Electrolyte and lithium ion battery

Abstract

The invention relates to an electrolyte and a lithium ion battery, the electrolyte comprises fluorine-containing lithium salt, a composite additive and a solvent, the composite additive comprises organic weak acid aluminum salt and lithium difluoro (oxalato) borate, the mass fraction of the organic weak acid aluminum salt in the electrolyte is 0.4%-1.6%, and the mass fraction of the lithium difluoro (oxalato) borate in the electrolyte is 0.1%-0.5%; wherein the standard reduction potential of the organic weak acid radical in the organic weak acid radical aluminum salt is greater than or equal to-0.490 V by taking a standard hydrogen electrode as a reference at 25 DEG C. Through reasonable electrolyte composition design and proportion regulation and control of the composite additive, the standard reduction potential of the organic weak acid radical is controlled within a certain range, HF corrosion can be inhibited, a stable positive electrode interface film and a stable negative electrode interface film are formed, the overall stability of an electrolyte system is maintained, and the service life of the electrolyte system is prolonged. And the high-temperature stability of the lithium ion battery is synergistically improved.

Description

Technical Field

[0001] This disclosure relates to the field of battery technology, and in particular to electrolytes and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in new energy vehicles, energy storage systems and other fields due to their advantages of high energy density and long cycle life. With the large-scale application of high-nickel ternary materials and silicon-carbon anodes, the energy density of batteries has been significantly improved, but the problem of high-temperature stability has become more prominent. The specific problems are as follows: (1) In high-nickel ternary materials, Ni 3+ Disproportionation reaction is easy to occur. At the same time, lithium hexafluorophosphate in the electrolyte is easy to decompose into hydrofluoric acid (HF) at high temperature. HF will accelerate the dissolution of transition metals such as Ni, Co, and Mn in the positive electrode lattice, eventually leading to the collapse of the positive electrode structure. (2) The volume expansion rate of silicon-carbon negative electrode reaches 100%~300% during charging and discharging, which easily causes the surface solid electrolyte interphase (SEI film) to break, triggering the continuous decomposition of electrolyte, which not only consumes active lithium, but also produces a large number of by-products.

[0003] To address these issues, traditional electrolyte technologies typically incorporate alkaline additives to neutralize HF and film-forming additives to stabilize the SEI film. However, electrolytes are complex systems, and various additives may exhibit synergistic effects under harsh conditions of high temperature and high voltage, triggering unpredictable side reactions. This inter-component interference not only fails to achieve the desired synergistic protection but also exacerbates battery performance degradation, making it difficult to simultaneously maintain good cycle life and storage stability at high temperatures. Summary of the Invention

[0004] Therefore, it is necessary to provide an electrolyte and a lithium-ion battery to address the above problems. The electrolyte can inhibit HF corrosion, form a stable positive electrode interface film and a negative electrode interface film, maintain the overall stability of the electrolyte system, and achieve a synergistic improvement in the high-temperature stability of the lithium-ion battery.

[0005] An electrolyte comprises: a fluorinated lithium salt, a composite additive, and a solvent, wherein the composite additive comprises an organic weak acid aluminum salt and lithium difluorooxalate borate, the organic weak acid aluminum salt having a mass fraction of 0.4% to 1.6% in the electrolyte, and the lithium difluorooxalate borate having a mass fraction of 0.1% to 0.5% in the electrolyte;

[0006] Specifically, at 25°C, with a standard hydrogen electrode as a reference, the standard reduction potential of the organic weak acid anion in the organic weak acid aluminum salt is greater than or equal to -0.490V.

[0007] This disclosure achieves a synergistic effect of "HF suppression-interface protection" by rationally designing the electrolyte composition and controlling the ratio of composite additives, and by controlling the organic weak acid anion of the aluminum salt to be greater than or equal to -0.490V. This means that the organic weak acid anion has weak reducing properties, which can capture HF while preventing the organic weak acid anion from oxidizing and decomposing on the positive electrode surface, not interfering with LiDFOB film formation, and maintaining the overall stability of the electrolyte system. This improves the cycle and storage performance of lithium-ion batteries at high temperatures.

[0008] In one embodiment, at 25°C, with a standard hydrogen electrode as a reference, the standard reduction potential of the organic weak acid anion in the organic weak acid aluminum salt is -0.490V to 0.699V, which can better prevent the decomposition of the organic weak acid anion in the organic weak acid aluminum salt.

[0009] In one embodiment, the mass ratio of the organic weak acid aluminum salt to the lithium difluorooxalate borate is 1:0.10~1.25, which allows the organic weak acid aluminum salt to better neutralize hydrofluoric acid.

[0010] In one embodiment, the organic weak acid aluminum salt is selected from at least one of aluminum oxalate, aluminum malonate, aluminum citrate, or aluminum succinate, which can better avoid the decomposition of the organic weak acid in the organic weak acid aluminum salt.

[0011] In one embodiment, the aluminum oxalate has a mass fraction of 0.5% to 1.5% in the electrolyte;

[0012] And / or, the aluminum malonate has a mass fraction of 0.6% to 1.6% in the electrolyte;

[0013] And / or, the aluminum citrate has a mass fraction of 0.4% to 1.4% in the electrolyte;

[0014] And / or, the mass fraction of the aluminum succinate in the electrolyte is 0.5% to 1.5%.

[0015] By controlling the mass fractions of aluminum oxalate, aluminum malonate, aluminum citrate, and aluminum succinate in the electrolyte, their neutralizing effect on hydrofluoric acid can be better achieved.

[0016] In one embodiment, the particle size D of the aluminum oxalate 50 The range is 50nm to 100nm;

[0017] And / or, the particle size D of the aluminum malonate 50 The range is 60nm to 120nm;

[0018] And / or, the particle size D of the aluminum citrate 50 The range is 40nm to 90nm;

[0019] And / or, the particle size D of the aluminum succinate 50 The wavelength range is 55nm to 110nm.

[0020] By controlling the particle size of aluminum oxalate, aluminum malonate, aluminum citrate, and aluminum succinate in this way, their dispersion in the electrolyte can be improved.

[0021] In one embodiment, the concentration of the fluorinated lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L, which can better balance the ionic conductivity and viscosity of the electrolyte.

[0022] In one embodiment, the fluorinated lithium salt is selected from at least one of lithium hexafluorophosphate, lithium dibis(fluorosulfonyl)imide, or lithium tetrafluoroborate;

[0023] And / or, the solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, or diethyl carbonate.

[0024] In one embodiment, the solvent is composed of ethylene carbonate, dimethyl carbonate, and diethyl carbonate, and the mass ratio of ethylene carbonate, dimethyl carbonate, and diethyl carbonate is 1:(1~2):(1~2), which can better achieve Li + This facilitates dissociation and enhances the high-temperature stability of the electrolyte.

[0025] A high-nickel / silicon-carbon lithium-ion battery, wherein the high-nickel / silicon-carbon lithium-ion battery uses the electrolyte as described above.

[0026] In one embodiment, the positive electrode active material of the lithium-ion battery is a high-nickel ternary positive electrode material with the chemical formula LiNi. x Co y Mn z O2, where 0.8 ≤ x < 1.0, y ≠ 0, z ≠ 0, x + y + z = 1.0, and the negative electrode active material is silicon-carbon material with the chemical formula SiO2. x / C, x=0.5~1.0, Si in silicon-carbon material is 5%~15% by mass. Using the electrolyte, the precipitation of transition metal ions in the positive electrode of lithium-ion battery can be suppressed, and the expansion of the negative electrode can be suppressed. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Example 1 of this disclosure after 200 cycles.

[0029] Figure 2 A scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Example 7 of this disclosure after 200 cycles.

[0030] Figure 3 A scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Comparative Example 10 after 200 cycles.

[0031] Figure 4 The image shows a scanning electron microscope (SEM) image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Comparative Example 11 after 200 cycles. Detailed Implementation

[0032] To facilitate understanding of this disclosure, it will now be described in more detail. However, it should be understood that this disclosure can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing particular embodiments or practices only and is not intended to be limiting of this disclosure.

[0034] This disclosure provides an electrolyte comprising: a fluorinated lithium salt, a composite additive, and a solvent. The composite additive comprises an organic weak acid aluminum salt and lithium difluorooxalate borate. The organic weak acid aluminum salt has a mass fraction of 0.4% to 1.6% in the electrolyte, and the lithium difluorooxalate borate has a mass fraction of 0.1% to 0.5% in the electrolyte. At 25°C, with a standard hydrogen electrode as a reference, the standard reduction potential of the organic weak acid anion in the organic weak acid aluminum salt is greater than or equal to -0.490V.

[0035] In the electrolyte provided in this disclosure, a composite additive is constructed by using a specific combination of organic weak acid aluminum salt and lithium difluorooxalate borate. First, lithium difluorooxalate borate (LiDFOB) can form CEI and SEI films on the positive and negative electrode surfaces, respectively. Within the effective film-forming potential range of LiDFOB, the organic weak acid selected in this disclosure, due to its weak reducing properties, will not compete with borate for reduction. This ensures that LiDFOB can preferentially and uniformly form a dense and stable interface film on the electrode surface, laying the foundation for battery performance.

[0036] Secondly, organic weak acid aluminum salts, due to their organic properties, possess excellent solubility in solvents. This not only ensures the uniform distribution and complete reaction of organic weak acid aluminum salts in the electrolyte, but more importantly, it allows Al... 3+ It can efficiently and continuously capture HF generated by the hydrolysis of fluorinated lithium salts, i.e., Al. 3+ +6HF→[AlF6] 3- +6H + This prevents HF from corroding the cathode material at the source. At the same time, this characteristic also avoids the problem that traditional inorganic aluminum salts are prone to deposit on the cathode surface due to their low solubility, forming a passivation layer and thus increasing the interfacial impedance.

[0037] Furthermore, during battery charging, the positive electrode is at a high potential. If the reducing power of the organic weak acid anion is too strong, it is easily oxidized and decomposed on the surface of the positive electrode, producing gas and harmful impurities, damaging the integrity of the CEI film and causing continuous degradation of the electrolyte. By controlling its reduction potential to be no lower than -0.490V, the chemical inertness of this component under high voltage is ensured, effectively maintaining the long-term stability of the CEI film under high potential.

[0038] Furthermore, during long-term battery cycling, the weakly reducing organic acid radicals can inhibit their own irreversible reduction reactions, thereby avoiding the failure of electrolyte components due to the decomposition of additives into byproducts such as carboxylic acids and alcohols. This mechanism enhances the electrochemical stability of the electrolyte system under harsh conditions of high temperature and high pressure, effectively extending battery life.

[0039] Therefore, this disclosure achieves a synergistic effect of "HF suppression-interface protection" by rationally designing the electrolyte composition and controlling the ratio of composite additives, and by controlling the organic weak acid anion of the aluminum salt to be greater than or equal to -0.490V. This means that the organic weak acid anion has weak reducing properties, which can capture HF while preventing the organic weak acid anion from oxidizing and decomposing on the positive electrode surface, not interfering with LiDFOB film formation, and maintaining the overall stability of the electrolyte system. This improves the cycling and storage performance of lithium-ion batteries at high temperatures.

[0040] Furthermore, to avoid the reduction and decomposition of the organic weak acid anions in the organic weak acid aluminum salt, which would generate impurities and damage the interface, the standard reduction potential of the organic weak acid anions in the organic weak acid aluminum salt is preferably -0.490V to 0.699V at 25°C, using a standard hydrogen electrode as a reference. It can be selected as -0.490V, -0.400V, -0.300V, -0.200V, -0.100V, 0.000V, 0.100V, 0.200V, 0.300V, 0.400V, 0.500V, etc. The value is any point value of 0.600V or 0.699V, or any range between the two. Further, the organic weak acid aluminum salt is preferably at least one of the following: aluminum oxalate (Al2(C2O4)3) with a standard reduction potential of 0.4647V, aluminum malonate (Al2(C3H2O4)3) with a standard reduction potential of 0.380V, aluminum citrate (AlC6H5O7) with a standard reduction potential of 0.250V, and aluminum succinate (Al2(C4H4O4)3) with a standard reduction potential of 0.320V.

[0041] To better enable the organic weak acid aluminum salt to neutralize hydrofluoric acid, the mass fraction of aluminum oxalate in the electrolyte is preferably 0.5% to 1.5%, and can be any value or a range between 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, or 1.5%; the mass fraction of aluminum malonate in the electrolyte is preferably 0.6% to 1.6%, and can be any value among 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, or 1.6%. The mass fraction of aluminum citrate in the electrolyte is preferably 0.4% to 1.4%, and can be any value or a range between any two of 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, or 1.4%. The mass fraction of aluminum succinate in the electrolyte is preferably 0.5% to 1.5%, and can be any value or a range between any two of 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, or 1.5%.

[0042] To ensure the uniform dispersion of the organic weak acid aluminum salt in the electrolyte and avoid agglomeration leading to a decrease in reaction efficiency, the particle size D of the aluminum oxalate is [specified]. 50 Preferably, the particle size is 50nm~100nm, and can be any value among 50nm, 60nm, 70nm, 80nm, 90nm or 100nm or any range between two; the particle size D of the aluminum malonate is... 50 Preferably, the particle size is 60nm~120nm, and can be any value among 60nm, 70nm, 80nm, 90nm, 100nm or 120nm or any range between two; the particle size D of the aluminum citrate is... 50Preferably, the particle size is 40nm~90nm, and can be any value selected from 50nm, 60nm or 70nm or any range between two; the particle size D of the aluminum succinate is... 50 Preferably, the wavelength is 55nm to 110nm, and can be any value among 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or 110nm or any range between two of them.

[0043] To avoid the introduction of composite additives leading to an increase in the moisture content of the electrolyte, the moisture content of both the organic weak acid aluminum salt and lithium difluorooxalate borate is controlled below 10 ppm.

[0044] In order to enable the organic weak acid aluminum salt and lithium difluorooxalate borate to better exert their synergistic effect of "inhibiting HF corrosion and stabilizing the interface", the mass ratio of the organic weak acid aluminum salt to the lithium difluorooxalate borate is preferably 1:0.10~1.25, and more preferably 1:0.10~1.00.

[0045] Optionally, the fluorinated lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium difluorosulfonylimide (LiFSI), or lithium tetrafluoroborate (LiBF4). The concentration of the fluorinated lithium salt in the electrolyte is preferably 0.8 mol / L to 1.3 mol / L, and can be any value or a range between 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, or 1.3 mol / L, which can better balance the ionic conductivity and viscosity of the electrolyte.

[0046] Optionally, the solvent in the electrolyte is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), wherein EC has a high dielectric constant and can promote the dissociation of fluorinated lithium salts from Li. + DMC has low viscosity, which can improve the viscosity of Li. + Migration rate; DEC has a high boiling point, which can enhance the high-temperature stability of the electrolyte and inhibit solvent evaporation.

[0047] Furthermore, the solvent is composed of ethylene carbonate, dimethyl carbonate, and diethyl carbonate, and the mass ratio of ethylene carbonate, dimethyl carbonate, and diethyl carbonate is 1:(1~2):(1~2), preferably 1:1:1, which can better achieve the dissociation of Li. + , enhance Li + It improves the migration rate and enhances the high-temperature stability of the electrolyte.

[0048] This disclosure also provides a lithium-ion battery using the electrolyte described above. The electrolyte provided by this disclosure is widely applicable to various lithium-ion battery systems, achieving the technical effects of inhibiting HF corrosion, forming stable positive and negative electrode interface films, and maintaining the overall stability of the electrolyte system. In particular, it can solve the high-temperature stability problem of high-nickel / silicon-carbon lithium-ion batteries.

[0049] Specifically, the positive electrode active material of the high-nickel / silicon-carbon system lithium-ion battery is a high-nickel ternary positive electrode material with the chemical formula LiNi. x Co y Mn z O2, where 0.8 ≤ x < 1.0, y ≠ 0, z ≠ 0, x + y + z = 1.0; the negative electrode active material of the high-nickel / silicon-carbon system lithium-ion battery is silicon-carbon material with the chemical formula SiO2. x / C, x=0.5~1.0, and the mass fraction of Si in silicon-carbon materials is 5%~15%.

[0050] When the electrolyte of this disclosure is applied to a high-nickel / silicon-carbon lithium-ion battery, the weak organic acid anions, due to their weak reducing properties, will not compete with borate anions for reduction. This ensures that the fluorinated groups (-F) in LiDFOB react with the metal ions (Ni) on the cathode surface. 3+ Co 3+ This forms strong polar coordination bonds, generating oxidation-resistant components such as LiF and NiF2, forming an oxidation-resistant CEI film, which in turn causes the borate ions (BOB) in LiDFOB to form ... forming strong polar coordination bonds, generating strong polar coordination bonds, generating strong polar coordination bonds, generating strong polar coordination bonds, - The aluminum salt reacts with the hydroxyl groups (-OH) on the surface of the silicon-carbon anode to undergo esterification, generating inorganic components such as LiBO2 and Li2CO3, as well as organic components such as carbonate decomposition products. This forms an SEI film that can withstand the volume expansion of the silicon-carbon anode, preventing film rupture. Simultaneously, the Al in the organic weak acid aluminum salt... 3+ It can coordinate with HF produced by the high-temperature decomposition of fluorine-containing lithium salts in the electrolyte, efficiently neutralize HF, block the corrosion of high-nickel cathode by HF from the source, prevent the dissolution of transition metals such as Ni, Co, and Mn in the cathode lattice, maintain the integrity of the electrode structure, and prevent HF from damaging the CEI and SEI films formed by LiDFOB, thus forming a virtuous cycle of "inhibiting HF corrosion - interface protection".

[0051] The following specific embodiments will further illustrate the technical solution of this disclosure. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this disclosure. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0052] Raw material preparation: Lithium salts: LiPF6, LiBF4, and LiFSI are all battery-grade with a purity of 99.9%; EC, DMC, and DEC are all battery-grade with a moisture content ≤20ppm; Organic weak acid aluminum salts: Aluminum oxalate, aluminum malonate, aluminum citrate, and aluminum succinate are all 99.5% pure; LiDFOB is battery-grade with a purity of 99.9%; High-nickel cathode powder is composed of LiNi. 0.9 Co 0.05 Mn 0.05 O2; the silicon-carbon anode powder is composed of SiO2. x / C, x=0.8, Si content is 10wt.%; PP / PE / PP composite diaphragm with a thickness of 12μm; 21700 stainless steel shell.

[0053] Equipment: Argon glove box (water and oxygen content ≤0.1ppm), magnetic stirrer, ultrasonic disperser, core winding machine, vacuum liquid injection machine, battery packaging machine, charge and discharge tester (Landian CT2001A), scanning electron microscope (SEM, ZEISS Sigma300).

[0054] Example 1

[0055] In an argon glove box, a mixed solvent of EC / DMC / DEC was prepared at a mass ratio of 1:1:1. LiPF6 was then added and stirred for 1 hour to obtain a 1.0 mol / L basic electrolyte. Then, particles with a diameter of D were added to the basic electrolyte. 50 Aluminum oxalate at 80 nm was ultrasonically dispersed for 30 min, then LiDFOB was added, and stirring was continued for 2 h until homogeneous, resulting in an electrolyte with an aluminum oxalate mass fraction of 1.0% and a LiDFOB mass fraction of 0.3%.

[0056] Example 2

[0057] The only difference between Example 2 and Example 1 is that aluminum oxalate and LiDFOB were added to the basic electrolyte to obtain an electrolyte with an aluminum oxalate mass fraction of 1.2% and a LiDFOB mass fraction of 0.2%.

[0058] Example 3

[0059] The only difference between Example 3 and Example 1 is that aluminum oxalate and LiDFOB were added to the basic electrolyte to obtain an electrolyte with a mass fraction of 0.8% aluminum oxalate and a mass fraction of 0.4% LiDFOB.

[0060] Example 4

[0061] The only difference between Example 4 and Example 1 is that: particle size D is used. 50 Aluminum malonate with a particle size of 120 nm was used to replace particle size D. 50Aluminum oxalate with a mass fraction of 1.5% and LiDFOB with a mass fraction of 0.5% were obtained by adding aluminum malonate and LiDFOB to the basic electrolyte.

[0062] Example 5

[0063] The only difference between Example 5 and Example 1 is that: particle size D is used. 50 Aluminum citrate with a particle size of 60 nm was used to replace particle size D. 50 Aluminum oxalate with a mass fraction of 80 nm was used. After adding aluminum citrate and LiDFOB to the basic electrolyte, an electrolyte with a mass fraction of 0.4% aluminum citrate and 0.1% LiDFOB was obtained.

[0064] Example 6

[0065] The only difference between Example 6 and Example 1 is that: particle size D is used. 50 100 nm aluminum succinate instead of particle size D 50 Aluminum oxalate with a mass fraction of 1.2% and LiDFOB with a mass fraction of 0.3% were obtained by adding aluminum succinate and LiDFOB to the basic electrolyte.

[0066] Example 7

[0067] Example 7 differs from Example 1 only in that LiBF4 is used instead of LiPF6 fluorinated lithium salt to prepare a basic electrolyte with a concentration of 1.1 mol / L. After adding aluminum oxalate and LiDFOB to the basic electrolyte, an electrolyte with an aluminum oxalate mass fraction of 0.5% and a LiDFOB mass fraction of 0.3% is obtained.

[0068] Example 8

[0069] The only difference between Example 8 and Example 1 is that LiFSI is used instead of LiPF6 fluorinated lithium salt to prepare a basic electrolyte with a concentration of 1.3 mol / L. After adding aluminum oxalate and LiDFOB to the basic electrolyte, an electrolyte with a mass fraction of 1.5% aluminum oxalate and a mass fraction of 0.5% LiDFOB is obtained.

[0070] Comparative Example 1

[0071] The only difference between Comparative Example 1 and Example 1 is that aluminum silicate is used instead of aluminum oxalate. After adding aluminum silicate and LiDFOB to the basic electrolyte, an electrolyte with an aluminum silicate mass fraction of 1.0% and a LiDFOB mass fraction of 0.3% is obtained.

[0072] Comparative Example 2

[0073] The only difference between Comparative Example 2 and Example 1 is that aluminum sulfite was used instead of aluminum oxalate. At 25°C, with a standard hydrogen electrode as a reference, the standard reduction potential of aluminum sulfite ions was -0.66V. After adding aluminum sulfite and LiDFOB to the basic electrolyte, an electrolyte with an aluminum sulfite mass fraction of 1.0% and a LiDFOB mass fraction of 0.3% was obtained.

[0074] Comparative Example 3

[0075] The only difference between Comparative Example 3 and Example 1 is that calcium oxalate was used instead of aluminum oxalate. After adding calcium oxalate and LiDFOB to the basic electrolyte, an electrolyte with a mass fraction of 1.0% calcium oxalate and a mass fraction of 0.3% LiDFOB was obtained.

[0076] Comparative Example 4

[0077] The only difference between Comparative Example 4 and Example 1 is that aluminum oxalate and LiDFOB were added to the basic electrolyte to obtain an electrolyte with a mass fraction of 0.3% aluminum oxalate and a mass fraction of 0.2% LiDFOB.

[0078] Comparative Example 5

[0079] The only difference between Comparative Example 5 and Example 1 is that aluminum oxalate and LiDFOB were added to the basic electrolyte to obtain an electrolyte with an aluminum oxalate mass fraction of 1.8% and a LiDFOB mass fraction of 0.2%.

[0080] Comparative Example 6

[0081] The only difference between Comparative Example 6 and Example 1 is that only LiDFOB was added to the base electrolyte to obtain an electrolyte with a LiDFOB mass fraction of 0.3%.

[0082] Comparative Example 7

[0083] The only difference between Comparative Example 7 and Example 1 is that aluminum oxalate and LiDFOB were added to the basic electrolyte to obtain an electrolyte with an aluminum oxalate mass fraction of 1.0% and a LiDFOB mass fraction of 0.6%.

[0084] Comparative Example 8

[0085] The only difference between Comparative Example 8 and Example 1 is that only aluminum oxalate was added to the basic electrolyte to obtain an electrolyte with an aluminum oxalate mass fraction of 1.0%.

[0086] Comparative Example 9

[0087] The only difference between Comparative Example 9 and Example 4 is that only aluminum malonate was added to the basic electrolyte to obtain an electrolyte with an aluminum malonate mass fraction of 1.5%.

[0088] Comparative Example 10

[0089] The only difference between Comparative Example 10 and Example 1 is that a 1.0 mol / L LiPF6 base electrolyte was used as the electrolyte, and aluminum oxalate and LiDFOB were not added.

[0090] Comparative Example 11

[0091] The only difference between Comparative Example 11 and Example 7 is that a 1.0 mol / L LiBF4 base electrolyte was used as the electrolyte, and aluminum oxalate and LiDFOB were not added.

[0092] The electrolytes prepared in Examples 1-8 and Comparative Examples 1-11 were used to assemble lithium-ion batteries: high-nickel cathode powder, conductive carbon black, and PVDF were mixed in a mass ratio of 96:2:2, NMP was added to form a slurry, which was then coated onto an aluminum foil with a thickness of 12 μm, dried at 80°C for 12 h, and rolled to a surface density of 190 g / m³. 2 The positive electrode sheet is obtained by slitting. Silicon-carbon negative electrode powder, conductive carbon black, and CMC / SBR are mixed at a mass ratio of 92:3:5, and water is added to form a slurry. This slurry is then coated onto an 8μm thick copper foil, dried at 60℃ for 12 hours, and rolled to a surface density of 130g / m³. 2 The negative electrode sheet is obtained by slitting. The positive electrode sheet, separator, and negative electrode sheet are wound into a cylindrical core package, which is then placed into a 21700 stainless steel shell. 5g of electrolyte is injected under vacuum conditions. After encapsulation, the battery is aged at 85°C for 24 hours to form a lithium-ion battery.

[0093] The lithium-ion battery was subjected to high-temperature cycling test: it was charged at 60°C with a constant current of 0.5C to 4.2V and a constant voltage of 0.05C, and discharged with a constant current of 1C to 2.5V for 500 cycles. The results are shown in Table 1.

[0094] Table 1

[0095]

[0096] As shown in Table 1, when the electrolyte of this disclosure is used in lithium-ion batteries, the capacity retention rate reaches 82.8%~88.5% after 500 cycles at 60℃, exhibiting good high-temperature cycling stability. A comparison between Example 1 and Comparative Example 1 shows that using aluminum silicate instead of aluminum oxalate is ineffective because silicate ions compete with LiDFOB for reaction sites, inhibiting SEI / CEI film formation. A comparison between Example 1 and Comparative Example 2 shows that using aluminum sulfite instead of aluminum oxalate is ineffective because the sulfite ions (SO32-) in aluminum sulfite... 2- It is easily reduced and decomposed, producing impurities that damage the interface.

[0097] The lithium-ion battery was subjected to high-temperature cycling test: the battery was charged to a full charge of 4.2V at a constant current of 0.5C and a constant voltage of 0.05C, and then stored in a 60℃ constant temperature chamber for 30 days. The discharge capacity was tested at 25℃ before and after storage, and the discharge condition was 1C to 2.5V. The capacity recovery rate was calculated as: capacity recovery rate = capacity after storage / capacity before storage × 100%. The results are shown in Table 2.

[0098] Table 2

[0099]

[0100] As shown in Table 2, when the electrolyte of this disclosure is used in lithium-ion batteries, the capacity recovery rate during high-temperature storage exceeds 88%. Furthermore, the composite additive composed of organic weak acid aluminum salt and LiDFOB is compatible with various lithium salts such as LiPF6, LiBF4, and LiFSI, which significantly suppresses capacity decay during high-temperature storage and improves battery storage stability.

[0101] The lithium-ion battery was cycled at high temperature 200 times, then disassembled, the positive electrode was removed, cleaned three times with DMC, vacuum dried, and the morphology of the positive electrode particles was observed using a scanning electron microscope at 4000x magnification. Figure 1 A scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Example 1 after 200 cycles. Figure 2 A scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Example 7 after 200 cycles. Figure 3 A scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Comparative Example 10 after 200 cycles. Figure 4 This is a scanning electron microscope image of the positive electrode of a lithium-ion battery assembled using the electrolyte prepared in Comparative Example 11 after 200 cycles. Figure 1 and Figure 2 It can be seen that regardless of whether LiPF6 or LiBF4 is used as the fluorinated lithium salt, the simultaneous use of organic weak acid aluminum salts and lithium difluorooxalate borate can effectively inhibit the corrosion of positive electrode particles by HF and protect the integrity of the positive electrode particle structure; Figure 1 and Figure 3 Compare and Figure 2 and Figure 4 The comparison shows that when only the basic electrolyte is used as the electrolyte for lithium-ion batteries, the positive electrode particles of the lithium-ion batteries show obvious breakage and corrosion after charging and discharging.

[0102] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0103] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An electrolyte, characterized in that, include: The electrolyte contains fluorinated lithium salt, a composite additive, and a solvent. The composite additive includes an organic weak acid aluminum salt and lithium difluorooxalate borate, wherein the organic weak acid aluminum salt has a mass fraction of 0.4% to 1.6% in the electrolyte, and the lithium difluorooxalate borate has a mass fraction of 0.1% to 0.5% in the electrolyte. Specifically, at 25°C, with a standard hydrogen electrode as a reference, the standard reduction potential of the organic weak acid anion in the organic weak acid aluminum salt is greater than or equal to -0.490V.

2. The electrolyte according to claim 1, characterized in that, At 25°C, with a standard hydrogen electrode as a reference, the standard reduction potential of the organic weak acid anion in the organic weak acid aluminum salt is -0.490V~0.699V. And / or, the mass ratio of the organic weak acid aluminum salt to the lithium difluorooxalate borate is 1:0.10~1.

25.

3. The electrolyte according to claim 1, characterized in that, The organic weak acid aluminum salt is selected from at least one of aluminum oxalate, aluminum malonate, aluminum citrate, or aluminum succinate.

4. The electrolyte according to claim 3, characterized in that, The aluminum oxalate has a mass fraction of 0.5% to 1.5% in the electrolyte; And / or, the aluminum malonate has a mass fraction of 0.6% to 1.6% in the electrolyte; And / or, the aluminum citrate has a mass fraction of 0.4% to 1.4% in the electrolyte; And / or, the mass fraction of the aluminum succinate in the electrolyte is 0.5% to 1.5%.

5. The electrolyte according to claim 3, characterized in that, The particle size D of the aluminum oxalate 50 The range is 50nm to 100nm; And / or, the particle size D of the aluminum malonate 50 The range is 60nm to 120nm; And / or, the particle size D of the aluminum citrate 50 The range is 40nm to 90nm; And / or, the particle size D of the aluminum succinate 50 The range is 55nm to 110nm.

6. The electrolyte according to claim 1, characterized in that, The concentration of the fluorinated lithium salt in the electrolyte is 0.8 mol / L to 1.3 mol / L.

7. The electrolyte according to claim 1, characterized in that, The fluorinated lithium salt is selected from at least one of lithium hexafluorophosphate, lithium dibis(fluorosulfonyl)imide, or lithium tetrafluoroborate. And / or, the solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, or diethyl carbonate.

8. The electrolyte according to claim 7, characterized in that, The solvent is composed of ethylene carbonate, dimethyl carbonate and diethyl carbonate, and the mass ratio of ethylene carbonate, dimethyl carbonate and diethyl carbonate is 1:(1~2):(1~2).

9. A lithium-ion battery, characterized in that, The lithium-ion battery uses the electrolyte as described in any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that, The positive electrode active material of the lithium-ion battery is a high-nickel ternary positive electrode material with the chemical formula LiNi. x Co y Mn z O2, where 0.8 ≤ x < 1.0, y ≠ 0, z ≠ 0, x + y + z = 1.0, and the negative electrode active material is silicon-carbon material with the chemical formula SiO2. x / C, x=0.5~1.0, and the mass fraction of Si in silicon-carbon materials is 5%~15%.

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