High-temperature-resistant start-stop type lithium battery and preparation method thereof

Abstract

The application discloses a high-temperature-resistant start-stop type lithium battery and a preparation method thereof, and belongs to the technical field of lithium batteries. The lithium battery comprises a positive plate, an electrolyte, a diaphragm, a negative plate and an aluminum shell. The electrolyte comprises a lithium salt, an additive and a solvent. The lithium salt comprises an electrolyte inorganic lithium salt, lithium trifluoromethanesulfonylimide and lithium difluorophosphate. The solvent comprises a chain carbonate, a fluorinated ethylene carbonate, a vinyl ethylene glycol acrylate and 1,2-di(2-cyanoethoxy)ethane. The additive comprises tri(2-cyanoethyl)borate and a cyanosilicon-based phosphate ester. The cyanosilicon-based phosphate ester contains a siloxane chain, a phosphate ester group and a cyano group. Through the synergistic effect of the components in the optimized ratio, the electrolyte system can effectively inhibit solvent decomposition, electrode structure collapse and harmful side reactions at high temperatures. The start-stop type lithium battery prepared by the application can exhibit excellent cycle life, capacity retention rate and safety in a high-temperature environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a high-temperature-resistant start-stop type lithium battery and a preparation method thereof. BACKGROUND

[0002] The start-stop battery is the basis of the automobile start-stop system and determines the development level of the start-stop system. The start-stop battery not only needs to withstand the instantaneous large current during start-stop and the rapid charge-discharge during driving, but also needs to provide continuous and stable power to the electrical equipment of the vehicle after the engine is turned off. The working environment is very harsh.

[0003] The traditional lead-acid battery has been difficult to meet the needs of the modern high-efficiency start-stop system for rapid charge-discharge, high cycle number and compact space due to its low power density, short cycle life, slow response speed and large volume and weight.

[0004] Therefore, the lithium battery with high power density, long cycle life and rapid charge-discharge capability is considered as an ideal alternative power source for the start-stop system. However, the application of the lithium battery in the automobile start-stop system, especially in the high-temperature closed environment such as the engine compartment, faces severe technical challenges.

[0005] The temperature in the engine compartment of the automobile can be maintained at above 60 DEG C for a long time, and even locally reaches 80 DEG C. Under this high temperature, the carbonate-based electrolyte of the conventional lithium battery will decompose violently, oxidize with the positive active material, and reduce with the negative solid electrolyte interface film, generating a large amount of gas and consuming active lithium. This not only leads to the increase of the internal pressure of the battery, the swelling failure, but also sharply accelerates the capacity attenuation and power reduction, seriously affecting the cycle life and reliability of the battery. SUMMARY

[0006] The application provides a high-temperature-resistant start-stop type lithium battery and a preparation method thereof, which can solve the problem of serious performance attenuation of the lithium battery for the start-stop system under high temperature in the prior art.

[0007] The purpose of the application can be achieved by the following technical solutions.

[0008] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet and an aluminum shell.

[0009] The electrolyte comprises a lithium salt, an additive and a solvent.

[0010] The lithium salt comprises an electrolyte inorganic lithium salt, lithium trifluoromethanesulfonylimide and lithium difluorophosphate.

[0011] The solvent comprises a chain carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-bis(2-cyanoethoxy)ethane.

[0012] The additive includes tris (2-cyanoethyl) borate and cyanosilyl phosphate;

[0013] The cyanosilyl phosphate has the following structural formula:

[0014] .

[0015] In the above technical scheme, the lithium salt includes three components of lithium salt, the lithium battery for the automobile start-stop system needs to meet the requirement of long-term high-temperature resistance, and single electrolyte inorganic lithium salt (such as LiPF6) has poor high-temperature resistance and is easy to decompose to generate HF, corrodes the electrode, and is sensitive to moisture. The lithium trifluoromethanesulfonylimide and lithium difluorophosphate are synchronously added in the present application. On the one hand, lithium trifluoromethanesulfonylimide is a lithium salt with high thermal stability and is not sensitive to moisture, which can improve the thermal stability and hydrolysis resistance of the lithium salt system after being added, and its large anion structure helps to inhibit the growth of lithium dendrites under high-rate discharge. On the other hand, lithium difluorophosphate can be preferentially decomposed at the positive and negative electrodes to form a solid, dense and high ionic conductivity interface film rich in LiF and P-O components, which prevents the further decomposition of the electrolyte and the dissolution of the positive electrode transition metal ions at high temperature. The three kinds of lithium salts synergistically act to improve the thermal stability and interface strengthening ability under the premise of ensuring the basic performance, and enhance the high-temperature resistance.

[0016] On the basis of the above lithium salt system, the solvent system is designed and optimized in the present application. Fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-bis (2-cyanoethoxy) ethane are added in the chain carbonate system. The chain carbonate is easy to oxidize and decompose at high temperature, while the fluoroethylene carbonate can partially inhibit the decomposition of the electrolyte solvent and form an excellent solid electrolyte interface (SEI film) on the electrode surface, thereby reducing the battery impedance and improving the specific capacity and cycle stability of the battery. Vinyl ethoxy ethyl acrylate contains a double bond and an ethoxy segment. Due to the presence of the double bond, partial polymerization reaction can occur at high battery temperature to generate a polymer protective layer on the positive electrode surface, inhibit the oxidative decomposition of the electrolyte at high potential of the positive electrode, coat the positive electrode active material, reduce the positive electrode structure collapse and transition metal dissolution in high-temperature cycle, and the ethoxy segment endows the solvent with good polarity, which can be compatible with other solvents. 1,2-bis (2-cyanoethoxy) ethane contains multiple cyano groups. The cyano group has extremely high polarity and has strong complexation with transition metal ions, which can “capture” the metal ions dissolved from the positive electrode to prevent them from migrating to the negative electrode surface to damage the SEI film and inhibit the high-temperature capacity attenuation.

[0017] The present application adds an additive in the electrolyte, including tris (2-cyanoethyl) borate and cyanosilyl phosphate, wherein the tris (2-cyanoethyl) borate contains borate and cyano groups at the same time. The borate group helps to form a stable boron-containing interface film, improve the Li +The migration rate, the cyan group plays a role of complexing transition metal ions, and preferentially acts on the positive electrode surface, and forms a double insurance with the cyan compound in the aforementioned solvent. As can be seen from the structural formula, the cyanosilane-based phosphate ester of the present application is a compound that integrates siloxane chain, phosphate group and cyan group at the same time. The siloxane chain has good flexibility and high thermal stability. The phosphate is an excellent flame retardant and film-forming component. The cyan group is a strong polar group and metal ion chelating agent. The P=O / O-Si bond existing in the structure improves the interfacial adsorption performance of the compound. At high temperature, the cyan group and the phosphate participate in the formation of a more stable and tougher SEI / CEI film, and the siloxane structure gives the interfacial film better elasticity. At the same time, the cyanosilane-based phosphate ester can form a synergistic effect with the solvent vinyl ethoxy ethyl acrylate. Due to the introduction of the cyan group, the cyan group is a strong electron-withdrawing group, which will weaken the chemical bond connected to it, making these positions more susceptible to attack by free radicals. At high temperature, the double bond of vinyl ethoxy ethyl acrylate is activated and will undergo a free radical polymerization reaction. At this time, the cyanosilane-based phosphate ester will be embedded in the polymer network to form a polymer-inorganic composite protective layer on the electrode surface, which has chemical bonding and physical anchoring combination, flexibility (siloxane), flame retardancy (phosphate) and strong metal ion chelating ability (cyan), and at the same time has good ion transmission channel, enhances the high temperature resistance of the battery.

[0018] Further, the lithium salt accounts for 1-1.5 mol / L of the solvent concentration. The lithium salt concentration needs to balance the ionic conductivity and viscosity. Too high concentration will increase the viscosity, and too low conductivity will not be good, which will affect the high temperature performance.

[0019] Further, the additive is 0.12-0.30% of the mass of the electrolyte.

[0020] Further, the inorganic lithium salt of the electrolyte is one of LiPF6 and LiBF4. LiPF6 and LiBF4 are commonly used lithium salts, which provide basic ionic conductivity, while cooperating with other lithium salts.

[0021] Further, the mass ratio of the inorganic lithium salt of the electrolyte, lithium trifluoromethanesulfonylimide and lithium difluorophosphate in the lithium salt is 1:(0.4-0.6):(0.15-0.3).

[0022] Further, the chain carbonate is at least one of dimethyl carbonate, diethyl carbonate and ethylene carbonate. The chain carbonate is a commonly used solvent, which provides basic dissolving and conducting ability, while cooperating with other solvents.

[0023] Further, the mass ratio of the chain carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-bis(2-cyanoethoxy)ethane in the solvent is 1:(1.5-2.0):(0.2-0.4):(0.1-0.2).

[0024] Further, the mass ratio of the tris (2-cyanoethyl) borate and the cyanosilyl phosphate is 1: (1.0-1.4).

[0025] Further, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector.

[0026] The positive electrode material comprises a positive electrode active component, conductive carbon black and a positive electrode binder.

[0027] The positive electrode active component is one of a lithium iron phosphate material and a ternary lithium nickel cobalt manganese oxide material. The lithium iron phosphate (LFP) has excellent thermal stability (decomposition temperature > 300℃), and is suitable for high-temperature application scenarios; the ternary lithium nickel cobalt manganese oxide has higher energy density, and is suitable for scenarios emphasizing endurance, and both are mainstream positive electrode materials for start-stop batteries.

[0028] Further, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector.

[0029] The negative electrode material comprises a negative electrode active component, conductive carbon black and a negative electrode binder.

[0030] The negative electrode active component is at least one of graphite and soft carbon.

[0031] Further, the preparation method of the cyanosilyl phosphate is as follows:

[0032] Under a nitrogen atmosphere, cyanogen bromide is weighed and added to a flask, and tris (trimethylsilyl) phosphite is weighed according to a molar ratio of 1:1 of tris (trimethylsilyl) phosphite to cyanogen bromide, and is placed in a dropping funnel, the system is warmed to 50-55℃, tris (trimethylsilyl) phosphite is added while stirring, after the addition is completed, constant temperature stirring is continued for 2-4h, the temperature is raised to 60℃, and stirring is continued for 20-40min, the reaction is complete, and the product is obtained after cooling.

[0033] The reaction formula of the above preparation process is as follows:

[0034]

[0035] The application also provides a preparation method of a high-temperature-resistant start-stop type lithium battery, for preparing the high-temperature-resistant start-stop type lithium battery as described above, comprising the following steps:

[0036] Step 1, sequentially and repeatedly stacking the positive electrode sheet, the separator and the negative electrode sheet to form a bare battery cell;

[0037] Step 2, placing the bare battery cell in an aluminum shell, welding, injecting electrolyte, and then performing sealing, formation and capacity distribution processes to obtain the lithium battery.

[0038] The application has the following beneficial effects:

[0039] (1) The lithium salt in the electrolyte of the present application adopts a ternary compound system of electrolyte inorganic lithium salt, lithium trifluoromethanesulfonylimide and lithium difluorophosphate dioxalate. Lithium trifluoromethanesulfonylimide has high thermal stability and hydrolysis resistance, can improve the thermal safety of the overall lithium salt system, and inhibit the growth of lithium dendrites. Lithium difluorophosphate dioxalate can be preferentially decomposed on the electrode surface to form a dense, high-ionic-conductivity interface film rich in LiF and P-O components, effectively blocking the continuous decomposition of the electrolyte and the dissolution of the positive electrode metal ions at high temperatures. The three components synergistically ensure the basic electrical conductivity while significantly enhancing the thermal stability and interface mechanical and chemical stability of the battery.

[0040] (2) The traditional carbonate electrolyte is prone to volatilization and oxidative decomposition at high temperatures. In the present application, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-bis(2-cyanoethoxy)ethane are introduced into the chain carbonate base solvent. Fluoroethylene carbonate helps to form a low-impedance, stable SEI film. Vinyl ethoxy ethyl acrylate can polymerize at high temperatures to form a polymer protective layer on the positive electrode surface, inhibit electrolyte oxidative decomposition and protect the positive electrode structure. The multiple cyan groups in 1,2-bis(2-cyanoethoxy)ethane can strongly complex transition metal ions dissolved from the positive electrode, preventing them from damaging the negative electrode SEI film and thus slowing down the high-temperature capacity decay.

[0041] (3) The present application adds an additive to the electrolyte. The additive tris(2-cyanoethyl)borate has both the film-forming promoting effect of borate and the metal ion chelating function of cyan group. The cyanosilicon-based phosphate designed and prepared integrates siloxane chain (flexible and heat-resistant), phosphate group (flame-retardant and film-forming) and cyan group (strong polarity chelation), and its P=O / O-Si structure enhances the interface adsorption capacity. At high temperatures, the additive can react with vinyl ethoxy ethyl acrylate in the solvent to form a polymer-inorganic composite protective layer combined by chemical bonding and physical anchoring. The protective layer has elasticity, flame retardancy, strong ion chelating ability and good ion conductivity, greatly improving the mechanical strength and high-temperature stability of the SEI / CEI film.

[0042] (4) Through the synergistic effect of the components in the optimized ratio, the electrolyte system can effectively inhibit solvent decomposition, electrode structure collapse and harmful side reactions at high temperatures, and build a stable and high-ionic-conductivity double-electrode interface film. The start-stop lithium battery prepared by the present application can exhibit excellent cycle life, capacity retention rate and safety in high-temperature environment, solving the pain point of serious high-temperature performance decay of existing start-stop batteries. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0044] Preparation Example 1

[0045] Preparation of cyanosilyl phosphate:

[0046] Under the nitrogen atmosphere, cyanogen bromide was weighed and added into a flask, and tris (trimethylsilyl) phosphite was weighed according to the molar ratio of 1:1 of tris (trimethylsilyl) phosphite to cyanogen bromide, and was placed in a dropping funnel, the system was warmed to 55 DEG C, tris (trimethylsilyl) phosphite was added dropwise while stirring, after the addition was completed, constant temperature stirring was continued for 3 h, the temperature was raised to 60 DEG C, and stirring was continued for 30 min, the reaction was completed, and the product was obtained after cooling.

[0047] Example 1

[0048] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet and an aluminum shell.

[0049] The electrolyte comprises a solvent, lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte. The lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide and lithium difluorophosphate, and the mass ratio of the three is 1:0.5:0.20. The solvent is vinyl carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-bis (2-cyanoethoxy) ethane, and the mass ratio of the four is 1:1.8:0.3:0.15. The additive is (2-cyanoethyl) borate and cyanosilyl phosphate (prepared in Preparation Example 1), and the mass ratio of the two is 1:1.2.

[0050] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector. The positive electrode material comprises positive electrode active component, conductive carbon black and positive electrode binder (PVDF), and the mass ratio of the three is 95:3:2. The positive electrode active component is ternary nickel-cobalt-manganese lithium material. The double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0051] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector. The negative electrode material comprises negative electrode active component, conductive carbon black and negative electrode binder (SBR+CMC), and the mass ratio of the three is 96:2:2. The negative electrode active component is artificial graphite. The double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0052] The separator is a PP / PE / PP three-layer film.

[0053] Preparation of lithium battery:

[0054] Step 1, the positive plate, the diaphragm and the negative plate are repeatedly stacked in turn to form a bare battery.

[0055] Step 2, the bare battery is placed in an aluminum shell, and after welding, electrolyte is injected, and after sealing, formation, and capacity distribution processes, a lithium battery is obtained.

[0056] Example 2

[0057] The difference from example 1 is only that the mass ratio of ethylene carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-di(2-cyanoethoxy)ethane in the solvent is adjusted to 1:1.8:0.2:0.15.

[0058] A high-temperature-resistant start-stop type lithium battery, comprising a positive plate, an electrolyte, a diaphragm, a negative plate and an aluminum shell.

[0059] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a total mass of 0.20% of the electrolyte. The lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, and the mass ratio of the three is 1:0.5:0.20; the solvent is ethylene carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-di(2-cyanoethoxy)ethane, and the mass ratio of the four is 1:1.8:0.2:0.15; the additive is (2-cyanoethyl)borate and cyanosilicon-based phosphate (prepared in Preparation Example 1), and the mass ratio of the two is 1:1.2.

[0060] The positive plate comprises a positive current collector and a positive electrode material coated on the positive current collector, and the positive electrode material comprises a positive active component, conductive carbon black and a positive electrode binder (PVDF), and the mass ratio of the three is 95:3:2. The positive active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating surface density of the positive plate is 120 g / m 2 .

[0061] The negative plate comprises a negative current collector and a negative electrode material coated on the negative current collector, and the negative electrode material comprises a negative active component, conductive carbon black and a negative electrode binder (SBR+CMC), and the mass ratio of the three is 96:2:2. The negative active component is artificial graphite, and the double-sided coating surface density of the negative plate is 75 g / m 2 .

[0062] The diaphragm is selected from a PP / PE / PP three-layer film.

[0063] Preparation of lithium battery:

[0064] Step 1, the positive plate, the diaphragm and the negative plate are repeatedly stacked in turn to form a bare battery.

[0065] Step 2, place the bare battery cell in the aluminum shell, inject electrolyte after welding, and get lithium battery after sealing, formation and capacity distribution processes.

[0066] Example 3

[0067] The difference from Example 1 is only that the mass ratio of ethylene carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-di(2-cyanoethoxy)ethane in the solvent is adjusted to 1:1.8:0.4:0.15.

[0068] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet and an aluminum shell.

[0069] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte. The lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, and the mass ratio of the three is 1:0.5:0.20. The solvent is ethylene carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-di(2-cyanoethoxy)ethane, and the mass ratio of the four is 1:1.8:0.4:0.15. The additive is (2-cyanoethyl)borate and cyanosilicon-based phosphate prepared in Preparation Example 1, and the mass ratio of the two is 1:1.2.

[0070] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector. The positive electrode material comprises a positive electrode active component, conductive carbon black and a positive electrode binder (PVDF), and the mass ratio of the three is 95:3:2. The positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating surface density of the positive electrode sheet is 120 g / m 2 .

[0071] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector. The negative electrode material comprises a negative electrode active component, conductive carbon black and a negative electrode binder (SBR+CMC), and the mass ratio of the three is 96:2:2. The negative electrode active component is artificial graphite, and the double-sided coating surface density of the negative electrode sheet is 75 g / m 2 .

[0072] The separator is a PP / PE / PP three-layer film.

[0073] Preparation of lithium battery:

[0074] Step 1, stack the positive electrode sheet, separator and negative electrode sheet in turn to form a bare battery cell.

[0075] Step 2, place the bare battery cell in the aluminum shell, inject electrolyte after welding, and get lithium battery after sealing, formation and capacity distribution processes.

[0076] Example 4

[0077] The difference from Example 1 is only that the mass ratio of (2-cyanoethyl) borate and cyanosilyl phosphate (prepared in Preparation Example 1) in the additive is adjusted to 1:1.0.

[0078] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet and an aluminum shell.

[0079] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte. The lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate with a mass ratio of 1:0.5:0.20. The solvent is vinyl carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate and 1,2-bis(2-cyanoethoxy)ethane with a mass ratio of 1:1.8:0.3:0.15. The additive is (2-cyanoethyl) borate and cyanosilyl phosphate (prepared in Preparation Example 1) with a mass ratio of 1:1.0.

[0080] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector. The positive electrode material comprises a positive electrode active component, conductive carbon black and a positive electrode binder (PVDF) with a mass ratio of 95:3:2. The positive electrode active component is a ternary nickel-cobalt-manganese lithium material. The double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0081] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector. The negative electrode material comprises a negative electrode active component, conductive carbon black and a negative electrode binder (SBR+CMC) with a mass ratio of 96:2:2. The negative electrode active component is artificial graphite. The double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0082] The separator is a PP / PE / PP three-layer film.

[0083] The lithium battery is prepared as follows:

[0084] Step 1, the positive electrode sheet, the separator and the negative electrode sheet are repeatedly stacked in sequence to form a bare battery cell.

[0085] Step 2, the bare battery cell is placed in the aluminum shell, and after welding, the electrolyte is injected, and after sealing, formation and capacity distribution processes, the lithium battery is obtained.

[0086] Example 5

[0087] The difference from Example 1 is only that the mass ratio of (2-cyanoethyl) borate and cyanosilyl phosphate (prepared in Preparation Example 1) in the additive is adjusted to 1:1.4.

[0088] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet and an aluminum shell.

[0089] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte, the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, and the mass ratio of the three is 1:0.5:0.20; the solvent is vinyl carbonate, fluorinated vinyl carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane, and the mass ratio of the four is 1:1.8:0.3:0.15; the additive is (2-cyanoethyl) borate and cyanosilyl phosphate (prepared in Preparation Example 1), and the mass ratio of the two is 1:1.4.

[0090] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF), and the mass ratio of the three is 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0091] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC), and the mass ratio of the three is 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0092] The separator is selected from a PP / PE / PP three-layer film.

[0093] Preparation of a lithium battery:

[0094] Step 1, sequentially and repeatedly stack the positive electrode sheet, the separator, and the negative electrode sheet to form a bare battery cell.

[0095] Step 2, place the bare battery cell in an aluminum shell, weld, and then inject the electrolyte, and go through the processes of sealing, formation, and capacity distribution to obtain a lithium battery.

[0096] Example 6

[0097] The difference from Example 1 is only that the additive is adjusted to 0.12% of the total mass of the electrolyte.

[0098] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0099] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.12% in the total mass of the electrolyte, the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, and the mass ratio of the three is 1:0.5:0.20; the solvent is vinyl carbonate, fluorinated vinyl carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane, and the mass ratio of the four is 1:1.8:0.3:0.15; the additive is (2-cyanoethyl) borate and cyanosilyl phosphate (prepared in Preparation Example 1), and the mass ratio of the two is 1:1.2.

[0100] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF), and the mass ratio of the three is 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0101] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC), and the mass ratio of the three is 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0102] The separator is a PP / PE / PP three-layer film.

[0103] Preparation of a lithium battery:

[0104] Step 1, sequentially and repeatedly stack the positive electrode sheet, the separator, and the negative electrode sheet to form a bare battery cell.

[0105] Step 2, place the bare battery cell in an aluminum shell, weld, and then inject the electrolyte, and go through the processes of sealing, formation, and capacity distribution to obtain a lithium battery.

[0106] Example 7

[0107] The difference from Example 1 is only that the additive is adjusted to 0.30% of the total mass of the electrolyte.

[0108] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0109] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.30% in the total mass of the electrolyte, the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate with a mass ratio of 1:0.5:0.20, the solvent is vinyl carbonate, fluorinated vinyl carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane with a mass ratio of 1:1.8:0.3:0.15, and the additive is (2-cyanoethyl)borate and cyanosilyl phosphate prepared in Preparation Example 1 with a mass ratio of 1:1.2.

[0110] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF) with a mass ratio of 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0111] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC) with a mass ratio of 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0112] The separator is selected from a PP / PE / PP three-layer film.

[0113] Preparation of the lithium battery:

[0114] Step 1, the positive electrode sheet, the separator, and the negative electrode sheet are repeatedly stacked in sequence to form a bare battery cell.

[0115] Step 2, the bare battery cell is placed in an aluminum shell, and after welding, the electrolyte is injected, and after sealing, formation, and capacity distribution processes, the lithium battery is obtained.

[0116] Example 8

[0117] The difference from Example 1 is only that the mass ratio of LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate in the lithium salt is adjusted to 1:0.6:0.15.

[0118] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0119] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte; the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate with a mass ratio of 1:0.6:0.15; the solvent is vinyl carbonate, fluorinated vinyl carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane with a mass ratio of 1:1.8:0.3:0.15; and the additive is (2-cyanoethyl)borate and cyanosilyl phosphate (prepared in Preparation Example 1) with a mass ratio of 1:1.2.

[0120] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF) with a mass ratio of 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0121] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC) with a mass ratio of 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0122] The separator is a PP / PE / PP three-layer film.

[0123] The lithium battery is prepared as follows:

[0124] Step 1, the positive electrode sheet, the separator, and the negative electrode sheet are repeatedly stacked in sequence to form a bare battery cell.

[0125] Step 2, the bare battery cell is placed in an aluminum shell, and after welding, the electrolyte is injected, and the lithium battery is obtained after the processes of sealing, formation, and capacity distribution.

[0126] Example 9

[0127] The difference from Example 1 is that the mass ratio of LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate in the lithium salt is adjusted to 1:0.4:0.3.

[0128] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0129] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte; the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, with a mass ratio of 1:0.4:0.3; the solvent is vinyl carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane, with a mass ratio of 1:1.8:0.3:0.15; and the additive is (2-cyanoethyl)borate and cyanosilyl phosphate (prepared in Preparation Example 1), with a mass ratio of 1:1.2.

[0130] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF), with a mass ratio of 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0131] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC), with a mass ratio of 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0132] The separator is a PP / PE / PP three-layer film.

[0133] Preparation of a lithium battery:

[0134] Step 1, sequentially and repeatedly stack the positive electrode sheet, the separator, and the negative electrode sheet to form a bare battery cell.

[0135] Step 2, place the bare battery cell in an aluminum shell, inject electrolyte after welding, and obtain a lithium battery after the processes of sealing, formation, and capacity distribution.

[0136] Comparative Example 1

[0137] The difference from Example 1 is that the additive in the electrolyte does not contain cyanosilyl phosphate.

[0138] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0139] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte; the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, with a mass ratio of 1:0.5:0.20; the solvent is vinyl carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane, with a mass ratio of 1:1.8:0.3:0.15; and the additive is (2-cyanoethyl) borate.

[0140] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF), with a mass ratio of 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0141] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC), with a mass ratio of 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0142] The separator is a PP / PE / PP three-layer film.

[0143] The lithium battery is prepared as follows:

[0144] Step 1, the positive electrode sheet, the separator, and the negative electrode sheet are repeatedly and sequentially stacked to form a bare battery cell.

[0145] Step 2, the bare battery cell is placed in an aluminum shell, and after welding, electrolyte is injected, and the lithium battery is obtained after the processes of sealing, formation, and capacity distribution.

[0146] Comparative Example 2

[0147] The difference from Example 1 is that the additive in the electrolyte is replaced by tris(trimethylsilyl) phosphite instead of cyanosilyl phosphate.

[0148] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0149] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte; the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate, with a mass ratio of 1:0.5:0.20; the solvent is vinyl carbonate, fluoroethylene carbonate, vinyl ethoxy ethyl acrylate, and 1,2-bis(2-cyanoethoxy)ethane, with a mass ratio of 1:1.8:0.3:0.15; and the additive is (2-cyanoethyl)borate and tris(trimethylsilyl)phosphite, with a mass ratio of 1:1.2.

[0150] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF), with a mass ratio of 95:3:2; the positive electrode active component is a ternary nickel-cobalt-manganese lithium material; and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0151] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC), with a mass ratio of 96:2:2; the negative electrode active component is artificial graphite; and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0152] The separator is a PP / PE / PP three-layer film.

[0153] The lithium battery is prepared as follows:

[0154] Step 1, the positive electrode sheet, the separator, and the negative electrode sheet are repeatedly stacked in sequence to form a bare battery cell.

[0155] Step 2, the bare battery cell is placed in an aluminum shell, and after welding, the electrolyte is injected, and the lithium battery is obtained after the processes of sealing, formation, and capacity distribution.

[0156] Comparative Example 3

[0157] The difference from Example 1 is that the solvent in the electrolyte does not contain vinyl ethoxy ethyl acrylate.

[0158] A high-temperature-resistant start-stop type lithium battery comprises a positive electrode sheet, an electrolyte, a separator, a negative electrode sheet, and an aluminum shell.

[0159] The electrolyte comprises a solvent, a lithium salt with a concentration of 1.2 mol / L in the solvent, and an additive with a mass fraction of 0.20% in the total mass of the electrolyte, the lithium salt in the electrolyte is LiPF6, lithium trifluoromethanesulfonylimide, and lithium difluorophosphate with a mass ratio of 1:0.5:0.20, the solvent is ethylene carbonate, fluoroethylene carbonate, and 1,2-bis(2-cyanoethoxy)ethane with a mass ratio of 1:1.8:0.15, and the additive is (2-cyanoethyl)borate and cyanosilyl phosphate (prepared in Preparation Example 1) with a mass ratio of 1:1.2.

[0160] The positive electrode sheet comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material comprises a positive electrode active component, conductive carbon black, and a positive electrode binder (PVDF) with a mass ratio of 95:3:2, the positive electrode active component is a ternary nickel-cobalt-manganese lithium material, and the double-sided coating area density of the positive electrode sheet is 120 g / m 2 .

[0161] The negative electrode sheet comprises a negative electrode current collector and a negative electrode material coated on the negative electrode current collector, the negative electrode material comprises a negative electrode active component, conductive carbon black, and a negative electrode binder (SBR+CMC) with a mass ratio of 96:2:2, the negative electrode active component is artificial graphite, and the double-sided coating area density of the negative electrode sheet is 75 g / m 2 .

[0162] The separator is a PP / PE / PP three-layer film.

[0163] Preparation of the lithium battery:

[0164] Step 1, the positive electrode sheet, the separator, and the negative electrode sheet are repeatedly stacked in sequence to form a bare battery cell.

[0165] Step 2, the bare battery cell is placed in an aluminum shell, and after welding, the electrolyte is injected, and after sealing, formation, and capacity distribution processes, the lithium battery is obtained.

[0166] The lithium batteries prepared in Examples 1-9 and Comparative Examples 1-3 are subjected to electrochemical performance tests, and the results are shown in Table 1.

[0167] 60℃ cycle performance test: the lithium batteries prepared in the examples and the comparative examples are subjected to cycle performance tests, the initial SOC of the cycle test battery is 80%, and the battery is placed in a 60℃ constant temperature box for 6h, and then charged to 4.2V cutoff at 3C constant current, and then discharged to 2.8V at 3C constant current, which is recorded as 1 cycle, and the above cycle is repeated, and the capacity retention rate of the battery is tested after 300 cycles.

[0168] 80°C high temperature test: lithium batteries prepared by the examples and the comparative examples were prepared, the initial SOC of the batteries was tested to be 80%, the lithium batteries prepared by the examples and the comparative examples were placed in an 80°C constant temperature box for 32h, then charged at 3C constant current to 4.2V cut-off, and then discharged at 3C constant current to 2.8V, and the capacity retention rate of the batteries was calculated.

[0169] Table 1

[0170]

[0171] As can be seen from Table 1, the high-temperature cycle performance of the lithium battery of Example 1 of the present application is obviously superior to that of Comparative Example 1 and Comparative Example 2, and the cyanosilicon-based phosphate in the additive can improve the high-temperature resistance of the battery, so that it can exhibit excellent cycle life as a start-stop type lithium battery in a high-temperature environment. In combination with the test results of Example 1 and Comparative Example 3, the addition of vinyl ethyl ethoxy ethyl acrylate can slow down the capacity decay of the battery at high temperature, and improve the high-temperature stability of the battery.

[0172] It should be noted that, in this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0173] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A high-temperature resistant start-stop type lithium battery, characterized by, The lithium battery comprises a positive plate, an electrolyte, a diaphragm, a negative plate and an aluminum shell. The electrolyte comprises a lithium salt, an additive and a solvent. The lithium salt comprises an electrolyte inorganic lithium salt, lithium trifluoromethanesulfonylimide and lithium difluorophosphate. The solvent comprises a chain carbonate, a fluorinated ethylene carbonate, a vinyl ethoxy ethyl acrylate and 1,2-di(2-cyanoethoxy)ethane. The additive comprises tris(2-cyanoethyl)borate and cyanosilyl phosphate. The cyanosilyl phosphate has the following structural formula: 。 2. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The lithium salt accounts for 1-1.5 mol / L of the solvent concentration.

3. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The additive is 0.12-0.30% of the mass of the electrolyte.

4. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The electrolyte inorganic lithium salt is one of LiPF6 and LiBF4.

5. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The mass ratio of the electrolyte inorganic lithium salt, lithium trifluoromethanesulfonylimide and lithium difluorophosphate in the lithium salt is 1:(0.4-0.6):(0.15-0.3).

6. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The mass ratio of the chain carbonate, the fluorinated ethylene carbonate, the vinyl ethoxy ethyl acrylate and 1,2-di(2-cyanoethoxy)ethane in the solvent is 1:(1.5-2.0):(0.2-0.4):(0.1-0.2).

7. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The mass ratio of the tris(2-cyanoethyl)borate and the cyanosilyl phosphate is 1:(1.0-1.4).

8. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The positive plate comprises a positive current collector and a positive material coated on the positive current collector. The positive material comprises a positive active component, conductive carbon black and a positive binder. The positive active component is one of a lithium iron phosphate material and a ternary lithium nickel cobalt manganese oxide material. The negative plate comprises a negative current collector and a negative material coated on the negative current collector. The negative material comprises a negative active component, conductive carbon black and a negative binder. The negative active component is at least one of graphite and soft carbon.

9. The high-temperature resistant start-stop type lithium battery according to claim 1, characterized in that, The preparation method of the cyanosilyl phosphate is as follows: Under a nitrogen atmosphere, cyanogen bromide is weighed and added to a flask, tris(trimethylsilyl) phosphite is weighed according to a molar ratio of 1:1 with cyanogen bromide, and is placed in a dropping funnel, the system is warmed to 50-55°C, tris(trimethylsilyl) phosphite is added dropwise while stirring, after the addition is completed, constant temperature stirring is continued for 2-4h, the temperature is raised to 60°C and stirring is continued for 20-40min, the reaction is complete, and the product is obtained after cooling.

10. A method for preparing a high-temperature-resistant start-stop type lithium battery, characterized in that, The method for preparing the high-temperature resistant start-stop type lithium battery comprises the following steps: Step 1, the positive plate, the diaphragm and the negative plate are repeatedly stacked in sequence to form a bare battery cell; Step 2, the bare battery cell is placed in the aluminum shell, after welding, the electrolyte is injected, and after sealing, formation, and capacity distribution processes, the lithium battery is obtained.

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