Electrolyte and lithium ion battery

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to an electrolyte and a lithium ion battery. The electrolyte comprises an isoxazole compound and a fluorinated carboxylic acid ester compound, wherein the mass percentage content A% of the isoxazole compound is 3%-20% based on the total mass of the electrolyte, and the mass percentage content B% of the fluorinated carboxylic acid ester compound is 5%-40%. By combining the use of the isoxazole compound and the fluorinated carboxylic acid ester compound in the electrolyte, the electrolyte can have good kinetic performance and high-temperature stability, so as to widen the charging window of the lithium ion battery, improve the fast-charging capacity of the lithium ion battery, and have high-temperature stability at the same time.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to an electrolyte and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in 3C electronics, energy storage, new energy vehicles and other industries, bringing great convenience to people's daily life. At present, whether it is a battery for consumer electronics or a power battery, it is hoped that the charging time of the lithium ion battery can be faster to improve the experience of the terminal product.

[0003] The positive electrode material, the negative electrode material, the separator and the electrolyte are the four main components of the conventional lithium ion battery, and they all play a crucial role in the fast charging performance of the battery. In particular, the electrolyte component, due to the great influence of temperature, solubility, melting point, boiling point and viscosity on different electrolyte components, the kinetic performance of electrolytes with different formulations differs greatly. In addition, the development demand for the lightweight of lithium ion batteries makes the thickness of the electrode sheet and the compaction density of the material more stringent, which further puts forward higher requirements for the kinetic performance of lithium ion batteries.

[0004] At present, due to the limited kinetic performance of conventional carbonate and carboxylate-based electrolytes, and in order to enable lithium ion batteries to meet the performance of cycle and safety, some solvents and additives with poor thermodynamic stability have become essential components, which further limits the improvement of the kinetic performance of lithium ion electrolytes.

[0005] In order to break through the limitation of the kinetic performance of the electrolyte of the lithium ion battery at present, it is urgent to develop a lithium ion battery electrolyte with better kinetic performance and high temperature stability to broaden the charging window of the lithium ion battery and improve the fast charging capacity of the lithium ion battery. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to overcome the defects in the prior art that the kinetic performance and thermal stability of the electrolyte of the lithium ion battery cannot be considered, and the fast charging performance of the lithium ion battery needs to be further improved, so as to provide an electrolyte and a lithium ion battery.

[0007] To this end, the present application provides the following technical solutions:

[0008] According to one aspect of the present application, an electrolyte is provided, comprising: an isoxazole compound and a fluorinated carboxylate compound, wherein the mass percentage content A% of the isoxazole compound is 3%-20%, and the mass percentage content B% of the fluorinated carboxylate compound is 5%-40%, based on the total mass of the electrolyte.

[0009] In some preferred embodiments, the mass percentage content A% of the isoxazole compound and the mass percentage content B% of the fluoro-carboxylic acid ester compound satisfy the following relationship:

[0010] 15≤A+B≤50, and 0.5≤B / A≤10.

[0011] In some preferred embodiments, the isoxazole compound has the following structure:

[0012]

[0013] wherein R1, R2, R3 are each independently selected from at least one of H, halogen, cyano, alkyl, alkoxy, haloalkyl, haloalkoxy, alkylamino, haloalkylamino;

[0014] Preferably, R1, R2, R3 are each independently selected from at least one of H, halogen, cyano, C1-C2 alkyl, C1-C2 alkoxy, C1-C2 haloalkyl, C1-C2 haloalkoxy, C1-C2 alkylamino, C1-C2 haloalkylamino;

[0015] Further preferably, the isoxazole compound has any one of the following structures:

[0016]

[0017] Still further preferably, the isoxazole compound is a fluorine-containing isoxazole compound.

[0018] In some alternative embodiments, the fluoro-carboxylic acid ester compound includes at least one of fluoroacetic acid ethyl ester, fluoroacetic acid propyl ester, fluoropropionic acid methyl ester, fluoropropionic acid ethyl ester, fluoroacetic acid methyl ester, fluoropropionic acid propyl ester, fluoropropionic acid isopropyl ester, fluoroacetic acid isopropyl ester, fluoroacetic acid ethyl ester, fluoroisobutyric acid ethyl ester, fluoroisobutyric acid methyl ester, fluoroacetic acid butyl ester, fluoroacetic acid isobutyl ester, fluoroacetic acid tert-butyl ester;

[0019] Preferably, the fluoro-carboxylic acid ester compound has any one of the following structures:

[0020]

[0021] In some alternative embodiments, a carbonate solvent is further included;

[0022] Preferably, the mass percentage content of the carbonate solvent is 15%-45% based on the total mass of the electrolyte.

[0023] In some alternative embodiments, a lithium salt is further included, and the lithium salt includes LiPF6 and a lithium sulfonate salt;

[0024] Preferably, the mass percentage of LiPF6 is 8%-18% and the mass percentage of the lithium sulfonate is 3%-12% based on the total mass of the electrolyte.

[0025] Further preferably, the total addition amount of the lithium salt L% is 16%-26%.

[0026] In some alternative embodiments, a sulfur-containing additive and / or a nitrile compound is further included.

[0027] Preferably, the mass percentage of the sulfur-containing additive S% is 1%-5% based on the total mass of the electrolyte.

[0028] Further preferably, the mass percentage of the sulfur-containing additive S% and the mass percentage of the isoxazole compound A% satisfy the following relationship:

[0029] 1≤A / S≤10;

[0030] Preferably, the sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, bis ethylene sulfate, methane dithioate, trimethylsilylmethane sulfonate, dimethyl methylene sulfonate, 4-acetylphenyl trifluoromethyl sulfonate, phenyl trifluoromethane sulfonate, and 6-quinolyl trifluoromethane sulfonate.

[0031] Preferably, the nitrile compound includes at least one of benzonitrile, p-tolunitrile, 3,5-difluorobenzonitrile, adiponitrile, succinonitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetricarbonitrile, and 1,2,3-tris(2-cyanato)propane.

[0032] According to yet another aspect of the present application, a lithium ion battery is provided, including the above-mentioned electrolyte.

[0033] In some alternative embodiments, a negative electrode sheet is further included, which includes a negative electrode current collector and a negative electrode active material layer on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, the compaction density of the negative electrode active material being 1.65-1.80 g / cm 3 , and the porosity of the negative electrode sheet being 10%-45%.

[0034] In some alternative embodiments, the negative electrode active material layer is provided with a recessed area, the width of the recessed area being 50 μm-200 μm.

[0035] Preferably, the depth of the recessed area is 3 μm-45 μm.

[0036] The technical solution of the present application has the following advantages:

[0037] The electrolyte provided by the application comprises: an isoxazole compound and a fluorinated carboxylate compound, the mass percentage content A% of the isoxazole compound is 3%-20% based on the total mass of the electrolyte, and the mass percentage content B% of the fluorinated carboxylate compound is 5%-40%. By using the isoxazole compound and the fluorinated carboxylate compound in specific amounts in combination in the electrolyte, the electrolyte can have good kinetic performance and high-temperature stability, thereby widening the charging window of the lithium ion battery, improving the fast charging capability of the lithium ion battery, and having high-temperature stability at the same time. Specifically, the isoxazole compound can be compatible with conventional electrolyte components, and the isoxazole compound has a low melting point and small viscosity, which can reduce the viscosity of the electrolyte, improve the conductivity and wettability of the electrolyte, thereby improving the fast charging capability of the lithium ion battery, widening the charging window of the lithium ion battery, and improving the low-temperature performance of the lithium ion battery; the fluorinated carboxylate compound has good oxidation resistance, high-temperature stability, and moderate dielectric constant, the fluorinated carboxylate compound can inhibit the oxidative decomposition of the isoxazole compound at the positive electrode, and improve the thermal stability of the electrolyte, but the viscosity of the fluorinated carboxylate compound is relatively large, and the use of the fluorinated carboxylate compound in combination with the isoxazole compound can reduce the viscosity of the electrolyte while making the electrolyte have good kinetic performance and high-temperature stability, therefore, the combination of the two can widen the charging window of the lithium ion battery, improve the fast charging capability of the lithium ion battery, and have high-temperature stability at the same time.

[0038] Additional aspects and advantages of the embodiments of the application will be described in part in the description that follows, and will be shown in the drawings. DETAILED DESCRIPTION

[0039] The following examples are provided to better further understand the application and are not limited to the best mode, and do not limit the content and protection scope of the application, and any person under the enlightenment of the application or the combination of the application with other prior art features can obtain any product same or similar to the application, which falls within the protection scope of the application.

[0040] The specific experimental steps or conditions not mentioned in the examples can be carried out according to the conventional experimental steps described in the literature or the operation or conditions. The reagents or instruments not mentioned by the manufacturer are conventional reagent products that can be obtained by purchase.

[0041] In addition, the technical features involved in different embodiments of the application described below can be combined with each other as long as there is no conflict between them.

[0042] According to an aspect of the present application, an electrolyte is provided, comprising: an isoxazole compound and a fluorinated carboxylic acid ester compound, wherein the mass percentage of the isoxazole compound is A% (3%-20%) and the mass percentage of the fluorinated carboxylic acid ester compound is B% (5%-40%) based on the total mass of the electrolyte.

[0043] For example, the mass percentage of the isoxazole compound is A% (3%, 5%, 8%, 10%, 12%, 15%, 17%, 19%, 20%) or within a range defined by any of the above values, and the mass percentage of the fluorinated carboxylic acid ester compound is B% (5%, 8%, 10%, 12%, 15%, 17%, 19%, 20%, 23%, 25%, 28%, 30%, 35%, 40%) or within a range defined by any of the above values, based on the total mass of the electrolyte.

[0044] The present application can make the battery have better fast charging ability and high temperature stability by using a specific amount of isoxazole compound and fluorinated carboxylic acid ester compound in the electrolyte. Specifically, the isoxazole compound can be compatible with conventional electrolyte components, and the isoxazole compound has a low melting point and small viscosity, which can reduce the viscosity of the electrolyte, improve the conductivity and wettability of the electrolyte, thereby improving the fast charging ability of the lithium ion battery, widening the charging window of the lithium ion battery, and improving the low temperature performance of the lithium ion battery. The fluorinated carboxylic acid ester compound has good oxidation resistance, high temperature stability and moderate dielectric constant, and the fluorinated carboxylic acid ester compound can inhibit the oxidative decomposition of the isoxazole compound at the positive electrode, and improve the thermal stability of the electrolyte. However, due to the large viscosity of the fluorinated carboxylic acid ester compound, the use of the isoxazole compound can reduce the viscosity of the electrolyte while making the electrolyte have good kinetic performance. Therefore, the combination of the two can widen the charging window of the lithium ion battery, improve the fast charging ability of the lithium ion battery, and have high temperature stability. If the amount of the isoxazole compound is too small, the viscosity and conductivity of the electrolyte are less affected, and the performance of the battery is hardly improved. If the amount is too large, the oxidation and reduction stability and high temperature stability of the isoxazole compound are not as good as those of the conventional carbonate and carboxylic acid ester solvent, which can result in poor high temperature performance and cycle stability of the battery. If the amount of the fluorinated carboxylic acid ester compound is too small, its amount cannot inhibit the continuous oxidative decomposition of the isoxazole compound at the positive electrode. If the amount is too large, the viscosity of the electrolyte is too large, which is not conducive to the fast charging performance of the lithium ion battery.

[0045] In some optional embodiments, the mass percentage A% of the isoxazole compound and the mass percentage B% of the fluorinated carboxylic acid ester compound satisfy the following relationship:

[0046] 15≤A+B≤50, and 0.5≤B / A≤10.

[0047] As an example, A+B can have a value of 15, 18, 20, 23, 28, 30, 34, 37, 40, 45, 50, or within a range defined by any of the above values; B / A can have a value of 0.5, 1, 3, 5, 7, 9, 10, or within a range defined by any of the above values.

[0048] In the present application, the amount of the isoxazole compound and the carboxylic acid ester compound is within the above suitable range, and the electrolyte can have a low viscosity and good conductivity and wettability, so that the lithium ion battery has a good fast-charging lithium extraction window, a wide electrochemical window, and good cycle stability.

[0049] In some alternative embodiments, the isoxazole compound has a structure as shown below:

[0050]

[0051] wherein R1, R2, R3are each independently selected from at least one of H, halogen, cyano, alkyl, alkoxy, haloalkyl, haloalkoxy, alkylamino, haloalkylamino;

[0052] Preferably, R1, R2, R3are each independently selected from at least one of H, halogen, cyano, C1-C2alkyl, C1-C2alkoxy, C1-C2haloalkyl, C1-C2haloalkoxy, C1-C2alkylamino, C1-C2haloalkylamino;

[0053] Further preferably, the isoxazole compound has a structure as shown in any of the following:

[0054]

[0055] More preferably, the isoxazole compound is a fluorine-containing isoxazole compound.

[0056] In the present application, the fluorine-containing isoxazole compound has better oxidation stability and can be applied to a lithium ion battery with a higher voltage, for example, can be normally cycled in a lithium ion battery with a charging upper limit voltage of 4.2V-4.53V.

[0057] In some alternative embodiments, the fluorinated carboxylic acid ester compound includes at least one of fluorinated ethyl acetate, fluorinated propyl acetate, fluorinated methyl propionate, fluorinated ethyl propionate, fluorinated methyl acetate, fluorinated propyl propionate, fluorinated isopropyl propionate, fluorinated isopropyl acetate, fluorinated ethyl butyrate, fluorinated ethyl isobutyrate, fluorinated methyl isobutyrate, fluorinated butyl acetate, fluorinated isobutyl acetate, fluorinated tert-butyl acetate.

[0058] Preferably, the fluorinated carboxylate compound has any one of the following structures:

[0059]

[0060] In some alternative embodiments, the electrolyte further comprises a carbonate solvent.

[0061] Preferably, the mass percentage of the carbonate solvent in the total mass of the electrolyte is 15%-45%.

[0062] In the present application, the carbonate solvent includes a fluorinated carbonate solvent, which includes but is not limited to at least one of fluorinated ethylene carbonate, fluorinated propylene carbonate, fluorinated methyl ethylene carbonate, fluorinated diethyl carbonate, etc. The carbonate solvent has a high dielectric constant, and appropriate addition in the electrolyte can promote the dissolution of lithium salt; the fluorinated carbonate has good electrochemical oxidation resistance, and appropriate addition in the electrolyte can improve the overall oxidation resistance of the electrolyte and the high-voltage cycle stability of the battery. After appropriate addition of the carbonate solvent and the isoxazoles compound in the electrolyte, the easily film-forming carbonate solvent is preferably formed on the negative electrode, which blocks the direct contact of the isoxazoles compound with the negative electrode and improves the reduction stability of the isoxazoles compound. In addition, in the electrolyte, the carbonate solvent with high dielectric constant occupies the first solvent sheath layer of lithium ion, and the isoxazoles compound with good kinetic performance surrounds the first solvent sheath layer, which reduces the viscosity of the electrolyte and facilitates the rapid transmission of lithium ion in the electrolyte. The combination of the carbonate solvent and the isoxazoles compound can improve the oxidation-reduction stability of the electrolyte, and also has good conductivity and fast charging and discharging capacity.

[0063] In some alternative embodiments, the electrolyte further comprises a lithium salt, which includes LiPF6 and a lithium sulfonate salt.

[0064] In the present application, the lithium sulfonate salt refers to a sulfonic acid group structure in the anion structure of the lithium salt. Typically, the lithium sulfonate salt mainly includes but is not limited to: lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium trifluoromethylsulfonate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, etc.

[0065] LiPF6 is the most commercially used electrolyte at present, which has suitable conductivity and can passivate aluminum foil. However, in the face of increasingly high fast charging requirements, due to the small volume of hexafluorophosphate in LiPF6, the dissociation degree of positive and negative ions is not enough, and pure LiPF6 is difficult to meet the kinetic requirements. Therefore, further optimization is needed on lithium salt and solvent to improve the kinetic performance of lithium ion electrolyte. Lithium sulfonate generally has a larger anion structure, and the negative charge density on the anion is low and easy to be dissociated, so lithium sulfonate generally has a higher ion transference number. The combination of lithium sulfonate and LiPF6 can further improve the rapid charging capacity of lithium ion electrolyte to a certain extent.

[0066] Preferably, the mass percentage of LiPF6 is 8%-18%, and the mass percentage of lithium sulfonate is 3%-12%, based on the total mass of the electrolyte.

[0067] Further optionally, the total addition amount of lithium salt L% is 16%-26%.

[0068] For example, the mass percentage of LiPF6 is 8%, 10%, 12%, 15%, 18%, or within the range consisting of any of the above values, and the mass percentage of lithium sulfonate is 3%, 5%, 7%, 9%, 10%, 12%, or within the range consisting of any of the above values, and the total addition amount of lithium salt is 16%, 18%, 20%, 22%, 24%, 26%, or within the range consisting of any of the above values, based on the total mass of the electrolyte.

[0069] In this application, a higher concentration of lithium salt can make the electrolyte maintain good electrochemical stability and good fast charging performance. When isoxazole compounds are used in electrolyte, the viscosity of electrolyte can be reduced by adding appropriate isoxazole compounds due to the low viscosity of isoxazole compounds, so that the electrolyte with high lithium salt content maintains good kinetic performance. In addition, isoxazole compounds have a certain ability to attract lithium ions due to the -O-N- structure on the isoxazole structure, so the application of isoxazole compounds can further promote the dissociation degree of lithium sulfonate and improve the fast charging performance of lithium ion electrolyte. The combination of isoxazole compounds and appropriate concentration of mixed lithium salt can make the electrolyte have good oxidation stability and kinetics, which is beneficial to the lithium ion battery to have a wider charging window and faster charging and discharging capacity.

[0070] Further preferably, the total addition amount of lithium salt L% and the mass percentage of isoxazole compounds A% satisfy the following relationship:

[0071] 1≤L / A≤8.

[0072] As an example, the value of L / A can be 1, 3, 5, 7, 8, or within a range consisting of any of the above values.

[0073] When the lithium salt concentration is too high and the amount of the isoxazole solvent is too low, the viscosity of the electrolyte is too large, which deteriorates the fast-charging performance of lithium ions; when the lithium salt concentration is too low and the amount of the isoxazole solvent is too high, the stability of the electrolyte is poor due to too many free isoxazole solvent molecules, which easily leads to gas generation at the positive electrode. L / A in a suitable range enables the electrolyte to have good oxidation stability and kinetic performance.

[0074] In some optional embodiments, a sulfur-containing additive and / or a nitrile compound are further included;

[0075] In the present application, in order to prevent direct contact between the isoxazole compound and the positive and negative active materials and improve the oxidation and reduction stability of the isoxazole compound, an appropriate amount of a sulfur-containing additive can be added to the electrolyte. The sulfur-containing additive can form a film on the surface of the positive and negative active materials, reducing the oxidation and reduction decomposition of components with poor oxidation and reduction resistance in the electrolyte. Typically and non-limitingly, the sulfur-containing additive includes but is not limited to one or more of 1,3-propane sulfite (PS), 1,3-propylene sulfite (PST), vinyl sulfate (DTD), bis-vinyl sulfate (BiDTD), methane disulfite (MMDS), trimethylsilylmethane sulfite, dimethyl methylene sulfite, 4-acetylphenyl trifluoromethyl sulfonate, phenyl trifluoromethane sulfonate, and 6-quinolinyl trifluoromethane sulfonate. The nitrile compound includes but is not limited to at least one of benzonitrile, p-tolunitrile, 3,5-difluorobenzonitrile, adiponitrile, succinonitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetricarbonitrile, and 1,2,3-tris(2-cyanooxy)propane.

[0076] In addition, in order to further improve the oxidation stability of the isoxazole compound, an appropriate amount of a nitrile compound can also be added to the electrolyte. Since the nitrile compound is preferably adsorbed on the surface of the positive active material, when the isoxazole compound carrying lithium ions migrates to the surface of the positive active material, it will be physically hindered by the nitrile compound, causing the isoxazole compound to separate from the lithium ions in advance, thereby avoiding direct contact between the isoxazole compound molecules and the positive active material. Therefore, the combination of the isoxazole compound and the positive electrode protection additive can enable the electrolyte to have good kinetic performance and oxidation stability at the same time, thereby inhibiting the oxidation gas generation side reaction of the lithium ion battery.

[0077] Preferably, the mass percentage of the sulfur-containing additive S% is 1%-5% based on the total mass of the electrolyte; as an example, the mass percentage of the sulfur-containing additive is 1%, 2%, 3%, 3.5%, 4%, 5%, or within a range consisting of any of the above values.

[0078] Preferably, the mass percentage of the nitrile compound is 1% to 5% based on the total mass of the electrolyte; for example, the mass percentage of the nitrile compound is 1%, 2%, 3%, 3.5%, 4%, 5%, or within a range defined by any of the above values.

[0079] Further preferably, the mass percentage S% of the sulfur-containing additive and the mass percentage A% of the isoxazoles compound satisfy the following relationship:

[0080] 1≤A / S≤10.

[0081] For example, the ratio of A / S can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or within a range defined by any of the above values. In the present application, when the amount of isoxazoles compound is too much and the amount of sulfur-containing additive is too little, the sulfur-containing additive cannot effectively inhibit the high-temperature gas production of isoxazoles compound, and the high-temperature performance of the battery is poor; when the amount of isoxazoles compound is too low and the amount of sulfur-containing additive is too high, the kinetics of the battery is deteriorated, and although the high-temperature storage performance is excellent, the battery charging window and cycle performance are deteriorated.

[0082] According to another aspect of the present application, a lithium ion battery is provided, comprising the above-mentioned electrolyte.

[0083] In some optional embodiments, a negative electrode sheet is further included, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, and the compaction density of the negative electrode active material being 1.65-1.80 g / cm 3 , and the porosity of the negative electrode sheet being 10%-45%.

[0084] In some optional embodiments, a positive electrode sheet is further included, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, and the compaction density of the positive electrode active material being 4.0-4.3 g / cm 3 , and the porosity of the positive electrode sheet being 15%-35%.

[0085] For example, the compaction density of the negative electrode active material is 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.80 g / cm 3or within a range formed by any of the above values; the porosity of the negative electrode sheet is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or within a range formed by any of the above values; the compaction density of the positive electrode active material is 4.0 g / cm 3 , 4.1 g / cm 3 , 4.2 g / cm 3 , 4.25 g / cm 3 , 4.3 g / cm 3 , or within a range formed by any of the above values; the porosity of the positive electrode sheet is 15%, 20%, 25%, 30%, 35%, or within a range formed by any of the above values.

[0086] As understood by those skilled in the art, if the compaction density of the active material is too low, the porosity of the electrode sheet is too high, the energy density of the battery is small, and the conductivity of the electrode sheet is poor, which will increase the electrochemical impedance and deteriorate the kinetic performance of the battery; if the compaction density of the active material is too high, the porosity of the electrode sheet is too low, and the transmission of lithium ions is more difficult, which will easily lead to lithium precipitation or poor lithium intercalation of the battery.

[0087] In some alternative embodiments, the negative electrode active material layer is provided with a recessed area, and the width of the recessed area is 50 μm-200 μm; for example, the width of the recessed area is 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 170 μm, 200 μm, or within a range formed by any of the above values.

[0088] Preferably, the depth of the recessed area is 3 μm-45 μm; for example, the depth of the recessed area is 3 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or within a range formed by any of the above values.

[0089] In some alternative embodiments, the recessed area is prepared by laser scribing treatment.

[0090] In some alternative embodiments, the positive electrode sheet and / or the negative electrode sheet is further subjected to punching treatment; and the punching is optionally performed by laser.

[0091] In the present application, the electrode material with high compaction density can make the energy density of the battery higher, but high compaction density will cause the wettability of the electrolyte and the liquid retention of the battery to be poor, thereby deteriorating the interface of the electrode, resulting in poor cycle life of the battery. Although the addition of isoxazole compounds in the electrolyte can enhance the wettability of the electrolyte and improve the fast-charging performance of the battery. However, when the compaction density of the electrode material is higher, the gap between the electrode materials is less, the wettability of the electrolyte is poor, the migration of lithium ions in the electrode is slow, and the replenishment speed of lithium ions in the electrolyte will also be slow, so just improving the lithium ion electrolyte dynamics cannot effectively solve the problem of poor charging and discharging dynamics of high compaction density lithium ion batteries. Therefore, laser scribing and / or laser punching processing can be performed on the negative electrode sheet. Laser scribing or punching, on the one hand, shortens the migration path of lithium ions diffusing to the bottom of the electrode sheet, and on the other hand, the space formed by scribing or punching can promote the wettability of the electrolyte and store the electrolyte, reducing the risk of capacity diving due to lack of liquid in the later stage of lithium ion battery cycle. In addition, in order to further improve the dynamics of the lithium ion battery, punching processing can also be performed on the positive electrode sheet, which is also beneficial to improving the dynamics and liquid retention of the battery.

[0092] Preferably, the parameters of the laser scribing processing are: the distance between lines is 1-3 mm, and the depth of the line is 5-30 μm; as an example, the distance between lines is 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, or within the range consisting of any of the above values; the depth of the line is 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or within the range consisting of any of the above values.

[0093] Preferably, the distance between holes is 100-500 μm, and the depth of the hole is 5-30 μm. As an example, the distance between holes is 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 300 μm, 400 μm, 500 μm, or within the range consisting of any of the above values; the depth of the hole is 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or within the range consisting of any of the above values.

[0094] If the interval of laser scribing and punching is too large, the improvement of the dynamics of the battery is limited; if the interval of punching scribing is too close, the strain of the electrode material due to lithium intercalation and deintercalation is large during the cycle, and the internal space generated by punching scribing is too much, which is easy to cause the stress and strain of the electrode material to concentrate and release, thereby causing the battery to deform during the cycle, and the effect of increasing the energy density will be weakened and the risk of deformation of the lithium ion battery during the cycle will be increased.

[0095] In the present application, the lithium ion battery further comprises a separator.

[0096] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0097] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0098] In some alternative embodiments, the mass percentage of each component in the positive electrode active material layer is 90-99.4 wt% of the positive electrode active material, 0.3-5 wt% of the conductive agent, and 0.3-5 wt% of the binder.

[0099] In some alternative embodiments, the mass percentage of each component in the negative electrode active material layer is 90-99.4 wt% of the negative electrode active material, 0.2-5 wt% of the conductive agent, and 0.4-5 wt% of the binder.

[0100] In some alternative embodiments, the conductive agent is selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0101] In some alternative embodiments, the binder includes, but is not limited to, one or more of styrene butadiene rubber emulsion, polytetrafluoroethylene emulsion, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxylated chitosan.

[0102] In some alternative embodiments, the negative electrode active material includes a carbon-based negative electrode material.

[0103] In some alternative embodiments, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0104] In some alternative embodiments, the negative electrode active material can further include a silicon-based negative electrode material.

[0105] According to the battery of the present application, the silicon-based negative electrode material is selected from at least one of nano-silicon (Si), silicon-oxygen negative electrode material (SiO x (0 < x < 2) and silicon-carbon negative electrode material.

[0106] In some alternative embodiments, the positive electrode active material is selected from one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, and lithium-rich lithium manganate; and the chemical formula of the transition metal lithium oxide is Li 1+ x Ni y Co zM 1-y-z O2, wherein -0.5≤x≤0.5; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr.

[0107] According to yet another aspect of the present application, there is provided a power consuming device comprising the above lithium ion battery. The lithium ion battery can be used as a power source of the power consuming device, or as an energy storage unit of the power consuming device. The power consuming device can be, but is not limited to, a mobile device (e.g. a mobile phone, a laptop, etc.), an electric vehicle (e.g. a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0108] The present application will be further described in conjunction with specific examples, which are not to be construed as limiting the scope of the application. In all examples and comparative examples of the present application, the unit % represents mass percent.

[0109] Example 1

[0110] The present example provides an electrolyte, the specific composition and preparation method of which are as follows:

[0111] In an argon-filled glove box (H2O < 0.1 ppm, O2< 0.1 ppm), according to the total mass of the desired electrolyte, ethylene carbonate (EC), fluoroethylene carbonate (FEC), and trifluoromethyl ethylene carbonate (TFPC) were mixed uniformly in a mass ratio of 2:3:2, and then 30% di-fluoroethyl acetate (formula (II-1)) and 10% 2-fluoroisoxazole (formula (I-2)) based on the total mass of the electrolyte were added and mixed uniformly. Then 12 wt% lithium hexafluorophosphate (LiPF6) and 8 wt% lithium bis-trifluoromethylsulfonylimide (LiTFSI) based on the total mass of the electrolyte were quickly added, and after dissolution, 2.5 wt% 1,3-propane sultone (PS) and 2.5 wt% nitrile compound (including HTCN and SN in a mass ratio of 1.5:1) based on the total mass of the electrolyte were added, and after stirring uniformly, the obtained electrolyte passed the moisture and free acid detection.

[0112] Examples 2-17

[0113] Examples 2-17 differ from Example 1 in the specific selection and amount of isoxazole compound and fluoro-carboxylate compound, A+B, B / A, as shown in the following table:

[0114] Table 1

[0115]

[0116] Examples 18-27

[0117] Examples 18-27 differ from Example 1 in the specific selection and amount of lithium salt, L / A, S%, A / S, as detailed in the following table:

[0118] Table 2

[0119]

[0120] Comparative Example 1

[0121] This comparative example differs from Example 1 in that it does not contain an isoxazole compound and the additive is 40% difluoroethyl acetate.

[0122] Comparative Example 2

[0123] This comparative example differs from Example 1 in that it does not contain the fluoro carboxylate compound difluoroethyl acetate.

[0124] Comparative Example 3

[0125] This comparative example differs from Example 1 in that the amount of isoxazole compound added is 30%.

[0126] Comparative Example 4

[0127] This comparative example differs from Example 1 in that the amount of fluoro carboxylate compound difluoroethyl acetate added is 50%.

[0128] Comparative Example 5

[0129] This comparative example differs from Example 1 in that an equal amount of N-ethyl-5-phenylisoxazole-3'-sulfonate is used in place of the isoxazole compound.

[0130] Comparative Example 6

[0131] This comparative example differs from Example 1 in that an equal amount of fluoroethylene carbonate is used in place of the fluoro carboxylate compound difluoroethyl acetate.

[0132] Example El

[0133] This example provides a lithium ion battery having the following specific composition and method of preparation:

[0134] 1) Positive electrode sheet preparation

[0135] The positive electrode active material, lithium cobaltate (LiCoO2, tap density 4.2 g / cm3) was mixed with 0.5% of the additive, 5-phenylisoxazole-3'-sulfonate, and 0.5% of the binder, polyvinylidene fluoride (PVdF) in a ratio of 99.5 / 0.5 / 0.5 by weight. The mixture was then rolled into a sheet having a thickness of 0.1 mm. 3), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) was added, and stirring was performed under the action of a vacuum stirrer until the mixed system became a positive active paste with uniform fluidity; the positive active paste was uniformly coated on both surfaces of an aluminum foil, the single-sided coating thickness was 50 μm, and the area density was 15 mg / cm 2 ; the coated aluminum foil was dried, then subjected to rolling, slitting, laser drilling and other treatments, the distance between holes was 200 μm, and the depth of the holes was 30 μm to obtain the required positive electrode sheet, and the porosity was 20% after testing.

[0136] 2) Preparation of negative electrode sheet

[0137] The negative active material artificial graphite (compacted density 1.7 g / cm 3 ), sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, deionized water was added, and a negative active paste was obtained under the action of a vacuum stirrer; the negative active paste was uniformly coated on both surfaces of a copper foil, the single-sided coating thickness was 60 μm, and the area density was 7 mg / cm 2 ; the coated copper foil was dried at room temperature, then transferred to a 80°C oven for drying for 10 h, then subjected to rolling, slitting, laser scribing and other treatments to form a recessed area, the width of the recessed area was 120 μm, and the depth was 20 μm to obtain the negative electrode sheet, and the porosity was 30% after testing.

[0138] 3) Preparation of electrolyte

[0139] The required electrolyte was prepared according to Example 1.

[0140] 4) Preparation of lithium ion battery

[0141] The positive electrode sheet, the negative electrode sheet and the commercial conventional separator film (consisting of a 5 μm thick polyethylene porous base film plus two layers of 1 μm thick barium sulfate coating and one layer of 1 μm thick polyvinylidene fluoride binder coating on each side, the binder coating being on the outermost side, and the total thickness of the separator film being 9 microns) were stacked in the order of positive electrode sheet, separator film and negative electrode sheet, and then wound to obtain a cell; then, the cell was placed in an outer packaging aluminum foil, and after drying, the electrolyte provided in Example 1 was injected into the outer packaging, and then subjected to vacuum packaging, standing, formation, shaping, sorting and other processes to obtain a square soft-pack lithium ion battery, the total capacity of the battery was 5000 mAh, the thickness was 5.2 mm, the width was 6.5 cm, and the length was 8.0 cm.

[0142] Examples E2-E7

[0143] Examples E2-E7 differ from Example E1 in that the compaction density, porosity, and punching / scribing parameters of the negative active material are different, as shown in the following table:

[0144] Table 3

[0145]

[0146] Examples E8-E33

[0147] Examples E8-E33 differ from Example E1 in that the electrolyte of Examples 2-27 is used in turn.

[0148] Comparative Examples E1-E6

[0149] Comparative Examples E1-E6 differ from Example E1 in that the electrolyte of Comparative Examples 1-6 is used in turn.

[0150] Test Example

[0151] Test method for porosity of active material: The gas displacement method is used for testing, and the specific method is as follows: after the lithium ion battery is discharged to 0% SOC, the electrode sheet is disassembled and taken out, soaked in dimethyl carbonate (DMC) solvent for 12 h, and then rinsed with DMC to remove the lithium salt attached to the electrode sheet, and dried. After drying, the negative electrode sheet is cut into a circular sheet with a diameter of 12 mm using a slicing machine. The thickness of 20 circular sheets is measured using a micrometer, and the volume of each circular sheet is calculated and summed to obtain the sum of the volumes of the 20 circular sheets V1. Subsequently, the true density instrument (such as Jingwei Gaobo JW-M100A full-automatic true density tester) is used to test the true volume V2 of the 20 circular sheets, wherein the test gas is helium, and the test environment temperature is 25±2℃. The porosity of the electrode sheet is (V1-V2) / V1x100%.

[0152] Test method for compaction density of electrode sheet: compaction density = areal density / (thickness of electrode sheet after rolling - thickness of current collector). The areal density is the mass of the material loaded per unit of current collector.

[0153] Test method for battery performance:

[0154] (1) High-temperature storage test of lithium ion battery:

[0155] The lithium ion battery is charged to full capacity and placed in a constant temperature oven at 85℃. The thickness of the battery is measured every 4h until the thickness of the battery expands by more than 15% of the initial thickness. The time taken for the thickness to exceed 15% is taken as the storage life of the lithium ion battery at 85℃.

[0156] (2) High-temperature cycle performance test of lithium ion battery:

[0157] The voltage window of the test of lithium ion was set to 3.0-4.5V. The battery was placed in a 45℃ constant temperature box, and the battery was charged to 4.25V at an initial rate of 3C, then charged to 4.5V at a rate of 1.5C, then constant voltage charged to the current dropped to 0.05C, then the battery was discharged to 3.0V at a rate of 0.7C, which was one cycle. The maximum discharge capacity of the first three cycles was taken as the initial capacity of the battery, the discharge capacity retention rate of the battery was measured, and the cycle number when the discharge capacity retention rate was reduced to 80% of the initial capacity was taken as the high temperature cycle life of the battery.

[0158] (3) Analysis of lithium ion battery charging window:

[0159] The lithium ion battery was charged at a constant current of 3C to the upper limit voltage of 4.5V, and then charged to full power at a constant voltage, and then discharged to 3.0V at a rate of 1C. So cycle 20 times, disassemble the lithium ion battery in the state of full power, and observe the lithium precipitation on the surface of the negative electrode sheet.

[0160] (4) High voltage cycle stability test:

[0161] In a constant temperature box at 25℃, the lithium ion battery was charged to 4.53V at a rate of 1C and discharged to 3V at a rate of 1C, and cycled 300 times, and the capacity retention rate of the lithium ion battery was recorded.

[0162] (5) Wettability test: After the lithium ion battery was injected, it was aged for 12h, and the lithium ion battery was charged to full power at a current of 0.2C, and the battery interface was observed. The interface is golden and has no black spots, purple spots or lithium precipitation, which is good wettability. If a small amount of black spots, purple spots or lithium precipitation appears on the interface, it is poor wettability, and if a large amount of purple spots, black spots or lithium precipitation appears on the interface, it is very poor wettability.

[0163] The specific test results are shown in the following table:

[0164] Table 4

[0165]

[0166]

[0167] From the data in the above table, it can be seen from Examples E1-E7 that reasonable regulation of the parameters of the concave area, the compaction density and the porosity of the negative plate can make the lithium ion battery have good comprehensive performance. From Examples E1 and Examples E8-E33, it can be seen that reasonable adjustment of the content of each component in the lithium ion electrolyte can make the lithium ion battery have a good charging window (fast charging ability is improved), high-temperature storage performance, high-temperature cycle performance and high-voltage stability. From Examples E1 and Comparative Example E1, it can be seen that the absence of isoxazole compounds in the electrolyte leads to poor kinetics of the electrolyte, thereby deteriorating the cycle performance and the charging window, and the wettability of the electrolyte also becomes poor. From Examples E1 and Comparative Example E2, it can be seen that the absence of fluorinated carboxylic acid esters in the electrolyte leads to poor oxidation resistance, thereby deteriorating the cycle performance and the high-temperature storage performance. From Examples E1 and Comparative Example E3, it can be seen that the addition amount of isoxazole compounds is too high, although the charging window of the electrolyte is good, the high-voltage stability is poor, thereby deteriorating the cycle performance, and the high-temperature full-charge storage performance is also poor. From Examples E1 and Comparative Example E4, it can be seen that the content of fluorinated carboxylic acid esters is too high, although the high-voltage stability is good, the high-temperature cycle performance is poor because the repair ability of the SEI film is poor due to the relatively small amount of carbonate solvents during the cycle process. From Examples E1 and Comparative Example E5, it can be seen that the molecular weight of N-ethyl-5-phenylisoxazole-3'-sulfonate is too large, and the kinetics is poor, thereby deteriorating the charging window and the cycle performance of the lithium ion battery. From Examples E1 and Comparative Example E6, it can be seen that the use of equal mass of fluorinated ethylene carbonate instead of fluorinated carboxylic acid compounds leads to poor kinetics and stability of fluorinated ethylene carbonate compared with fluorinated carboxylic acid esters, and therefore the charging window, the high-temperature cycle and the storage performance of the lithium ion battery are deteriorated.

[0168] Obviously, the above examples are merely examples for the sake of clarity, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. All embodiments need not and cannot be exhaustively enumerated here. The obvious changes or variations derived therefrom are still within the scope of the present application.

Claims

1. An electrolyte, characterized in that: include: The isoxazole compound and the fluorocarboxylate compound, based on the total mass of the electrolyte, the mass percentage A% of the isoxazole compound is 3%-20%, and the mass percentage B% of the fluorocarboxylate compound is 5%-40%; The isoxazole compound has the following structure: ， Wherein, R1, R2, and R3 are each independently selected from at least one of H, halogen, cyano, alkyl, alkoxy, haloalkyl, haloalkoxy, alkylamino, and haloalkylamino.

2. The electrolyte according to claim 1, characterized in that The mass percentage A% of the isoxazole compound and the mass percentage B% of the fluorocarboxylate compound satisfy the following relationship: 15≤A+B≤50, and 0.5≤B / A≤10.

3. The electrolyte according to claim 1, characterized in that R1, R2, and R3 are each independently selected from at least one of H, halogen, cyano, C1-C2 alkyl, C1-C2 alkoxy, C1-C2 haloalkyl, C1-C2 haloalkoxy, C1-C2 alkylamino, and C1-C2 haloalkylamino.

4. The electrolyte according to claim 3, characterized in that The isoxazole compound has any of the following structures:

5. The electrolyte according to claim 4, characterized in that The isoxazole compound is a fluorine-containing isoxazole compound.

6. The electrolyte according to claim 1, characterized in that The fluorocarboxylate compound includes at least one of ethyl fluoroacetate, propyl fluoroacetate, methyl fluoropropionate, ethyl fluoropropionate, methyl fluoroacetate, propyl fluoropropionate, isopropyl fluoropropionate, isopropyl fluoroacetate, ethyl fluorobutyrate, ethyl fluoroisobutyrate, methyl fluoroisobutyrate, butyl fluoroacetate, isobutyl fluoroacetate, and tert-butyl fluoroacetate.

7. The electrolyte according to claim 6, characterized in that The fluorocarboxylate compound has any of the following structures:

8. The electrolyte according to claim 1, characterized in that Also included are carbonate solvents.

9. The electrolyte according to claim 8, characterized in that Based on the total mass of the electrolyte, the mass percentage of the carbonate solvent is 15%-45%.

10. The electrolyte according to claim 1, characterized in that Also included are lithium salts including LiPF6 and sulfonic acid lithium salts.

11. The electrolyte according to claim 10, characterized in that Based on the total mass of the electrolyte, the mass percentage of the LiPF6 is 8%-18%; the mass percentage of the sulfonic acid lithium salt is 3%-12%.

12. The electrolyte according to claim 11, characterized in that Based on the total mass of the electrolyte, the total addition amount L% of the lithium salt is 16%-26%.

13. The electrolyte according to any one of claims 1 to 12, characterized in that Sulfur-containing additives and / or nitrile compounds are also included.

14. The electrolyte according to claim 13, characterized in that Based on the total mass of the electrolyte, the mass percentage S% of the sulfur-containing additive is 1%-5%; and / or, the sulfur-containing additive comprises at least one of 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl bissulfate, methylene methanedisulfonate, trimethylsilylmethanesulfonate, dimethylmethylenesulfonate, 4-acetylphenyl trifluoromethanesulfonate, phenyl trifluoromethanesulfonate, and 6-quinolyl trifluoromethanesulfonate; And / or, the nitrile compound includes at least one of benzonitrile, p-toluonitrile, 3,5-difluorobenzonitrile, adiponitrile, succinonitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrinitrile, and 1,2,3-tris(2-cyano)propane.

15. The electrolyte according to claim 14, characterized in that The mass percentage content S% of the sulfur-containing additive and the mass percentage content A% of the isoxazole compound satisfy the following relationship: 1≤A / S≤10.

16. A lithium ion battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 15.

17. The lithium-ion battery according to claim 16, characterized in that The negative electrode sheet also includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the compaction density of the negative electrode active material is 1.65-1.80 g / cm 3 The porosity of the negative electrode sheet ranges from 10% to 45%.

18. The lithium-ion battery according to claim 17, wherein: A recessed area is provided on the negative electrode active material layer, and the width of the recessed area is 50 μm-200 μm; And / or, the depth of the recessed area is 3 μm-45 μm.

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