Electrolyte based on dianion solvation structure and application thereof

Abstract

This invention provides an electrolyte based on a dual-anion solvation structure and its application. The electrolyte comprises a phosphate ester organic solvent and a lithium salt dissolved in the phosphate ester organic solvent. The lithium salt includes a first lithium salt and a second lithium salt. The anion of the first lithium salt contains boron, and the anion of the second lithium salt contains nitrate ions. The anions of the first and second lithium salts jointly participate in the formation of the first solvation sheath layer of the lithium ion. This invention introduces a dual-anion complementary lithium salt into the phosphate ester organic solvent system to construct a multi-anion synergistic lithium-ion solvation structure. This creates a stable positive electrode electrolyte interface film on the positive electrode surface and inhibits the formation and growth of lithium dendrites on the negative electrode surface, improving the stability of the lithium metal negative electrode under long-cycle and high-rate conditions. This electrolyte not only possesses intrinsic non-flammability, ensuring battery safety, but also significantly improves cycle stability and interface reliability under high-voltage conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and more specifically, to an electrolyte based on a dual anion solvation structure and its application. Background Technology

[0002] With the rapid development of high-energy-density lithium-ion batteries in electric transportation and large-scale energy storage, high-voltage cathode materials (including but not limited to high-nickel layered oxide cathodes and high-voltage layered oxide cathodes) are widely considered an effective way to improve battery energy density. However, when the operating voltage is increased to above 4.3 V, LiPF6, commonly used in traditional carbonate electrolytes, is prone to oxidative decomposition under high voltage conditions, accompanied by the generation of HF. This leads to instability of the cathode interface film and continuous electrolyte consumption, resulting in a rapid decline in battery cycle life. In addition, carbonate solvents have low flash points, are easily volatile and combustible, significantly increasing the risk of battery thermal runaway, which poses a significant safety hazard to lithium-ion batteries.

[0003] To address safety concerns, the development of novel safe electrolytes has garnered significant attention. Current research on safe electrolytes primarily relies on the addition of flame-retardant organic solvents. Phosphate esters, with their high flash point and intrinsically non-flammable properties, are widely considered ideal candidates for constructing high-safety electrolyte systems. However, in conventional lithium salt systems, phosphate esters struggle to form a stable and dense cathode-electrolyte interface film on the high-voltage cathode surface. This leads to a continuous increase in interfacial impedance, impacting the cycle life of lithium batteries and limiting their practical application in high-voltage systems. Summary of the Invention

[0004] This invention aims to provide an electrolyte based on a dual-anion solvation structure and its application. This electrolyte introduces a complementary dual-anion compound lithium salt consisting of boron-containing lithium salt and nitrate-containing lithium salt into a phosphate ester organic solvent system, constructing a lithium-ion solvation structure with multi-anion synergy. This results in the in-situ formation of a stable positive electrode electrolyte interface film rich in inorganic components at the high-voltage positive electrode interface, inhibiting the formation and growth of lithium dendrites on the negative electrode surface. While achieving the intrinsic non-flammability of the electrolyte, it significantly improves the cycle stability and interface reliability under high-voltage conditions.

[0005] To address the aforementioned problems, a first aspect of the present invention provides an electrolyte based on a dual anionic solvation structure, comprising a phosphate ester organic solvent and a lithium salt dissolved in the phosphate ester organic solvent, wherein the lithium salt comprises a first lithium salt and a second lithium salt, the anion of the first lithium salt containing boron and the anion of the second lithium salt containing nitrate ions.

[0006] In this process, the anions of the first lithium salt and the second lithium salt jointly participate in the formation of the first solvation sheath of the lithium ions.

[0007] Further, the first lithium salt comprises at least one of lithium difluorooxalate borate, lithium tetrafluoroborate, or a fluorinated organoboronate lithium salt, wherein the fluorinated organoboronate lithium salt is selected from lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethyl)difluoroborate (LiDFB), lithium bis(malonic acid)borate (LiBMB), lithium bis(ethylmalonic acid)borate (LiBMB-A), lithium bis(n-butylmalonic acid)borate (LiBMB-B), lithium bis(n-octylmalonic acid)borate (LiBMB-C), and lithium di(ethylmalonic acid)borate (LiBMB-C). At least one of the following: lithium 1-methylpropylmalonium borate (LiBMB-D), lithium bis-2-methylpropylmalonium borate (LiBMB-D2), lithium bis-cyclopentylmalonium borate (LiBMB-E), lithium bis-cyclohexylmalonium borate (LiBMB-E2), lithium bis(2-methyl-2-fluoromalonium)borate (LiBMFMB), lithium perfluoropinacol borate (LiFPB), or lithium 1,1,1-trifluoro-2,5,8-trioxaborate (LiFTOB).

[0008] Further, the second lithium salt includes lithium nitrate, lithium nitrate-derived lithium salt, and organic nitrate; the lithium nitrate-derived lithium salt is a lithium salt complex formed by nitrate and organic cation; the organic nitrate is selected from isosorbide dinitrate.

[0009] Furthermore, the molar ratio of the first lithium salt to the second lithium salt is (1-20):1.

[0010] Furthermore, the molar ratio of the first lithium salt to the second lithium salt is (1-2):1.

[0011] Furthermore, the total concentration of lithium salt in the electrolyte is 0.1%. Up to 10 .

[0012] Furthermore, the phosphate ester organic solvent includes at least one of trialkyl phosphate, dialkyl phosphate, or fluorophosphate.

[0013] A second aspect of the present invention provides a lithium secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte described in the first aspect.

[0014] Furthermore, the electrolyte is suitable for positive electrode plates with an operating voltage greater than 4.3 V.

[0015] Furthermore, the positive electrode is a high-voltage layered oxide positive electrode or a high-nickel ternary positive electrode, and the negative electrode is a lithium metal negative electrode or a lithium-containing carbon material negative electrode.

[0016] The electrolyte based on a dual-anion solvation structure provided by this invention selects a first lithium salt containing boron anions and a second lithium salt containing nitrate anions for compounding. These two salts complement each other, maximizing their respective advantages. The first lithium salt provides high-voltage tolerance and positive electrode interface stability, while the second lithium salt enhances the ion conductivity and kinetic uniformity of the negative electrode interface. Furthermore, the synergistic effect of the anions in the first and second lithium salts significantly improves the uniformity of lithium metal deposition on the negative electrode, inhibits lithium dendrite growth, and maintains a stable positive electrode electrolyte interphase (CEI) film under high-voltage positive electrode conditions. This achieves high capacity retention and long lifespan performance of the lithium metal battery under high-voltage cycling. In addition, the first lithium salt containing boron anions and the second lithium salt containing nitrate anions have stronger coordination capabilities in phosphate ester organic solvents, which is beneficial for actively inducing anions in the electrolyte to participate in the lithium-ion solvation structure. The synergistic regulation of the two anions simultaneously optimizes interfacial chemical stability and ion migration performance, achieving synergistic enhancement of the negative and positive electrode interfaces. This invention uses phosphate ester organic solvents as the main component. Phosphate ester organic solvents not only possess intrinsic non-flammability and excellent thermal safety properties, but also have a large overall donor number, enabling them to coordinate with lithium salts through the cooperative arrangement of oxygen atoms within the molecule. This enhances the solubility and ion dissociation of lithium salts, thereby improving the ionic conductivity of the electrolyte while ensuring safety. Therefore, the electrolyte of this invention uses phosphate ester organic solvents as the main component, and allows the anions of the first and second lithium salts to participate in the formation of the first solvation sheath layer of lithium ions. This significantly increases the proportion of anions in the solvation sheath layer, forming BO, BF, and... The inorganic SEI / CEI content reduces the reactivity of free phosphate ester organic solvents, effectively inhibits electrolyte oxidation and decomposition under high voltage conditions, and constructs a stable positive electrode electrolyte interface film on the positive electrode surface. It also inhibits the formation and growth of lithium dendrites on the negative electrode surface, improving the stability of the lithium metal negative electrode under long cycles and high rates. Thus, this electrolyte not only has intrinsic non-flammability, ensuring the safety performance of the battery, but also significantly improves cycle stability and interface reliability under high voltage conditions.

[0017] The lithium secondary battery provided by the present invention contains the electrolyte based on the above-mentioned dual anion solvation structure, which not only ensures the safety performance of the lithium secondary battery, but also significantly improves the capacity retention and cycle life of the lithium secondary battery under high voltage and long cycle conditions. The electrolyte based on the above-mentioned dual anion solvation structure is particularly suitable for high energy density lithium secondary battery systems. Attached Figure Description

[0018] Figure 1 The lithium secondary batteries assembled with electrolytes from Examples 1 to 4 and Comparative Examples 1 to 2 provided for embodiments of the present invention exhibit rapid charge-discharge cycle performance test graphs.

[0019] Figure 2 shows the cycle performance test of the lithium secondary batteries assembled with the electrolytes of Example 3 and Comparative Example 1 under different voltages and rates.

[0020] Figure 3 CV cycle performance test graphs of Li / / Al half-cells assembled with electrolytes of Example 3, Comparative Example 1 and Comparative Example 2 provided for embodiments of the present invention;

[0021] Figure 4 is a combustion performance test diagram of the electrolytes of Example 3 and Comparative Example 1 provided by the present invention;

[0022] Figure 5 The morphology and thickness of the CEI passivation layer on the positive electrode surface of the secondary lithium battery assembled with electrolytes of Example 3, Comparative Example 1 and Comparative Example 2 after cycling are provided for the embodiments of the present invention.

[0023] Figure 6 The positive and negative electrode morphology of the secondary lithium batteries assembled with electrolytes of Example 3, Comparative Example 1 and Comparative Example 2 after cycling, provided as embodiments of the present invention.

[0024] Figure 7 The interface of the secondary battery assembled with electrolyte in Example 3 of this invention after cycling is analyzed by etching XPS to obtain a chemical composition diagram. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] Furthermore, the terms "comprising," "including," "containing," and "having" are non-restrictive and can refer to the addition of other steps and components that do not affect the results. Unless otherwise specified, all materials, equipment, and reagents are commercially available.

[0028] The first aspect of this application provides an electrolyte based on a dual anionic solvation structure, comprising a phosphate ester organic solvent and a lithium salt dissolved in the phosphate ester organic solvent, wherein the lithium salt comprises a first lithium salt and a second lithium salt, the anion of the first lithium salt contains boron, and the anion of the second lithium salt contains nitrate ions.

[0029] In this process, the anions of the first lithium salt and the second lithium salt jointly participate in the formation of the first solvation sheath of the lithium ions.

[0030] In lithium-ion battery electrolytes, Li +It does not exist as a "bare ion," but is surrounded by solvent molecules, forming a solvated structure. The first solvated sheath of a lithium ion refers to the layer closest to the Li... + The first solvation sheath of lithium ions, consisting of solvent molecules directly coordinated through strong interactions (coordination bonds / dipole orientation) and a small number of anions, is crucial to the performance of lithium metal batteries.

[0031] In this embodiment, a phosphate ester organic solvent is used as the main component. A first lithium salt containing boron anions and a second lithium salt containing nitrate anions are added to the phosphate ester organic solvent, wherein:

[0032] The anion of the first lithium salt contains boron (B). The B atom exhibits significant Lewis acidity and can react with electron-rich species, such as F. - The formation of coordinate bonds allows the boron atom to capture HF generated during the reaction under high-voltage electrochemical conditions, effectively reducing the corrosive effect of HF on electrode materials and current collectors. Alternatively, boron atoms can form complexes with electron-rich species, such as lone pairs of electrons in H₂O, capturing trace amounts of H₂O in the system under high-voltage electrochemical conditions, effectively reducing the corrosive effect of H₂O on electrode materials and current collectors, thereby inhibiting the dissolution of current collectors under high-voltage conditions. Simultaneously, the first lithium salt containing boron as anion preferentially participates in interfacial reactions during electrochemical reactions, forming a stable interfacial film rich in BO and / or BF bonds on the electrode surface. This is beneficial for constructing a dense and stable solid-state electrolyte interface (SEI) and / or cathode electrolyte interface (CEI), improving interfacial stability and electrochemical cycle life. However, the low ion conductivity of the first lithium salt containing only boron results in high interfacial charge transfer impedance, making it difficult to balance high-voltage stability and rapid ion transport performance under high-rate or long-cycle conditions. The second lithium salt contains nitrate ions as its anion, giving it strong electron-withdrawing and easily reduced properties. This allows it to preferentially participate in interfacial reactions, readily reducing it near the negative electrode and contributing to the formation of a nitrogen-rich elastic inorganic interfacial layer (containing...). (or other inorganic nitrides), this nitrogen-rich inorganic interface layer can improve the uniformity, mechanical strength, and ion conductivity of SEI / CEI, wherein... The components can improve Li + The migration rate of Li induces + Uniform flux distribution and uniform deposition behavior can reduce the local current density on the lithium metal surface, thereby inhibiting the formation and growth of lithium dendrites and significantly improving the compatibility between the electrolyte and the lithium anode. However, a single second lithium salt containing nitrate ions has limited oxidizing power under high-voltage cathode conditions, making it difficult to independently achieve long-term stability under high-voltage cycling.

[0033] In this embodiment, a first lithium salt containing boron anions and a second lithium salt containing nitrate anions are selected for compounding. These two salts complement each other, maximizing their respective advantages. The first lithium salt provides high-voltage tolerance and positive electrode interface stability, while the second lithium salt enhances the ion conductivity and kinetic uniformity of the negative electrode interface. Furthermore, the synergistic effect of the anions in the first and second lithium salts significantly improves the uniformity of lithium metal deposition on the negative electrode, inhibits lithium dendrite growth, and maintains a stable positive electrode electrolyte interphase (CEI) film under high-voltage positive electrode conditions. This achieves high capacity retention and long lifespan performance of the lithium metal battery under high-voltage cycling. In addition, while phosphate ester organic solvents are intrinsically non-flammable and have excellent thermal safety properties, they often form solvent-molecule-dominated solvent-separated ion pairs, resulting in insufficient anion participation in lithium-ion solvation. This makes it difficult to form a stable and dense CEI on the high-voltage positive electrode surface, leading to a continuous increase in interfacial impedance and limiting their practical application in high-voltage systems. In this embodiment, this defect can be overcome by adding a first lithium salt containing boron anions and a second lithium salt containing nitrate anions to a phosphate ester organic solvent. In phosphate ester organic solvents, the first lithium salt containing boron anions and the second lithium salt containing nitrate anions have stronger coordination capabilities, which is beneficial for actively inducing anions in the electrolyte to participate in the lithium-ion solvation structure. The synergistic regulation of the two anions can simultaneously optimize interfacial chemical stability and ion migration performance, achieving synergistic enhancement of the negative and positive electrode interfaces. Furthermore, the phosphate ester molecule has a large overall donor number, which can coordinate with the lithium salt through the synergistic interaction of oxygen atoms in the molecule, improving the solubility and ion dissociation of the lithium salt, thereby enhancing the ionic conductivity of the electrolyte while ensuring safety.

[0034] Therefore, in this embodiment, an intrinsically non-flammable phosphate ester organic solvent is used as the main component, and the anions of the first and second lithium salts participate in the formation of the first solvation sheath layer of lithium ions. This significantly increases the proportion of anions in the solvation sheath layer, forming BO, BF, and The inorganic SEI / CEI content reduces the reactivity of free phosphate ester organic solvents, effectively inhibits electrolyte oxidation and decomposition under high voltage conditions, and constructs a stable positive electrode electrolyte interface film on the positive electrode surface. It also inhibits the formation and growth of lithium dendrites on the negative electrode surface, improving the stability of the lithium metal negative electrode under long cycles and high rates. Thus, this electrolyte not only has intrinsic non-flammability, ensuring the safety performance of the battery, but also significantly improves cycle stability and interface reliability under high voltage conditions.

[0035] Based on the above embodiments, as an optional implementation, the first lithium salt includes lithium bis(oxalato)borate (LiBOB) and lithium tetrafluoroborate (LiBOB). ) or at least one of the following fluorinated organoboronate lithium salts, wherein the fluorinated organoboronate lithium salt is selected from lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethyl)difluoroborate (LiDFB), lithium bis(malonic acid)borate (LiBMB), lithium bis(ethylmalonic acid)borate (LiBMB-A), lithium bis(n-butylmalonic acid)borate (LiBMB-B), lithium bis(n-octylmalonic acid)borate (LiBMB-C), lithium bis(1-methylpropylmalonic acid)borate ( Lithium first salts selected from at least one of the following: lithium bis(2-methylpropylmalonate-borate) (LiBMB-D), lithium bis(2-methyl-2-fluoromalonate)borate (LiBMB-D2), lithium bis(fluoropinacol-borate)borate (LiBMB-E), lithium bis(2-methyl-2-fluoromalonate)borate (LiBMFMB), lithium perfluoropinacol-borate (LiFPB), or lithium 1,1,1-trifluoro-2,5,8-trioxaborate (LiFTOB). These first lithium salts not only possess excellent thermal stability and good electrochemical stability, remaining stable under extreme conditions such as high temperature and high pressure, which is beneficial for extending the life of lithium batteries, but also can form a stable interface layer rich in BO and / or BF bonds under high pressure conditions, which can effectively inhibit the high-temperature decomposition of the electrolyte and improve the cycle performance of the battery.

[0036] Based on the above embodiments, as an optional implementation, the second lithium salt includes lithium nitrate (LiNO3), lithium nitrate-derived lithium salt, and organic nitrate; wherein, the lithium nitrate-derived lithium salt is a lithium salt complex formed by nitrate and organic cation, preferably a lithium-quaternary ammonium nitrate complex, including but not limited to lithium tetramethylammonium nitrate and lithium tetraethylammonium nitrate; the organic nitrate is selected from isosorbide dinitrate. These second lithium salts can release nitrate or nitrogen-containing active species in situ at the electrolysis interface under electrochemical conditions to participate in the interfacial film-forming reaction.

[0037] Based on the above embodiments, as an optional implementation, the molar ratio of the first lithium salt and the second lithium salt is (1-20):1. Here, the first lithium salt serves as the main lithium salt, and the second lithium salt as the secondary lithium salt. The molar ratio of the first and second lithium salts within the above range is beneficial for further optimizing interfacial chemical stability and ion migration performance, achieving synergistic enhancement of the anode and cathode interface. As a preferred implementation, the molar ratio of the first lithium salt and the second lithium salt is (1-2):1, which is beneficial for constructing a dual-anion synergistic solvation structure and for further suppressing electrolyte oxidative decomposition under high voltage conditions.

[0038] Based on the above embodiments, as an optional implementation, the total concentration of lithium salt in the electrolyte is 0.1%. Up to 10 Therefore, with the total concentration of lithium salt in the electrolyte within the above range, sufficient Li can be ensured. +The concentration is adjusted to maintain conductivity while avoiding excessive electrolyte viscosity, and also ensures an appropriate amount of anions enter the first solvated sheath layer and interfacial film, which is beneficial for the formation of a stable SEI / CEI. As a preferred embodiment, the total lithium salt concentration in the electrolyte is 1... Up to 3 This ensures a sufficient supply of Li. + The concentration can also increase the proportion of anions in the solvated sheath.

[0039] Based on the above embodiments, as an optional implementation, the phosphate ester organic solvent includes at least one of trialkyl phosphate, dialkyl phosphate, or fluorophosphate. Specifically, the trialkyl phosphate includes at least one of triethyl phosphate, trimethyl phosphate, or tripropyl phosphate; the dialkyl phosphate includes at least one of dimethyl phosphate, diethyl phosphate, dipropyl phosphate, or dibutyl phosphate; and the fluorophosphate includes at least one of tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1-trifluoropropyl) phosphate, or fluorodialkyl phosphate. Therefore, the above-mentioned phosphate ester organic solvent exhibits excellent flame retardant properties, good thermal stability, and is beneficial for dissolving lithium salts and improving ion dissociation.

[0040] Based on the above embodiments, as an optional implementation, the electrolyte in this embodiment remains electrochemically stable under a cutoff voltage greater than 4.3 V. Therefore, this electrolyte possesses the characteristic of stable operation under high voltage environments and can be applied to high-voltage lithium-ion batteries, lithium metal batteries, and energy storage batteries. It is particularly well-suited for cathode material systems with operating voltages greater than 4.3 V, effectively improving battery performance and safety under high-voltage conditions.

[0041] The electrolyte based on the dual anion solvation structure in this embodiment can be prepared using the following method:

[0042] An electrolyte based on a dual-anionic solvation structure was prepared by adding a first lithium salt and a second lithium salt to a phosphate ester organic solvent and stirring until homogeneous. The total concentration of lithium salts in the electrolyte was 0.1%. Up to 10 .

[0043] The second aspect of this embodiment provides a lithium secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte described in the first aspect.

[0044] In this embodiment, the above-mentioned electrolyte is added to the lithium secondary battery. While ensuring the safety performance of the lithium secondary battery, it also significantly improves the cycle stability and interface reliability under high voltage conditions, which is beneficial to improving the cycle life of the lithium secondary battery.

[0045] Based on the above embodiments, as an optional implementation, the positive electrode is a high-voltage layered oxide positive electrode or a high-nickel ternary positive electrode, and the negative electrode is a lithium metal negative electrode or a lithium-containing carbon material negative electrode. The high-voltage layered oxide positive electrode includes lithium cobalt oxide positive electrodes and high-voltage ternary material positive electrodes (such as...). ) and lithium-rich manganese-based cathode materials ( M is at least one of Ni / Co / Mn. High-nickel ternary cathodes include LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and at least one of ultra-high nickel ternary materials (Ni≥90%).

[0046] The diaphragm in this embodiment can be a commonly used diaphragm in the art, including but not limited to one or more combinations of polyethylene, polypropylene, polyethyleneimine, nonwoven fabric or polyfiber material.

[0047] To provide a more detailed description of the present invention, specific embodiments will be used to further illustrate the invention. Unless otherwise specified, the experimental methods used in the embodiments of the present invention are conventional methods; unless otherwise specified, the materials and reagents used in the embodiments of the present invention are commercially available.

[0048] Example 1

[0049] This embodiment provides an electrolyte based on a dual anionic solvation structure, and the preparation method of the electrolyte is as follows:

[0050] The concentration is 1.2 The LiDFOB concentration was 0.2%. LiNO3 was dissolved in triethyl phosphate and mixed thoroughly to prepare an electrolyte based on a dianionic solvation structure, hereinafter referred to as 12LD2NT. The total lithium salt concentration in this electrolyte was 1.4%. .

[0051] Example 2

[0052] This embodiment provides an electrolyte based on a dual anionic solvation structure, and the preparation method of the electrolyte is as follows:

[0053] The concentration is 1.2 The LiDFOB concentration was 0.4%. LiNO3 was dissolved in triethyl phosphate and mixed thoroughly to prepare an electrolyte based on a dianionic solvation structure, hereinafter referred to as 12LD4NT. The total lithium salt concentration in this electrolyte was 1.6%. .

[0054] Example 3

[0055] This embodiment provides an electrolyte based on a dual anionic solvation structure, and the preparation method of the electrolyte is as follows:

[0056] The concentration is 1.2 The LiDFOB concentration was 0.6%. LiNO3 was dissolved in triethyl phosphate and mixed thoroughly to prepare an electrolyte based on a dianionic solvation structure, hereinafter referred to as 12LD6NT. The total lithium salt concentration in this electrolyte was 1.8%. .

[0057] Example 4

[0058] This embodiment provides an electrolyte based on a dual anionic solvation structure, and the preparation method of the electrolyte is as follows:

[0059] The concentration is 1.2 The LiDFOB concentration was 0.8%. LiNO3 was dissolved in triethyl phosphate and mixed thoroughly to prepare an electrolyte based on a dianionic solvation structure, hereinafter referred to as 12LD8NT. The total lithium salt concentration in this electrolyte was 2.0%. .

[0060] Comparative Example 1

[0061] This comparative example provides an electrolyte with a concentration of 1.0. The LiPF6 carbonate electrolyte has a solvent system of ethylene carbonate / diethyl carbonate / fluoroethylene carbonate (i.e., EC / DEC / FEC, with a volume ratio of 1:1:1, abbreviated as CCE).

[0062] Comparative Example 2

[0063] This comparative example provides an electrolyte, the preparation method of which is as follows:

[0064] The concentration is 1.2 LiDFOB was dissolved in triethyl phosphate and mixed thoroughly to prepare an electrolyte, hereinafter referred to as 12LDT. The total lithium salt concentration in this electrolyte was 1.2%. .

[0065] The electrolytes used in Examples 1 to 4, as well as Comparative Examples 1 and 2, were used to prepare secondary lithium batteries. The preparation methods are as follows:

[0066] Using lithium metal sheets as the negative electrode and high-nickel ternary material NCM811 as the positive electrode, and using the electrolytes from Examples 1 to 4, Comparative Examples 1 and 2 as the electrolytes, the positive electrode sheet, separator and negative electrode sheet are assembled into a cell, the cell is installed in a casing, and electrolyte is injected into the casing. After encapsulation, it is assembled into a secondary lithium battery.

[0067] Each secondary lithium battery was subjected to 1C charge-1C discharge cycles at a cutoff voltage of 4.5V to test its cycle performance, and the results are as follows: Figure 1 The results are shown below. The secondary lithium batteries in Comparative Example 1 and Example 3 were subjected to 0.3 C charge-0.5 C discharge cycles at a cutoff voltage of 4.5 V to test their cycle performance, yielding the following results: Figure 2A The results are shown below. The secondary lithium batteries in Comparative Example 1 and Example 3 were subjected to 0.1 C charge-0.3 C discharge cycles at a cutoff voltage of 4.3 V to test their cycle performance, yielding the following results: Figure 2B The results are shown.

[0068] Depend on Figure 1 It can be seen that the secondary lithium batteries of Examples 1 to 4 exhibit excellent cycle stability. The secondary lithium battery of Example 4 shows the fastest capacity decay, followed by the secondary lithium battery of Example 1, which also shows relatively fast capacity decay. Figure 2 shows that the secondary lithium battery of Example 3 has excellent cycle stability, while the secondary lithium battery of Comparative Example 1 shows relatively fast capacity decay. This indicates that the electrolyte with the dual anion solvation structure constructed in this example can significantly improve battery capacity retention and cycle life under high voltage and long cycling conditions. Furthermore, from... Figure 2A and Figure 2B It can be seen that the electrolyte with the dual anionic solvation structure constructed in this embodiment is suitable for high voltage conditions of 4.3 V to 4.5 V.

[0069] The electrolytes from Example 3, Comparative Example 1, and Comparative Example 2 were assembled into Li / / Al half-cells, and cyclic voltammetry (CV) tests were performed (scan rate 0.1). (Voltage window is 2.8–4.5 V), resulting in the following: Figure 3 The results are shown. (By...) Figure 3 It can be seen that the half-cell using carbonate electrolyte exhibits obvious aluminum current current corrosion characteristics during high-voltage scanning, indicating that the carbonate electrolyte has poor stability for the aluminum current collector under high-voltage conditions. In contrast, the half-cell using anionic boron-containing electrolyte did not show obvious current current corrosion during the entire CV test, indicating that adding anionic boron-containing lithium salt to the electrolyte can effectively suppress the corrosion behavior of the aluminum current collector under high-voltage conditions, demonstrating excellent high-voltage stability and current collector protection capability.

[0070] Glass fiber membranes were immersed in the electrolytes of Example 3 and Comparative Example 1, and then combustion tests were performed on the two immersed glass fiber membranes. The glass fiber membrane of Comparative Example 1 ignited and burned after an external ignition source was brought near, and it took more than 1 minute to extinguish after the source was removed. Figure 4A The electrolyte in Comparative Example 1 remained in a burning state after ignition. In contrast, the glass fiber membrane in Example 3 did not burn when an external ignition source was brought near, indicating that the electrolyte in Example 3 possesses intrinsic non-flammable properties. Figure 4B The electrolyte in Example 3 exhibits a non-flammable state after ignition.

[0071] The secondary lithium batteries assembled with the electrolytes of Example 3, Comparative Example 1, and Comparative Example 2 were disassembled after 50 cycles. The morphology and surface state of the positive and negative electrodes of the secondary lithium batteries of Example 3, Comparative Example 1, and Comparative Example 2 were compared and analyzed. The key interface components of the positive and negative electrodes of the secondary lithium battery of Example 3 were also compared and analyzed. The results are as follows: Figures 5 to 7 The results are shown.

[0072] from Figure 5 It can be seen that a thick and irregular CEI passivation layer is formed on the positive electrode surface of Comparative Example 1, while a thinner and more uniform and dense CEI passivation layer is formed on the positive electrode surface of Example 3 compared to Comparative Example 2. Figure 6 It can be seen that the positive electrode material in Comparative Example 1 experienced structural collapse, and obvious lithium dendrites formed on the negative electrode surface. Compared with Comparative Example 2, the positive electrode material in Example 3 maintained a more complete structure, and the negative electrode surface exhibited a uniform lithium deposition morphology, effectively suppressing the formation of lithium dendrites. This indicates that the electrolyte in this example, by constructing a dual-anion synergistic solvation structure in a phosphate ester organic solvent, preferentially forms a stable CEI rich in BO / BF on the high-voltage positive electrode surface with the first lithium salt containing boron anions, suppressing electrolyte oxidation decomposition and interfacial side reactions, thereby maintaining the long-term integrity of the positive electrode material structure. Simultaneously, the second lithium salt containing nitrate anions generates a fast-ion conductor-rich structure in situ on the lithium metal negative electrode surface. The SEI film induces a uniform lithium-ion flux distribution and deposition behavior, and reduces the local current density, thereby effectively suppressing lithium dendrite formation. The positive and negative electrode interface structure and ion transport capability are optimized through the synergistic effect of the first and second lithium salts.

[0073] from Figure 7 As can be seen, BF (193.8 eV) and BO species (191.9 eV) were observed in the B1s spectrum of the positive electrode CEI of Example 3, and BF (193.8 eV) and BO species (191.9 eV) were also observed in the B1s spectrum of the negative electrode SEI. These species are all derived from DFOB. -The oxidation or reduction decomposition of BO and BF, two inorganic enriched components, together construct a mechanically strong and chemically inert electrode interface framework, which can effectively block electron tunneling and suppress the occurrence of continuous side reactions, thereby significantly improving the structural stability of the positive and negative electrode interfaces. This is clearly observed in the N1s spectrum. (399.3 eV) and The (396-397 eV) signal confirmed the presence of NO3. - Decomposition plays a significant role in the construction of the electrode interface, and its high ionic conductivity is beneficial for promoting Li + Rapid migration. This demonstrates that the positive electrode CEI and negative electrode SEI of Example 3 exhibit BO / BF and Enrichment characteristics. Furthermore, in the etched C1s spectrum, the CC / CH, CO, and C=O components show rapid decay or even disappearance with etching depth, reflecting the enrichment characteristics of this BO / BF and... The inorganic-dominated interface structure significantly inhibited the further reduction of the solvent in triethyl phosphate to organic components at the interface, thereby achieving synergistic optimization of interface stability and ion transport capability.

[0074] Depend on Figures 5 to 7 As can be seen, under the synergistic effect of multiple anions, the electrolyte of this embodiment can form a stable SEI / CEI film in situ on the positive and negative electrode surfaces by constructing a bi-anion synergistic solvation structure in the phosphate ester organic solvent. This film can effectively protect the electrode surface, significantly improve the ion diffusion kinetics performance, and effectively suppress the side reactions and decomposition processes of the solvent in triethyl phosphate.

[0075] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. An electrolyte based on a dual anionic solvation structure, characterized in that, The mixture includes phosphate ester organic solvents and lithium salts dissolved in the phosphate ester organic solvents. The lithium salts include a first lithium salt and a second lithium salt. The anion of the first lithium salt contains boron, and the anion of the second lithium salt contains nitrate ions. In this process, the anions of the first lithium salt and the second lithium salt jointly participate in the formation of the first solvation sheath of the lithium ions.

2. The electrolyte based on a dual anionic solvation structure according to claim 1, characterized in that, The first lithium salt comprises at least one of lithium dioxaborate, lithium tetrafluoroborate, or a fluorinated organoboronic acid ester lithium salt; the fluorinated organoboronic acid ester lithium salt is selected from at least one of lithium dioxaborate, lithium bis(trifluoromethyl)difluoroborate, lithium bis(malonic acid)borate, lithium bisethylmalonic acidborate, lithium bis-n-butylmalonic acidborate, lithium bis-n-octylmalonic acidborate, lithium bis-1-methylpropylmalonic acidborate, lithium bis-2-methylpropylmalonic acidborate, lithium biscyclopentylmalonic acidborate, lithium bis(2-methyl-2-fluoromalonate)borate, lithium perfluoropinacol borate, or lithium 1,1,1-trifluoro-2,5,8-trioxaborate.

3. The electrolyte based on a dual anionic solvation structure according to claim 1, characterized in that, The second lithium salt includes lithium nitrate, lithium nitrate-derived lithium salt, and organic nitrate; the lithium nitrate-derived lithium salt is a lithium salt complex formed by nitrate and organic cation; the organic nitrate is selected from isosorbide dinitrate.

4. The electrolyte based on a dual anionic solvation structure according to claim 1, characterized in that, The molar ratio of the first lithium salt to the second lithium salt is (1-20):

1.

5. The electrolyte based on a dual anionic solvation structure according to claim 4, characterized in that, The molar ratio of the first lithium salt to the second lithium salt is (1-2):

1.

6. The electrolyte based on a dual anionic solvation structure according to claim 1, characterized in that, The total concentration of lithium salt in the electrolyte is 0.1%. Up to 10 .

7. The electrolyte based on a dual anionic solvation structure according to claim 1, characterized in that, The phosphate ester organic solvents include at least one of trialkyl phosphate, dialkyl phosphate, or fluorophosphate.

8. A lithium secondary battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, characterized in that, The electrolyte is suitable for positive electrode plates with a working voltage greater than 4.3V.

10. The lithium secondary battery according to claim 8 or 9, characterized in that, The positive electrode is a high-voltage layered oxide positive electrode or a high-nickel ternary positive electrode, and the negative electrode is a lithium metal negative electrode or a lithium-containing carbon material negative electrode.

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