A battery

Abstract

The embodiment of the present application provides a kind of battery.The battery includes positive pole piece, negative pole piece, diaphragm and electrolyte;Positive pole piece includes positive pole current collector and the positive pole active material layer arranged on the surface of at least one side of positive pole current collector, and the positive pole active material layer includes positive pole active material, and the positive pole active material includes lithium cobaltate, and lithium cobaltate includes nickel element, manganese element;Electrolyte includes 1,2,4-butanetrinitrile;Battery satisfies 0.4≤d≤300, wherein, d=c / a;C is the mass fraction of 1,2,4-butanetrinitrile in electrolyte, unit is with wt% as the unit;A is the mass fraction of manganese element in lithium cobaltate, unit is with wt% as the unit;0.0125wt%≤a≤0.5wt%.The positive pole stability of the battery of the embodiment of the present application is higher, and the degree of electrolyte side reaction is lower, with good high-temperature cycle performance and safety performance.

Description

Technical Field

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

[0002] In recent years, with the continuous increase in requirements for battery energy density, lithium cobalt oxide (LiCoO2) cathode materials have been widely used in consumer batteries due to their high voltage plateau (greater than 4.5V) and high specific capacity. To meet the ever-increasing energy density requirements, common improvement strategies for lithium cobalt oxide include: increasing its charging cutoff voltage plateau and developing novel lithium cobalt oxide materials, such as optimizing energy density through bulk doping or structural design. However, these energy density improvement measures are often accompanied by new technical problems, such as decreased structural stability of lithium cobalt oxide under high temperature and high pressure, easier dissolution of metal ions, catalysis of electrolyte reactions, damage to the negative electrode interface protective film, and initiation of lithium plating at the negative electrode.

[0003] In summary, while ensuring battery energy density, developing a technology that can effectively address the structural stability issues and safety problems caused by metal ion dissolution under high temperature and high pressure after the improvement of lithium cobalt oxide is a key technical challenge that urgently needs to be solved in the current development of high-energy-density lithium cobalt oxide-based lithium-ion battery technology. Summary of the Invention

[0004] This invention provides a battery with good high-temperature cycling and safety performance.

[0005] This invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte;

[0006] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector. The positive active material layer includes a positive active material, which includes lithium cobalt oxide, and the lithium cobalt oxide includes nickel and manganese.

[0007] The electrolyte comprises 1,2,4-butanetrionitrile;

[0008] The battery satisfies 0.4≤d≤300, where d=c / a;

[0009] c represents the mass percentage of the 1,2,4-butanetrionitrile in the electrolyte, expressed in wt%.

[0010] a represents the mass percentage of manganese in the lithium cobalt oxide, expressed in wt%.

[0011] 0.0125wt%≤a≤0.5wt%.

[0012] In some embodiments of the present invention, the mass percentage b of manganese in the lithium cobalt oxide is 0.01wt% ≤ b ≤ 0.3wt%;

[0013] And / or, 0.1wt%≤c≤5wt%.

[0014] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0015] (1) The mass percentage of manganese on the surface of the lithium cobalt oxide is greater than the mass percentage of manganese inside the lithium cobalt oxide;

[0016] (2) The Dv50 of the lithium cobalt oxide is 5μm~25μm;

[0017] (3) The lithium cobalt oxide further includes at least one element selected from aluminum and magnesium; preferably, the mass percentage f of aluminum in the lithium cobalt oxide is 3000ppm≤f≤15000ppm; preferably, the mass percentage g of magnesium in the lithium cobalt oxide is 100ppm≤g≤3000ppm;

[0018] (4) Based on the mass of the lithium cobalt oxide, the mass percentage of manganese is greater than the mass percentage of nickel.

[0019] In some embodiments of the present invention, the electrolyte further includes methylene methane disulfonate, wherein the mass percentage e of methylene methane disulfonate in the electrolyte is 0.05wt%≤e≤5wt%.

[0020] In some embodiments of the present invention, the electrolyte further includes cyclic carbonates, which include one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, vinylene carbonate, and difluoroethylene carbonate.

[0021] Preferably, the mass percentage h of the cyclic carbonate in the electrolyte satisfies 10wt%≤h≤60wt%.

[0022] In some embodiments of the present invention, the separator includes a base membrane and an organic coating disposed on at least one surface of the base membrane, the organic coating comprising organic particles; preferably, the organic particles comprise nitrogen-containing organic particles, and the separator satisfies at least one of the following conditions:

[0023] (1) The Dv50 of the nitrogen-containing organic particles is 0.1 μm to 3 μm;

[0024] (2) The thickness of the organic coating is 0.3 μm to 5 μm;

[0025] (3) The nitrogen-containing organic particles include one or more of the following: melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, melamine chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, 2-amino-4,6-methoxy-1,3,5-triazine, 4-amino-2,6-dihydroxypyrimidine, uracil, cytosine, and guanine.

[0026] In some embodiments of the present invention, the battery includes a cell, which is formed by stacking and winding the positive electrode, the separator, and the negative electrode. Along the winding direction, the positive electrode includes, from the starting end, a first straight portion, a first arc segment, a second straight portion, and a second arc segment in sequence. The first arc segment and the second arc segment are connected through the second straight portion.

[0027] The thickness H1 of the positive electrode active material layer of the first arc segment facing the inside of the core is less than the thickness H3 of the positive electrode active material layer of the second straight portion facing the inside of the core; and / or, the thickness H2 of the positive electrode active material layer of the second arc segment facing the inside of the core is less than the thickness H3 of the positive electrode active material layer of the second straight portion facing the inside of the core.

[0028] In some embodiments of the present invention, the battery satisfies the following conditions: the difference between H3 and H1 is 2μm to 30μm; and / or, the difference between H3 and H2 is 2μm to 30μm.

[0029] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material. The silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material, elemental silicon, and silicon alloy. Preferably, the mass percentage of the silicon-based material in the negative electrode active material layer is 2wt% to 80wt%.

[0030] In some embodiments of the present invention, the charging cut-off voltage of the battery is greater than or equal to 4.53V.

[0031] The present invention provides a battery that improves the high-temperature cycle performance and safety performance by doping lithium cobalt oxide with nickel and manganese, adding 1,2,4-butanetrionitrile to the electrolyte, and controlling the relationship between the content of 1,2,4-butanetrionitrile in the electrolyte and the mass ratio of manganese in lithium cobalt oxide. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0033] Figure 1 This is a top view of the positive electrode plate of the battery according to an embodiment of the present invention;

[0034] Figure 2 This is a side view of the positive electrode plate of the battery according to an embodiment of the present invention.

[0035] Explanation of reference numerals in the attached figures

[0036] 1: Second straight section; 2: First arc segment; 3: Second arc segment; 4: Positive current collector; 5: Positive active material layer; 6: First straight section.

[0037] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] To meet the current market demand for battery energy density, and to improve the stability of lithium cobalt oxide materials in the cathode and the side reaction problem of the electrolyte, so as to improve the high-temperature cycle performance and safety performance of the battery.

[0040] This invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes lithium cobalt oxide, and the lithium cobalt oxide includes nickel and manganese. The electrolyte includes 1,2,4-butanetrionitrile. The battery satisfies 0.4 ≤ d ≤ 300, where d = c / a; c is the mass percentage of 1,2,4-butanetrionitrile in the electrolyte, in wt%; a is the mass percentage of manganese in lithium cobalt oxide, in wt%; 0.0125wt% ≤ a ≤ 0.5wt%.

[0041] The battery of this invention addresses the structural stability problem of lithium cobalt oxide cathodes under high-temperature and high-pressure cycling through a combination of three factors: nickel-manganese co-doping modification of the positive electrode active material, the synergistic effect of 1,2,4-butanetrionitrile (BTCN) in the electrolyte, and the matching of parameters d=c / a (0.1≤d≤300) and the manganese mass percentage of 0.0125wt%≤a≤0.5wt%. This also optimizes the stability of the electrolyte system. The inventors explain the specific reasons as follows: by using manganese (Mn) doping of lithium cobalt oxide and controlling the percentage to 0.0125wt%≤a≤0.5wt%, both the high specific capacity of the positive electrode active material and the disordered crystal structure are ensured. When using Ni doping, Ni can be introduced... 2+ / Ni 3+ / Ni 4+ The redox couple simultaneously broadens the lithium-ion insertion / extraction channels, enabling the storage and release of more lithium ions per unit mass of cathode material within the same operating voltage window. This effectively improves the specific capacity of lithium cobalt oxide, and appropriate Ni doping does not cause excessive lithium-nickel mixing, ensuring smooth lithium-ion diffusion at high temperatures. Mn doping relies on its stable +4 valence state (Mn... 4+ The Mn-O bond can effectively suppress oxygen loss and harmful phase transition caused by deep delithiation of lithium cobalt oxide under high temperature and high pressure, while Mn 4+ With an ionic radius similar to that of lithium ions, Ni can be reduced. 2+ The migration driving force towards the lithium layer improves the lithium-nickel mixing phenomenon, further ensures the smooth flow of lithium-ion diffusion channels, enhances the structural stability of lithium cobalt oxide, and enables nickel-doped lithium cobalt oxide to withstand higher charging voltages, fully leveraging the high capacity potential of the Ni redox couple and improving the battery's capacity stability under high-temperature cycling. However, under high temperature and high pressure, the manganese doping in the aforementioned lithium cobalt oxide material is prone to dissolution. The dissolved manganese ions catalyze side reactions in the electrolyte and migrate to the negative electrode for deposition during charging, interfering with Li... + Uniform embedding of lithium into the electrolyte disrupts the SEI film on the negative electrode, leading to localized lithium plating on the electrode surface. The introduction of 1,2,4-butanetrionitrile (BTCN) into the electrolyte, synergistically with nickel-manganese co-doped lithium cobalt oxide, forms a beneficial relationship. BTCN molecules are rich in multiple -CN functional groups and possess characteristics such as low viscosity, low impedance, and good kinetic performance. It adsorbs and coordinates with Mn ions dissolved from the surface of the positive electrode active material, effectively suppressing the dissolution of Mn ions under high temperature and pressure. This effectively prevents Mn ion dissolution from contaminating the electrolyte system, inhibits the decomposition and gas production of electrolyte components due to Mn ion catalysis, ensures the stability of the electrolyte under high voltage, and reduces the increase in interfacial impedance. Furthermore, it prevents the dissolved Mn ions from depositing on the negative electrode during charging, avoiding interference with Li. +Uniform embedding and disruption of the negative electrode SEI film improves the safety of localized lithium plating on the electrode surface. Simultaneously, BTCN stabilizes the highly reactive oxygen atoms on the positive electrode surface and exhibits good fluidity and miscibility, ensuring a good solvation structure for Li⁺. This structure adsorbs locally dissolved Mn ions on the membrane surface during migration and intercepts their penetration through the membrane to the negative electrode interface, forming a secondary protection that further blocks Mn ions from damaging the negative electrode interface. Furthermore, its superior electrochemical window, interfacial properties, and solvation forces, unlike other nitrile compounds (such as 1,3,6-hexanetrionitrile HTCN), more effectively suppress electrolyte side reactions, prevent electrical performance degradation, and ensure capacity retention at high voltages.

[0042] Meanwhile, by controlling the constraint d=c / a (1≤d≤300, where c is the mass percentage of BTCN in the electrolyte and a is the mass percentage of Mn in lithium cobalt oxide), the present invention achieves a match between the amount of BTCN and the amount of Mn doping, ensuring maximum synergistic effect and further improving the high-temperature and high-pressure structural stability of lithium cobalt oxide while maintaining battery energy density, thereby improving the high-temperature cycling and safety performance of the battery (e.g., lithium plating safety). This parameter constraint allows the amount of BTCN to be matched with the risk of Mn ion dissolution and oxygen release brought about by Ni and Mn doping: if d is too small, the amount of BTCN is insufficient, and it cannot fully adsorb and coordinate Mn ions and stabilize oxygen atoms, making it difficult to effectively suppress Mn dissolution and oxygen release, and failing to play a synergistic protective role; if d is too large, the amount of BTCN is too large, which may affect the ionic conductivity of the electrolyte or cause adverse interactions with other components in the electrolyte, resulting in a decrease in battery kinetic performance and accelerated cycle decay.

[0043] The structure of 1,2,4-butanetrionitrile of this invention is as follows: .

[0044] The components of the electrolyte can be tested using conventional testing methods and instruments in the art, such as gas chromatography-mass spectrometry (GC-MS).

[0045] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the nickel and manganese elements and their distribution and content in lithium cobalt oxide, such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0046] In some embodiments of the present invention, the mass percentage b of nickel in lithium cobalt oxide is 0.01wt% ≤ b ≤ 0.3wt%, which can further enhance the stabilizing effect of nickel-manganese co-doping on the lithium cobalt oxide cathode structure, better coordinate the effect of nickel doping with the synergistic effect of BTCN in the electrolyte, and is more conducive to improving the structural stability of the cathode active material under high temperature and high pressure cycling, thereby further optimizing the high temperature cycling performance and safety performance of the battery. For example, the mass percentage b of nickel in lithium cobalt oxide is, for example, 0.0125wt%, 0.1wt%, 0.3wt%, 0.5wt%, or any combination thereof.

[0047] In some embodiments, when 0.1wt% ≤ c ≤ 5wt%, it can better synergize with the nickel-manganese co-doping of the positive electrode active material, enhancing the battery's high-temperature cycle performance and safety performance. This is beneficial for optimizing the stability of the electrolyte system and the electrode interface performance, supporting the structural stability of the lithium cobalt oxide positive electrode under high-temperature and high-pressure cycling, and further leveraging the inherent advantages of BTCN. For example, the mass percentage c of BTCN in the electrolyte is, for instance, 0.1wt%, 1wt%, 3wt%, 5wt%, or any combination thereof.

[0048] In some embodiments of the present invention, the battery satisfies at least one of the following conditions:

[0049] (1) The mass percentage of manganese on the surface of lithium cobalt oxide is greater than that inside lithium cobalt oxide;

[0050] (2) The Dv50 of lithium cobalt oxide materials is 5μm~25μm;

[0051] (3) The lithium cobalt oxide material also includes at least one element selected from aluminum and magnesium; preferably, the mass percentage f of aluminum in the lithium cobalt oxide material is 3000ppm≤f≤15000ppm; preferably, the mass percentage g of magnesium in the lithium cobalt oxide material is 100ppm≤g≤3000ppm.

[0052] (4) Based on the mass of lithium cobalt oxide, the mass percentage of manganese is greater than that of nickel.

[0053] In some embodiments, the mass percentage of manganese on the surface of lithium cobalt oxide is greater than that inside the lithium cobalt oxide. This allows the battery to maintain a high energy density while ensuring the structural stability and safety of the material under high temperature and high pressure. Specifically, the enrichment of manganese on the surface of lithium cobalt oxide can form a protective barrier with BTCN adsorbed on the surface, more effectively stabilizing lattice oxygen, improving the structural stability of lithium cobalt oxide, further suppressing the release of metal ions and oxygen under high temperature and high pressure (≥4.53V), better reducing the oxidation of nickel, and better ensuring that the metal-doped cathode active material exhibits good electrochemical performance. In addition, when the mass percentage of manganese on the surface of lithium cobalt oxide is greater than that inside the lithium cobalt oxide, it is more conducive to optimizing the overall efficiency of nickel and manganese, further optimizing the lithium ion insertion / extraction efficiency on the material surface, better achieving a balance between energy density, high-temperature cycling, and safety, and is more suitable for high-temperature and high-pressure operating scenarios of the battery. In detail, the aforementioned mass percentage of manganese on the surface of lithium cobalt oxide is greater than that inside the lithium cobalt oxide particle. This means that in the positive electrode active material, which includes multiple lithium cobalt oxide particles, the mass percentage of manganese on the surface of the lithium cobalt oxide particles is greater than that inside the lithium cobalt oxide particles. Specifically, the particle surface refers to the outer boundary interface and adjacent surface layer of the particle (the area extending from the outer boundary contact inwards by 1% of the total radius); the area inside the particle other than the aforementioned area is considered the particle interior.

[0054] In some embodiments, the Dv50 of the lithium cobalt oxide material is 5 μm to 25 μm, which can further optimize the dispersion uniformity of each component in the cathode, facilitate the rapid penetration of BTCN into the cathode, further improve the uniformity and speed of solvent wetting, and allow BTCN to reach and interact with each Ni / Mn doping site of lithium cobalt oxide more quickly and fully, thereby further improving the high-temperature cycle performance and safety performance of the battery. For example, the Dv50 of the lithium cobalt oxide material is, for example, a range of 5 μm, 10 μm, 18 μm, 25 μm, or any combination thereof.

[0055] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the Dv50 (referring to the volume median particle size, i.e. the particle size corresponding to 50% of the cumulative volume distribution of the particles) of lithium cobalt oxide materials, such as a laser particle size analyzer.

[0056] The embodiments of the present invention can use conventional testing methods and instruments in the art to test the content of elements Ni and Mn in lithium cobalt oxide materials. For example, it can be tested by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), etc. For example, the battery is discharged to 0% SOC (e.g., the battery is discharged to 3V), the positive electrode is disassembled and removed, soaked in dimethyl carbonate (DMC) solvent for 12 hours, and then rinsed with DMC solvent to remove the lithium salt attached to the positive electrode. After calcining the positive electrode in air at 450 degrees for 2-4 hours, the lithium cobalt oxide positive electrode material is scraped off the positive electrode with a ceramic knife, and the mass content of elements Ni and Mn in the lithium cobalt oxide particles is obtained by testing with inductively coupled plasma optical emission spectrometry (ICP-OES).

[0057] In some embodiments, the lithium cobalt oxide material also includes at least one element selected from aluminum and magnesium, which can enhance the structural stability of lithium cobalt oxide, further improve the high-temperature and high-pressure stability, high-temperature cycling and safety performance of the battery, and thus be more suitable for adapting to the long-term working requirements of the battery under high temperature and high pressure.

[0058] In some embodiments, the mass percentage f of aluminum in the lithium cobalt oxide material is 3000ppm ≤ f ≤ 15000ppm, and / or the mass percentage g of magnesium in the lithium cobalt oxide material is 100ppm ≤ g ≤ 3000ppm. This better leverages the doping advantages of aluminum and / or magnesium, enhances the structural and thermal stability of lithium cobalt oxide, and is more conducive to synergistic effects with Ni / Mn doping and BTCN, further improving the overall electrochemical performance of the battery. For example, the mass percentage f of aluminum in lithium cobalt oxide is, for example, a range of 3000ppm, 6000ppm, 10000ppm, 15000ppm, or any combination thereof. The mass percentage g of magnesium in lithium cobalt oxide is, for example, a range of 100ppm, 800ppm, 2000ppm, 3000ppm, or any combination thereof.

[0059] In some embodiments, based on the mass of lithium cobalt oxide, the mass percentage of manganese is greater than that of nickel, and the higher proportion of manganese can more effectively weaken the nickel content. 2+ The migration driving force to the lithium layer is more conducive to improving the lithium-nickel mixing phenomenon, further optimizing the smoothness of the lithium-ion insertion / extraction channel, and better cooperating with the Ni introduced by the nickel element. 2+ / Ni 3+ / Ni 4+ The redox couple ensures high specific capacity while maintaining capacity stability under high-temperature cycling, further improving the battery's high-voltage stability, high-temperature cycling performance, and safety performance.

[0060] The aluminum and magnesium elements in lithium cobalt oxide can be tested in the above manner in the embodiments of the present invention, which will not be described in detail here.

[0061] The embodiments of the present invention can synthesize lithium cobalt oxide having the above-described composition using conventional methods in the art. In some embodiments, lithium cobalt oxide can be prepared by the following method: Step 1: A first Co source and a first Li source having specific Al, Mg, Mn, and Ni contents are mixed uniformly, and a first sintering is performed in a dry air atmosphere at a sintering temperature of 900℃-1050℃ for 8-12 hours. After sintering, the mixture is allowed to cool naturally to room temperature. Step 2: A second Co source and a second Li source having specific Al and Mg contents are mixed uniformly, and a second sintering is performed in a dry air atmosphere at a sintering temperature of 900℃-1050℃ for 5-10 hours. After sintering, the mixture is allowed to cool naturally to room temperature. The mixture obtained above is then placed in a crucible and placed in a high-temperature sintering device such as a muffle furnace, tunnel furnace, roller kiln, or tube furnace, and sintered at high temperature in an air or oxygen atmosphere to obtain the doped material. The sintering temperature is 700-900℃, and the time is 8-50 hours. Step 3: Mix the materials prepared in Step 1 and Step 2 evenly, and perform a third sintering at a temperature of 700℃-950℃ for 1h-5h. Then, allow the materials to cool naturally to room temperature to obtain the lithium cobalt oxide of the present invention.

[0062] In this embodiment of the invention, the term "optional" means that it can be added or not.

[0063] In this embodiment of the invention, in the third step, the materials obtained in the first and second steps can be mixed in any mass ratio.

[0064] In the embodiments of the present invention, the first Co source and the second Co source each independently include at least one of cobalt tetroxide, cobalt hydroxide and cobalt carbonate; the first Li source and the second Li source each independently include at least one of lithium carbonate and lithium fluoride; the first Al source includes at least one of Al2O3, Al(OH)3, Al2(SO4)3, Al2(CO3)3 and Al(NO3)3.

[0065] In one specific embodiment, the first Al source includes Al2(SO4)3.

[0066] In some embodiments of the present invention, the electrolyte further includes methylene methane disulfonate (MMDS), wherein the mass percentage (e) of MMDS in the electrolyte is 0.05 wt% ≤ e ≤ 5 wt%. This can improve the problem of metal ions dissolved from the positive electrode depositing on the negative electrode surface at high temperatures, and is more conducive to alleviating the problem of excessive impedance that may be caused by excessive BTCN addition. Furthermore, MMDS in this mass percentage range can participate in the construction of a protective positive electrode-electrolyte interface film, further improving the electrochemical window of the electrolyte, which is more conducive to widening the battery operating voltage range. At the same time, it can further optimize the electrode-electrolyte interface stability, thereby better maintaining capacity stability and battery safety performance in the later stages of cycling. For example, the mass percentage (e) of MMDS in the electrolyte is, for example, 0.05 wt%, 1 wt%, 3 wt%, 5 wt%, or any combination thereof.

[0067] In some embodiments of the present invention, the electrolyte further includes cyclic carbonates, including one or more of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), vinylene carbonate (VC), and difluoroethylene carbonate (DFEC), which can form a better solvation structure with BTCN and lithium ions, and are more conducive to improving the stability and safety performance of the battery during high-temperature cycling.

[0068] In some embodiments, the mass percentage h of cyclic carbonate in the electrolyte satisfies 10wt%≤h≤60wt%. For example, the mass percentage h of cyclic carbonate in the electrolyte is, for example, a range of 10wt%, 25wt%, 45wt%, 60wt%, or any two of these.

[0069] In some embodiments of the present invention, the electrolyte includes lithium salts, including lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium perchlorate (LiClO4), lithium oxalate borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), etc., and the mass percentage of lithium salts in the electrolyte can be, for example, 10wt% to 30wt%.

[0070] In some embodiments, the electrolyte includes at least one of linear carbonates and linear carboxylic acid esters, which is beneficial to further improve the stability of the electrolyte at high temperatures and better enhance the high-temperature stability of the battery.

[0071] In some embodiments, the solvent content in the electrolyte is 10% to 80% by mass, which is beneficial for further improving the stability of the electrolyte at high temperatures and thus better enhancing the high-temperature stability of the battery. The solvent content in the electrolyte may be, for example, 10%, 30%, 55%, 80%, or any combination thereof.

[0072] In some embodiments, the solvent includes diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propyl propionate, ethyl propionate, ethyl butyrate, ethyl acetate, fluorobenzene, and fluorosulfonamides.

[0073] In some embodiments, the electrolyte further includes other additives, including one or more of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, vinyl sulfate, succinic acid, adiponitrile, and 1,3,6-hexanetrionitrile.

[0074] In some embodiments, the mass percentage of other additives in the electrolyte is 0.1 wt% to 10 wt%. For example, the mass percentage of other additives in the electrolyte is, for example, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, or any combination thereof.

[0075] In some embodiments of the present invention, the separator includes a base membrane and an organic coating disposed on at least one surface of the base membrane, the organic coating including organic particles; preferably, the organic particles include nitrogen-containing organic particles, and the separator satisfies at least one of the following conditions:

[0076] (1) The Dv50 of nitrogen-containing organic particles is 0.1 μm to 3 μm;

[0077] (2) The thickness of the organic coating is 0.3μm~5μm;

[0078] (3) Nitrogen-containing organic particles include one or more of the following: melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, melamine chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, 2-amino-4,6-methoxy-1,3,5-triazine, 4-amino-2,6-dihydroxypyrimidine, uracil, cytosine, and guanine;

[0079] (4) The thickness of the base film is 3μm~18μm;

[0080] (5) An organic coating is disposed between the positive electrode and the base film.

[0081] In some embodiments, the Dv50 of nitrogen-containing organic particles is 0.1 μm to 3 μm, which is beneficial for further enhancing the adsorption capacity of manganese ions, inhibiting the dissolution of manganese ions and the migration of negative electrodes, and improving lithium plating at the negative electrode. Simultaneously, it can better cooperate with BTCN and MMDS to exert a synergistic protective effect. Furthermore, nitrogen-containing organic particles in this particle size range are more conducive to optimizing the structural characteristics of the separator. The gas generated by its high-temperature decomposition can better dilute active oxygen, further reducing the possibility of thermal runaway in electrochemical devices, thereby better leveraging the role of nitrogen-containing organic particles in improving battery safety performance. For example, the Dv50 of nitrogen-containing organic particles may be, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.8 μm, 2 μm, 3 μm, or any combination thereof.

[0082] In some embodiments, the thickness of the organic coating is 0.3 μm to 5 μm, for example, the thickness of the organic coating is a range of 0.3 μm, 1.5 μm, 3 μm, 5 μm or any combination thereof.

[0083] In some embodiments, nitrogen-containing organic particles include melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, and 2,4,6-tris(2-pyridyl) One or more of the following: triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, 2-amino-4,6-methoxy-1,3,5-triazine, 4-amino-2,6-dihydroxypyrimidine, uracil, cytosine, and guanine. The gases produced by the decomposition of the above nitrogen-containing organic particles can better dilute active oxygen, further reduce the possibility of thermal runaway in electrochemical devices, and fully leverage the role of organic coatings in improving battery safety performance.

[0084] In some embodiments, the thickness of the base film is 3 μm to 18 μm. For example, the thickness of the base film is, for example, a range of 3 μm, 8 μm, 13 μm, 18 μm or any combination thereof.

[0085] In some embodiments, the base film material may be selected from polyethylene or polypropylene.

[0086] In some embodiments, an organic coating is disposed between the positive electrode and the base film to further enhance the adsorption capacity for manganese ions dissolved from the positive electrode. This helps to strengthen the inhibition effect of manganese ion dissolution from the source, providing a strong guarantee for the stability of the bulk phase performance of the electrolyte system inside the battery, and further improving the safety performance and high-temperature cycle performance of the battery.

[0087] In some embodiments of the present invention, the organic coating further includes an adhesive, such as one or more of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, polyvinylpyrrolidone, polyurethane, polyvinylidene fluoride, acrylate adhesives, styrene-acrylic latex, polyacrylonitrile, polyacrylic acid, polyvinyl acetate, polyurethane-modified polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, or copolymer systems derived from the above polymers.

[0088] The embodiments of the present invention do not impose special limitations on the mass ratio of the binder in the organic coating, and can be selected according to the actual situation.

[0089] In some embodiments of the present invention, the diaphragm further includes an adhesive layer, and the diaphragm satisfies at least one of the following conditions:

[0090] (1) The adhesive layer is disposed on at least one side surface of the base film;

[0091] (2) The adhesive layer is disposed on the surface of the organic coating that is away from the base film;

[0092] (3) The thickness of the adhesive layer is 0.5μm~5μm;

[0093] (4) The adhesive layer includes at least one of polybutyl acrylate, polyethyl acrylate, polybutyl methacrylate, polymethyl methacrylate, methacrylate-acrylonitrile copolymer, methacrylate-ethylene copolymer, methacrylate-styrene copolymer, butadiene and isobutyl acrylate copolymer, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0094] In some embodiments, the thickness of the adhesive layer is 0.5 μm to 5 μm, further enhancing battery safety performance and ensuring long-term stable battery operation. For example, the thickness of the adhesive layer can be 0.5 μm, 2 μm, 3.5 μm, 5 μm, or any combination thereof.

[0095] In some embodiments of the present invention, the battery includes a cell, which is formed by stacking and winding a positive electrode sheet, a separator, and a negative electrode sheet. Along the winding direction, the positive electrode sheet, starting from the starting end, sequentially includes a first straight portion, a first arc segment, a second straight portion, and a second arc segment. The first arc segment and the second arc segment are connected through the second straight portion. The thickness H1 of the positive active material layer of the first arc segment facing the inside of the winding core is less than the thickness H3 of the positive active material layer of the second straight portion facing the inside of the winding core; and / or, the thickness H2 of the positive active material layer of the second arc segment facing the inside of the winding core is less than the thickness H3 of the positive active material layer of the second straight portion facing the inside of the winding core. When the battery of the embodiments of the present invention has the above structure, it can better provide sufficient thickness space for the arc region, further alleviate the stress generated at the arc during battery winding, and is more conducive to releasing the expansion at the arc during battery cycling, better reserving space for negative electrode expansion, and further alleviating the problem of positive electrode sheet breakage during cycling.

[0096] like Figure 1 and Figure 2 As shown, the positive electrode sheet of the battery in this embodiment of the invention includes a positive current collector 4 and positive active material layers 5 disposed on both sides of the positive current collector. The positive electrode sheet includes a first straight portion 6, a second straight portion 1, a first arc segment 2, and a second arc segment 3. In this embodiment of the invention, the thickness H1 of the positive active material layer 5 facing the inner side of the first arc segment 2 is set to be less than the thickness H3 of the positive active material layer 5 facing the inner side of the second straight portion 1. Alternatively, the thickness H2 of the positive active material layer 5 facing the inner side of the second arc segment 3 is set to be less than the thickness H3 of the positive active material layer 5 facing the inner side of the second straight portion 1.

[0097] It should be clarified that, along the winding direction, the positive electrode sheet includes N straight sections (from the first straight section to the Nth straight section) and 2N arc segments (from the first arc segment to the 2Nth arc segment). In this embodiment of the invention, the thickness of the positive electrode active material layer on the side of the first arc segment and the second arc segment facing the inside of the winding core is reduced (that is, the thickness of the positive electrode active material layer on the side of the arc segment facing the inside of the winding core is less than the thickness of the positive electrode active material layer on the side of the straight section facing the inside of the winding core).

[0098] In some embodiments, the difference between H3 and H1 is 2μm to 30μm, which can alleviate the stress generated at the arc during battery winding, facilitate the release of expansion at the arc during battery cycling, better reserve space for negative electrode expansion, and further alleviate the problem of positive electrode sheet breakage during cycling. For example, the difference between H3 and H1 is, for example, a range of 2μm, 3μm, 10μm, 20μm, 30μm, or any combination thereof.

[0099] In some embodiments, the difference between H3 and H2 is 2μm to 30μm, which can alleviate the stress generated at the arc during battery winding, facilitate the release of expansion at the arc during battery cycling, better reserve space for negative electrode expansion, and further alleviate the problem of positive electrode breakage during cycling. For example, the difference between H3 and H2 is, for example, a range of 2μm, 3μm, 10μm, 20μm, 30μm, or any combination thereof.

[0100] In some embodiments, the first and second arc segments of the dried positive electrode sheet can be thinned by laser scanning, thereby achieving a difference between H3 and H1 and a difference between H3 and H2.

[0101] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material. This can further improve the specific capacity of the negative electrode active material, thereby better improving the energy density of the battery.

[0102] In some embodiments, the silicon-based material accounts for 2wt% to 80wt% of the mass of the negative electrode active material layer, which is beneficial for further improving the specific capacity of the negative electrode active material, thereby better improving the energy density of the battery. Furthermore, the silicon-based material accounts for 2wt% to 50wt% of the mass of the negative electrode active material layer, achieving even better results.

[0103] In some embodiments of the present invention, the silicon-based material includes silicon-carbon material, which includes a porous carbon matrix and silicon material deposited in the porous carbon matrix.

[0104] This invention allows for the testing of silicon-carbon material content in the negative electrode active material layer using conventional testing methods and instruments. For example, the content can be calculated using ash content testing and EDS testing results. EDS testing: The battery is discharged to 0% SOC, disassembled, and the negative electrode is removed. The negative electrode containing the silicon-carbon composite material is treated with an argon ion polisher to obtain the cross-section of the negative electrode. Then, a scanning electron microscope (SEM) in backscatter mode is used for testing at a magnification of 10K. A single silicon-carbon particle is selected, and EDS is used to test the location points within the particle. The silicon content (wt%) at that point is calculated using standard-free analysis. EDS sampling tests are performed on the silicon content at five points in different regions within a single particle. The average value is calculated as the silicon content of the single particle. The silicon content of 10 different silicon-carbon composite material particles is statistically analyzed, and the average value is taken as the silicon content of the silicon-carbon composite material. Ash content test: After discharging the lithium-ion secondary battery to 0% SOC, the negative electrode sheet is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC to remove lithium salts adhering to the electrode sheet. After drying, the electrode sheet is subjected to high-temperature treatment at 400℃ in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active material layer can then be peeled off from the current collector, and the negative electrode active material is collected. For silicon content testing, a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer) is used. The sample amount is 5-15 mg. Under air or oxygen atmosphere, the temperature is increased from room temperature to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40 minutes. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the entire testing process is the ash content of the negative electrode active layer. Ignoring the mass percentage of trace impurities that may be present in the ash, and treating all the ash as silicon dioxide, the mass of silicon in the negative electrode active material can be calculated using the following formula: Mass percentage of silicon in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0105] Based on the EDS test results and ash content test results mentioned above, and according to the silicon content ratio of the silicon-carbon composite material and the silicon mass ratio in the negative electrode active material, the mass content of the silicon-carbon composite material in the negative electrode active layer can be calculated in reverse.

[0106] In some embodiments of the present invention, at least one surface of the negative electrode active material layer is provided with linear grooves (obtained by laser wire drawing method), the groove depth is 5μm~40μm, the groove width is 30μm~500μm, and the spacing between adjacent grooves is 0.5 mm~10 mm. The structural design of providing grooves on at least one surface of the negative electrode active material layer in the embodiments of the present invention is more conducive to reducing local lithium plating, further reducing the risk of separator puncture and short circuit caused by lithium plating, better suppressing the accompanying rapid heat generation problem, and more fully realizing the built-in thermal management of the negative electrode, thereby further improving the cycle stability and overall safety performance of the battery.

[0107] In some embodiments, the battery charging cutoff voltage is greater than or equal to 4.53V.

[0108] In this embodiment of the invention, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited thereto.

[0109] In this embodiment of the invention, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. In the positive electrode active material layer, the positive electrode active material accounts for 80% to 99.8% by mass percentage, the conductive agent accounts for 0.1% to 10%, and the binder accounts for 0.1% to 10%.

[0110] In this embodiment of the invention, the conductive agent in the positive electrode active material layer can be a conventional conductive material in the art. For example, the positive electrode conductive agent in the positive electrode active material layer may include one or more of conductive carbon black, conductive graphite, carbon nanotubes (CNTs), carbon fibers, graphene, acetylene black, and Ketjen black.

[0111] In this embodiment of the invention, the binder in the positive electrode active material layer can be a conventional binder in the art. For example, the positive electrode binder in the positive electrode active material layer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0112] The embodiments of the present invention may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0113] In this embodiment of the invention, the negative electrode active material layer may include a negative electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; the negative electrode binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0114] In the negative electrode active material layer, by mass percentage, the negative electrode active material is 80wt%~98.5wt%, the conductive agent is 0.1%~10wt%, and the binder is 0.1%~10wt%.

[0115] The embodiments of the present invention may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors include copper foil.

[0116] This invention also provides a battery pack comprising at least two of the aforementioned batteries, which has advantages corresponding to the aforementioned batteries, and will not be described in detail hereafter.

[0117] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0118] Example 1

[0119] The battery in this embodiment is prepared through the following process:

[0120] 1) Positive electrode preparation: The positive electrode active material (lithium cobalt oxide doped with metal elements, LiCoO2, where the mass ratio of manganese on the surface of lithium cobalt oxide is greater than the mass ratio of manganese inside lithium cobalt oxide), polyvinylidene fluoride (PVDF), and conductive agent SP (super... P) and carbon nanotubes (CNTs) are mixed in a mass ratio of 96:2:1.5:0.5, and N-methylpyrrolidone (NMP) solvent is added. The mixture is stirred under vacuum until a uniform and fluid positive electrode slurry is formed. The positive electrode slurry is uniformly coated on both surfaces of an aluminum foil. The aluminum foil coated with the positive electrode slurry is dried, and then rolled and slit to obtain a dried positive electrode sheet. The first and second arc segments of the dried positive electrode sheet are processed by laser scanning to prepare a first concave portion with a depth h1 of 8.2 μm, which is the difference in active layer thickness between the second flat region and the arc region of 8.2 μm. All positive electrode active layers are removed in a specific area of ​​the positive electrode sheet to form a positive electrode tab groove. The positive electrode tab is welded into the positive electrode tab groove to obtain the positive electrode sheet.

[0121] 2) Negative electrode preparation: Graphite, silicon carbide, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 64.5:30:2.5:1.5:1:0.5, and deionized water was added. The mixture was stirred under vacuum to obtain a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on both surfaces of a copper foil. The copper foil coated with the negative electrode slurry was dried at room temperature and then transferred to an 85°C oven for drying for 8 hours. After drying, the negative electrode was subjected to cold pressing and slitting processes to obtain a preliminary negative electrode sheet. The slitting negative electrode sheet was treated with laser grooving to create a matrix of grooves on the entire surface of the negative electrode sheet. The grooves were 220 μm wide, 14 μm deep, and 5 mm apart. The laser-treated negative electrode sheet was then cleaned and processed to obtain the desired negative electrode sheet.

[0122] 3) Electrolyte preparation: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), solvents EC, PC, PP, and EP were mixed evenly. Reagents were quickly added to the above mixed solvents, and the amount of each reagent added was calculated based on the total mass of the electrolyte: fully dried lithium hexafluorophosphate (LiPF6) 9 wt%, BTCN 2%, LiDFOB 1 wt%, LiTFSI 3 wt%, MMDS 2 wt%. The above system was stirred evenly, and the moisture and free acid of the stirred system were tested. After passing the test, the electrolyte was obtained, in which the cyclic carbonate EC:PC:FEC = 2:1:1, the total content of cyclic carbonate was 35%, and the balance of the electrolyte was PP and EP (ratio 1:2).

[0123] 4) Preparation of the diaphragm: Melamine cyanurate, thickener (sodium carboxymethyl cellulose), and polybutyl acrylate were mixed in a weight ratio of 92:3:5 to prepare a slurry (with a solid content of 28%). The slurry was coated on the positive electrode-facing side of the substrate layer (polyethylene, 9 μm thick) to form an organic coating. Polymer particles (polymethyl methacrylate (first polymer)) and deionized water were mixed to obtain a mixed slurry with a solid content of 10%. After thorough stirring and dispersion, the slurry was applied to both sides of the carrier layer prepared above by gravure roller dotting. After drying in a multi-section oven at 60°C, a coating was formed.

[0124] 5) Preparation of lithium-ion batteries: The positive electrode, separator, and negative electrode prepared above are stacked in the order of "positive electrode → separator → negative electrode". After stacking, a winding process is performed to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte prepared above is injected. Then, it goes through vacuum sealing, standing, formation, shaping, and sorting processes in sequence to obtain a lithium-ion battery. The charge and discharge range of this lithium-ion battery is 3.0-4.55V.

[0125] The differences between Examples 2-25, Comparative Examples 1-6 and Example 1 are as follows: the mass percentage of nickel in lithium cobalt oxide (a), the mass percentage of manganese in lithium cobalt oxide (b), the mass percentage of 1,2,4-butanetrionitrile in the electrolyte (c), the d value, the Dv50 of lithium cobalt oxide, the mass percentage of aluminum in lithium cobalt oxide (f), the mass percentage of magnesium in lithium cobalt oxide (g), the mass percentage of methanedisulfonate in the electrolyte (e), the mass percentage of cyclic carbonate solvent in the electrolyte (h), the Dv50 of nitrogen-containing organic particles, the thickness of the organic coating, the thickness of the nitrogen-containing organic particles, the thickness of the base film, the thickness of the adhesive layer, the difference between the thickness of the positive active material layer in the first flat section and the thickness of the positive active material layer in the first arc section, the difference between the thickness of the positive active material layer in the first flat section and the thickness of the positive active material layer in the second arc section, and the mass percentage of silicon-based material in the negative active material layer. See Tables 1 and 2 for details. In the above embodiments and comparative examples, the mass of the components added or reduced in the electrolyte was reduced or increased accordingly using non-cyclic carbonate solvents (specifically EP and PP in a ratio of 1:2), while the remaining components remained unchanged.

[0126]

[0127]

[0128] Test case

[0129] High-temperature 45℃ cycle performance test: The lithium-ion batteries prepared in the above examples and comparative examples were placed in a constant temperature environment of 45℃ and left to stand for 10 minutes. After the battery temperature stabilized at 45±2℃, they were charged at a constant current of 1 C to the upper limit voltage (4.53V), and then charged at a constant voltage of 4.53V to 0.05C and left to stand for 5 minutes. Then they were discharged at a constant current of 0.5C to 3V, and the discharge capacity at this time was recorded as Q1. After standing for 5 minutes, this was one charge-discharge cycle. The above process is a complete charge-discharge cycle. The discharge capacity of the first cycle was recorded as x1mAh, and the discharge capacity of the Nth cycle was recorded as y1mAh. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the capacity retention rate of the Nth cycle R1=y1 / x1. The number of cycles of the battery when the capacity retention rate R1 was 80% was recorded. The results are shown in Table 3.

[0130] High temperature and high pressure lithium plating test

[0131] The lithium-ion batteries prepared in the above embodiments and comparative examples were placed in a constant temperature environment of 45°C and left to stand for 10 minutes. After the battery temperature stabilized at 45±2°C, they were charged at a constant current of 1 C to the upper limit voltage (4.53V), and then charged at a constant voltage of 4.53V to 0.05C. After standing for 5 minutes, they were discharged at a constant current of 0.5C to 3V. The discharge capacity at this time was recorded as Q1. After standing for 5 minutes, this was one charge-discharge cycle. The above process constituted one complete charge-discharge cycle. After a total of 500 charge-discharge cycles, the batteries were discharged and disassembled in a glove box to observe the surface of the negative electrode. The results were divided into four levels: no lithium deposition, slight lithium deposition, moderate lithium deposition, and severe lithium deposition. No lithium deposition means that no purple spot-like lithium deposition appears at the top, bottom, or middle area of ​​the negative electrode sheet. Slight lithium deposition means that purple spot-like lithium deposition appears at the top and bottom of the negative electrode sheet. Moderate lithium deposition means that purple spot-like lithium deposition appears at the top and bottom of the negative electrode sheet and spreads to the middle area. Severe lithium deposition means that purple spot-like lithium deposition appears on the entire surface of the negative electrode sheet. The results are shown in Table 3.

[0132]

[0133] As shown in Table 3, compared with the comparative example, the embodiments of the present invention can improve the high-temperature cycle and safety performance of the battery by doping nickel and manganese elements into the lithium cobalt oxide of the battery positive electrode, adding 1,2,4-butanetrionitrile to the electrolyte, and controlling the relationship between the content of 1,2,4-butanetrionitrile in the electrolyte and the mass ratio of manganese element in lithium cobalt oxide.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, Includes positive electrode, negative electrode, separator, and electrolyte; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector. The positive active material layer includes a positive active material, which includes lithium cobalt oxide, and the lithium cobalt oxide includes nickel and manganese. The electrolyte comprises 1,2,4-butanetrionitrile; The battery satisfies 0.4≤d≤300, where d=c / a; c represents the mass percentage of the 1,2,4-butanetrionitrile in the electrolyte, expressed in wt%. a represents the mass percentage of manganese in the lithium cobalt oxide, expressed in wt%. 0.0125wt%≤a≤0.5wt%.

2. The battery according to claim 1, characterized in that, The mass percentage (b) of nickel in the lithium cobalt oxide is 0.01wt% ≤ b ≤ 0.3wt%. And / or, 0.1wt%≤c≤5wt%.

3. The battery according to claim 1 or 2, characterized in that, The battery satisfies at least one of the following conditions: (1) The mass percentage of manganese on the surface of the lithium cobalt oxide is greater than the mass percentage of manganese inside the lithium cobalt oxide; (2) The Dv50 of the lithium cobalt oxide is 5μm~25μm; (3) The lithium cobalt oxide further includes at least one element selected from aluminum and magnesium; preferably, the mass percentage f of aluminum in the lithium cobalt oxide is 3000ppm≤f≤15000ppm; preferably, the mass percentage g of magnesium in the lithium cobalt oxide is 100ppm≤g≤3000ppm; (4) Based on the mass of the lithium cobalt oxide, the mass percentage of manganese is greater than the mass percentage of nickel.

4. The battery according to any one of claims 1-3, characterized in that, The electrolyte also includes methylene methane disulfonate, wherein the mass percentage e of methylene methane disulfonate in the electrolyte is 0.05wt%≤e≤5wt%.

5. The battery according to any one of claims 1-4, characterized in that, The electrolyte also includes cyclic carbonates, which include one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, vinylene carbonate, and difluoroethylene carbonate. Preferably, the mass percentage h of the cyclic carbonate in the electrolyte satisfies 10wt%≤h≤60wt%.

6. The battery according to any one of claims 1-5, characterized in that, The diaphragm includes a base membrane and an organic coating disposed on at least one surface of the base membrane, the organic coating comprising organic particles; preferably, the organic particles comprise nitrogen-containing organic particles, and the diaphragm satisfies at least one of the following conditions: (1) The Dv50 of the nitrogen-containing organic particles is 0.1 μm to 3 μm; (2) The thickness of the organic coating is 0.3 μm to 5 μm; (3) The nitrogen-containing organic particles include one or more of the following: melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, melamine thiocyanate, symmetrical triaminotriazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, melamine chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, 2-amino-4,6-methoxy-1,3,5-triazine, 4-amino-2,6-dihydroxypyrimidine, uracil, cytosine, and guanine.

7. The battery according to any one of claims 1-6, characterized in that, The battery includes a cell, which is formed by stacking and winding the positive electrode, the separator, and the negative electrode. Along the winding direction, the positive electrode includes a first straight portion, a first arc segment, a second straight portion, and a second arc segment in sequence from the starting end. The first arc segment and the second arc segment are connected through the second straight portion. The thickness H1 of the positive electrode active material layer of the first arc segment facing the inside of the core is less than the thickness H3 of the positive electrode active material layer of the second straight portion facing the inside of the core; and / or, the thickness H2 of the positive electrode active material layer of the second arc segment facing the inside of the core is less than the thickness H3 of the positive electrode active material layer of the second straight portion facing the inside of the core.

8. The battery according to claim 7, characterized in that, The battery satisfies the following conditions: the difference between H3 and H1 is 2μm to 30μm; and / or the difference between H3 and H2 is 2μm to 30μm.

9. The battery according to any one of claims 1-8, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-based material. The silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material, elemental silicon, and silicon alloy. Preferably, the mass percentage of the silicon-based material in the negative electrode active material layer is 2wt% to 80wt%.

10. The battery according to any one of claims 1-9, characterized in that, The charging cutoff voltage of the battery is greater than or equal to 4.53V.

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