Ultra-low temperature discharge lithium ion battery and preparation method thereof

Abstract

The present invention relates to a lithium ion battery for ultra-low temperature discharge and a preparation method thereof. The lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and a gel electrolyte. The gel electrolyte comprises the following raw materials in parts by weight: 60-70 parts of an organic solvent, 15-20 parts of a lithium salt, 5-10 parts of an additive, 2-5 parts of a polymerized monomer and 0.01-0.05 parts of an initiator; wherein the additive is phenyl trifluoromethanesulfonate, 12-crown ether-4 and N,N-dimethyltrifluoroacetamide, and the polymerized monomer is polyethylene glycol ditoluene sulfonate and propenyltrimethoxysilane. The present invention optimizes the low-temperature physicochemical properties of the electrolyte by adding additives to the gel electrolyte, and adds polymerized monomers to construct a stable ion transport network. The two synergistically solve the three core problems of lithium ion migration hysteresis, interface instability and lithium dendrites at low temperatures, ultimately achieving efficient discharge performance of the lithium ion battery in an ultra-low temperature environment (-40°C).

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an ultra-low temperature discharge lithium ion battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, with their high energy density, low self-discharge rate, long lifespan, environmental friendliness, and cost-effectiveness, have become the automotive industry's ideal choice for manufacturing pure electric vehicles (EVs). However, their application in low-temperature environments faces challenges, primarily due to increased electrolyte viscosity and reduced lithium-ion transfer efficiency. Therefore, optimizing the performance of electric vehicles at low temperatures while ensuring their high-temperature performance has become a pressing issue.

[0003] Under low-temperature conditions, the main failure mechanisms of lithium-ion batteries include slowed reaction kinetics and liquid-solid phase transitions of the electrolyte. These factors lead to a decrease in electrolyte conductivity, an increase in the desolvation energy of solvated lithium ions at the electrode / electrolyte interface, and a slowdown in the diffusion rate of lithium ions in the electrode material, which in turn causes battery performance degradation, such as capacity loss. In addition, slowed reaction kinetics will also aggravate the polarization phenomenon of the electrochemical reaction, prompting lithium ions to deposit on the negative electrode surface to form metallic lithium, promoting the formation of lithium dendrites, and increasing safety risks such as battery short circuits. Under high-temperature conditions, the degradation of lithium-ion batteries is mainly due to severe side reactions and interface instability, especially the dissolution of transition metal ions in the positive electrode material caused by hydrofluoric acid produced by the thermal decomposition of the electrolyte.

[0004] Gel polymer electrolytes can maintain 10 -4 to 10 -3 S / m ionic conductivity. This property stems from its preparation method, namely, by adding plasticizers or electrolytes to the all-solid-state electrolyte, the solvent or electrolyte is absorbed by the polymer matrix, thus avoiding the risk of leakage. At the same time, the movement of alkali metal salts in the solvent microregions improves the ion transfer rate. Therefore, gel polymer electrolytes combine the advantages of all-solid-state polymer electrolytes and organic electrolytes and are considered an ideal candidate for the next generation of commercial lithium-ion battery electrolytes.

[0005] However, the electrochemical performance of batteries made with conventional gel polymer electrolytes is still difficult to match that of liquid electrolytes. The main problems are the poor compatibility of gel polymer electrolytes with electrodes and the slow lithium ion transport caused by the strong interaction between lithium ions and the polymer backbone, which seriously limits their application in low-temperature environments. Therefore, the development of a gel polymer electrolyte with excellent electrochemical performance and stable operation under low-temperature conditions is crucial for the future development of lithium-ion batteries. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a lithium ion battery capable of ultra-low temperature discharge and a method for preparing the same.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides an ultra-low temperature discharge lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a gel electrolyte, wherein the gel electrolyte comprises the following raw materials in parts by weight: 60-70 parts of an organic solvent, 15-20 parts of a lithium salt, 5-10 parts of an additive, 2-5 parts of a polymerizable monomer, and 0.01-0.05 parts of an initiator; wherein the additive is phenyl trifluoromethanesulfonate, 12-crown ether-4, and N,N-dimethyltrifluoroacetamide, and the polymerizable monomer is polyethylene glycol ditoluenesulfonate and propenyltrimethoxysilane;

[0009] The preparation method of the gel electrolyte comprises the following steps:

[0010] (1) First, dissolve the lithium salt in an organic solvent, then add additives to obtain an electrolyte;

[0011] (2) Adding a polymerization monomer and an initiator to the electrolyte, polymerizing for 12-24 hours at 20-40° C. in a nitrogen atmosphere to obtain the gel electrolyte.

[0012] The phenyl triflate in the additive of this invention acts as a film-forming agent and fluorine source, participating in the formation of a LiF-rich SEI (solid electrolyte interface) film. LiF's high ionic conductivity and low-temperature stability can reduce lithium ion aggregation at low temperatures, thereby improving lithium ion migration efficiency and reducing polarization at low temperatures. Phenyl triflate, as a compound with a strong electron-withdrawing group, can lower the activation energy of the polymerization reaction. Its sulfonate group coordinates with free radicals generated by the decomposition of initiators (such as azobisisoheptonitrile), accelerating the free radical generation rate and enabling efficient polymerization initiation at temperatures as low as -40°C.

[0013] 12-Crown ether-4 as a crown ether additive to regulate Li + The solvation structure of the crown ether allows for more uniform deposition of lithium ions on the electrode surface, reducing the formation of lithium dendrites caused by excessive local current density, thereby improving interfacial stability. At the same time, the lithiophilic properties of the crown ether enhance the compatibility of the lithium salt with the polymerized monomer, preventing the precipitation of the lithium salt during the polymerization process due to insufficient solvation capacity.

[0014] N,N-dimethyltrifluoroacetamide has a low freezing point and high dielectric constant, maintaining electrolyte fluidity at low temperatures while enhancing lithium ion dissociation and improving electrolyte conductivity. Furthermore, its low viscosity and high fluidity improve the dispersion of polymerized monomers in the electrolyte, preventing localized excessive crosslinking caused by monomer aggregation. The N,N-dimethyltrifluoroacetamide and phenyl trifluoromethanesulfonate in the additive lower the solvent's freezing point and viscosity, while the gel network formed by the polymerized monomers stabilizes the solvent molecules, preventing crystallization at low temperatures and collectively maintaining the electrolyte's liquid fluidity and ionic conductivity.

[0015] The monomers used in this invention are polyethylene glycol ditoluene sulfonate and allyltrimethoxysilane. The long-chain structure of polyethylene glycol ditoluene sulfonate forms an elastic network within the gel, maintaining a deformation recovery rate of over 50% even at low temperatures (-40°C), preventing voids from forming at the electrolyte-electrode interface due to shrinkage. During the in-situ polymerization process, polyethylene glycol ditoluene sulfonate and allyltrimethoxysilane form a gel structure with flexible conductive channels (PEG segments) and moderately cross-linked support (Si-O-Si network), which enhances the gel's frost heave resistance. The three-dimensional network formed by the monomers secures small molecule additives within the gel's pores, reducing their excessive consumption on the electrode surface and prolonging their effectiveness. This is particularly advantageous under long-cycle, low-temperature operating conditions.

[0016] Preferably, the mass ratio of phenyl trifluoromethanesulfonate, 12-crown 4-oxadiazole and N,N-dimethyltrifluoroacetamide is 1:(2-4):(3-6).

[0017] Preferably, the mass ratio of the polyethylene glycol ditoluene sulfonate to propenyltrimethoxysilane is 1:(0.5-1.5).

[0018] Preferably, the organic solvent is ethylene carbonate and ethyl methyl carbonate. More preferably, the mass ratio of ethylene carbonate to ethyl methyl carbonate is 1:(0.5-2).

[0019] Preferably, the lithium salt is at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate and lithium hexafluoroarsenate, more preferably lithium hexafluorophosphate.

[0020] Preferably, the initiator is azobisisoheptanonitrile and boron trifluoride in a 1:1 mass ratio. Initiators (such as azobisisoheptanonitrile and boron trifluoride) can effectively control the rate and uniformity of the polymerization reaction, ensuring that the polymerized monomers form a uniform three-dimensional network structure in the electrolyte. This synergistic effect enhances the performance of the gel electrolyte, significantly improving the low-temperature performance of lithium-ion batteries. Specifically, azobisisoheptanonitrile efficiently decomposes at 20-40°C to generate free radicals (such as methyl radicals), which initiate the copolymerization of polyethylene glycol ditoluene sulfonate and allyltrimethoxysilane. Boron trifluoride, as a strong Lewis acid, accelerates the hydrolysis reaction and promotes the rapid formation of a three-dimensional network structure of allyltrimethoxysilane. These two initiators control the rate and uniformity of the polymerization reaction.

[0021] In a second aspect, the present invention provides a method for preparing an ultra-low temperature discharge lithium-ion battery, comprising the following steps:

[0022] The components are stacked and assembled in the order of positive electrode sheet, gel electrolyte, separator, gel electrolyte and negative electrode sheet to obtain the ultra-low temperature discharge lithium ion battery.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The main components of the gel electrolyte of the present invention are additives and polymerized monomers, among which 12-crown ether-4 and N,N-dimethyltrifluoroacetamide can reduce the resistance to lithium ion migration, and polyethylene glycol ditoluene sulfonate provides a flexible polymer network to maintain a continuous transmission channel, thereby significantly improving the ion conductivity at low temperatures. The LiF-rich SEI film formed by phenyl trifluoromethanesulfonate and the silane chemical bonding layer in propenyltrimethoxysilane synergistically inhibit the growth of lithium dendrites, reduce the formation of dead lithium, and improve interface stability. N,N-dimethyltrifluoroacetamide is a low-melting-point solvent, and the polymer network formed by it and the polymerized monomer jointly inhibits the coagulation of the electrolyte, avoids the interruption of ion transmission at low temperatures, and improves the stability of the gel electrolyte structure. The present invention adds additives to the gel electrolyte to optimize the low-temperature physicochemical properties of the electrolyte, and adds polymerized monomers to construct a stable ion transmission network. The two synergistically solve the three core problems of lithium ion migration hysteresis, interface instability, and lithium dendrites at low temperatures, ultimately achieving high-efficiency discharge performance of lithium-ion batteries in ultra-low temperature environments (-40°C). DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0026] Example 1

[0027] A lithium-ion battery capable of ultra-low-temperature discharge, comprising a positive electrode, a negative electrode, a separator, and a gel electrolyte. The gel electrolyte comprises the following raw materials in parts by weight: 65 parts of an organic solvent, 18 parts of a lithium salt, 8 parts of an additive, 3 parts of a polymerizable monomer, and 0.03 parts of an initiator. The additive comprises phenyl trifluoromethanesulfonate, 12-crown ether-4, and N,N-dimethyltrifluoroacetamide in a mass ratio of 1:3:4, the polymerizable monomer comprises polyethylene glycol ditoluenesulfonate and allyltrimethoxysilane in a mass ratio of 1:1, the organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a mass ratio of 1:1, the lithium salt comprises lithium hexafluorophosphate, and the initiator comprises azobisisoheptonitrile and boron trifluoride in a mass ratio of 1:1.

[0028] The preparation method of the gel electrolyte comprises the following steps:

[0029] (1) First, dissolve the lithium salt in an organic solvent, then add additives to obtain an electrolyte;

[0030] (2) Adding a polymerization monomer and an initiator to the electrolyte, polymerizing for 18 hours at 25° C. in a nitrogen atmosphere, to obtain the gel electrolyte.

[0031] The method for preparing the ultra-low temperature discharge lithium ion battery comprises the following steps:

[0032] The components are stacked and assembled in the order of positive electrode sheet, gel electrolyte, separator, gel electrolyte and negative electrode sheet to obtain the ultra-low temperature discharge lithium ion battery; wherein the separator is a polypropylene PP separator.

[0033] The method for preparing a positive electrode sheet comprises the following steps:

[0034] Lithium iron phosphate positive electrode active material, carbon black, and PVDF are thoroughly stirred and mixed in an appropriate amount of N-methylpyrrolidone in a mass ratio of 96:3:1 to obtain a positive electrode active material slurry; the positive electrode active material slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, cold pressing, and die-cutting, a positive electrode sheet is obtained.

[0035] The method for preparing a negative electrode sheet comprises the following steps:

[0036] Artificial graphite, acetylene black, and sodium carboxymethyl cellulose are fully stirred in an appropriate amount of deionized water in a mass ratio of 94:3:3 to form a uniform negative electrode active material slurry; the negative electrode active material slurry is coated on the surface of the negative electrode current collector copper foil, and after drying, cold pressing, and die-cutting, a negative electrode active material layer is formed on the surface of the copper foil to obtain a negative electrode sheet.

[0037] Example 2

[0038] A lithium-ion battery capable of ultra-low-temperature discharge, comprising a positive electrode, a negative electrode, a separator, and a gel electrolyte. The gel electrolyte comprises the following raw materials in parts by weight: 60 parts of an organic solvent, 15 parts of a lithium salt, 10 parts of an additive, 2 parts of a polymerizable monomer, and 0.01 parts of an initiator. The additive comprises phenyl trifluoromethanesulfonate, 12-crown ether-4, and N,N-dimethyltrifluoroacetamide in a mass ratio of 1:2:3, the polymerizable monomer comprises polyethylene glycol ditoluenesulfonate and allyltrimethoxysilane in a mass ratio of 1:0.5, the organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a mass ratio of 1:0.5, the lithium salt comprises lithium perchlorate, and the initiator comprises azobisisoheptonitrile and boron trifluoride in a mass ratio of 1:1.

[0039] The preparation method of the gel electrolyte comprises the following steps:

[0040] (1) First, dissolve the lithium salt in an organic solvent, then add additives to obtain an electrolyte;

[0041] (2) Adding a polymerization monomer and an initiator to the electrolyte, polymerizing for 24 hours at 20° C. in a nitrogen atmosphere, to obtain the gel electrolyte.

[0042] The preparation method of the ultra-low temperature discharge lithium ion battery is the same as that of Example 1.

[0043] Example 3

[0044] A lithium-ion battery capable of ultra-low-temperature discharge, comprising a positive electrode, a negative electrode, a separator, and a gel electrolyte. The gel electrolyte comprises the following raw materials in parts by weight: 70 parts of an organic solvent, 20 parts of a lithium salt, 5 parts of an additive, 5 parts of a polymerizable monomer, and 0.05 parts of an initiator. The additive comprises phenyl trifluoromethanesulfonate, 12-crown ether-4, and N,N-dimethyltrifluoroacetamide in a mass ratio of 1:4:6, the polymerizable monomer comprises polyethylene glycol ditoluenesulfonate and allyltrimethoxysilane in a mass ratio of 1:1.5, the organic solvent comprises ethylene carbonate and ethyl methyl carbonate in a mass ratio of 1:2, the lithium salt comprises lithium tetrafluoroborate, and the initiator comprises azobisisoheptonitrile and boron trifluoride in a mass ratio of 1:1.

[0045] The preparation method of the gel electrolyte comprises the following steps:

[0046] (1) First, dissolve the lithium salt in an organic solvent, then add additives to obtain an electrolyte;

[0047] (2) Adding a polymerization monomer and an initiator to the electrolyte, polymerizing for 12 hours at 30° C. in a nitrogen atmosphere, to obtain the gel electrolyte.

[0048] The preparation method of the ultra-low temperature discharge lithium ion battery is the same as that of Example 1.

[0049] Example 4

[0050] The difference between Example 4 and Example 1 is that the total amount of initiator remains unchanged, azobisisoheptanonitrile is not added, and an equal amount of boron trifluoride is used to make up the missing amount.

[0051] Example 5

[0052] The difference between Example 5 and Example 1 is that the total amount of initiator remains unchanged, boron trifluoride is not added, and an equal amount of azobisisoheptanonitrile is used to make up the missing amount.

[0053] Comparative Example 1

[0054] The difference between Comparative Example 1 and Example 1 is that the total amount of additives remains unchanged, phenyl trifluoromethanesulfonate is not added, and 12-crown-4 and N,N-dimethyltrifluoroacetamide are used in a mass ratio of 3:4 to make up the missing amount.

[0055] Comparative Example 2

[0056] Comparative Example 2 differs from Example 1 in that the total amount of additives remains unchanged, 12-crown ether-4 is not added, and phenyl trifluoromethanesulfonate and N,N-dimethyltrifluoroacetamide in a mass ratio of 1:4 are used to make up the missing amount.

[0057] Comparative Example 3

[0058] Comparative Example 3 differs from Example 1 in that the total amount of additives remains unchanged, N,N-dimethyltrifluoroacetamide is not added, and phenyl trifluoromethanesulfonate and 12-crown ether-4 in a mass ratio of 1:3 are used to make up the missing amount.

[0059] Comparative Example 4

[0060] The difference between Comparative Example 4 and Example 1 is that the total amount of polymerizable monomers remains unchanged, polyethylene glycol ditoluene sulfonate is not added, and an equal amount of propenyltrimethoxysilane is added to make up for the missing amount.

[0061] Comparative Example 5

[0062] The difference between Comparative Example 5 and Example 1 is that the total amount of polymerizable monomers remains unchanged, propenyltrimethoxysilane is not added, and an equal amount of polyethylene glycol ditoluene sulfonate is added to make up for the missing amount.

[0063] Comparative Example 6

[0064] The difference between Comparative Example 6 and Example 1 is that the total amount of the additives remains unchanged, and the additives are phenyl trifluoromethanesulfonate, 12-crown 4-ether, and N,N-dimethyltrifluoroacetamide in a mass ratio of 3:1:4.

[0065] Comparative Example 7

[0066] The difference between Comparative Example 7 and Example 1 is that the total amount of the additives remains unchanged, and the additives are phenyl trifluoromethanesulfonate, 12-crown 4, and N,N-dimethyltrifluoroacetamide in a mass ratio of 4:3:1.

[0067] Performance Testing

[0068] 1. Ionic conductivity test

[0069] The gel electrolytes prepared in Examples 1-5 and Comparative Examples 1-7 were placed between two 16 mm diameter stainless steel sheets to form a symmetrical stainless steel / electrolyte / stainless steel cell. Electrochemical impedance spectroscopy (EIS) was used to measure the ionic conductivity of the electrolytes using an electrochemical workstation with a voltage amplitude of 15 mV and a frequency range of 0.5 Hz to 1.5 MHz. The electrolyte ionic conductivity was measured at approximately -40°C.

[0070] 2. Lithium ion migration number test

[0071] The gel electrolytes prepared in Examples 1-5 and Comparative Examples 1-7 were used to assemble Li / electrolyte / Li symmetric cells. The lithium ion migration number of the electrolyte at about -40°C was measured by chronoamperometry using an electrochemical workstation, and a constant potential polarization process was performed at a potential of 0.01V.

[0072] 3. Normal temperature cycle performance test

[0073] At 25°C, the lithium ion batteries of Examples 1-5 and Comparative Examples 1-7 were charged to 3.65V at a constant current and constant voltage of 0.2C, with a cut-off current of 0.02C, and then discharged to 2.0V at a constant current of 0.2C. The charge and discharge cycles were repeated for 2500 times, and the 2500th capacity retention rate was calculated. The calculation formula is as follows: 2500th cycle capacity retention rate (%) = (2500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0074] 4. Low temperature cycle performance test

[0075] At 25°C, the lithium ion batteries of Examples 1-5 and Comparative Examples 1-7 after capacity separation were charged to 3.65V at 0.2C constant current and constant voltage, with a cut-off current of 0.02C. Then, at -40°C, they were discharged to 2.0V at 0.2C constant current. After 2500 cycles of charge and discharge, the 2500th capacity retention rate was calculated. The calculation formula is as follows: 2500th cycle capacity retention rate (%) = (2500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0076] Table 1 Test results of each group of samples

[0077] Group Ionic conductivity (S / cm) Ion mobility Capacity retention rate after 2500 cycles at room temperature (%) Capacity retention rate after 2500 low-temperature cycles (%) Example 1 <![CDATA[5.23×10 -3 ]]> 0.91 99.15 89.96 Example 2 <![CDATA[4.08×10 -3 ]]> 0.97 97.53 86.32 Example 3 <![CDATA[4.99×10 -3 ]]> 0.92 98.71 89.30 Example 4 <![CDATA[9.37×10 -4 ]]> 0.69 91.35 82.94 Example 5 <![CDATA[8.64×10 -4 ]]> 0.55 90.72 82.67 Comparative Example 1 <![CDATA[1.06×10 -6 ]]> 0.29 70.53 65.38 Comparative Example 2 <![CDATA[1.29×10 -6 ]]> 0.26 70.20 65.46 Comparative Example 3 <![CDATA[9.41×10 -7 ]]> 0.21 67.36 64.69 Comparative Example 4 <![CDATA[5.52×10 -6 ]]> 0.49 82.25 72.53 Comparative Example 5 <![CDATA[2.11×10 -6 ]]> 0.45 81.61 73.39 Comparative Example 6 <![CDATA[2.16×10 -5 ]]> 0.52 83.23 76.52 Comparative Example 7 <![CDATA[1.75×10 -5 ]]> 0.55 84.67 77.20

[0078] As can be seen from Table 1, in combination with Example 1 and Examples 4-5, the initiator of Example 1 is a combination of azobisisoheptanonitrile and boron trifluoride, and its battery performance at low temperature is higher than that of Examples 4-5. This may be because azobisisoheptanonitrile and boron trifluoride can synergistically improve the low-temperature stability of the electrolyte.

[0079] Combining the data of Example 1 and Comparative Examples 1-3 and 6-7, it can be seen that Example 1 uses phenyl trifluoromethanesulfonate, 12-crown ether-4, and N, N-dimethyl trifluoroacetamide in specific dosage ratios as additives, and its low-temperature performance is significantly improved compared to Comparative Examples 1-3 and 6-7. This may be because phenyl trifluoromethanesulfonate can lower the freezing point, N, N-dimethyl trifluoroacetamide reduces viscosity, and phenyl trifluoromethanesulfonate and N, N-dimethyl trifluoroacetamide further enhance the conductivity of the electrolyte by reducing the viscosity of the electrolyte and improving ionic conductivity. 12-crown ether-4 improves the ion solvation structure and, through complexation with lithium ions, improves the migration path of lithium ions and reduces the formation of lithium dendrites. Therefore, phenyl trifluoromethanesulfonate, 12-crown ether-4, and N, N-dimethyl trifluoroacetamide can synergistically prevent solvent crystallization at low temperatures and jointly maintain the liquid fluidity and ionic conductivity of the electrolyte.

[0080] Combining the data of Example 1 and Comparative Examples 4-5, it can be seen that the polymerization monomers are polyethylene glycol ditoluene sulfonate and propenyltrimethoxysilane. When one of them is missing, the low-temperature performance of the battery is significantly reduced. This may be because polyethylene glycol ditoluene sulfonate provides flexibility, while propenyltrimethoxysilane provides mechanical strength and thermal stability. Polyethylene glycol ditoluene sulfonate and propenyltrimethoxysilane interact with each other during the polymerization process to form a uniform cross-linked network. This cross-linked network structure can maintain the integrity and stability of the electrolyte at low temperatures, indicating that the synergistic effect of polyethylene glycol ditoluene sulfonate and propenyltrimethoxysilane can significantly improve the elastic recovery ability of the gel electrolyte and enhance the anti-freeze heave ability of the gel.

[0081] In summary, the gel electrolyte of the present invention optimizes the low-temperature physicochemical properties of the electrolyte through additives and constructs a stable ion transport network through polymerized monomers. The two work together to solve the three core problems of lithium ion migration hysteresis, interface instability and lithium dendrites at low temperatures, ultimately achieving efficient discharge performance of lithium-ion batteries in ultra-low temperature environments (-40°C).

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery for ultra-low temperature discharge, comprising a positive electrode sheet, a negative electrode sheet, a separator and a gel electrolyte, characterized in that: The gel electrolyte comprises the following raw materials in parts by weight: 60-70 parts of an organic solvent, 15-20 parts of a lithium salt, 5-10 parts of an additive, 2-5 parts of a polymerizable monomer, and 0.01-0.05 parts of an initiator; wherein the additive is phenyl trifluoromethanesulfonate, 12-crown ether-4, and N,N-dimethyltrifluoroacetamide, and the polymerizable monomer is polyethylene glycol ditoluenesulfonate and propenyltrimethoxysilane; The preparation method of the gel electrolyte comprises the following steps: (1) First, dissolve the lithium salt in an organic solvent, then add additives to obtain an electrolyte; (2) Adding a polymerization monomer and an initiator to the electrolyte, polymerizing for 12-24 hours at 20-40° C. in a nitrogen atmosphere to obtain the gel electrolyte.

2. The ultra-low temperature discharge lithium-ion battery according to claim 1, wherein: The mass ratio of phenyl trifluoromethanesulfonate, 12-crown 4-ether and N,N-dimethyltrifluoroacetamide is 1:(2-4):(3-6).

3. The ultra-low temperature discharge lithium-ion battery according to claim 1, wherein: The mass ratio of the polyethylene glycol ditoluene sulfonate to propenyltrimethoxysilane is 1:(0.5-1.5).

4. The ultra-low temperature discharge lithium-ion battery according to claim 1, wherein: The organic solvents are ethylene carbonate and ethyl methyl carbonate.

5. The ultra-low temperature discharge lithium-ion battery according to claim 1, wherein: The lithium salt is at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate and lithium hexafluoroarsenate.

6. The ultra-low temperature discharge lithium-ion battery according to claim 1, wherein: The initiator is azobisisoheptanonitrile and boron trifluoride in a mass ratio of 1:

1.

7. The method for preparing an ultra-low temperature discharge lithium ion battery according to any one of claims 1 to 6, characterized in that: The following steps are involved: The components are stacked and assembled in the order of positive electrode sheet, gel electrolyte, separator, gel electrolyte and negative electrode sheet to obtain the ultra-low temperature discharge lithium ion battery.