High-temperature-resistant fast-charging electrolyte and lithium ion battery

Abstract

The invention discloses a high-temperature-resistant fast-charging electrolyte and a lithium ion battery. The electrolyte is composed of a non-aqueous organic solvent, two electrolyte salts and two additives. The two electrolyte salts are respectively a P-containing lithium salt and an S-containing lithium salt; the two additives are a fluoro-carbonic ester compound and carbonic ester containing unsaturated bonds respectively; the sigma is calculated according to a dual-mode synergistic conductivity formula, 0.5 < = CP < = 1.5, 0.3 < = CS < = 1, 1 < = CP / CS, 1 < = AF < = 5, 0.5 < = AU < = 3, CP and CS are concentrations of lithium salts containing P and S respectively, and AF and AU are concentrations of two additives respectively. According to the electrolyte, the two additives cooperate with the two electrolyte salts, under the condition of sigma, lithium precipitation of a negative electrode in the fast charging process is effectively avoided, the fast charging time is only 8 min, and meanwhile, the 8min 6C fast charging and cycle life are improved.

Description

Technical Field

[0001] The present application relates to the technical field of rapid charging of batteries, and particularly to an electrolyte for high-temperature fast charging and a lithium-ion battery. Background Art

[0002] At present, the functional requirements for lithium-ion batteries in the market are getting higher and higher. In the field of new energy vehicles, as the cruising range of the whole vehicle generally exceeds 500 kilometers, the pain points of new energy vehicles have gradually changed from "range anxiety" to "charging anxiety". At present, the charging time of electric vehicles is mostly more than 2 hours, which is much longer than the traditional refueling time of 5 minutes. The rapid charging technology is an important means to solve the "charging anxiety" problem.

[0003] In order to improve the fast charging performance of lithium-ion batteries, many researchers have made unremitting efforts, and many studies have improved the fast charging performance from the perspective of electrolytes. The patent application with publication number CN113851725A discloses a fast charging electrolyte for lithium-ion batteries, whose solvent is MF:EC:EMC:DMC = 1:3:2:4, the electrolyte is LiPF6:LiClO4 = 2:1, the total electrolyte content is 2 mol / L, and the negative electrode film-forming additive is allyloxytrimethylsilane (AMSL). The formed SEI can passivate the material interface, reduce the lithium-ion migration impedance, and improve the 5C fast charging performance and cycle life of the battery. However, LiClO4 itself is prone to explosion when impacted and is a strong oxidant, so its safety in batteries is not good and it is not suitable for large-scale industrial use of lithium-ion batteries. The patent application with publication number CN111193071A discloses an electrolyte formula containing 7 additives to improve the normal-temperature fast charging performance and low-temperature performance of the battery. However, polystyrene (PS) used in this method belongs to carcinogenic controlled substances and has been restricted by the European Union. Moreover, this method uses a variety of additives, resulting in a complex configuration process and higher cost of the electrolyte.

[0004] The XFC fast charging technical indicators released by the US Department of Energy are as follows: 1) Charging time ≤ 10 min, 2) Battery energy density ≥ 180 Wh / kg, 3) Battery fast charging cycle life ≥ 500 cycles. The fact that a lithium-ion power battery can be charged to 80% SOC in 10 minutes indicates that its charging current rate is at least 5C. For existing lithium-ion batteries, the charging time is higher than 10 minutes. Therefore, it is still very difficult for the existing technology to achieve extremely fast charging within 8 minutes while the battery has a long life.

[0005] In summary, how to achieve extremely fast charging within 8 minutes while ensuring the battery life is still the research focus and difficulty in the field of extremely fast charging battery technology. Summary of the Invention

[0006] The object of the present application is to provide an improved high-temperature resistant electrolyte for ultra-fast charging, and a lithium-ion battery using the electrolyte.

[0007] The present application adopts the following technical solutions:

[0008] One aspect of the present application discloses a high-temperature resistant fast-charging electrolyte, which is composed of a non-aqueous organic solvent, electrolyte salt 1, electrolyte salt 2, additive 1, and additive 2; electrolyte salt 1 is a lithium salt containing a P atom, electrolyte salt 2 is a lithium salt containing an S atom, additive 1 is a fluorinated carbonate compound, and additive 2 is a carbonate containing an unsaturated bond; the fitted conductivity σ of the electrolyte at 30 °C satisfies 10 mS / cm ≤ σ ≤ 20 mS / cm, and the calculation formula of the fitted conductivity σ is as follows,

[0009]

[0010] Wherein,

[0011] C P is the molar concentration of electrolyte salt 1, with the unit of mol / L, 0.5 ≤ C P ≤ 1.5;

[0012] C S is the molar concentration of electrolyte salt 2, with the unit of mol / L, 0.3 ≤ C S ≤ 1, and 1 ≤ C P / C S ;

[0013] A F is the mass percentage of additive 1, with the unit of wt%, 1 ≤ A F ≤ 5;

[0014] A U is the mass percentage of additive 2, with the unit of wt%, 0.5 ≤ A U ≤ 3;

[0015] σ0 is the conductivity of the solvent plus lithium salt system, and 4 mS / cm ≤ σ0.

[0016] In the σ calculation formula of the present application, is the equilibrium factor, is the synergistic factor, and σ0 is the reference conductivity.

[0017] Equilibrium factor: Based on the Nernst-Einstein equation and the dynamic interfacial adsorption theory, this factor reflects the synergistic dissociation of the double salts. The double salt concentration ratio C P / C S affects the ion transference number. This factor also needs to consider the competitive adsorption of the additive on the negative electrode. Through A F / A URegulate the fluorination degree and crosslinking degree of the SEI film. The square root form reflects the non-linear response of ionic conductivity to the concentration ratio (refer to the modified Kohlrausch's law). Synergistic factor: The sulfonyl group in the sulfur-containing electrolyte salt 2 (C S ) reacts with additive 1 and additive 2 to form a low-impedance fluorinated layer with sulfur-carbon crosslinking (the content of S-C bonds in the SEI detected by XPS is positively correlated with the conductivity). This factor quantifies the dynamic synergistic effect between the mixed salt and the film-forming additives. σ0 is determined by the solvent + lithium salt system. Experiments show that in a carbonate solvent system, a reference conductivity σ0 lower than 4 mS / cm will seriously affect the lithium ion conduction rate, leading to severe lithium deposition during fast charging of lithium batteries and unable to achieve the basic fast charging performance of lithium batteries. Therefore, in a carbonate solvent system, the reference conductivity σ0 is set to be greater than or equal to 4 mS / cm.

[0018] The electrolyte of this application, through the synergistic effect of two electrolyte salts and two additives, greatly improves the lithium ion conduction rate during fast charging, effectively avoids the problems of lithium deposition during fast charging and high-temperature attenuation. The charging time is only 8 minutes, and the 6C / 1C cycle life reaches 2800 cycles. With a charging heating and discharging cooling system, the high-temperature time of the cycle period can be greatly shortened, and the 6C fast charging cycle life is further increased to 5300 cycles, meeting the usage requirements of commercial lithium ion power batteries. The electrolyte and lithium ion battery of this application well solve the problem that existing lithium ion batteries cannot meet the requirement of ultra-fast charging from 0 to 80% SOC within 8 minutes.

[0019] In one implementation of this application, the non-aqueous organic solvent is one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethylene glycol dimethyl ether, acetonitrile, tetrahydrofuran, and 1,3-dioxolane.

[0020] In one implementation of this application, the non-aqueous organic solvent is specifically composed of ethylene carbonate and dimethyl carbonate.

[0021] In one implementation of this application, the P atom of electrolyte salt 1 is provided by a phosphate group.

[0022] In one implementation of this application, electrolyte salt 1 is at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate, and lithium difluorooxalate phosphate.

[0023] In one implementation of this application, electrolyte salt 1 is specifically lithium hexafluorophosphate.

[0024] In one implementation of this application, electrolyte salt 2 is at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate, and lithium bis(trifluoromethyl)sulfonylimide.

[0025] In one implementation of the present application, the electrolyte salt 2 is specifically lithium bis(fluorosulfonyl)imide.

[0026] In one implementation of the present application, the additive 1 is at least one of vinylene carbonate, difluoro vinylene carbonate, fluoromethyl ethyl carbonate, fluorodimethyl carbonate, and fluoro diethyl carbonate.

[0027] In one implementation of the present application, the additive 1 is specifically vinylene carbonate.

[0028] In one implementation of the present application, the additive 2 is at least one of vinylene carbonate, vinyl vinylene carbonate, methylene vinylene carbonate, divinyl vinylene carbonate, ethynyl vinylene carbonate, allyl methyl carbonate, and allyl ethyl carbonate.

[0029] In one implementation of the present application, the additive 2 is specifically vinylene carbonate.

[0030] Another aspect of the present application discloses a lithium-ion battery using the electrolyte of the present application.

[0031] It should be noted that for the lithium-ion battery of the present application, due to the use of the electrolyte of the present application, through the chemical coupling mechanism and dynamic ratio optimization theory of dual salts - additives, during use, a new type of composite SEI film, namely the SEI / CEI film, can be formed at the negative electrode interface. This composite SEI film has high ionic conductivity and high thermal stability, thus greatly improving the conduction rate of Li ions during the extreme fast charging process, and effectively avoiding the problem of lithium deposition at the negative electrode. The lithium-ion battery of the present application has a charging time of only 8 minutes, and the 6C / 1C cycle life reaches 2800 cycles. With a heating and cooling system, the 6C fast charging cycle life of the battery can be further increased to 5300 cycles, achieving extreme fast charging in 8 minutes while ensuring the battery life, and being able to simultaneously improve the problems of lithium deposition during 8-minute @ 6C fast charging and long cycle life of the lithium-ion battery.

[0032] It should also be noted that the key to the lithium-ion battery of the present application lies in using the electrolyte of the present application, enabling it to achieve extreme fast charging in 8 minutes while ensuring the battery life. For other components of the lithium-ion battery, reference can be made to existing lithium-ion batteries. For example, the positive electrode sheet, negative electrode sheet, separator, and housing can all refer to the existing technology.

[0033] In one implementation of the present application, the lithium-ion battery of the present application is composed of the electrolyte of the present application, a positive electrode sheet, a negative electrode sheet, a separator, and a housing.

[0034] Preferably, the positive electrode sheet of the present application includes a positive current collector and a double-sided positive electrode film uniformly coated on the surface of the positive current collector, and the positive electrode film contains a positive active material, a binder, and a conductive agent.

[0035] Preferably, the positive active material is one or more of lithium cobaltate, lithium manganate, ternary nickel cobalt manganese, nickel cobalt aluminum material, and lithium iron phosphate.

[0036] Preferably, the negative electrode sheet of the present application includes a negative current collector and a double-sided negative electrode film uniformly coated on the surface of the negative current collector, and the negative electrode film contains a negative active material, a binder, and a conductive agent.

[0037] Preferably, the negative active material is one or more of natural graphite, artificial graphite, mesocarbon microbeads, and metallic lithium.

[0038] Preferably, the positive current collector is aluminum foil with a thickness of 6-18 μm.

[0039] Preferably, the negative current collector is copper foil with a thickness of 5-17 μm.

[0040] Preferably, the extreme fast charging current of the lithium-ion battery of the present application is ≥4C.

[0041] Preferably, the extreme fast charging current of the lithium-ion battery of the present application is 6C.

[0042] Preferably, when the lithium-ion battery of the present application is charged at room temperature, the charging current is ≥0.2C.

[0043] The beneficial effects of the present application are as follows:

[0044] The electrolyte for extreme fast charging of the present application is based on a new type of dual-mode cooperative conductivity equation. This equation takes into account key fast charging influencing factors such as the dissociation degree balance of double salts, the regulation of SEI fluorination degree by additive adsorption competition, and the interface impedance determined by the cross-linking density of S-C bonds, condensing the complex interfacial chemical process into a quantifiable mathematical expression. The error between the formula-fitted conductivity σ and the actual conductivity σ real value is ≤5%. Therefore, this equation can be used for high-throughput screening of electrolyte formulations, accelerating the development work of new materials, and opening up a new method for electrolyte research and development.

[0045] The electrolyte for ultra-fast charging in this application combines fluorinated carbonate compounds with carbonates containing unsaturated bonds, synergistically with P-containing electrolyte salts and S-containing electrolyte salts. Under the condition of satisfying the dual-mode synergistic conductivity equation, the Li-ion conduction rate during fast charging is improved, effectively avoiding the problem of lithium deposition on the negative electrode during fast charging and the side reaction problem caused by the rupture of the composite SEI film at high temperature. For a lithium-ion battery using the electrolyte of this application, the fast charging time is only 8 minutes, and the 6C fast charging cycle life can reach 5300 cycles, which can simultaneously improve the lithium deposition problem during 8-minute 6C fast charging and the long cycle life problem of lithium-ion batteries. Description of the Drawings

[0046] Figure 1 It is a diagram showing the observation results of lithium deposition on the negative electrode interface of the battery cells prepared with the electrolytes of Test 1 and Comparative Test 1 in the examples of this application under a 6C charging current;

[0047] Figure 2 It is a diagram showing the test results of the capacity retention rate of the battery cells prepared with the electrolyte of Test 1 in the examples of this application;

[0048] Figure 3 It is a diagram showing the fast charging test results of the battery cells prepared with the electrolyte of Test 1 in the examples of this application;

[0049] Figure 4 It is the measured conductivity of the electrolyte of Test 1 in the examples of this application. Detailed Description of the Invention

[0050] The technical difficulty of ultra-fast charging lies in that a large-rate charging current may bring a series of negative problems, such as lithium deposition on the negative electrode or battery heating, which will further accelerate the attenuation of battery capacity and the risk of spontaneous combustion. Therefore, this application believes that the bottleneck of ultra-fast charging technology lies in the lithium intercalation ability of the negative electrode, the Li-ion conduction rate inside the electrolyte, the Li-ion transport ability and high-temperature resistance of the interface SEI, etc. The electrolyte is an important link restricting the Li-ion conduction rate. Developing an electrolyte suitable for ultra-fast charging, long cycle life and high temperature resistance has always been the research focus and difficulty of major battery manufacturers.

[0051] In summary, this application has developed a high-temperature resistant lithium-ion ultra-fast charging electrolyte to solve the problem that existing lithium-ion batteries cannot meet the ultra-fast charging of 0-80% SOC within 8 minutes. For a lithium-ion battery using the electrolyte of this application, the fast charging time is only 8 minutes, and the 6C / 1C cycle life reaches 2800 cycles. With a heating and cooling system, its 6C fast charging cycle life can be further increased to 5300 cycles.

[0052] It should be noted that the present application adopts fluorocarbonate compounds. On the one hand, due to the electron-withdrawing induction effect of F atoms, the binding energy between fluorocarbonate and lithium ions is weakened, and the desolvation of the interface SEI is easier; on the other hand, the SEI interface film containing F formed by the reduction of fluorocarbonate at the negative electrode has better ion conductivity, which can reduce the battery impedance and effectively avoid the occurrence of lithium precipitation. Both aspects are conducive to improving the extremely fast charging performance of lithium-ion batteries. However, the SEI / CEI film formed by a single fluorocarbonate contains a large proportion of inorganic salts, such as LiCO3, LiF, etc. As the extremely fast charging pole piece expands / contracts, the SEI / CEI is easy to break, resulting in aggravated interface side reactions, increased impedance, and deterioration of the cycle life and fast charging performance of lithium-ion batteries. Carbonates containing unsaturated bonds will form a PEO-like polymer SEI / CEI film at the interface of the positive and negative electrodes, which has good elasticity and lithium ion conductivity. Under the condition of extremely fast charging, it can effectively avoid the SEI / CEI rupture caused by the rapid expansion of the pole piece during fast charging, thereby improving the cycle life of the battery. This application combines fluorinated carbonate compounds and carbonates containing unsaturated bonds, combining the advantages of both, and cooperating with electrolyte salts. Under the condition of satisfying the dual-mode synergistic conductivity equation, the constructed SEI / CEI has excellent high-temperature stability, good elasticity and low interface impedance, effectively avoiding negative electrode lithium precipitation during extremely fast charging, and side reactions caused by high-temperature rupture of SEI / CEI. By matching low-viscosity solvents and high-conductivity electrolytes, the extremely fast charging performance of the battery is effectively improved.

[0053] The present application is further described in detail below through specific examples and drawings. The following examples are only used to further illustrate the present application and should not be construed as limiting the present application.

[0054] Example

[0055] 1. Preparation of electrolyte

[0056] In a glove box filled with argon (water <20ppm, oxygen <20ppm), ethylene carbonate EC and dimethyl carbonate DMC were mixed evenly in a mass ratio of 3:7, and then frozen to 0°C. Lithium hexafluorophosphate LiPF6 with a molar fraction of 0.75M and 0.75M lithium bis(fluorosulfonyl)imide LiFSI were slowly added to the mixed solvent and stirred to completely dissolve. 4.0% fluoroethylene carbonate FEC and 0.5% vinylene carbonate VC were added to obtain the electrolyte of this experiment, i.e., Experiment 1, marked as E1.

[0057] According to the preparation method of the electrolyte E1, according to the content ratio in the embodiment formula table 1, electrolytes E2 to E11, namely test 2 to test 11, were prepared.

[0058] Experiment 12: Using the electrolyte of Experiment 1, an external battery heating system and a cooling circulation system, which can realize the thermal regulation function of quickly heating the battery to the specified temperature before charging and cooling it to the specified temperature before discharging.

[0059] Comparative Experiment 1: In a glove box filled with argon (moisture < 20 ppm, oxygen content < 20 ppm), ethylene carbonate EC and dimethyl carbonate DMC were mixed evenly in a mass ratio of 3:7, and then frozen to 0 °C. Lithium hexafluorophosphate LiPF6 with a molar fraction of 1.5 M and lithium bis(fluorosulfonyl)imide LiFSI with a molar fraction of 0.001 M (the denominator of the dual-mode synergistic conductivity equation cannot be 0, so 0.001 M can be considered as an extremely low dosage, having little impact on battery performance and equivalent to no addition) were slowly added to the mixed solvent, and stirred until completely dissolved. 4.0% fluoroethylene carbonate FEC and 0.5% vinylene carbonate VC were added to obtain the electrolyte of this experiment, labeled as Comparative Example 1.

[0060] Comparative Experiment 2: In a glove box filled with argon (moisture < 20 ppm, oxygen content < 20 ppm), ethylene carbonate EC and dimethyl carbonate DMC were mixed evenly in a mass ratio of 3:7, and then frozen to 0 °C. Lithium hexafluorophosphate LiPF6 with a molar fraction of 0.001 M (the denominator of the dual-mode synergistic conductivity equation cannot be 0, so 0.001 M can be considered as an extremely low dosage, having little impact on battery performance and equivalent to no addition) and lithium bis(fluorosulfonyl)imide LiFSI with a molar fraction of 1.5 M were slowly added to the mixed solvent, and stirred until completely dissolved. 3.0% fluoroethylene carbonate FEC and 0.5% vinylene carbonate VC were added to obtain the electrolyte of this experiment, labeled as Comparative Example 2.

[0061] Comparative Experiment 3: In a glove box filled with argon (moisture < 20 ppm, oxygen content < 20 ppm), ethylene carbonate EC and dimethyl carbonate DMC were mixed evenly in a mass ratio of 3:7, and then frozen to 0 °C. Lithium hexafluorophosphate LiPF6 with a molar fraction of 0.75 M and lithium bis(fluorosulfonyl)imide LiFSI with a molar fraction of 0.75 M were slowly added to the mixed solvent, and stirred until completely dissolved. 0.001% fluoroethylene carbonate FEC (the denominator of the dual-mode synergistic conductivity equation cannot be 0, so 0.001% can be considered as an extremely low dosage, having little impact on battery performance and equivalent to no addition) and 2% vinylene carbonate VC were added to obtain the electrolyte of this experiment, labeled as Comparative Example 3.

[0062] Comparative Test 4: In a glove box filled with argon (moisture < 20 ppm, oxygen content < 20 ppm), ethylene carbonate EC and dimethyl carbonate DMC were mixed evenly at a mass ratio of 3:7, and then frozen to 0 °C. Lithium hexafluorophosphate LiPF6 with a molar fraction of 0.75 M and lithium bis(fluorosulfonyl)imide LiFSI with a molar fraction of 0.75 M were slowly added to the mixed solvent, and stirred until completely dissolved. 4.0% fluoroethylene carbonate FEC and 0.001% vinylene carbonate VC were added (the denominator of the dual-mode synergistic conductivity equation cannot be 0, so 0.001% can be considered as an extremely low addition dose with little impact on battery performance, equivalent to no addition), obtaining the electrolyte for this test, labeled as Comparative Example 4.

[0063] II. Battery Assembly and Testing

[0064] The electrolytes of the above tests and comparative tests were respectively made into lithium-ion power batteries with a soft-pack capacity design of 2000 mAh. The positive electrode used in the battery: The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black SuperP, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 93:4:3, and they were dispersed in N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. The slurry was evenly coated on both sides of the aluminum foil, and after drying, rolling, and vacuum drying, a positive electrode with a tap density of 3.55 g / cm 3 was obtained. After welding the aluminum lead wire with an ultrasonic welder, the positive electrode plate was obtained, and the thickness of the electrode plate was 130 μm. The negative electrode used in the battery: The negative electrode active material artificial graphite, conductive carbon black SuperP, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed at a mass ratio of 94:1:2.5:2.5, and then they were dispersed in deionized water to obtain the negative electrode slurry. The slurry was coated on both sides of the copper foil, and after drying, rolling, and vacuum drying, the tap density was controlled at about 1.5 g / cm 3 . After welding the nickel lead wire with an ultrasonic welder, the negative electrode plate was obtained, and the thickness of the electrode plate was between 130 μm. The separator used was a commercial 2320 separator (Keluode), with a material of PP / PE / PP, a thickness of 20 μm, and a porosity of 39%.

[0065] The battery preparation process is as follows: The positive electrode plate, separator, and negative electrode plate were assembled into an electric core by a stacking process, sealed with an aluminum-plastic film and baked to meet the requirement of electrode moisture. After baking, the electric core was subjected to processes such as liquid injection, aging, formation, aging, secondary sealing, and grading to obtain a finished soft-pack electric core. The battery energy density can reach 280 Wh / kg.

[0066] For the above-prepared soft-pack lithium-ion electric cores, performance tests were carried out, mainly including the following contents:

[0067] 1C Standard Capacity Test: At room temperature, the battery cell is charged to 100% SOC at a current of 0.2C, with a cut-off current of 0.05C. After standing for 1h, it is discharged to 2.8V at a standard discharge current of 1C to obtain the standard 1C discharge capacity of the single battery cell.

[0068] 5C Rate Discharge Test: At room temperature, the battery cell is charged to 100% SOC at a current of 0.2C, with a cut-off current of 0.05C. After standing for 1h, it is discharged to 2.8V at a standard discharge current of 5C to obtain the standard 5C discharge capacity of the single battery cell.

[0069] 6C Interfacial Lithium Deposition Test: The battery cell is charged to 80% SOC at a charging current of 6C in a 60°C constant temperature oven. Subsequently, the battery is disassembled in a glove box, and the lithium deposition state of the negative electrode is observed by combining with a scanning electron microscope.

[0070] 6C Rate Fast Charge Cycle Test: The battery cell is cycled in a 60°C constant temperature oven at a charge and discharge current of 6C / 1C within the capacity range of 0 - 80% SOC. The charge and discharge capacity of each cycle is recorded. A 0.2C / 0.2C (0 - 100% SOC) charge and discharge test is performed every 100 cycles to monitor the capacity retention rate of the battery. And the DCIR growth rate is recorded every 100 cycles.

[0071] The different electrolyte formulations are shown in Table 1, and the conductivity test results and battery performance test results are shown in Table 2. The conductivity test is carried out using a Leici conductivity meter DDSJ - 307F, as Figure 4 shown, Figure 4 showing the conductivity test results of E1.

[0072] Table 1 Different Electrolyte Formulations

[0073]

[0074] Table 2 Test Results of Soft Pack Lithium - Ion Batteries Assembled with Different Electrolytes

[0075]

[0076]

[0077] [1] The test of the cycle life of 5300 cycles for Experiment 12 is carried out in a 25°C incubator. Before extreme fast charging, the battery is quickly heated to 60°C through an external thermal regulation device, and the battery temperature is quickly cooled to 25°C before discharging, so as to conduct a fast charge cycle test.

[0078] III. Construction of Fitted Conductivity Formula

[0079] To further study and reflect the cooperative dissociation of double salts and the synergistic effect of two additives, a fitting conductivity formula was studied and constructed in this example.

[0080] Among them, in the theoretical modeling stage: select the basic electrochemical laws (Kohlrausch, Langmuir), extend them to multi-component systems, and construct non-linear coupling terms. In the numerical simulation stage: use COMSOL to establish a multi-physics model to predict the synergistic trend, and use the MATLAB optimization toolbox to pre-calibrate the parameter range. In the experimental calibration stage: design a full-factor experiment to obtain training data, and determine the formula coefficients through non-linear regression. In the verification and correction stage: use an independent validation set to test the generalization ability of the model, and introduce hidden high-order terms to control errors.

[0081] The specific construction steps are as follows:

[0082] 1. Basic theory

[0083] Basic Kohlrausch's law: Describes the relationship between the concentration of a single electrolyte and conductivity

[0084]

[0085] Basic Langmuir adsorption model: Describes the coverage rate of additives on the electrode surface

[0086]

[0087] 2. Extension of multi-component systems

[0088] Cooperative correction of double salts: Expand the single-salt concentration C into a dynamic equilibrium term of double salts and introduce the concentration product to reflect the synergistic effect

[0089]

[0090] Competitive adsorption of double additives: Expand the single-component Langmuir model into a two-component competitive form

[0091]

[0092] In the above formulas, C P is the molar concentration of electrolyte salt 1, with the unit of mol / L; C S is the molar concentration of electrolyte salt 2, with the unit of mol / L; A F is the mass percentage of additive 1, with the unit of wt%; A U is the mass percentage of additive 2, with the unit of wt%.

[0093] 3. Non-linear coupling design

[0094] Integrate the double salt and additive effects in product form, and the square root form reflects the non-linear response of ionic conductivity to the concentration ratio (refer to the correction of Kohlrausch's law).

[0095] σ ∝ (salt effect term × additive effect term)^0.5

[0096] Introduce a synergistic factor to strengthen the effect of sulfur salt - unsaturated additive / fluorinated carbonate on the low-impedance SEI at the interface. When LiPF6 / LiFSI and FEC / VC coexist and are proportionally adapted, the conductivity enhancement shows superlinear growth. The traditional linear terms (such as C P + C S + A U + A F ) cannot describe this phenomenon. Using cross-ratio terms can also maintain dimensional consistency and boundary condition rationality. For example, when C S = 0 or A U = 0, the synergistic factor = 1 (degenerates to the reference conductivity).

[0097] 4. Numerical Simulation and Parametric Tools

[0098] COMSOL Multiphysics: Build a multi-physics model (ion migration + interface reaction)

[0099] Module selection: Electrolyte module (Nernst-Planck equation), Surface reaction module (Butler-Volmer kinetics)

[0100] MATLAB Optimization Toolbox: Fit experimental data to determine formula coefficients

[0101] 5. Formula Correction

[0102] 1) Confirmation of σ0

[0103] Solvent reference: EC / DMC (3:7 volume ratio) + x M LiPF6,

[0104] The results with different concentrations of LiPF6 are shown in Table 3.

[0105] Table 3 Results with different concentrations of LiPF6 and the corresponding measured conductivities

[0106] x value (mol / L) <![CDATA[Measured conductivity σ real (mS / cm)]]> Lithium precipitation during 0.5C charging 0 0.8 Lithium precipitation 0.2 2.1 Lithium precipitation 0.4 4.0 No lithium precipitation 0.6 7.3 No lithium precipitation 0.8 7.8 No lithium precipitation 1 8.3 No lithium precipitation

[0107] The measured conductivity σ of critical lithium deposition real is 4.0 mS / cm. Therefore, in the carbonate solvent system, the reference conductivity σ0 is set to be greater than or equal to 4 mS / cm. In this example, σ0 = 4.0 mS / cm is specifically used.

[0108] 2) Formula model simplification and correction

[0109] By introducing multiple sets of full-factor experimental data and using the Levenberg-Marquardt algorithm to optimize the formula parameters, the final fitted conductivity σ formula is as follows:

[0110]

[0111] Among them, C P is the molar concentration of electrolyte salt 1, in mol / L; C S is the molar concentration of electrolyte salt 2, in mol / L; A F is the mass percentage of additive 1, in wt%; A U is the mass percentage of additive 2, in units of wt%; σ0 is the conductivity of the solvent plus lithium salt system, and 4mS / cm≤σ0, in this example σ0=4.0mS / cm.

[0112] Parameters satisfy 0.5≤C P ≤1.5, 0.3≤C S ≤1, and 1≤C P / C S , 1≤A F ≤5, 0.5≤A U Under the condition of ≤3, 10mS / cm≤σ≤20mS / cm can meet the demand of ultra-fast charging. The σ value calculated by not meeting the parameter requirements deviates seriously from the actual conductivity (offset rate ≥5%), the data is distorted, and has no practical reference significance.

[0113] The conductivity σ of the electrolyte shown in Table 1 was calculated and compared with the measured conductivity σ real The comparison is shown in Table 4; the fitted conductivity σ of different electrolytes and their corresponding assembled soft-pack lithium-ion battery test results are shown in Table 5.

[0114] Table 4 Electrolyte fitted conductivity σ and measured σ real Error comparison

[0115]

[0116]

[0117] Table 5 Fitted conductivity σ of different electrolytes and their corresponding assembled soft-pack lithium-ion battery test results

[0118]

[0119]

[0120] The results in Table 5 show that for Electrolyte Salt 1, Electrolyte Salt 2, Additive 1, and Additive 2 in E1 to E6, they satisfy the dual-mode collaborative conductivity equation: 10 mS / cm ≤ σ ≤ 20 mS / cm, and the parameters satisfy 0.5 ≤ C P ≤ 1.5; 0.3 ≤ C S ≤ 1; and 1 ≤ C P / C S ; 1 ≤ A F ≤ 5; 0.5 ≤ A U ≤ 3. Therefore, the corresponding soft-pack battery has good fast-charging cycle life.

[0121] E7 to E9 do not satisfy 0.5 ≤ C P ≤ 1.5; 0.3 ≤ C S ≤ 1; 1 ≤ C P / C S in the equation; resulting in an imbalance in the dual-salt collaborative dissociation. Although the battery has a lower initial impedance and better high-power performance when C P / C S ≤ 1, there is corrosion of the current collector by Electrolyte Salt 2, leading to a significant attenuation of the cycle life.

[0122] E10 to E11 do not satisfy 1 ≤ A F ≤ 5; 0.5 ≤ A U ≤ 3 in the equation. The adsorption competition - collaborative effect of the two additives is imbalanced, the interfacial impedance increases, and the fluorination degree and crosslinking degree of the SEI film are not suitable for the extreme fast charging of the battery, resulting in serious lithium plating during the fast-charging cycle process and a sharp drop in the cycle life.

[0123] Comparative Examples 1 to 4 demonstrate the importance of the collaborative effect of dual-salt + dual-additives. The lack of any component will cause the results of the dual-mode collaborative conductivity equation to deviate significantly from the conventional threshold of the actual conductivity. Moreover, the experimental results show that the lack of any one of the four key materials will lead to a serious attenuation of the fast-charging cycle life and cannot meet the actual requirements.

[0124] In addition, for the battery cells prepared with the electrolytes of Test 1 and Comparative Test 1, the lithium plating results at the negative electrode interface under a 6C charging current were observed, and the results are as Figure 1 shown. Figure 1 Among them, the left figure is the 6C fast-charging negative electrode interface diagram of Comparative Test 1, and the right figure is the 6C fast-charging negative electrode interface diagram of Test 1.

[0125] Figure 1 The results show that for the electrolyte formulation of Comparative Test 1, lithium plating occurs at the negative electrode interface; while for Test 1, with Electrolyte Salt 1, Electrolyte Salt 2, Additive 1, and Additive 2 satisfying the dual-mode collaborative conductivity equation, it has better 6C high-temperature fast-charging performance, specifically manifested as no lithium plating at the 6C current fast-charging negative electrode interface.

[0126] The test results of the capacity retention rate of Test 1 are as follows Figure 2 shown Figure 2 The results show that the battery cell prepared with the electrolyte of Test 1 still has a capacity retention rate of more than 80% after 2800 cycles

[0127] In addition, the fast charging time of the battery of Test 1 was tested. Test method: Connect a newwei battery tester to a ternary lithium-ion soft-pack battery with a calibrated capacity of 2000 mAh. The battery is placed in a 60 °C incubator and kept at a constant temperature for 4 h. The tester sets the charging current to 12000 mA (i.e., 6C current). The charging voltage can represent the change in battery capacity. The charging cut-off condition is that the capacity reaches 1600 mAh (i.e., 80% SOC). After the test starts, data such as charging capacity and charging voltage are recorded. The test results are as follows Figure 3 shown

[0128] Figure 3 The results show that for the lithium-ion battery using E1 electrolyte, the fast charging time under 0-80% SOC is only 8 minutes. Combining the foregoing experimental results, it can be seen that the E1 electrolyte combined with the heating and cooling system greatly reduces the holding time of the battery fast charging cycle at high temperatures, improves high-temperature aging, and can further increase the 6C fast charging cycle life of the battery to 5300 cycles, and can simultaneously improve the problems of lithium deposition during 8-minute @ 6C fast charging and long cycle life of the lithium-ion battery

[0129] The above content is a further detailed description of the present application in combination with specific implementation manners. It cannot be determined that the specific implementation of the present application is only limited to these descriptions. For those of ordinary skill in the technical field to which the present application belongs, without departing from the concept of the present application, several simple deductions or substitutions can still be made

Claims

1. A high-temperature resistant and fast-charging electrolyte, characterized in that: It is composed of a non-aqueous organic solvent, electrolyte salt 1, electrolyte salt 2, additive 1, and additive 2; the electrolyte salt 1 is a lithium salt containing a P atom, the electrolyte salt 2 is a lithium salt containing an S atom, the additive 1 is a fluorinated carbonate compound, and the additive 2 is a carbonate containing an unsaturated bond; The fitted conductivity σ of the electrolyte at 30 °C satisfies 10 mS / cm ≤ σ ≤ 20 mS / cm, and the calculation formula of the fitted conductivity σ is as follows, wherein, C P is the molar concentration of electrolyte salt 1, in mol / L, 0.5 ≤ C P ≤ 1.5; C S is the molar concentration of electrolyte salt 2, with the unit of mol / L, 0.3 ≤ C S ≤ 1, and 1 ≤ C P / C S ; A F is the mass percentage of additive 1, in wt%, 1 ≤ A F ≤ 5; A U is the mass percentage of additive 2, in wt%, 0.5 ≤ A U ≤ 3; σ0 is the conductivity of the solvent plus lithium salt system, and 4 mS / cm ≤ σ0.

2. The electrolyte according to claim 1, characterized in that: The non-aqueous organic solvent is one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethylene glycol dimethyl ether, acetonitrile, tetrahydrofuran, and 1,3-dioxolane; Preferably, the non-aqueous organic solvent is composed of ethylene carbonate and dimethyl carbonate.

3. The electrolyte according to claim 1, characterized in that: The P atom of the electrolyte salt 1 is provided by a phosphate group; Preferably, the electrolyte salt 1 is at least one of lithium hexafluorophosphate, lithium difluorophosphate, and lithium difluorooxalate phosphate; Preferably, the electrolyte salt 1 is lithium hexafluorophosphate.

4. The electrolyte according to claim 1, wherein: The electrolyte salt 2 is at least one of lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, and lithium bis(trifluoromethyl)sulfonylimide; Preferably, the electrolyte salt 2 is lithium bis(fluorosulfonyl)imide.

5. The electrolyte according to claim 1, characterized in that: The additive 1 is at least one of fluoroethylene carbonate, difluoroethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, and fluoroethyl ethyl carbonate; Preferably, the additive 1 is fluoroethylene carbonate.

6. The electrolyte according to claim 1, wherein: The additive 2 is at least one of vinylene carbonate, vinyl ethylene carbonate, methylene carbonate, divinyl ethylene carbonate, ethynyl ethylene carbonate, allyl methyl carbonate, and allyl ethyl carbonate; Preferably, the additive 2 is vinylene carbonate.

7. A lithium-ion battery using the electrolyte according to any one of claims 1-6.

8. The lithium-ion battery according to claim 7, wherein: It is composed of the electrolyte according to any one of claims 1-6, a positive electrode sheet, a negative electrode sheet, a separator, and a housing.

9. The lithium ion battery according to claim 8, characterized in that: The positive electrode sheet includes a positive electrode current collector and a double-sided positive electrode film uniformly coated on the surface of the positive electrode current collector, and the positive electrode film contains a positive electrode active material, a binder, and a conductive agent; Preferably, the negative electrode sheet includes a negative electrode current collector and a double-sided negative electrode film uniformly coated on the surface of the negative electrode current collector, and the negative electrode film contains a negative electrode active material, a binder, and a conductive agent; Preferably, the positive electrode active material is one or more of lithium cobaltate, lithium manganate, ternary nickel cobalt manganese, nickel cobalt aluminum material, and lithium iron phosphate; Preferably, the negative electrode active material is one or more of natural graphite, artificial graphite, mesophase carbon microspheres, and metallic lithium; Preferably, the positive electrode current collector is aluminum foil with a thickness of 6-18 μm; Preferably, the negative electrode current collector is copper foil with a thickness of 5-17 μm.

10. The lithium ion battery according to any one of claims 7-9, characterized in that: The ultra-fast charging current of the lithium-ion battery ≥ 4C; Preferably, the ultra-fast charging current of the lithium-ion battery is 6C; Preferably, when the lithium-ion battery is charged at room temperature, the charging current ≥ 0.2C.

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