Battery

Abstract

A battery, comprising a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material and a coating layer covering at least part of the surface of the positive electrode active material; the electrolyte comprises a benzonitrile compound having a structure as shown in formula 1; 125-a) / 24000≤b≤5%; a is 5-100 nm; and b is 0.1%-5%, wherein a is the average thickness (nm) of the coating layer, and b is the mass percentage content of the benzonitrile compound in the electrolyte. The battery has high rate performance and high cycle performance.

Description

A battery TECHNICAL FIELD

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

[0002] Lithium ion batteries are widely used in smart phones, notebook computers, Bluetooth, wearable devices and other fields due to their high platform voltage, large energy density, no memory effect, long service life and other advantages, and play an important role in people's lives.

[0003] However, during the charging and discharging process, some impurities generated by the electrolyte will corrode the positive electrode, leading to the dissolution of positive metal ions, thereby destroying the structure of the positive active material, and further leading to the deterioration of the rate performance and cycle performance of the battery.

[0004] Therefore, it is urgent to develop a battery with high rate performance and cycle performance. SUMMARY

[0005] The present disclosure provides a battery that exhibits high rate performance and cycle performance.

[0006] The present disclosure provides a battery, wherein the battery comprises a positive electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material and a coating layer coated on at least part of the surface of the positive electrode active material.

[0007] The electrolyte comprises a benzenemonocarbonitrile compound having a structure shown in Formula 1:

[0008] wherein R1 is selected from C1-C6 alkyl or alkoxy, and R2, R3, R4, R5 and R6 are each independently selected from F, Cl, Br, I, H, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 sulfonate, C1-C6 sulfate, C2-C6 carboxylate.

[0009] (125-a) / 24000≤b≤5%;

[0010] a is 5-100; and b is 0.1-5%;

[0011] wherein a is the average thickness of the coating layer, in nm; and b is the mass percentage content of the benzenemonocarbonitrile compound in the electrolyte.

[0012] The battery provided by the present disclosure controls the selection of the benzonitrile compound in the electrolyte, as well as the relationship between the thickness of the coating layer on the surface of the positive electrode active material and the mass percentage of the benzonitrile compound, so that the strain capacity of the positive electrode active material to stress is improved, the damage to the structure of the positive electrode active material is reduced, and the transmission power of lithium ions is enhanced, thereby improving the rate performance and cycle performance of the battery. At the same time, the benzonitrile compound can form a CEI film on the surface of the positive electrode active material, thereby protecting the positive electrode active material and further improving the cycle performance of the battery.

[0013] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG1 is a TEM image of lithium nickel cobalt manganese oxide having an aluminum oxide coating layer according to Example 1. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions, and advantages of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present disclosure.

[0016] The present disclosure provides a battery, which includes a positive electrode sheet and an electrolyte, wherein the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material and a coating layer coated on at least a portion of the surface of the positive electrode active material;

[0017] The electrolyte includes a benzonitrile compound having a structure shown in Formula 1:

[0018] wherein R1 is selected from a single bond, a C1-C6 alkyl group or an alkoxy group, and R2, R3, R4, R5, and R6 are each independently selected from F, Cl, Br, I, H, a C1-C6 alkyl group, a C1-C6 alkoxy group, a C1-C6 sulfonate group, a C1-C6 sulfate group, and a C2-C6 carboxylate group;

[0019] (125-a) / 24000≤b≤5%; a is 5-100; b is 0.1-5%;

[0020] Wherein, a is the average thickness of the coating layer, unit is nm; b is the mass percentage content of the benzenemonocarbonitrile compound in the electrolyte.

[0021] According to the scheme provided by the present disclosure, the positive electrode sheet and the electrolyte are applied to a battery, and the battery has excellent rate performance and cycle performance. The reason may be that the present disclosure controls the thickness of the coating layer on the surface of the positive electrode active material, the mass percentage content of the benzenemonocarbonitrile compound in the electrolyte, and the relationship between the two is within the above range. On the one hand, the positive electrode active material surface is covered with a coating layer with a suitable thickness, which can effectively protect the positive electrode active material, improve the strain capacity of the positive electrode active material under stress, avoid the destruction of the electrolyte to the structure of the positive electrode active material during the charging and discharging process, and improve the cycle performance of the battery. On the other hand, the cyano group of a specific amount of benzenemonocarbonitrile compound can coordinate with high-valent metal ions in the positive electrode active material and complex them on the surface of the positive electrode active material to form a CEI film. In the case of a thin coating layer, it cooperates with the positive electrode active material to avoid damage to the positive electrode active material, while ensuring that the positive electrode has low impedance. While improving the cycle performance of the battery, it can also improve the rate performance. In addition, the benzene ring in the benzenemonocarbonitrile compound has good thermal stability, so that the benzenemonocarbonitrile compound can still play its role at a higher temperature, which is beneficial to improve the high-temperature performance and safety performance of the battery.

[0022] The coating of the coating layer on the surface of the positive electrode active material can form a protective layer on the surface of the positive electrode active material, avoid the corrosion of impurities in the electrolyte to the positive electrode active material, avoid the dissolution of positive electrode metal ions, inhibit the damage to the structure of the positive electrode active material, and improve the rate performance and cycle performance of the battery. However, the introduction of a too thick coating layer will cause the impedance of the battery to increase, reduce the transmission rate of lithium ions in the battery, and cause the rate performance of the battery to deteriorate. A too thin coating layer also has no obvious protective effect on the positive electrode. When a is within this range, a protective layer with a suitable thickness can be formed on the surface of the positive electrode active material, and the impedance of the battery can also be controlled within a lower range, thereby improving the rate performance and cycle performance of the battery.

[0023] The battery of the present disclosure comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material and a coating layer, and the coating layer is coated on at least part of the surface of the positive electrode active material. The present disclosure does not limit the selection of the positive electrode active material and the coating layer, which can be selected according to actual needs. For example, lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, etc. can be used as the positive electrode active material, and aluminum oxide, magnesium oxide, cobalt oxide, etc. can be used as the material of the coating layer.

[0024] The electrolyte of the present disclosure includes a benzonitrile compound having a structure shown in Formula 1, wherein R1is selected from a single bond, a C1-C6alkyl group, or an alkoxy group, R2, R3, R4, R5, R6are each independently selected from F, Cl, Br, I, H, a C1-C6alkyl group, a C1-C6alkoxy group, a C1-C6sulfonate group, a C1-C6sulfate group, a C2-C6carboxylate group.

[0025] In the present disclosure, R1being a single bond means that the cyano group is directly connected to the benzene ring through this single bond, such as shown in Formulae 10 to 13 below.

[0026] C1-C6alkyl group of the present disclosure refers to an alkyl group having a carbon number of 1-6, such as -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, etc.; C1-C6alkoxy group of the present disclosure refers to an alkoxy group having a carbon number of 1-6, such as -O-CH2-, -O-CH2CH2-, -O-CH2CH2CH2-, -O-CH(CH3)CH2-, etc.; C1-C6sulfonate group of the present disclosure refers to a sulfonate group having a carbon number of 1-6, such as -SO2O-CH3, -SO2OCH2CH3, -SO2OCH2CH2CH3, etc.; C1-C6sulfate group of the present disclosure refers to a sulfate group having a carbon number of 1-6, such as -OSO2OCH3, -OSO2OCH2CH3, -OSO2OCH2CH2CH3, etc.; C2-C6carboxylate group of the present disclosure refers to a carboxylate group having a carbon number of 2-6, such as -COOCH3, -COOCH2CH3, -COOCH2CH2CH3. When a substituent is specified as a group having a specific number of carbons, all geometric isomers having that number of carbons are included, for example, R1may be selected from -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, -O-CH2-, -O-CH2CH2-, etc., R2-R6are each independently selected from F, Cl, Br, I, H, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)CH3, -O-CH3, -O-CH2CH3, -SO2O-CH3, -SO2OCH2CH3, -OSO2OCH3, -OSO2OCH2CH3, -COOCH3, -COOCH2CH3, etc.

[0027] In one embodiment, the electrolyte includes at least one of the benzonitrile compounds having a structure shown in Formula 1, Formula 10, Formula 11, Formula 12, and Formula 13:

[0028] wherein R1 is selected from C1-C6 alkyl or alkoxy, and R2, R3, R4, R5, R6 are each independently selected from F, Cl, Br, I, H, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 sulfonate, C1-C6 sulfate, C2-C6 carboxylate.

[0029] In the present disclosure, a is 5-100, for example, a is 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100, i.e., the average thickness of the coating layer is 5-100 nm, for example, can be 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

[0030] In the present disclosure, b is 0.1-5%, for example, b is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0031] The present disclosure does not limit the preparation method of the coating layer, for example, the positive electrode active material can be mixed with a solution containing the coating layer material, and then calcined to obtain the positive electrode active material with the coating layer.

[0032] The present disclosure does not limit the preparation method of the positive electrode sheet, which can be prepared by conventional technical means or other preparation processes, and can be selected according to the needs.

[0033] The present disclosure does not limit the method for achieving the above relationship, for example, the thickness of the coating layer and the mass percentage of the benzenemonocarbonitrile compound in the electrolyte can be controlled to obtain the above relationship.

[0034] Specifically, the thickness of the coating layer in the present disclosure can be obtained by transmission electron microscopy.

[0035] In one specific embodiment, (125-a) / 24000≤b≤3%. When the relationship between the thickness of the coating layer and the mass percentage of the benzenemonocarbonitrile compound is within the above range, the coating layer can protect the positive electrode active material to a greater extent, avoid the destruction of the structure of the positive electrode active material by the electrolyte during charging and discharging, further improve the cycle performance of the battery, and the benzenemonocarbonitrile compound can participate in the construction of a more stable CEI film, thereby making the cycle performance and rate performance of the battery more optimal, while ensuring that the benzenemonocarbonitrile compound can still play its role at a higher temperature, further improving the high-temperature performance and safety performance of the battery.

[0036] In one specific embodiment, a is 10-60, for example a is 10, 20, 30, 40, 50 or 60, and b is 0.1-3%, for example b is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%. When the thickness of the coating layer and the mass percentage of the benzonitrile compound in the electrolyte are within the above ranges, the coating layer can protect the positive electrode material to a greater extent while achieving a smaller impedance, avoiding damage to the structure of the positive electrode active material, thereby making the battery exhibit higher cycle performance and rate performance, and the benzonitrile compound can better coordinate with high-valent metal ions, forming a more dense and uniform CEI film on the surface of the positive electrode active material, thereby synergistically protecting the positive electrode active material with the coating layer, further improving the cycle performance of the battery, and the benzonitrile compound can also play a role at a higher temperature, further improving the high-temperature performance and safety performance of the battery.

[0037] In one specific embodiment, the chemical formula of the coating layer material is M x O y wherein M includes at least one of the metal elements Al, Ti, Mg, Zr, Li, Zn, Co, Cr, V, Sn, Mo, Ru, Sb, Nb, and x, y are stoichiometric numbers that can vary depending on the different valence states of the specific metal element, for example when M is Al, x is 2 and y is 3. The coating layer material can be Al2O3, TiO2, MgO, ZrO2, Li2O, ZnO, Nb2O5, etc. When the coating layer uses the above metal oxides, the metal oxides can form a dense and uniform film on the surface of the positive electrode active material, which can protect the positive electrode active material and improve the structural stability of the positive electrode active material, thereby making the cycle performance of the battery more optimal.

[0038] In one specific embodiment, the benzonitrile compound includes a compound having one of the structures shown in Formulas 2-13:

[0039] When the above compounds are used as additives, the benzonitrile compound can better coordinate with high-valent metal ions (such as Co ions) in the positive electrode active material, thereby forming a CEI film on the surface of the positive electrode active material, achieving synergistic protection of the positive electrode active material with a thinner coating layer, further improving the cycle performance and rate performance of the battery, and the above compounds have better thermal stability, making the high-temperature performance and safety performance of the battery higher.

[0040] In an embodiment, the positive active material comprises at least one of doped or undoped lithium cobaltate, doped or undoped lithium manganate, doped or undoped lithium iron phosphate, and doped or undoped lithium nickel cobalt manganate, and the doping element comprises at least one of Al, Mg, Ti, Zr, and Zn. When the above positive active material is used, the positive active material can provide lithium ions for the battery, and the lithium ions can be rapidly transported in the battery, which is beneficial to achieve high rate performance of the battery, and the surface of the positive active material can be better coated with metal oxides, thereby further improving the cycle performance of the battery.

[0041] In an embodiment, the positive active layer comprises, by mass percentage, 92-99% of the positive active material with the coating layer, for example, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, 0.5-4% of the conductive agent, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%, and 0.5-4% of the binder, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%. When the content of each component in the positive active layer is within the above range, the positive active layer has higher conductivity, and can be better attached to the positive current collector, thereby improving the electron and ion transport performance, and further improving the rate performance and cycle performance of the battery.

[0042] The disclosure does not limit the selection of the conductive agent and the binder in the positive active layer. For example, the conductive agent and the binder can be selected from conventional materials in the art, and can be set as needed.

[0043] In an embodiment, the electrolyte further comprises a lithium salt and an organic solvent. When the lithium salt is selected from the above lithium-containing compounds, the lithium salt can be completely dissolved in the organic solvent to form an electrolyte with high stability, so that the lithium ions can be rapidly dissociated and transported in the electrolyte, further improving the conductivity of the electrolyte, and thereby greatly improving the cycle performance and rate performance of the battery.

[0044] In an embodiment, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium trifluoromethylsulfonate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluoro oxalate borate, and lithium dioxalate borate.

[0045] In an embodiment, the organic solvent includes at least one of a carbonate, a carboxylate, a nitrile solvent, a sulfone solvent. The carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC); the carboxylate can include, but is not limited to, at least one of ethyl acetate, ethyl propionate, propyl propionate, methyl propionate, methyl butyrate, ethyl butyrate; the nitrile solvent can include, but is not limited to, at least one of acetonitrile, propionitrile, butyronitrile, ethanedinitrile, propanedinitrile, butanedinitrile; the sulfone solvent can include, but is not limited to, at least one of sulfolane, dimethyl sulfoxide, methyl ethyl sulfoxide (EMS). When the above-mentioned organic solvent is selected, the organic solvent can completely dissolve the lithium salt, achieve an electrolyte with high conductivity and strong stability, thereby facilitating the improvement of the electrochemical performance of the lithium ion battery.

[0046] In an embodiment, the mass percentage of the lithium salt in the electrolyte is 10-20%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0047] In an embodiment, the mass percentage of the organic solvent in the electrolyte is 60-80%, for example, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%.

[0048] When the lithium salt and the organic solvent in the electrolyte are within the above-mentioned ranges, respectively, an electrolyte with high conductivity and stable properties can be prepared, thereby reducing the impedance of the battery and improving the rate performance and cycle performance of the battery.

[0049] In an embodiment, the electrolyte further includes a fluorinated additive; the fluorinated additive includes at least one of fluorinated ethylene carbonate, bis-fluorinated ethylene carbonate, pentafluoropropyl ethyl carbonate, 2-fluoropropyl ethyl carbonate, pentafluoropropyl methyl carbonate, trimethylsilyl methyl trifluorosulfate.

[0050] In an embodiment, the mass percentage of any fluorinated additive in the electrolyte is 1-15%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. When the above-mentioned fluorinated additive is added to the electrolyte and its mass percentage is controlled, the fluorinated additive has high oxidation resistance, can preferentially form a SEI film rich in LiF on the surface of the negative electrode, and makes the stability of the SEI film higher, thereby further improving the cycle performance of the battery.

[0051] In one embodiment, the electrolyte further comprises a sulfur-containing additive; the sulfur-containing additive comprises at least one of ethylene sulfite, propylene sulfite, ethylene sulfate, 1,3-propane sultone, 1,3-propanediol cyclic sulfate.

[0052] In one embodiment, the mass percentage of any sulfur-containing additive in the electrolyte is 0.1-5%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0053] The present disclosure does not limit the preparation method of the electrolyte, in one embodiment, the lithium salt, organic solvent, benzonitrile compound, etc. can be mixed according to a specified ratio.

[0054] Further, when the electrolyte further comprises a fluorinated additive and a sulfur-containing additive, the lithium salt, organic solvent, benzonitrile compound, fluorinated additive, sulfur-containing additive, etc. can be mixed according to a specified ratio.

[0055] In one embodiment, the battery further comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, and the negative electrode current collector is generally a copper foil. The negative electrode active layer can comprise a negative electrode active material, a conductive agent, and a binder.

[0056] The present disclosure does not limit the selection of the negative electrode active material in the negative electrode sheet, for example, it can be selected from one or more of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, nano-silicon, amorphous silicon, and a composite material thereof, and the specific selection can be made according to requirements.

[0057] The present disclosure also does not limit the selection of the conductive agent and the binder in the negative electrode active layer, for example, the conductive agent and the binder can be selected from conventional materials in the art, and the specific selection can be made according to requirements.

[0058] The present disclosure also does not limit the preparation method of the negative electrode sheet, which can be selected from conventional technical means in the art or other preparation processes, and the specific selection can be made according to requirements, for example, the additive is physically mixed with the negative electrode active material, then the mixture is mixed into a solvent for homogenization, and finally the slurry is coated on the negative electrode current collector and dried to obtain the negative electrode sheet.

[0059] In one specific embodiment, the negative active layer comprises 90-99% (e.g. 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) of the negative active material, 0.5-5% (e.g. 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%) of the conductive agent, and 0.5-5% (e.g. 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%) of the binder. When the components in the negative active layer are within this range, the negative active layer has high electrical conductivity and is able to adapt to the electrolyte, so that lithium ions can be rapidly transported in the negative active layer, thereby improving the rate performance and cycle performance of the battery.

[0060] In one specific embodiment, the battery further comprises a separator, which is a separator known in the art that can be used in a battery and is stable to the electrolyte used, and can comprise one or more of polyolefin, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, and can be provided as needed.

[0061] The present disclosure is further described in detail by specific examples below.

[0062] Example 1

[0063] The battery provided in this example is prepared by the following steps:

[0064] 1. Preparation of positive active material with coating layer: lithium nickel cobalt manganese oxide ternary positive active material powder is added to an ethanol solution of aluminum isopropoxide, and is shaken and dispersed for 45 min to uniformly disperse the active material particles, then is stirred at 85°C for 16 h, then is dried at 85°C, and finally is heat treated at 500°C for 12 h to obtain lithium nickel cobalt manganese oxide with an aluminum oxide coating layer.

[0065] The mass ratio of lithium nickel cobalt manganese oxide to aluminum isopropoxide is 0.14:1. Transmission electron microscopy testing of the lithium nickel cobalt manganese oxide with an aluminum oxide coating layer shows that the average thickness of the aluminum oxide coating layer is 6 nm, as shown in FIG. 1.

[0066] 2. Preparation of positive electrode sheet: lithium nickel cobalt manganese oxide with an aluminum oxide coating layer, conductive carbon black, and binder PVDF (polyvinylidene fluoride) are dispersed in an appropriate amount of N-methylpyrrolidone at a mass ratio of 94.5:3:2.5, and after being thoroughly stirred, a uniform positive electrode slurry is formed. The positive electrode slurry is coated on a positive electrode current collector aluminum foil by a coating machine, and then is dried, rolled, cut, and the like to obtain a positive electrode sheet.

[0067] 3. Preparation of the negative electrode sheet: the negative electrode active material artificial graphite, conductive carbon black, SBR (styrene-butadiene rubber), CMC (sodium carboxymethyl cellulose) are dispersed in a proper amount of deionized water in a mass fraction of 93:2.5:3.0:1.5, and a uniform negative electrode slurry is formed after being fully stirred, then the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil by a coating machine, and then the negative electrode sheet is obtained after drying, rolling, cutting and other processes.

[0068] 4. Preparation of the electrolyte: in a glove box filled with argon and with water oxygen content less than 0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) are mixed uniformly in a mass ratio of 20:20:20:20:20, then 12.5% of lithium hexafluorophosphate (LiPF6) of the total mass of the electrolyte is added, and 3% of fluoroethylene carbonate (FEC) and 1.5% of propylene sulfite (PS) and 0.5% of 4-(trifluoromethoxy)benzonitrile are added and mixed uniformly to obtain the required electrolyte.

[0069] The positive electrode sheet, the ordinary separator, and the negative electrode sheet are stacked to completely separate the positive and negative electrode sheets by the separator material, and a roll core is prepared by winding. Then, the roll core is packaged with an aluminum plastic film and injected with electrolyte, and a lithium ion battery is obtained after packaging, aging, formation, and two-sealing processes.

[0070] Example 2

[0071] The preparation method of the lithium ion battery provided in this example is basically the same as that of Example 1, except that the mass percentage of 4-(trifluoromethoxy)benzonitrile in the electrolyte is 2.0%.

[0072] Example 3

[0073] The preparation method of the lithium ion battery provided in this example is basically the same as that of Example 1, except that the mass percentage of 4-(trifluoromethoxy)benzonitrile in the electrolyte is 5.0%.

[0074] Example 4

[0075] The preparation method of the lithium ion battery provided in this example is basically the same as that of Example 1, except that the thickness of the aluminum oxide coating layer is 32 nm.

[0076] Example 5

[0077] The preparation method of the lithium ion battery provided in this example is basically the same as that of Example 1, except that the thickness of the aluminum oxide coating layer is 32 nm, and the mass percentage of 4-(trifluoromethoxy)benzonitrile in the electrolyte is 2.5%.

[0078] Example 6

[0079] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 32 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 4.0%.

[0080] Embodiment 7

[0081] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 57 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 0.3%.

[0082] Embodiment 8

[0083] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 57 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 1.5%.

[0084] Embodiment 9

[0085] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 57 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 3.0%.

[0086] Embodiment 10

[0087] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 98 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 0.15%.

[0088] Embodiment 11

[0089] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 98 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 1.5%.

[0090] Embodiment 12

[0091] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 98 nm, and the mass percentage of 4-(trifluoromethoxy) benzonitrile in the electrolyte is 3.0%.

[0092] Embodiment 13

[0093] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the 4-(trifluoromethoxy)benzonitrile is replaced by phenylacetonitrile, and the mass percentage of the phenylacetonitrile in the electrolyte is 1.0%.

[0094] Embodiment 14

[0095] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 32 nm, the 4-(trifluoromethoxy)benzonitrile is replaced by phenylacetonitrile, and the mass percentage of the phenylacetonitrile in the electrolyte is 1.0%.

[0096] Embodiment 15

[0097] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 57 nm, the 4-(trifluoromethoxy)benzonitrile is replaced by phenylacetonitrile, and the mass percentage of the phenylacetonitrile in the electrolyte is 1.0%.

[0098] Embodiment 16

[0099] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is 98 nm, the 4-(trifluoromethoxy)benzonitrile is replaced by phenylacetonitrile, and the mass percentage of the phenylacetonitrile in the electrolyte is 1.0%.

[0100] Embodiment 17

[0101] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 0.5%, and the coated positive electrode active material is lithium cobaltate.

[0102] Embodiment 18

[0103] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 2.0%, and the coated positive electrode active material is lithium cobaltate.

[0104] Embodiment 19

[0105] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 5.0%, and the coated positive electrode active material is lithium cobaltate.

[0106] Embodiment 20

[0107] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the coated oxide layer substance is magnesium oxide.

[0108] Embodiment 21

[0109] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the coated oxide layer substance is titanium dioxide.

[0110] Embodiment 22

[0111] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass ratio of the lithium nickel cobalt manganese oxide with an aluminum oxide coating layer, the conductive carbon black, and the binder PVDF (polyvinylidene fluoride) in the positive active layer is 95.5:2.5:2.0.

[0112] Embodiment 23

[0113] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass ratio of the lithium nickel cobalt manganese oxide with an aluminum oxide coating layer, the conductive carbon black, and the binder PVDF (polyvinylidene fluoride) in the positive active layer is 92.5:4.5:3.0.

[0114] Embodiment 24

[0115] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the fluorinated ethylene carbonate and the propylene sulfite are not added in the electrolyte.

[0116] Embodiment 25

[0117] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage content of lithium hexafluorophosphate in the electrolyte is 15%.

[0118] Embodiment 26

[0119] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage content of lithium hexafluorophosphate in the electrolyte is 25%.

[0120] Embodiment 27

[0121] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage content of fluorinated ethylene carbonate in the electrolyte is 10%.

[0122] Embodiment 28

[0123] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage of the fluoroethylene carbonate in the electrolyte is 18%.

[0124] Embodiment 29

[0125] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage of the fluoroethylene carbonate in the electrolyte is 18%.

[0126] Embodiment 30

[0127] The preparation method of the lithium ion battery provided in the embodiment is basically the same as that in Embodiment 1, except that the mass percentage of the fluoroethylene carbonate in the electrolyte is 18%.

[0128] Comparative Example 1

[0129] The preparation method of the lithium ion battery provided in the comparative example is basically the same as that in Embodiment 1, except that the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 0.2%.

[0130] Comparative Example 2

[0131] The preparation method of the lithium ion battery provided in the comparative example is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is about 32 nm, and the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 0.2%.

[0132] Comparative Example 3

[0133] The preparation method of the lithium ion battery provided in the comparative example is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is about 57 nm, and the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 0.1%.

[0134] Comparative Example 4

[0135] The preparation method of the lithium ion battery provided in the comparative example is basically the same as that in Embodiment 1, except that the thickness of the aluminum oxide coating layer is about 98 nm, and the electrolyte does not contain 4-(trifluoromethoxy)benzonitrile.

[0136] Comparative Example 5

[0137] The preparation method of the lithium ion battery provided in the comparative example is basically the same as that in Embodiment 1, except that the mass percentage of the 4-(trifluoromethoxy)benzonitrile in the electrolyte is 8%.

[0138] Comparative Example 6

[0139] The preparation method of the lithium ion battery provided by the present comparative example is basically the same as that of Example 1, except that the mass percentage of 4-(trifluoromethoxy)benzonitrile in the electrolyte is 0.1%.

[0140] Comparative Example 7

[0141] The preparation method of the lithium ion battery provided by the present comparative example is basically the same as that of Example 1, except that the surface of the lithium nickel cobalt manganese oxide is not coated with an aluminum oxide coating layer.

[0142] Comparative Example 8

[0143] The preparation method of the lithium ion battery provided by the present comparative example is basically the same as that of Example 1, except that the thickness of the aluminum oxide coating layer is about 220 nm.

[0144] Table 1 shows the preparation parameters of the lithium ion batteries of Examples 1-30 and Comparative Examples 1-8.

[0145] Table 1 shows the preparation parameters of the lithium ion batteries of Examples 1-30 and Comparative Examples 1-8.

[0146] Test Example

[0147] The lithium ion batteries of the examples and comparative examples were subjected to electrochemical performance tests, and the specific test methods were as follows:

[0148] Rate performance: the batteries obtained in the above examples and comparative examples were placed in an environment at 25°C, and charged at a constant current of 0.05C to 4.3V, with a cutoff current of 0.05C. After the batteries were fully charged, they were discharged at a constant current of 0.05C to a cutoff voltage of 3.0V. The initial capacity Q was recorded. Subsequently, the batteries were discharged at rates of 0.5C, 1C, and 2C to 3.0V, and the discharge capacities were recorded as Q1, Q2, and Q3, respectively. The 0.5C capacity retention rate (%) = Q1 / Q x 100%, the 1C capacity retention rate (%) = Q2 / Q x 100%, and the 2C capacity retention rate (%) = Q3 / Q x 100%. The results are shown in Table 2.

[0149] Cycle performance: the batteries obtained in the above examples and comparative examples were placed in an environment at 25°C, and charged at a constant current of 1C to 4.3V, with a cutoff current of 0.05C. After the batteries were fully charged, they were discharged at a constant current of 1C to a cutoff voltage of 3.0V. The initial capacity Q was recorded. When the batteries were cycled for 300 times, the discharge capacity Q4 of the batteries at the 300th cycle was recorded, and the cycle capacity retention rate (%) = Q4 / Q x 100%. The results are shown in Table 2.

[0150] Table 2 shows the rate performance and cycle performance of the lithium ion batteries of Examples 1-30 and Comparative Examples 1-8.

[0151] From Table 2, it can be seen that:

[0152] According to Examples 1-3, a thinner Al2O3 coating layer combined with an appropriate amount of benzonitrile can achieve better rate performance and cycle performance; according to Examples 4-16, as the thickness of the coating layer increases, the rate performance gradually decreases due to the increased migration resistance of lithium ions, but the cycle stability is still good; according to Examples 17-19, when the positive electrode material is lithium cobaltate particles, a thinner Al2O3 coating layer combined with an appropriate amount of benzonitrile on the surface of the positive electrode material can also achieve good rate performance and cycle performance; according to Examples 1 and Examples 20-21, the batteries prepared by coating different oxide layers have the same level of electrochemical performance; according to Examples 1 and Examples 22-23, adjusting the positive electrode material formula within an appropriate range has little effect on the electrochemical performance of the battery; according to Example 24, when the fluorinated additive and the sulfur-containing additive are absent in the electrolyte, the stability of the SEI film and the CEI film formed is poor, resulting in poor cycle performance of the battery; according to Examples 25-30, the content of lithium salt and additive in the electrolyte has a certain effect on the electrochemical performance of the battery; according to Comparative Examples 1-4 and Comparative Example 6, when the content of benzonitrile is too low or benzonitrile is not added to the electrolyte, the cycle performance of the battery is poor; according to Comparative Example 5, although the thickness of the coating layer is small, when the addition amount of benzonitrile is too large, the performance of the electrolyte is affected, and the rate performance of the battery is significantly deteriorated; in Comparative Example 7, since the positive active material is not coated, the stability of the material is poor, and therefore the capacity retention rate of the cycle is poor; according to Comparative Example 8, when the thickness of the coating layer is too large, exceeding 200 nm, although the cycle stability is good, the rate performance is very poor.

[0153] In summary, when the thickness of the coating layer is too large or the addition amount of benzonitrile is too large, the migration of lithium ions will be inhibited, thereby affecting the rate performance of the battery. Adding an appropriate amount of benzonitrile can stabilize the positive electrode material in cooperation with the coating layer, reduce the thickness of the coating layer, effectively improve the rate of the battery, and at the same time, take into account the cycle performance.

[0154] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present disclosure, but not to limit them; although the present disclosure has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A battery, characterized in that: The battery comprises a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material and a coating layer coated on at least a portion of the surface of the positive electrode active material; The electrolyte includes a benzonitrile compound having a structure shown in Formula 1: wherein R1 is selected from a single bond, a C1-C6 alkyl group or an alkoxy group, and R2, R3, R4, R5, and R6 are each independently selected from F, Cl, Br, I, H, a C1-C6 alkyl group, a C1-C6 alkoxy group, a C1-C6 sulfonate group, a C1-C6 sulfate group, and a C2-C6 carboxylate group; (125-a) / 24000≤b≤5%; a is 5-100; b is 0.1-5%; Wherein, a is the average thickness of the coating layer, in nm; b is the mass percentage of the benzonitrile compound in the electrolyte.

2. The battery according to claim 1, characterized in that (125-a) / 24000≤b≤3%.

3. The battery according to claim 1 or 2, characterized in that a is 10-60, and / or b is 0.1-3%.

4. The battery according to any one of claims 1 to 3, characterized in that The chemical formula of the coating material is M x O y , wherein M includes at least one of the metal elements Al, Ti, Mg, Zr, Li, Zn, Co, Cr, V, Sn, Mo, Ru, Sb, and Nb.

5. The battery according to any one of claims 1 to 4, characterized in that: The benzonitrile compound includes a compound having one of the structures shown in Formula 2 to Formula 13:

6. The battery according to any one of claims 1 to 5, characterized in that: The positive electrode active material includes at least one of doped or undoped lithium cobalt oxide, doped or undoped lithium manganese oxide, doped or undoped lithium iron phosphate and doped or undoped lithium nickel cobalt manganese oxide, and the doping element includes at least one of Al, Mg, Ti, Zr and Zn.

7. The battery according to any one of claims 1 to 6, characterized in that: The positive electrode active layer comprises, by mass percentage, 92-99% of a positive electrode active material with a coating layer, 0.5-4% of a conductive agent, and 0.5-4% of a binder.

8. The battery according to any one of claims 1 to 7, characterized in that: The electrolyte further comprises a lithium salt and an organic solvent; Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium trifluoromethylsulfonate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium dioxalatoborate; Preferably, the organic solvent comprises at least one of carbonate, carboxylate, nitrile solvent, and sulfone solvent; Preferably, the mass percentage of the lithium salt in the electrolyte is 10-20%; Preferably, the mass percentage of the organic solvent in the electrolyte is 60-80%.

9. The battery according to any one of claims 1 to 8, characterized in that: The electrolyte further includes a fluorinated additive; The fluorinated additive includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, ethyl pentafluoropropionate, ethyl 2-fluoropropionate, methyl pentafluoropropionate, and methyl trimethylsilyl trifluorosulfonate; Preferably, the mass percentage of any one of the fluorinated additives in the electrolyte is 1-15%.

10. The battery according to any one of claims 1 to 9, characterized in that: The electrolyte further includes a sulfur-containing additive; The sulfur-containing additive includes at least one of vinyl sulfite, propylene sulfite, vinyl sulfate, 1,3-propylene sultone, and 1,3-propylene glycol cyclic sulfate; Preferably, the mass percentage of any one of the sulfur-containing additives in the electrolyte is 0.1-5%.

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