρ1, except that the positive electrode sheet located in the non-groove area is used as the test sample.

[0073] In this invention, the size of the groove is less than or equal to the width of the positive electrode sheet along the width direction of the positive electrode sheet.

[0074] In this invention, along the winding direction of the positive electrode sheet, the orthographic projection of the groove and the orthographic projection of the arc region at least partially overlap. "At least partially overlap" means that the orthographic projection of the groove can completely overlap with the orthographic projection of the arc region, the orthographic projection of the groove can be within the orthographic projection area of ​​the arc region, or the orthographic projection of the groove can extend beyond the orthographic projection of the arc region.

[0075] In one embodiment, along the winding direction of the positive electrode sheet, the size of the arc region is L', and the size of the orthographic projection of the groove on the surface of the positive electrode active layer is L, where L and L' satisfy: L≥L'.

[0076] In one embodiment, the size of the groove is equal to the size of the arc region along the width direction of the positive electrode sheet.

[0077] At least one arc region includes a groove, and the groove can completely cover the arc region in the winding direction of the positive electrode sheet. The positive electrode sheet can also extend to a certain extent to a part of the flat region. The groove is provided through the width direction of the positive electrode sheet. At the same time, the groove on the arc region is provided continuously to ensure that stress release and the increase of average CB value are continuous and uniform in the entire axial direction of the arc region, and to avoid the generation of new stress or lithium plating concentration points due to the interruption of the groove.

[0078] In this invention, the outer surface of the cobalt-containing cathode material includes a coating layer, which at least partially covers the cobalt-containing cathode material. The phrase "at least partially covers" means that the projected area of ​​the coating layer can be 100% or less than 100% of the projected area of ​​the cobalt-containing cathode material.

[0079] In one embodiment, the coating layer is a dotted coating.

[0080] In this invention, the coating layer includes at least one of the elements Ti, Zr, Y, La, Li, Al, Ba, Co, Cr, Mg, Sn, Sr and Ti.

[0081] In this invention, the thickness of the coating layer is 10nm-500nm, for example, 10nm, 15nm, 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 80nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, or within any two of the above values.

[0082] In one embodiment, the cobalt-containing cathode material includes lithium cobalt oxide, which includes at least one of the elements Al, Mg, Ti, Zr, Y, La, F, W, B, Nb, Sr, Ni, Mn and P.

[0083] In yet another embodiment, the lithium cobalt oxide comprises element Al.

[0084] The surface coating of cobalt-containing cathode materials creates a stable and controllable buffer layer between the highly active electrode material and the corrosive electrolyte. This stable coating (e.g., including spinel and / or rock salt phase structures) provides three-dimensional Li +The diffusion path forms a continuous ion transport network, improving the overall ionic conductivity of the positive electrode active material. On the other hand, it can anchor surface oxygen, increasing structural stability under high pressure, suppressing phase transitions and oxygen release in cobalt-containing positive electrode materials, absorbing volumetric strain during charging and discharging, thereby suppressing particle crack propagation under high delithiation driving force, reducing electrolyte side reactions, and improving the structural stability of cobalt-containing positive electrode materials. When the coating thickness is too low (e.g., <10nm), the coating layer is insufficient to stabilize the positive electrode and suppress electrolyte side reactions. The possibility of structural collapse of the cobalt-containing positive electrode material located in the groove under deep delithiation increases, which is detrimental to improving battery cycle stability. When the coating thickness is too high (e.g., >500nm), the transport distance of lithium ions in the cobalt-containing positive electrode material increases, which is detrimental to further improvement of battery rate performance.

[0085] In this invention, the thickness of the coating layer can be obtained by conventional testing methods in the art, such as by transmission electron microscopy (TEM). Specifically, after polishing the cross-section of the cobalt-containing cathode material with an argon ion mill, at least 5 cobalt-containing cathode materials are selected in the TEM image, and the thickness of the coating layer is measured at 5 different points on the cross-section of each cobalt-containing cathode material, and the average value is taken.

[0086] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector. The negative electrode active layer includes silicon-carbon composite material and / or graphite. The OI value of the negative electrode sheet is C, and A and C satisfy: 5.3≤A×C≤85, for example, 5.3, 5.5, 6, 7, 8, 9, 10, 12, 14, 16, 17, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 85 or within any two of the above values.

[0087] In this invention, C satisfies: 5≤C≤80, for example, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80 or within any two of the above values.

[0088] In this invention, the OI value of the negative electrode sheet can be adjusted in a manner conventional in the art, such as by adjusting the compaction density of the negative electrode active layer, the proportion of graphite in the negative electrode active material, or by using a magnetic device.

[0089] Adjusting C within a suitable range can regulate graphite orientation, thereby achieving controllable lithium-ion transport. This makes the C-axis of the graphite crystals in the negative electrode more parallel to the negative electrode current collector, raising the energy barrier of lithium-ion transport kinetics, reducing the lithium-ion transport rate in the grooved arc region, and slowing down localized deep lithium delithiation in the arc region of the positive electrode. By limiting A... Within the aforementioned range, C can synergistically regulate the delithiation driving force of the positive electrode in the arc region and the lithium insertion efficiency of the negative electrode, thereby preventing local overcharging of the positive electrode. When A×C is too large (e.g., >85), A and / or C are too large, the CB value of the arc region with grooves is too large, the orientation of graphite in the negative electrode tends to be perpendicular to the current collector, the lithium ion insertion path is short, the energy barrier is low, and the insertion kinetics are fast, which exacerbates the local overload of the positive electrode active material at the groove. When A×C is too low (e.g., <5.3), A or C is too small, the CB value of the arc region with grooves is not sufficiently improved, and the lithium plating problem of the negative electrode in the arc region cannot be effectively improved. At the same time, the orientation of graphite in the negative electrode tends to be parallel to the current collector, the lithium ion transport energy barrier is high, which is not conducive to further improvement of the battery rate performance.

[0090] In this invention, C can be obtained by conventional testing methods in the art, such as by X-ray powder diffraction. The specific method is as follows: After discharging the battery to 0% SOC, disassemble and remove the negative electrode sheet. Soak it in dimethyl carbonate (DMC) solvent for 12 hours, then rinse it with DMC to remove the lithium salt attached to the negative electrode sheet. After drying, test it with an X-ray powder diffraction instrument (such as Shimadzu XRD-6100 X-ray diffraction instrument). The diffraction peak appearing at 2θ=54-55° in the obtained diffraction pattern is the (004) peak of graphite, and the intensity is recorded as I004. The diffraction peak appearing at 2θ=77-78° is the (110) peak of graphite, and the intensity is recorded as I110. The OI value of the negative electrode sheet is I004 / I110.

[0091] In this invention, the sphericity of the silicon-carbon composite material is greater than 0.9, for example, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or within any two of the above values.

[0092] In this invention, the particle size Dv10, median particle size Dv50, and particle size Dv90 of the silicon-carbon composite material satisfy the following: 0.2≤(Dv90-Dv10) / Dv50≤0.7, for example, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.4, 0.45, 0.5, 0.55, 0.6, 0.7, or fall within the range of any two of the above values.

[0093] In this invention, the particle size Dv10 of the silicon-carbon composite material is 4μm-9.5μm, for example, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, or within any two of the above values. The median particle size Dv50 is 5.5μm-12.5μm, for example, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 11μm, 12μm, 12.5μm, or within any two of the above values. The particle size Dv90 is 6.5μm-13.5μm, for example, 6.5μm, 6.6μm, 6.8μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 12μm, 13μm, 13.5μm or within any two of the above values.

[0094] In one embodiment, the silicon-carbon composite material has a particle size Dv10 of 5 μm-8.5 μm, a median particle size Dv50 of 6.5 μm-10 μm, and a particle size Dv90 of 7.5 μm-12.5 μm.

[0095] Limiting the sphericity, particle size concentration, and volume distribution of silicon-carbon composite materials within appropriate ranges ensures uniform lithium insertion / extraction paths in the negative electrode, preventing excessively short lithium-ion transport paths and abrupt lithium depletion at the positive electrode, which could damage the crystal structure of cobalt-containing positive electrode materials. When the sphericity of the silicon-carbon composite material is too small (e.g., less than 0.9), the length of the lithium-ion insertion path varies in different directions, potentially causing abrupt lithium depletion in the positive electrode when the average CB value is large in the arc region. Higher particle size concentration in the silicon-carbon composite material improves the battery's high-temperature cycling and rate performance. A large (Dv90-Dv10) / Dv50 ratio (e.g., greater than 0.7) indicates the presence of extremely large and extremely small particles. Small-sized silicon-carbon composite materials have a very large specific surface area, increasing the contact area with the electrolyte and exacerbating electrolyte side reactions at the negative electrode. Conversely, large-sized silicon-carbon composite materials increase the diffusion distance of lithium ions within them, which is detrimental to improving battery kinetic performance. When (Dv90-Dv10) / Dv50 is small (e.g., <0.2), the particle size distribution of the silicon-carbon composite material is too narrow, which leads to a decrease in the compaction density of the negative electrode and a decrease in the proportion of active material per unit volume, which is not conducive to improving the energy density of the battery.

[0096] In this invention, the sphericity of the silicon-carbon composite material can be tested using methods conventional in the art.

[0097] In this invention, the particle size Dv10, median particle size Dv50, and particle size Dv90 of the silicon-carbon composite material can be obtained by conventional testing methods in the art.

[0098] In this invention, the diaphragm includes a substrate layer having a porous structure. In a pore size distribution diagram obtained by arranging the pore sizes of the substrate layer from largest to smallest, the pore size corresponding to a cumulative percentage of 10% of the porous structures is D1, and the pore size corresponding to a cumulative percentage of 90% of the porous structures is D2. D1 and D2 satisfy: 1.05≤D1 / D2≤3, for example, 1.05, 1.06, 1.08, 1.1, 1.2, 1.3, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, or within any two of the above values.

[0099] Adjusting D1 / D2 within the above range can provide a uniform transport path for lithium ions at the electrode-separator interface, optimize the efficiency and uniformity of electrolyte wetting of the electrode, and avoid local liquid shortages caused by uneven and insufficient electrolyte filling in the arc area due to small gaps or expansion stress in the arc area, which is not conducive to lithium ion transport, resulting in excessively high local lithium concentration, and is not conducive to improving the lithium deposition problem in the arc area.

[0100] In the pore size distribution diagram obtained by arranging the pores of the substrate layer from largest to smallest, the pore size D1 corresponding to a cumulative percentage of 10% refers to the pore size within any 10mm × 10mm area on the substrate layer surface, based on the total number of all pores, arranged from largest to smallest, where the cumulative percentage of pores is 10%. This is measured using a mercury porosimeter from PMI. Specifically, a substrate layer with an arbitrary area of ​​10mm × 10mm was cut, vacuum dried, and then used. Based on the Laplace equation r = γ / ( (γ is the surface tension of mercury, which is 0.485 N / m at room temperature, and P is the mercury injection pressure) Measure the pore radius r, calculate the corresponding pore size, count the number of pores with different pore sizes and arrange them in ascending order to draw a pore size-number distribution diagram. The pore size corresponding to the cumulative percentage of pores is 10% is D1, and the unit is nm.

[0101] In this invention, in the pore size distribution diagram obtained by arranging the pore sizes of the substrate layer from largest to smallest, the pore size D2 corresponding to a cumulative pore number ratio of 90% refers to the pore size within any 10mm × 10mm area on the surface of the substrate layer, based on the total number of all pores, arranged from largest to smallest, where the cumulative pore number ratio is 90%. This is measured using a mercury porosimeter from PMI. Specifically, a substrate layer with an arbitrary area of ​​10mm × 10mm is cut, vacuum dried, and then used. Based on the Laplace equation r = γ / ( (γ is the surface tension of mercury, which is 0.485 N / m at room temperature, and P is the mercury injection pressure) Measure the pore radius r, calculate the corresponding pore size, count the number of pores with different pore sizes and draw a pore size-number distribution diagram according to the pore size from smallest to largest. The pore size corresponding to the cumulative percentage of the number of pores is 90% is D2, and the unit is nm.

[0102] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0103] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0104] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0105] The following examples illustrate the battery of the present invention.

[0106] Example 1: (1) Preparation of the positive electrode: Lithium cobalt oxide (with a 300 nm thick titanium oxide coating and an Al content M of 9632 ppm) and oxide electrolyte Li 1.5 La 0.5 Nb₂O₆F (with a dotted carbon coating, secondary particle Dv₅₀ of 1.2 μm, and secondary particle Dv₉₀ of 5.7 μm), a conductive agent (conductive carbon black and carbon nanotubes mixed at a mass ratio of 1:1), and polyvinylidene fluoride (PVDF) were placed in N-methylpyrrolidone (NMP) at a mass ratio of 97:0.2:2:0.8 and stirred evenly to obtain a positive electrode active slurry. This positive electrode active slurry was then uniformly coated onto both sides of an aluminum foil to obtain... A positive electrode active layer is formed, and multiple grooves (k1 = 1.6, k2 = 1.6, α1 = 122°, α2 = 122°, h = 8μm, L = 10mm) are formed on both sides of the positive electrode sheet by reducing the loading of positive electrode active material in part of the arc area. The positive electrode sheet is then obtained by drying, rolling and slitting. The entire positive electrode active layer is removed in a specific area to form a positive electrode tab groove, and the positive electrode tab is welded into the positive electrode tab groove.

[0107] (2) Preparation of the negative electrode: A negative electrode active material (50% silicon carbide + 50% artificial graphite), conductive carbon black, PVDF, and sodium carboxymethyl cellulose were mixed in deionized water at a mass ratio of 97.2:0.25:2.1:0.45 and stirred until homogeneous to obtain a negative electrode active slurry. This slurry was then uniformly coated onto both sides of a copper foil to obtain a negative electrode active layer. The layer was subsequently dried, rolled, and slit, then cleaned and sheet-formed to obtain a negative electrode sheet (OI value C = 32), with corresponding negative electrode tab grooves and tabs. The silicon carbide material had a particle size Dv10 of 9.5 μm, a particle size Dv50 of 10.3 μm, a particle size Dv90 of 12.6 μm, and a (Dv90-Dv10) / Dv50 ratio of 0.3.

[0108] (3) Diaphragm: The diaphragm uses 6μm PE as the substrate layer. One side of the substrate layer has a 1.5μm thick boehm coating. Both sides of the boehm coating are covered with a 1μm thick PVDF adhesive layer. The D1 / D2 ratio is 2.1.

[0109] (4) Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (EMC) were mixed in a mass ratio of 1:1:1 to obtain a base solvent. Based on the total weight of the electrolyte, 3% of 1,3-propanesulfonyl lactone (PS), 12% of fluoroethylene carbonate (FEC), 2% of nitrile additives (composed of SN:AND:HTCN in a mass ratio of 1:1:3) and 1M of LiPF6 were added to the solvent and mixed thoroughly to obtain the electrolyte.

[0110] (5) Battery fabrication: After the above-mentioned cut positive electrode sheet, separator and negative electrode sheet are stacked, they are wound into a wound electrode assembly. Then, after encapsulation, injection of the electrolyte prepared in step (4), formation and secondary sealing, the battery is obtained.

[0111] At this point, A is 1.053, M / A is 9147, and A×C is 33.7.

[0112] Example 2: (1) Preparation of the positive electrode: Based on Example 1, the difference lies in the rheological parameters of the positive electrode active slurry. In this case, lithium cobalt oxide has a titanium oxide coating layer with a thickness of 12 nm, M is 5024 ppm, and the oxide electrolyte Li 1.5 La 0.5 The secondary particles in Nb₂O₆F have a Dv₅₀ of 0.5 μm and a Dv₹₀ of 1.3 μm; k₁ is 2.14, k₂ is 2.14, α₁ is 115°, and α₂ is 115°.

[0113] (2) Preparation of the negative electrode: Based on Example 1, the difference is that the compaction density of the silicon-carbon material and the negative electrode active layer is different. In this case, the particle size of the silicon-carbon material is Dv10 of 5.3 μm, Dv50 of 5.7 μm, Dv90 of 6.5 μm, (Dv90-Dv10) / Dv50 of 0.21, and C of 5.3.

[0114] (3) Diaphragm: Based on Example 1, the only difference is that the substrate layer of the diaphragm is different, and in this case, D1 / D2 is 1.08.

[0115] (4) Preparation of electrolyte: Based on Example 1, the difference is that the content of nitrile additives is 0.5%, and the nitrile additives are composed of SN:AND:HTCN in a mass ratio of 2:1:2.

[0116] At this point, A is 1.012, M / A is 4964, and A×C is 5.36.

[0117] Example 3: (1) Preparation of the positive electrode: Based on Example 1, the difference lies in the rheological parameters of the positive electrode active slurry. In this case, lithium cobalt oxide has a titanium oxide coating layer with a thickness of 490 nm, M is 9964 ppm, and the oxide electrolyte Li 1.5 La 0.5 The secondary particles in Nb₂O₆F have a Dv₅₀ of 1.5 μm and a Dv₹₀ of 7.9 μm; k₁ is 11.43, k₂ is 11.43, α₁ is 95°, and α₂ is 95°.

[0118] (2) Preparation of the negative electrode: Based on Example 1, the difference is that the compaction density of the silicon-carbon material and the negative electrode active layer are different. In this case, the particle size of the silicon-carbon material is Dv10 of 4.4 μm, Dv50 of 12.5 μm, Dv90 of 13.2 μm, (Dv90-Dv10) / Dv50 of 0.7, and C of 77.

[0119] (3) Diaphragm: Based on Example 1, the only difference is that the substrate layer of the diaphragm is different, and in this case, D1 / D2 is 2.9.

[0120] (4) Preparation of electrolyte: Based on Example 1, the difference is that the content of nitrile additives is 8.0%, and the nitrile additives are composed of SN:AND:HTCN in a mass ratio of 1:2:2.

[0121] At this point, A is 1.097, M / A is 9083, and A×C is 84.47.

[0122] The specific settings for Examples 4-6 and Comparative Examples 1-5 are shown in Tables 1 and 2.

[0123] Table 1: Table 2: in," "" indicates that the data is the same as or similar to the referenced embodiment; " / " indicates that the data does not exist.

[0124] In the above embodiments, g1 / g2 are both in the range of 60%-98%, and ρ1 / ρ2 are both in the range of 60%-90%.

[0125] Test example: (1) Cyclic performance test: The batteries obtained in the embodiments and comparative examples of this invention were placed in a constant temperature chamber at 25°C for 2 hours, then charged at a constant current of 3C to 4.2V, then charged at a constant current and constant voltage of 2.5C to 4.25V, then charged at a constant current and constant voltage of 2C to 4.48V, and finally charged at 0.05C. The batteries were then placed in a constant temperature chamber for 10 minutes. Afterwards, they were discharged at 0.7C to 3.0V. This cycle was repeated 500 times. The initial discharge capacity and the discharge capacity after 500 cycles were recorded, and the cycle capacity retention rate of the batteries was calculated. The test results are recorded in Table 3.

[0126] (2) Circular arc lithium plating test: After the batteries obtained in the embodiments and comparative examples of the present invention were cycled for 500T according to the cycling regime described in (1), they were fully charged and disassembled to observe the lithium deposition at the arc of the negative electrode sheet. Slight lithium deposition was defined as only small dots or only slight gray lithium deposition; obvious silver lithium deposition connected in strips was defined as lithium deposition; severe lithium deposition was defined as lithium deposition not only at the arc but also around the arc, i.e., lithium deposition spreading from the arc area to the periphery; and no lithium deposition was defined as only golden negative electrode powder at the arc of the negative electrode sheet and only white in the corresponding separator area. The test results are recorded in Table 3.

[0127] Table 3: As can be seen from Table 3, the battery prepared by the present invention significantly improves the lithium deposition problem in the arc region compared with the comparative example, and the battery also has good cycle stability.

[0128] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode that are stacked and wound together. The electrode assembly includes a flat region and arc regions located at both ends of the flat region. The positive electrode includes a positive current collector and a positive active layer located on at least one side of the surface of the positive current collector; the positive active layer includes a cobalt-containing positive electrode material and an oxide electrolyte, wherein the mass content of Al element is M (in ppm) based on the total mass of the cobalt-containing positive electrode material, and the chemical formula of the oxide electrolyte is Li. a La b Nb c D d O6F, wherein 1.5≤a≤2.01, 0.33≤b≤0.5, 1.9≤c≤2, 0≤d≤0.1, and D includes at least one of Al, S, Bi, Gd, Nd, Eu, Y, Yb, Ho, Zr, Ti, Ce, Hf, Ta and W; The positive electrode active layer has a groove formed on at least a portion of the arc region along the winding direction of the positive electrode sheet. The groove includes a first inclined wall, a bottom wall, and a second inclined wall, with the first inclined wall and the second inclined wall respectively connected to both ends of the bottom wall. The ratio of the average CB value of the arc region including the groove to the average CB value of the straight region is A, and A and M satisfy: 4900≤M / A≤13700; The electrolyte includes nitrile additives, and the content of the nitrile additives is 0.5%-8% based on the total mass of the electrolyte.

2. The battery according to claim 1, wherein, A is 1.01-1.1; And / or, M is 5000ppm-15000ppm; And / or, the oxide electrolyte comprises secondary particles, wherein the median particle size Dv50 of the secondary particles is 0.2 μm-1.5 μm and the particle size Dv90 is 1 μm-8 μm; And / or, at least a portion of the surface of the oxide electrolyte includes a carbon coating layer distributed in a dotted pattern; And / or, the nitrile additives include at least one of benzonitrile, succinic anionyl, fluorobenzonitrile, adiponitrile, 1,3,6-hexanetrionitrile, glyceryltrionitrile, 1,4-dicyano-2-butene, and ethylene glycol bis(propionitrile) ether.

3. The battery according to claim 1 or 2, wherein, The first inclined wall and the bottom wall form a first included angle α1, where 90° < α1 ≤ 150°; And / or, a second included angle α2 is formed between the second inclined wall and the bottom wall, where 90° < α2 ≤ 150°; Preferably, the slope of the first inclined wall is k1, and |k1| is 0.55-20; Preferably, the slope of the second inclined wall is k2, and |k2| is 0.55-20.

4. The battery according to claim 1 or 2, wherein, Along the winding direction of the positive electrode sheet, the size of the orthographic projection of the groove on the surface of the positive electrode active layer is L, where L is 5mm-20mm; More preferably, the depth of the groove is h, where h is 2μm-20μm.

5. The battery according to claim 1 or 2, wherein, The positive electrode sheet also includes a non-groove region adjacent to the groove. The areal density of the positive electrode active layer located in the groove region is ρ1, and the areal density of the positive electrode active layer located in the non-groove region is ρ2. ρ1 and ρ2 satisfy the following condition: ρ1 / ρ2 is 60%-90%. And / or, the positive electrode sheet further includes a non-groove region adjacent to the groove, the compaction density of the positive electrode active layer located in the groove is g1, the compaction density of the positive electrode active layer located in the non-groove region is g2, and g1 and g2 satisfy: g1 / g2 is 60%-98%.

6. The battery according to claim 1 or 2, wherein, Along the width direction of the positive electrode sheet, the size of the groove is less than or equal to the width of the positive electrode sheet; Preferably, along the winding direction of the positive electrode sheet, the size of the arc region is L', and the size of the orthographic projection of the groove on the surface of the positive electrode active layer is L, where L and L' satisfy: L≥L'; Preferably, along the width direction of the positive electrode sheet, the size of the groove is equal to the size of the arc region.

7. The battery according to claim 1 or 2, wherein, The outer surface of the cobalt-containing cathode material includes a coating layer, which at least partially covers the cobalt-containing cathode material; Preferably, the coating layer comprises at least one of the elements Ti, Zr, Y, La, Li, Al, Ba, Co, Cr, Mg, Sn, Sr and Ti; Preferably, the thickness of the coating layer is 10nm-500nm; Preferably, the cobalt-containing cathode material includes lithium cobalt oxide, which includes at least one of the elements Al, Mg, Ti, Zr, Y, La, F, W, B, Nb, Sr, Ni, Mn and P.

8. The battery according to claim 1 or 2, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector. The negative electrode active layer includes silicon-carbon composite material and / or graphite. The OI value of the negative electrode sheet is C, and A and C satisfy: 5.3≤A×C≤85. And / or, C satisfies: 5≤C≤80.

9. The battery according to claim 8, wherein, The sphericity of the silicon-carbon composite material is greater than 0.9; And / or, the particle size Dv10, median particle size Dv50 and particle size Dv90 of the silicon-carbon composite material satisfy: 0.2≤(Dv90-Dv10) / Dv50≤0.7; And / or, the particle size Dv10 of the silicon-carbon composite material is 4μm-9.5μm, the median particle size Dv50 is 5.5μm-12.5μm, and the particle size Dv90 is 6.5μm-13.5μm; Preferably, the silicon-carbon composite material has a particle size Dv10 of 5μm-8.5μm, a median particle size Dv50 of 6.5μm-10μm, and a particle size Dv90 of 7.5μm-12.5μm.

10. The battery according to claim 1 or 2, wherein, The diaphragm includes a substrate layer with a porous structure. In a pore size distribution diagram obtained by arranging the pore sizes of the substrate layer from largest to smallest, the pore size corresponding to the cumulative percentage of the number of porous structures is 10%, and the pore size corresponding to the cumulative percentage of the number of porous structures is 90%. D1 and D2 satisfy: 1.05≤D1 / D2≤3.

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