A battery

Abstract

The application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, the positive electrode sheet comprises a current collector and a positive electrode coating arranged on at least one functional surface of the current collector, the positive electrode coating comprises a positive electrode active material, and the chemical composition of the positive electrode active material comprises: LiNi x Co y M z O2, wherein M is Mn and / or Al, x+y+z=1, and y<0.3; the electrolyte comprises a first additive and a second additive, and the battery of the application can exhibit excellent performances of low impedance, long cycle and high / low temperature resistance under high voltage and high nickelization conditions by introducing the first additive and the second additive.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a battery. BACKGROUND

[0002] In order to meet market demand and promote the further development of the lithium battery industry, developing a ternary positive electrode material with higher energy density has become the goal pursued by many industry personnel. At present, the energy density of the positive electrode can be improved by reducing the cobalt content. Because reducing the cobalt content brings two results, one is to increase the charging cutoff voltage of the battery. Taking the 5 series ternary as an example, when the charging cutoff voltage is increased from 4.2V to 4.3V, the discharge gram capacity of the positive electrode material is significantly improved. The second is to increase the nickel content in the system, which also significantly improves the discharge gram capacity of the positive electrode material.

[0003] However, in practical application, high voltage or high nickelization also brings great challenges to the comprehensive performance of lithium batteries. Among them, increasing the charging voltage will lead to poor cycle stability of the material, which is specifically manifested in: nickel, cobalt, manganese and other transition metals are dissolved and deposited on the negative electrode surface, electrolyte is oxidized and decomposed, and the battery produces a large amount of gas, etc. Increasing the nickel content will affect the thermal stability of the material, which is specifically manifested in: when the battery faces higher temperature (equal to or greater than 40℃), the residual LiOH and high-activity Ni-O on the surface of the material react with the electrolyte, the released O2 reacts with the electrolyte to produce thermal runaway, etc. SUMMARY

[0004] The present application provides a battery which can effectively improve the cycle and storage stability of lithium ion batteries under high voltage and / or high nickelization conditions. Specifically, the battery can solve at least one of the problems of nickel, cobalt, manganese and other transition metals being dissolved and deposited on the negative electrode surface, electrolyte being oxidized and decomposed, and the battery producing a large amount of gas, etc. caused by high voltage, and can solve at least one of the problems of the residual LiOH and high-activity Ni-O on the surface of the material reacting with the electrolyte, the released O2 reacting with the electrolyte to produce thermal runaway, etc. caused by high nickelization.

[0005] In detail, the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet comprising a current collector and a positive electrode coating layer disposed on at least one functional surface of the current collector, the positive electrode coating layer comprising a positive electrode active material, the chemical composition of the positive electrode active material comprising: LiNi x Co y M z O2, wherein M is Mn and / or Al, x+y+z=1, y<0.3; the electrolyte comprising: a first additive and a second additive, the first additive containing at least one of the silicon-based fluorophosphonate compounds shown as formula I-1 to formula I-4:

[0006]

[0007] The second additive includes at least one of cyclic sulfate compounds, cyclic sulfite compounds, and cyclic sulfonate compounds.

[0008] Further, x ≥ 0.8.

[0009] Further, 0.5 ≤ x ≤ 0.7, and / or, the charge cut-off voltage of the battery ≥ 4.3 V.

[0010] Further, the chemical composition of the positive electrode active material includes: LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.8 Co 0.1 Al 0.1 O2.

[0011] Further, the chemical composition of the positive electrode active material includes: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.55 Co 0.15 Mn 0.30 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.65 Co 0.07 Mn 0.28 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.55 Co 0.15 Mn 0.30 O2.

[0012] Further, the cyclic sulfate compound includes at least one of vinyl sulfate, propylene sulfate, vinylene sulfate, catechol sulfate, bispropylene disulfate, bisvinylene disulfate, 4,5-di(4-vinyl sulfate) ethylene carbonate, and methylene methane disulfonate;

[0013] The cyclic sulfite compound includes vinyl sulfite and / or propylene sulfite.

[0014] The cyclic sulfonic acid ester compound includes at least one of 1,3-propane sulfonic acid lactone, 1,3-propylene sulfonic acid lactone, 1,4-butane sulfonic acid lactone, 2,4-butane sulfonic acid lactone, 3-fluoro-1,3-propane sulfonic acid lactone, 2-fluoro-1,3-propane sulfonic acid lactone, 1-fluoro-1,3-propane sulfonic acid lactone, and lithium difluorophosphate ethylene sulfonic acid triethylamine salt.

[0015] Further, the mass percentage content of the first additive in the electrolyte is 0.05wt%-5.0wt%;

[0016] Further, the mass percentage content of the second additive in the electrolyte is 0.1wt%-4.0wt%.

[0017] Further, the mass percentage content of the first additive in the electrolyte is 0.5wt%-2.5wt%;

[0018] Further, the mass percentage content of the second additive in the electrolyte is 0.5-3wt%.

[0019] Further, the mass ratio of the first additive to the second additive in the electrolyte is 1:0.1-4.

[0020] Further, the electrolyte further includes a lithium salt and a non-aqueous organic solvent.

[0021] Further, the mass percentage content of the lithium salt in the electrolyte is 6wt%-25wt%.

[0022] The battery provided by the application can exhibit low impedance, long cycle, and high / low temperature resistance under high voltage and / or high nickel conditions by adding the non-aqueous electrolyte of the first additive and the second additive. In detail, the first additive, i.e., the silicon-based fluorophosphonate compound, has a lower redox potential, reacts preferentially to the solvent and inhibits the decomposition of the solvent. When the first additive and the second additive are both applied to the high nickel system, on the one hand, the first additive can be preferentially oxidized to polysiloxane to construct an organic interface film, avoiding the oxidation of the electrolyte components by the oxygen released from the electrode material. The first additive rich in Si-O structure has good affinity to the transition metal of the positive electrode, especially to the high content of Ni component, has good stability to the Ni metal in the positive electrode material, and can inhibit the Li+ / Ni 2+Further, the CEI film of polysiloxane has high mechanical strength, which can inhibit the grain boundary cracking caused by the volume change of high-nickel positive electrode during charging and discharging. In addition, the interface film rich in inorganic sulfate, sulfite, lithium alkyl sulfonate, lithium alkyl sulfate, and lithium sulfide components constructed by the second additive can improve the stability of the interface film while maintaining a low interface impedance, thereby improving the high-temperature stability and cycle stability of the high-nickel system battery as a whole. When the first additive and the second additive are applied to the high-voltage system at the same time, the first additive, the silicon-based fluorophosphonate compound, not only shows the construction of an interface film with good stability, but also shows good combination and consumption of free radical ions generated by the second additive, avoiding the decomposition and consumption of solvents and lithium salts by the second additive. In particular, when inhibiting the abnormality of acidity caused by decomposition by-products, the silicon-based structure can combine acidic components in the electrolyte and further participate in polymerization, converting free acidic substances into beneficial interface film components, effectively alleviating the problems of high-temperature gas production, capacity decay, and cycle diving caused by the increase in electrolyte acidity. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and serve to explain the principles of the application. It is to be noted, however, that the drawings shown are intended solely for purposes of illustration and are not intended to limit the scope of the application.

[0024] Figure 1 The graph of the cycle capacity retention rate at room temperature for lithium ion batteries containing the electrolytes of Examples 1, 2, and Comparative Example 1;

[0025] Figure 2 The graph of the cycle capacity retention rate at high temperature for lithium ion batteries containing the electrolytes of Examples 1, 2, and Comparative Example 1;

[0026] Figure 3 The graph of the change in battery thickness and impedance after high-temperature storage for lithium ion batteries containing the electrolytes of Examples 1, 2, and Comparative Example 1;

[0027] Figure 4 The graph of the change in low-temperature discharge capacity retention rate for lithium ion batteries containing the electrolytes of Examples 1, 2, and Comparative Example 1. DETAILED DESCRIPTION

[0028] In order for those skilled in the art to better understand the solutions of the present application, the present application will be further described in detail below. The following specific embodiments are only used to describe the principles and characteristics of the present application, and the examples are used to explain the present application, but not to limit the scope of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] In one aspect, the present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet comprising a current collector and a positive electrode coating disposed on at least one functional surface of the current collector, the positive electrode coating comprising a positive electrode active material, the chemical composition of the positive electrode active material comprising: LiNi x Co y M z O2, wherein M is Mn and / or Al, x+y+z = 1, y < 0.3; the electrolyte comprising: a first additive and a second additive, the first additive containing at least one of the silicon-based fluorophosphonate compounds as shown in formula I-1 to formula I-4:

[0030]

[0031] The second additive comprises at least one of the cyclic sulfate compounds, cyclic sulfite compounds and cyclic sulfonate compounds.

[0032] For the ternary lithium ion battery under the conventional system, the introduction of sulfate compounds (such as vinyl sulfate (DTD)) and / or sulfonate compounds (PS) has good film forming performance, and can produce free radical structure in the first charge-discharge process, and combine with solvent and lithium ion to form inorganic sulfate, sulfite, alkyl lithium sulfonate, alkyl lithium sulfate, lithium sulfide and other components that can construct SEI / CEI interface film, thereby avoiding the corrosion of HF, F - and other components in the electrolyte on the positive electrode active material, thereby improving the cycle stability and high temperature storage performance of the battery. However, in the battery under the high nickel system or high voltage nickel system, the interface film constructed by the sulfate compounds and / or sulfonate compounds has limited protection effect on the electrode / electrolyte. For the high nickel system, the thermal stability of the electrode material is reduced, the surface residual LiOH and high active Ni -O and electrolyte side reactions, the release of O2 and electrolyte component reaction to produce thermal runaway, etc. will cause a large amount of consumption of the film forming process of sulfur ester compounds and / or sulfonate compounds, etc. and cannot maintain the protection or repair effect on the SEI / CEI film, which leads to serious damage to the interface film after the cycle / storage period, the oxidation of electrolyte is intensified and the problem of by-product accumulation; for high-voltage systems, the increase of the voltage of the electrode interface will cause the sulfur ester compound and / or sulfonate compound to produce more free radical ion pairs to consume the solvent and lithium salt, reduce the initial capacity, and increase the interface film thickness to cause the interface impedance to increase, especially during the long-term cycle / storage process, the by-products produced by the decomposition of the sulfur ester compound and / or sulfonate compound under high voltage will increase the acidity of the electrolyte, accelerate the corrosion of the electrolyte components, electrode / electrolyte interface and electrode active material, which is not conducive to solving the problems of poor stability of electrode active material, dissolution of nickel, cobalt and manganese transition metals and deposition on the negative electrode surface, electrolyte oxidation and decomposition, and battery gas production, but will cause the battery capacity to plunge and safety hazards. Therefore, in order to avoid the problems of sulfur ester compounds and / or sulfonate compounds in high-nickel systems or high-voltage nickel systems, the first additive and the second additive are introduced to solve these problems, wherein the first additive silicon-based fluorophosphonate compound has a lower oxidation-reduction potential, is preferentially reacted with the solvent and inhibits the decomposition of the solvent. When the first additive and the second additive are applied to the high-nickel system, the first additive can be preferentially oxidized to polysiloxane to construct an organic interface film, avoiding the release of oxygen from the electrode material to oxidize the electrolyte components, wherein the Si-O structure is rich in transition metals of the positive electrode, especially the high content of Ni components, has a good affinity for the positive electrode material, has a good stabilizing effect on the Ni metal, can inhibit Li+ / Ni 2+Further, the CEI film of the polysiloxane has high mechanical strength, which can inhibit the crack of the grain boundary caused by the volume change of the high-nickel positive electrode during the charging and discharging process. The interface film rich in inorganic sulfate, sulfite, lithium alkyl sulfonate, lithium alkyl sulfate, and lithium sulfide components is constructed by the second additive, which can improve the stability of the interface film while maintaining a low interface impedance, and overall improve the high-temperature stability and cycle stability of the high-nickel system battery. When the first additive and the second additive are applied to the high-voltage system at the same time, the first additive not only shows the construction of an interface film with good stability, but also shows good combination and consumption of free radical ions generated by the second additive, avoiding its consumption and decomposition of the solvent and lithium salt. In particular, when inhibiting the abnormality of acidity caused by decomposition by-products, it shows excellent results. The silicon-based structure can combine acidic components in the electrolyte and further participate in polymerization, converting free acidic substances into beneficial interface film components, effectively alleviating the problems of high-temperature gas production, capacity decay, and cycle diving caused by the increase in electrolyte acidity. In addition, when the first additive includes the structure shown in Formula I-3 and / or Formula I-2, the solubility in the electrolyte can be reduced. When the first additive includes the structure shown in Formula I-1, the introduction of an unsaturated alkenyl group at the end group can further construct a protective layer with a cross-linked network structure, thereby increasing the adhesion of the CEI film on the positive electrode side. When the first additive includes the structure shown in Formula I-4, the introduction of a phenyl structure at the end group can also improve the deformation resistance of the interface film, thereby further improving the mechanical strength of the CEI film.

[0033] For the above reasons, the battery of the present application can exhibit excellent performance of low impedance, long cycle, and high / low temperature resistance under high voltage and / or high nickel conditions.

[0034] In a specific embodiment, x≥0.8. As described in the above embodiments, by further increasing the nickel content in the positive electrode system, the energy density of the battery can be further improved.

[0035] In a specific embodiment, 0.5≤x≤0.7, and / or the charge cut-off voltage of the battery is≥4.3V. As described in the above embodiments, by further limiting the nickel content, and / or the charge cut-off voltage of the battery, the capacity and output power of the battery can be further improved.

[0036] In a specific embodiment, the chemical composition of the positive electrode active material includes: LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.92 Co 0.05 Mn 0.03O2, LiNi 0.8 Co 0.1 Al 0.1 at least one of O2, LiNi

[0037] In one embodiment, the positive active material has a chemical composition comprising: LiNi 0.5 Co 0.2 Mn 0.3 at least one of O2, LiNi 0.55 Co 0.15 Mn 0.30 at least one of O2, LiNi 0.6 Co 0.2 Mn 0.2 at least one of O2, LiNi 0.65 Co 0.07 Mn 0.28 at least one of O2, LiNi 0.6 Co 0.1 Mn 0.3 at least one of O2, LiNi 0.55 Co 0.15 Mn 0.30 O2.

[0038] As for the negative electrode sheet of the battery, the present application is not particularly limited, and in some embodiments, the negative electrode sheet comprises a current collector and a negative electrode coating disposed on at least one functional surface of the current collector, the negative electrode coating comprises a negative active material, which can be conventional materials in the art, including but not limited to one or more of carbonaceous materials, silicon-carbon materials, alloy materials, lithium-containing metal composite oxides, and further, the negative active material is one or more of graphite, soft carbon, hard carbon, silicon, silicon oxide compounds, silicon-carbon composites, and lithium titanate.

[0039] In some embodiments, the positive electrode coating and the negative electrode coating described above further comprise: a conductive agent, a binder, and optionally a dispersant, the conductive agent of the positive electrode coating is at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, metal powder, graphene; the conductive agent of the negative electrode coating is different from the negative active material and can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, metal powder, graphene; the binder of the positive electrode coating and the negative electrode coating is independently at least one of carboxymethyl cellulose, styrene butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; the dispersant of the positive electrode coating and the negative electrode coating is independently at least one of sodium carboxymethyl cellulose, triethylhexyl phosphoric acid, and sodium dodecyl sulfate.

[0040] The thickness, surface density, thickness of the negative electrode coating, and thickness of the positive electrode coating of the positive electrode sheet and the negative electrode sheet are not specifically limited in the present application. In a specific embodiment, the thickness of the positive electrode sheet or the negative electrode sheet is 40-120 μm, the surface density is 3-10 mg / cm 2 , and the thickness of the negative electrode coating or the thickness of the positive electrode coating is 20-60 μm. In some embodiments, the negative electrode coating comprises, by mass percentage, 94%-97% of a negative electrode active material, 1%-2.5% of a conductive agent, 1.2%-2.5% of a binder, and 0.5%-1.5% of a dispersant.

[0041] In some embodiments, the positive electrode coating comprises, by mass percentage, 94%-97% of a positive electrode active material, 1%-2.5% of a conductive agent, 1.2%-2.5% of a binder, and 0.5%-1.5% of a dispersant.

[0042] The separator can be a conventional separator selected by a person skilled in the art, such as polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, etc.

[0043] In a specific embodiment, the cyclic sulfate compound comprises at least one of vinyl sulfate (DTD), propylene sulfate, vinylene sulfate, catechol sulfate, bispropylene sulfate, bisvinyl sulfate, 4,5-bis(4-vinyl sulfate) ethylene carbonate, and methanedisulfonate methylene (MMDS).

[0044] The cyclic sulfite compound comprises vinylene sulfite and / or propylene sulfite.

[0045] The cyclic sulfonic acid ester compound comprises at least one of 1,3-propane sulfonic acid lactone (PS), 1,3-propylene sulfonic acid lactone (PES), 1,4-butane sulfonic acid lactone, 2,4-butane sulfonic acid lactone, 3-fluoro-1,3-propane sulfonic acid lactone, 2-fluoro-1,3-propane sulfonic acid lactone, 1-fluoro-1,3-propane sulfonic acid lactone, and lithium difluorophosphate triethylamine salt of ethylene sulfonic acid.

[0046] In a specific embodiment, the mass percentage of the first additive in the electrolyte is 0.05wt%-5.0wt%;

[0047] And / or, the mass percentage of the second additive in the electrolyte is 0.1wt%-4.0wt%.

[0048] The first additive in the above mass percentage range has a significant effect on reducing battery impedance, improving low-temperature discharge and cycle performance. If the mass percentage of the first additive is higher than 5.0wt%, it will cause too much disiloxane and fluorosilane components, which will have a negative effect on battery impedance, gas production and capacity retention. If the mass percentage of the first additive is lower than 0.05wt%, there will be less silane structure, Li3PO3, Li x PO y F z and other lithium salt film-forming components, which cannot effectively coat the positive / negative electrode materials, and the improvement effect on battery performance is limited.

[0049] The second additive in the above mass percentage range can achieve a good balance between solvent consumption and the construction of SEI / CEI interface films rich in inorganic sulfates, sulfites, lithium alkyl sulfonates, lithium alkyl sulfates, and lithium sulfides. If the content of the second additive is too low, although the consumption of electrolyte is greatly reduced, the inorganic lithium salt containing sulfur in the interface film is less, which cannot further reduce the impedance and improve the cycle and storage stability under high temperature conditions. If the content of the second additive is too high, not only will it cause excessive consumption of electrolyte, but the battery will also produce gas, the thickness of the SEI / CEI interface film will increase, leading to increased battery impedance and poor cycle and storage performance.

[0050] In a more preferred embodiment, the mass percentage of the first additive in the electrolyte is 0.5wt%-2.5wt%;

[0051] and / or, the mass percentage of the second additive in the electrolyte is 0.5-3wt%.

[0052] In a specific embodiment, the mass ratio of the first additive to the second additive in the electrolyte is 1:0.1-4.

[0053] The silicon-based fluorophosphonate compound produces a certain quenching effect on the alkyl radical after ring-opening reaction, which blocks the reaction of alkyl radical with solvent molecules to cause serious gas production and impedance increase. The above embodiment can better play the synergistic effect of the two additives by controlling the ratio of the two additives, and construct a low-impedance interface film with uniform thickness, dense structure, corrosion resistance and high-temperature stability, which can hinder the corrosion of HF on the electrolyte and the electrode, reduce the battery impedance, inhibit the battery gas expansion, improve the low-temperature performance, and thus make the cycle and storage performance of the battery under different temperature conditions optimal.

[0054] In a specific embodiment, it further includes a lithium salt and a non-aqueous organic solvent.

[0055] The lithium salt is not particularly limited in the present application, and a person skilled in the art can select a conventional lithium salt material. Exemplarily, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorodioxalato-phosphate, lithium tetrafluorodioxalato-phosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perfluorobutylsulfonate, and lithium fluoroaliphatic acid, etc.

[0056] The non-aqueous organic solvent is not particularly limited in the present application, and a person skilled in the art can select a conventional non-aqueous organic solvent. Exemplarily, the non-aqueous organic solvent includes at least one of cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), and carboxylic acid esters such as ethyl acetate (EA), propyl acetate (PA), ethyl propionate (EP), and propyl propionate (PP).

[0057] In one embodiment, the mass percentage of the lithium salt in the electrolyte is 6wt%-25wt%.

[0058] When the lithium salt is within the above range, the lithium salt can be dissolved in the organic solvent to form an electrolyte with high stability and good lithium ion conductivity, and the viscosity of the electrolyte is suitable for the rapid migration of lithium ions in the electrolyte, thereby making the battery exhibit excellent cycle performance.

[0059] In a more preferred embodiment, the mass percentage of the lithium salt is 10wt%-15wt%.

[0060] Exemplarily, the mass percentage of the non-aqueous organic solvent is 60wt%-92wt%, preferably 65wt%-85wt%.

[0061] When the organic solvent is within the above range, the lithium salt can be fully dissolved in the electrolyte, which is helpful to prepare an electrolyte with high conductivity and strong stability, and the electrochemical performance of the battery is stable.

[0062] The present application is further described below in conjunction with specific embodiments:

[0063] The CAS number of the silicon-based fluorophosphonate compound represented by the following formula I-1 is 2708941-25-5.

[0064] The CAS number of the silicon-based fluorophosphonate compound represented by the following formula I-2 is 4414-25-9.

[0065] The CAS number of the silicon-based fluorophosphonate compound represented by the following formula I-3 is 4414-26-0.

[0066] The CAS number of the silicon-based fluorophosphonate compound represented by the following formula I-4 is: 6231-57-8.

[0067] Example 1

[0068] The example provides a battery, including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet includes an aluminum foil and a positive electrode material layer arranged on the front and back of the aluminum foil, the positive electrode active material of the positive electrode material layer is LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), the electrolyte includes 12.5% LiPF6, 1.0% first additive, 1.5% second additive, and the balance is non-aqueous organic solvent in terms of mass fraction, wherein the first additive is a silicon-based fluorophosphonate compound represented by formula I-2, the second additive is vinyl sulfate (DTD), and the non-aqueous organic solvent is composed of vinyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) with a mass ratio of 3:5:2.

[0069] The preparation method comprises the following steps:

[0070] 1. Positive electrode preparation: uniformly mix LiNi 0.5 Co 0.2 Mn 0.3 O2 positive electrode active material, conductive agent Super P (conductive carbon black), conductive agent CNT (carbon nanotube), and adhesive PVDF (polyvinylidene fluoride) in a mass ratio of 96.3:2:0.5:1.2, vacuum stirring until the fluidity is uniform, then uniformly coating (coating thickness is 50 μm) the slurry on the front and back of the aluminum foil, sequentially drying at 85°C, cold pressing, edge cutting, sheet cutting, striping, and vacuum drying at 85°C for 12 hours, and welding the tab to obtain a positive electrode sheet with a surface density of 33 mg / cm 2 .

[0071] 2. Negative electrode preparation: uniformly mix graphite negative electrode active material, conductive agent Super P (conductive carbon black), thickening agent CMC (sodium carboxymethyl cellulose), and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 96:1.5:1.5:2, coat on both sides of the copper foil (coating thickness is 60 μm), then dry at 85°C, cold press, edge cut, sheet cut, stripe, and finally dry at 85°C under vacuum conditions for 12 hours, and weld the tab to obtain a negative electrode sheet with a surface density of 19.3 mg / cm 2 .

[0072] 3. Separator: take a polyethylene porous polymer film with a thickness of 9 μm as a substrate, and coat a 2 μm adhesive coating on both sides of the substrate.

[0073] 4. Battery preparation

[0074] The positive electrode sheet, the separator and the negative electrode sheet are sequentially stacked and then subjected to a winding process to produce a bare cell having a theoretical capacity of 1600 mAh (the actual capacity will be less than the theoretical capacity), the bare cell is placed in an outer packaging aluminum foil, vacuum baked at 75°C for 10 hours, and then different electrolytes are injected, and after processes such as vacuum packaging, standing, formation, aging, and capacity distribution, a lithium ion battery is completed.

[0075] Example 2-30

[0076] The example is basically the same as Example 1, except that the conditions shown in Table 1 are changed.

[0077] Example 31

[0078] The example provides a lithium ion battery including the electrolyte of Example 1. The preparation and assembly process of each part of the lithium ion battery is basically the same as Example 1, except that the positive electrode material is LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0079] Example 32

[0080] The example provides a lithium ion battery including the electrolyte of Example 1. The preparation and assembly process of each part of the lithium ion battery is basically the same as Example 1, except that the positive electrode material is LiNi 0.8 Co 0.1 Al 0.1 O2.

[0081] Example 33

[0082] The example provides a lithium ion battery including the electrolyte of Example 1. The preparation and assembly process of each part of the lithium ion battery is basically the same as Example 1, except that the positive electrode material is LiNi 0.92 Co 0.05 Mn 0.03 O2.

[0083] Comparative Example 1

[0084] The example is basically the same as Example 1, except that no first additive is added to the electrolyte.

[0085] Comparative Example 2

[0086] The example is basically the same as Example 1, except that no second additive is added to the electrolyte.

[0087] Comparative Example 3

[0088] The example is basically the same as Example 1, except that the structure of the first additive in the electrolyte is shown as Formula II:

[0089]

[0090] Comparative Example 4

[0091] This example provides a lithium ion battery comprising the electrolyte of Example 1 above. The lithium ion battery was prepared and assembled in substantially the same manner as in Test Example 1, except that the positive electrode material was LiNi 0.6 Co 0.3 Mn 0.1 O2.

[0092] Comparative Example 5

[0093] This example provides a lithium ion battery substantially the same as Example 1, except that the first additive in the electrolyte has the structure shown in Formula Ш:

[0094]

[0095] Table 1

[0096]

[0097]

[0098] Performance Test:

[0099] 1. Impedance, cycle and high-low temperature performance tests were performed on each of the lithium ion batteries above, using the following test methods, and the test results are shown in Table 2:

[0100] 1.1. 25°C ambient temperature cycle test: charge at 1.0C constant current to 4.4V, charge at constant voltage 4.4V to the cut-off current 0.05C, then discharge at 1.0C constant current to 2.75V, repeat the charge and discharge steps 1000 times, record the discharge capacity of the 1000th cycle and the 1st cycle, divide the two to get the capacity retention rate, wherein the ambient temperature cycle capacity retention rate curves of Examples 1, 2 and Comparative Example 1 are shown in Figure 1 .

[0101] 1.2. 45°C high temperature cycle test: charge at 1.0C constant current to 4.4V, charge at constant voltage 4.4V to the cut-off current 0.05C, then discharge at 1.0C constant current to 2.75V, repeat the charge and discharge steps 800 times, record the discharge capacity of the 800th cycle and the 1st cycle, divide the two to get the capacity retention rate; wherein the high temperature cycle capacity retention rate curves of Examples 1, 2 and Comparative Example 1 are shown in Figure 2 .

[0102] 1.3, 60°C high temperature 30 days storage test: charge the battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, then discharge the battery with 1.0C constant current to 2.75V, the discharge capacity is recorded as C1. Charge the battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, then transfer the battery to 60°C for 30 days, then discharge the battery with 1.0C constant current to 2.75V, the discharge capacity is recorded as C2, the capacity retention rate of 60°C storage for 30 days = C2 / C1*100%.

[0103] 1.4, -20°C low temperature discharge test: charge the battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, then discharge the battery with 0.5C constant current to 2.75V, the discharge capacity is recorded as C3. Charge the battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, then transfer the battery to -20°C for 240 min, then discharge the battery with 0.5C constant current to 2.75V, the discharge capacity is recorded as C4, the discharge rate at -20°C = C4 / C3*100%; wherein the low temperature discharge capacity retention rate of examples 1, 2 and comparative example 1 is shown in Table 1. Figure 4 .

[0104] 1.5, 60°C storage 30 days thickness change rate (high temperature storage expansion rate test): charge the lithium ion battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, after the battery is fully charged, test the thickness of the battery, and record the value as T0. The battery that has completed the 60°C high temperature 30 days storage test is tested for battery thickness, and the recorded value is T1. The battery expansion rate η6 = (T1-T0) / T0*100%; wherein the high temperature storage battery thickness change rate of examples 1, 2 and comparative example 1 is shown in Table 1. Figure 3 .

[0105] 1.6, initial DCIR test: charge the lithium ion battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, then discharge the battery with 1.0C constant current for 30 min, after 1h of standing, discharge with 2.0C constant current for 10s, and calculate the DCIR impedance value at 50% SOC of the battery.

[0106] 1.7, low temperature DCIR test: charge the lithium ion battery at 25°C with 1.0C constant current to 4.4V, constant voltage 4.4V to the cut-off current 0.05C, then discharge the battery with 1.0C constant current for 30 min, after 1h of standing, transfer the battery to -20°C for 240 min, then discharge with 1.0C constant current for 10s, and calculate the DCIR impedance value at 50% SOC of the battery.

[0107] 1.8, Impedance change rate at 60℃ for 30 days (high temperature impedance change rate test): the lithium ion battery was charged at 1.0C constant current to 4.4V, charged at constant voltage 4.4V to the cut-off current 0.05C, then discharged at 1.0C constant current for 30min, after 1h rest, discharged at 2.0C constant current for 10s, the DCIR at 50% SOC of the battery was calculated, and the value was recorded as D1. The battery completed the 60℃ high temperature 30-day storage test, was charged at 1.0C constant current to 4.4V at 25℃, charged at constant voltage 4.4V to the cut-off current 0.05C, then discharged at 1.0C constant current for 30min, after 1h rest, discharged at 2.0C constant current for 10s, the DCIR at 50% SOC of the battery was calculated, and the value was recorded as D2. The impedance change rate of the battery = D2 / D1*100%; wherein the high temperature storage battery impedance change rate of examples 1, 2 and comparative example 1 is shown in Table 1. Figure 3 .

[0108] 2, The lithium ion battery prepared in example 31 was subjected to impedance, cycle and high and low temperature performance tests, and the test method referred to test 1 above, the only difference was that the charging voltage was 4.45V; the test results are shown in Table 2.

[0109] 3, The lithium ion battery prepared in example 32 was subjected to impedance, cycle and high and low temperature performance tests, and the test method referred to test 1 above, the only difference was that the charging voltage was 4.25V; the test results are shown in Table 2.

[0110] 4, The lithium ion battery prepared in example 33 was subjected to impedance, cycle and high and low temperature performance tests, and the test method referred to test 1 above, the only difference was that the charging voltage was 4.2V; the test results are shown in Table 2.

[0111] Table 2:

[0112]

[0113]

[0114]

[0115] From Table 2, compared with the comparative example, the battery of the example showed lower impedance, longer cycle life and more resistance to high / low temperature under high voltage and / or high nickelization conditions;

[0116] Further, by comparing examples 1-4, it can be seen that the battery of example 1 has better comprehensive performance, the cycle capacity retention at 45℃ and the capacity retention after 30 days storage at 60℃ of the batteries of examples 2 and 4 are better; the thickness change of the battery of example 3 after 30 days storage at 60℃ is smaller.

[0117] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the positive electrode sheet comprising a current collector and a positive electrode coating provided on at least one functional surface of the current collector, the positive electrode coating comprising a positive electrode active material, characterized in that, The chemical composition of the positive electrode active material includes: LiNi x Co y M z O2, wherein M is Mn and / or Al, x+y+z=1, y<0.3; the electrolyte includes: a first additive and a second additive, the first additive contains at least one of the silicon-based fluorophosphonate compounds as shown in formulas I-1 to I-4: Formula I-1, Formula I-2, Formula I-3, Formula I-4; The second additive comprises at least one of a cyclic sulfate compound, a cyclic sulfite compound and a cyclic sulfonate compound. The mass percentage of the first additive in the electrolyte is 0.05wt%-5.0wt%. And / or, the mass percentage of the second additive in the electrolyte is 0.1wt%-4.0wt%.

2. The battery of claim 1, wherein, x≥0.8。 3. The battery of claim 1, wherein, 0.5≤x≤0.7， And / or, the charge cut-off voltage of the battery is greater than or equal to 4.3V.

4. The battery of claim 2, wherein, The chemical composition of the positive electrode active material includes: LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.83 Co 0.11 Mn 0.06 O2, LiNi 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.8 Co 0.1 Al 0.1 O2.

5. The battery of claim 3, wherein, The chemical composition of the positive electrode active material includes: LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.55 Co 0.15 Mn 0.30 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.65 Co 0.07 Mn 0.28 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.55 Co 0.15 Mn 0.30 O2.

6. The battery of claim 1, wherein, The cyclic sulfate compound comprises at least one of vinyl sulfate, propylene sulfate, vinylene sulfate, catechol sulfate, bispropylene sulfate, bisvinyl sulfate, 4,5-bis(4-vinyl sulfate) ethylene carbonate, and methylene methane disulfonate. The cyclic sulfite compound comprises vinyl sulfite and / or propylene sulfite. The cyclic sulfonate compound comprises at least one of 1,3-propane sulfonate, 1,3-propylene sulfonate, 1,4-butane sulfonate, 2,4-butane sulfonate, 3-fluoro-1,3-propane sulfonate, 2-fluoro-1,3-propane sulfonate, 1-fluoro-1,3-propane sulfonate, and lithium ethylene sulfonate difluorophosphate triethylamine salt.

7. The battery of claim 1, wherein, The mass percentage of the first additive in the electrolyte is 0.5wt%-2.5wt%. And / or, the mass percentage of the second additive in the electrolyte is 0.5-3wt%.

8. The battery of any of claims 1 or 7, wherein the cathode comprises a lithium metal oxide. The mass ratio of the first additive to the second additive in the electrolyte is 1:0.1-4.

9. The battery of any one of claims 1-7, wherein, Further comprising a lithium salt and a non-aqueous organic solvent; the mass percentage of the lithium salt is 6wt%-25wt%.

10. The battery of claim 8, wherein, Further comprising a lithium salt and a non-aqueous organic solvent; the mass percentage of the lithium salt is 6wt%-25wt%.

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