A heterogeneous bifunctional electrolyte and its use

Abstract

The application discloses a kind of for high nickel layer positive electrode and lithium metal negative electrode lithium secondary battery heterogeneous dual-function electrolyte and its application, the heterogeneous dual-function electrolyte include solvent, conductive lithium salt and additive, the additive contains fluorine-containing silver salt, fluorine-containing film forming agent and silver salt, film forming agent and fluorine-containing silver salt, fluorine-containing lithium salt and silver salt, lithium salt and fluorine-containing silver salt one or several, the heterogeneous dual-function electrolyte is suspended electrolyte with Tyndall effect.This application provides heterogeneous dual-function electrolyte in negative electrode side rich in fluorine element and silver element, provide high mechanical strength interface while lithium-silver alloy layer induces lithium uniform dense deposition, effectively inhibit the growth of lithium dendrite;In positive electrode side rich in fluorine and other beneficial component elements form heterostructure, on the one hand, by eliminating the HF generated by lithium salt hydrolysis, reduce the corrosion of HF to interface, on the other hand, LiF passivates positive electrode surface at high voltage, inhibits the dissolution of transition metal ions.

Description

Technical Field

[0001] This invention relates to the field of lithium secondary battery technology, specifically to a heterogeneous bifunctional electrolyte suitable for a combination system of a high-nickel layered positive electrode and a lithium metal negative electrode, and the application of this electrolyte in high-energy-density lithium batteries. Background Technology

[0002] With the rapid development of electric transportation and large-scale energy storage systems, the demand for lithium-ion battery energy density is constantly increasing. Currently, commercial lithium-ion batteries are gradually approaching their theoretical limits in terms of cathode capacity and operating voltage, posing a significant challenge to further improving energy density. Combining a high-voltage layered cathode with a lithium metal anode is considered one of the important technical pathways to improve battery specific energy. However, this system is severely limited in practical applications by insufficient stability at the electrode-electrolyte interface.

[0003] Both the solid-electrolyte interface (SEI) on lithium metal surfaces and the cathode-electrolyte interface (CEI) on layered oxide surfaces originate from the spontaneous decomposition of the electrolyte under strong reducing or oxidizing potentials. The resulting solvent derivative layers are typically thick, highly heterogeneous, and rich in organic matter, leading to poor mechanical strength, low chemical stability, and an inability to effectively control interfacial reactions. On the negative electrode side, repeated breakage and repair of the SEI result in low coulombic efficiency, lithium dendrite growth, and rapid loss of active lithium; these problems are particularly severe under thin lithium conditions. On the positive electrode side, the fragile CEI cannot buffer lattice strain or inhibit transition metal dissolution; these factors collectively lead to rapid battery degradation during high-voltage cycling. Therefore, stabilizing the two-phase interface is crucial for achieving high energy density and long-term operation.

[0004] Electrolyte engineering has been widely applied to improve interfacial stability, including strategies such as introducing functional additives, weak solvation solvents, and (locally) high-concentration electrolytes. These strategies aim to construct more stable interfacial layers by adjusting the Li+ solvation structure or altering the interfacial reaction pathway (Chem. Soc. Rev., 2023, 52, 5255-5316). However, in traditional homogeneous electrolyte systems, electrolyte components need to exist in a completely dissolved form. The formation of the interphase layer originates from the random decomposition of completely solvated species on the electrode surface, making it difficult to precisely control the interfacial composition and structure. Furthermore, during charging, additives in the Li+ solvation sheath are influenced by the interfacial electric field gradient and tend to migrate towards the negative electrode with Li+, hindering their effective enrichment at the positive electrode (Joule, 2026, 10, 102219). This not only weakens the regulatory effect of additives on the positive electrode CEI but may also induce side reactions on the lithium metal surface, further exacerbating interfacial instability. These thermodynamic and kinetic constraints indicate that the challenge lies not only in the chemistry of the additives themselves, but also in the fundamental assumption that the electrolyte components must be completely dissolved. Simply relying on a completely dissolved additive system makes it difficult to simultaneously meet the interfacial stability requirements of both the layered cathode and the lithium metal anode.

[0005] On the other hand, existing studies have attempted to introduce insoluble or slightly soluble solid particles as interfacial precursors to improve electrode-electrolyte interface properties. However, these particles typically have large macroscopic sizes, limiting their dispersibility and migration capabilities in the electrolyte. This makes it difficult for them to pass through the membrane and simultaneously act on the positive and negative electrode interfaces, thus limiting their application in the synergistic regulation of dual interfaces (Nature Materials, 2022, 21, 445-454). In summary, current electrolyte technologies are generally limited by the design paradigm of homogeneous electrolytes. Whether using completely dissolved additives or macroscopic solid particles, it is difficult to achieve the synergistic construction of the positive electrode CEI and the negative electrode SEI while maintaining electrochemical mobility. Therefore, a new electrolyte design approach is urgently needed. Summary of the Invention

[0006] The purpose of this invention is to improve the instability of the positive and negative electrode interface in high-nickel layered positive electrode and lithium metal negative electrode battery; to provide a heterogeneous bifunctional electrolyte design scheme, and to improve the positive and negative electrode interface, thereby effectively improving at least one of the cycle life, rate performance and energy density of lithium battery.

[0007] In a first aspect, the present invention provides a heterogeneous bifunctional electrolyte for a lithium secondary battery with a high-nickel layered positive electrode and a lithium metal negative electrode; the heterogeneous bifunctional electrolyte comprises a solvent, a conductive lithium salt, and additives; the additives contain one or more of the following: fluorinated silver salt, fluorinated film-forming agent and silver salt, film-forming agent and fluorinated silver salt, fluorinated lithium salt and silver salt, lithium salt and fluorinated silver salt; the heterogeneous bifunctional electrolyte is a suspension electrolyte exhibiting the Tyndall effect.

[0008] Preferably, the solvent comprises one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), butenyl carbonate (BC), dimethyl sulfite (DMS), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), diethyl sulfite (DES), dibutyl carbonate (DBC), γ-butyrolactone (GBL), methyl butyl carbonate (BMC), dipropyl carbonate (DPC), ethylene ethylene carbonate (VEC), methyl propyl carbonate (MPC), diisopropyl carbonate (DIPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), ethyl butyrate (EB), methyl propionate (MP), ethyl formate (EF), and ethyl propionate (EP).

[0009] Preferably, the conductive lithium salt includes one or more of the following: lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoride (LiF), lithium carbonate (Li2CO3), lithium nitrate (LiNO3), lithium sulfide (Li2S), lithium sulfite (Li2SO3), lithium sulfate (Li2SO4), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium (trifluoromethanesulfonyl)(fluorosulfonyl)imide (LiFTFSI), and lithium thiocyanate (LiSCN).

[0010] The fluorinated film-forming agent or film-forming agent is one or more of the following: vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), difluoroethylene carbonate (DFEC), trifluoropropylene carbonate (TFPC), propylene-1,3-sulfonyl lactone (ASIR), tetravinylsilane (TVSi), vinyl sulfite (ES), propylene sulfite (PS), cyclopentyl sulfite (RPS), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilane)borate (TMSB), and triargyl phosphate (TPP).

[0011] The fluorinated silver salts or silver salts are silver tetrafluoroborate (AgBF4), silver bis(trifluoromethanesulfonyl)imide (AgTFSI), silver hexafluorophosphate (AgPF6), and silver diphenyl phosphate (AgC). 12 H 11Silver carbonate (AgCO3), silver succinimide (AgC4H4NO2), silver lactate (AgC3H5O3), silver benzoate (AgC7H6O2), silver sulfadiazine (AgC4H4NO2), silver sulfadiazine (AgC4H5O3), silver benzoate (AgC4H5O2), silver sulfadiazine (AgC4H5O3 ... 10 One or more of the following: silver (H9N4O2S), silver acetate (AgC2H3O2), silver p-toluenesulfonate (AgC7H7O3S), silver trifluoromethanesulfonate (AgCF3SO3), silver trifluoroacetate (AgC2F3O2), silver metaphosphate (AgPO3), silver pentafluoropropionate (AgC3F5O2), silver methanesulfonate (AgCH3SO3), silver fluorosulfonyl difluoroacetate (AgC2HF3SO4), and silver heptafluorobutyrate (AgC4F7O2).

[0012] The fluorinated lithium salt or lithium salt is one or more of lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorodioxophosphate (LiODFP), lithium bis(oxo)borate (LiBOB), lithium difluorooxo)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), lithium 4-benzonitrile-1,3-bis(trimethylboronic acid) (LBTA), and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (LiDFTFSI).

[0013] The heterogeneous bifunctional lithium battery electrolyte additive contains both fluorine and silver elements; it can be any random combination of fluorine-containing silver salt, fluorine-containing film-forming agent and silver salt, film-forming agent and fluorine-containing silver salt, fluorine-containing lithium salt and silver salt, and lithium salt and fluorine-containing silver salt.

[0014] The heterogeneous bifunctional electrolyte, due to its limited solubility, forms a heterogeneous suspension electrolyte with the Tyndall effect. The total concentration of additives in the electrolyte ranges from 0.005 to 0.05 mol / L.

[0015] Secondly, this invention provides the application of the above-mentioned heterogeneous bifunctional electrolyte, which is suitable for layered positive electrodes Li[Ni] x Co y Mn 1-x-y High-nickel layered cathode lithium metal batteries in O2 (x ≥ 0.7).

[0016] The present invention also provides a lithium secondary battery, comprising:

[0017] The positive electrode is a high-nickel layered oxide with the general formula Li[Ni]. x Co y Mn 1-x-y O2, where x ≥ 0.7;

[0018] The negative electrode is lithium metal or a lithium alloy;

[0019] The diaphragm; and the heterogeneous bifunctional electrolyte.

[0020] The heterogeneous bifunctional electrolyte provided by this invention is rich in fluorine and silver on the negative electrode side, providing a high mechanical strength interface while the lithium-silver alloy layer induces uniform and dense lithium deposition, effectively inhibiting the growth of lithium dendrites; on the positive electrode side, it is rich in fluorine and other beneficial component elements to form a heterostructure, which on the one hand reduces the corrosion of the interface by HF generated by lithium salt hydrolysis, and on the other hand, LiF passivates the positive electrode surface under high voltage, inhibiting the dissolution of transition metal ions.

[0021] The heterogeneous bifunctional electrolyte provided by this invention simultaneously regulates the composition of the interface (SEI / CEI) between the lithium metal anode and the high-nickel ternary cathode, forming a highly stable, fast-conducting, and metalophilic compound or mixture-based inorganic component interface. This effectively suppresses dendrite growth and accelerates the rapid transport of lithium ions. Furthermore, it passivates the cathode surface under high voltage, inhibits transition metal dissolution, and absorbs HF generated by electrolyte decomposition. In practical commercial electrolytes, a true balance can be achieved between interface stability, ionic conductivity, and overall battery performance.

[0022] Within a voltage range of 2.75 V–4.3 V, the first two activation cycles are performed using 0.1 C, and long-cycle testing is conducted at a 1 C rate. After 200 cycles, the capacity retention is not less than 85%, and the average coulombic efficiency is not less than 99%. Attached Figure Description

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 The Tyndall effect diagrams for Example 1 and Comparative Example 1 are shown.

[0025] Figure 2 This is a cryo-electron microscopy image of the electrolyte in Example 1.

[0026] Figure 3 This is a comparison of the cycle performance curves of the battery provided in Example 1 with the addition of the heterogeneous bifunctional additive and that of Comparative Example 1 without the addition of the additive.

[0027] Figure 4 The battery charge / discharge curves are for Comparative Example 1.

[0028] Figure 5 The battery charge / discharge curves are from Example 1.

[0029] Figure 6 A rate comparison of the electrolytes used in Example 1 and Comparative Example 1 for assembled batteries.

[0030] Figure 7This is a comparison of the long-cycle performance curves of batteries assembled with electrolytes from Examples 1, 2, 3, and Comparative Example 1.

[0031] Figure 8 This is a comparison of the long-cycle performance curves of the batteries assembled with the electrolytes of Example 4 and Comparative Example 1.

[0032] Figure 9 This is a comparison of the long-cycle performance curves of the batteries assembled with the electrolytes of Example 5 and Comparative Example 1. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The present invention adopts the following technical solution:

[0035] Preparation of the electrolyte: In an inert atmosphere glove box with a water / oxygen ratio of less than 0.1 ppm, organic solvents were mixed in a volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:1. 50 mL of the mixture was taken, and 7.6 g of lithium hexafluorophosphate (LiPF6) was added to prepare a solution. The mixture was stirred until homogeneous to obtain the base electrolyte. Examples of the bifunctional electrolyte of this invention were obtained by adding 0.005-0.05 mol / L of additives to the base electrolyte (Examples 1-23).

[0036] Preparation of the positive electrode: Commercial high-nickel ternary positive electrodes NCM811 / NCM90 / NCM712, polyvinylidene fluoride (PVDF5130) with a solid content of 5 wt%, and conductive carbon black (Super P) were weighed at a mass ratio of 8:1:1. 2.1 g of N-methylpyrrolidone (NMP) was added, and the mixture was ball-milled at 300 r / min for 6 h. The slurry was then uniformly coated onto aluminum foil using a 250 μm scraper. After coating, the mixture was dried in a 60 ℃ forced-air oven for 2 h, followed by drying in a 120 ℃ vacuum oven for 10 h. The positive electrode was then sliced ​​into 12 mm diameter sheets, each containing approximately 3 mg of active material. The remaining positive electrode sheets were stored in a glove box.

[0037] Battery assembly: The negative electrode uses commercially available lithium-copper composite strip with a lithium metal thickness of 20 μm, cut into circular pieces with a diameter of 15.8 mm; the battery assembly sequence is as follows: positive electrode shell, positive electrode sheet, electrolyte addition, PP separator, negative electrode sheet, stainless steel sheet, gasket, negative electrode shell, electrolyte addition amount is 75 μL, Celgard 2325 separator is used, and the battery is pressed under 650 kg pressure. After standing for 8~10 h, electrochemical tests are performed.

[0038] Room temperature performance testing: All assembled batteries underwent constant current charge-discharge testing using a Blue Electric System tester to evaluate cycle stability. The constant current charge-discharge cycle stability voltage test range for NCM811||Li, NCM90||Li, and NCM712||Li batteries was 2.75 V-4.3 V. The first two cycles were activated using 0.1 C, and long-term cycle testing was performed using 1 C. Rate charge-discharge testing was conducted at 0.2 C, 0.5 C, 1 C, 1.5 C, 2 C, 2.5 C, 3 C, and 1 C for five cycles to evaluate rate performance.

[0039] Example 1

[0040] In this embodiment, the dual-functional electrolyte uses silver tetrafluoroborate (AgBF4) as a heterogeneous electrolyte additive to improve the performance of NCM811||Li lithium batteries.

[0041] 1. Weigh a certain mass of silver tetrafluoroborate and add it to the base electrolyte to obtain a 1M LiPF6 / EC-DMC-EMC electrolyte containing 0.01mol / L silver tetrafluoroborate additive.

[0042] 2. For example Figure 1 As shown, the base electrolyte (Comparative Example 1) did not exhibit a significant Tyndall effect, while the electrolyte with added AgBF4 (Example 1) showed a significant Tyndall effect; and the intrinsic electrolyte characterization is as follows. Figure 2 As shown, AgBF4 dissolves in the electrolyte and exists as nanoparticles / aggregates, constructing a heterogeneous electrolyte structure.

[0043] 3. Battery test results are as follows Figure 3 As shown, the battery containing 0.01 mol / L silver tetrafluoroborate maintained a stable cycle efficiency of over 99.8%, and its capacity retention rate was as high as 86% after 200 cycles. In contrast, the battery with electrolyte in Comparative Example 1 had a coulombic efficiency of 96.4%, and its capacity retention rate was only 60% after 200 cycles.

[0044] 4. Comparison of cyclic coulombic efficiency from Table 1 and Figure 4 and Figure 5 The charge-discharge curves show that the battery containing Example 1 has higher coulombic efficiency and longer cycle life. Figure 6The rate performance curves show that the battery in Example 1 has better rate performance. This indicates that the heterogeneous additives containing fluorine and silver increase the stability of the interface layer.

[0045] Example 2

[0046] The difference between this embodiment and Example 1 is that the additive silver tetrafluoroborate (AgBF4) is a heterogeneous electrolyte with a content of 0.005 mol / L; all other aspects are the same as in Example 1.

[0047] Example 3

[0048] The difference between this embodiment and Example 1 is that the additive silver tetrafluoroborate (AgBF4) is a heterogeneous electrolyte with a content of 0.05 mol / L; all other aspects are the same as in Example 1.

[0049] Example 4

[0050] The difference between this embodiment and Example 1 is that the additive silver tetrafluoroborate (AgBF4) content is 0.01 mol / L, which is a heterogeneous electrolyte, and the lithium battery is NCM90||Li. Everything else is the same as in Example 1.

[0051] Example 5

[0052] The difference between this embodiment and Example 1 is that the additive silver tetrafluoroborate (AgBF4) content is 0.01 mol / L, which is a heterogeneous electrolyte, and the lithium battery is NCM712||Li. Everything else is the same as in Example 1.

[0053] Example 6

[0054] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of silver bis(trifluoromethanesulfonyl)imide (AgTFSI) at a concentration of 0.01 mol / L. Everything else is the same as in Example 1.

[0055] Example 7

[0056] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of silver trifluoromethanesulfonylAgCF3SO3 with a content of 0.01 mol / L. Everything else is the same as in Example 1.

[0057] Example 8

[0058] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of fluoroethylene carbonate (FEC) and silver benzoate (AgC7H5O2) at a concentration of 0.01 mol / L. Everything else is the same as in Example 1.

[0059] Example 9

[0060] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of fluoroethylene carbonate (FEC) and silver benzoate (AgC7H5O2) at a concentration of 0.02 mol / L. Everything else is the same as in Example 1.

[0061] Example 10

[0062] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of fluoroethylene carbonate (FEC) and silver methanesulfonate (AgCH3SO3), with a content of 0.01 mol / L. Everything else is the same as in Example 1.

[0063] Example 11

[0064] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of fluoroethylene carbonate (FEC) and silver methanesulfonate (AgCH3SO3), with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0065] Example 12

[0066] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of vinyl sulfate DTD and silver trifluoroacetate AgC2F3O2, with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0067] Example 13

[0068] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of vinyl sulfate DTD and silver pentafluoropropionate AgC3F5O2, with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0069] Example 14

[0070] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of vinylene carbonate (VC) and silver hexafluorophosphate (AgPF6) at a concentration of 0.02 mol / L. Everything else is the same as in Example 1.

[0071] Example 15

[0072] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte consisting of tris(trimethylsilyl)phosphate TMSP and silver heptafluorobutyrate AgC4F7O2, with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0073] Example 16

[0074] The difference between this embodiment and Example 1 is that the additives used are lithium difluorophosphate (LiPO2F2) and silver diphenyl phosphate (AgC). 12 H11 The heterogeneous electrolyte O4P was used, with a concentration of 0.02 mol / L, and all other parameters were the same as in Example 1.

[0075] Example 17

[0076] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte consisting of lithium bis(fluorosulfonyl)imide (LiFSI) and silver succinimide (AgC4H4NO2), with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0077] Example 18

[0078] The difference between this embodiment and Example 1 is that the additives used are lithium difluorodioxazophosphate (LiODFP) and silver sulfadiazine (AgC). 10 The heterogeneous electrolyte H9N4O2S was used, with a concentration of 0.02 mol / L, and all other parameters were the same as in Example 1.

[0079] Example 19

[0080] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte of lithium difluorooxalate borate (LiDFOB) and silver metaphosphate (AgPO3) at a concentration of 0.02 mol / L. Everything else is the same as in Example 1.

[0081] Example 20

[0082] The difference between this embodiment and Example 1 is that the heterogeneous electrolytes, lithium bis(oxalato)borate (LiBOB) and silver hexafluorophosphate (AgPF6), are present in a concentration of 0.02 mol / L. All other aspects are the same as in Example 1.

[0083] Example 21

[0084] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte consisting of lithium difluorooxalate borate (LiDFOB) and silver difluoroacetate (AgC2HF3SO4) with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0085] Example 22

[0086] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte consisting of 4-benzonitrile-1,3-bis(trimethylborate)lithium (LBTA) and silver bis(trifluoromethanesulfonyl)imideAgTFSI, with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0087] Example 23

[0088] The difference between this embodiment and Example 1 is that the additive used is a heterogeneous electrolyte consisting of lithium 4-benzonitrile-1,3-bis(trimethylborate)lithium (LBTA) and silver trifluoromethanesulfonate AgCF3SO3, with a content of 0.02 mol / L. Everything else is the same as in Example 1.

[0089] Comparative Example 1

[0090] Comparative Example 1 uses the substrate electrolyte in the technical solution.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Comparative Example 1 is that 0.01 mol / L vinyl sulfate DTD was added to the base electrolyte to form a homogeneous electrolyte, while the other steps and conditions were the same.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Comparative Example 1 is that silver benzoate C7H5AgO2 with a content of 0.01 mol / L was added to the base electrolyte to form a heterogeneous electrolyte, while the other steps and conditions were the same.

[0095] Comparative Example 4

[0096] The difference between this comparative example and Comparative Example 1 is that 0.01 mol / L lithium tetrafluoroborate (LiBF4) was added to the base electrolyte to form a homogeneous electrolyte, while the other steps and conditions were the same.

[0097] The average coulombic efficiency and cycle capacity retention of the lithium batteries prepared using the various examples and comparative examples are shown in Table 1. When fluorine- or silver-containing additives are added, both the average coulombic efficiency and cycle capacity retention of the batteries are improved.

[0098] like Figure 7 As shown, when the content of the fluorinated silver salt additive is in the range of 0.005-0.05 mol / L, it improves battery performance, coulombic efficiency and cycle life compared to Comparative Example 1.

[0099] like Figure 8 As shown, with the addition of the additives in Example 4, the unstable ultra-high nickel ternary cathode NCM90 can retain 93% of its capacity after 200 cycles, while the electrolyte in Comparative Example 1 can only retain 72% of its capacity, indicating that the CEI interface has a significant effect on inhibiting the dissolution of transition metals.

[0100] like Figure 9 As shown, with the additives of Example 5 added and using the NCM712 ternary cathode, 89% of the capacity can be retained after 200 cycles, while the electrolyte of Comparative Example 1 can only retain 79% of the capacity. Example 5 shows improvements in both coulombic efficiency and capacity retention.

[0101] Compared to the four additive combinations of fluorinated silver salt and fluorinated film-forming agent and silver salt, film-forming agent and fluorinated silver salt, fluorinated lithium salt and silver salt, and lithium salt and fluorinated silver salt, the additive content of fluorinated silver salt is reduced, thereby reducing production costs and achieving a balance between content, cost and performance.

[0102] In the comparative examples, the present invention presents four electrolytes: Comparative Example 1 and Comparative Example 2 (without fluorine and silver additives), Comparative Example 3 (without fluorine additives), and Comparative Example 4 (without silver additives). It can be found that none of them are as effective as those containing both fluorine and silver additives.

[0103] In summary, the heterogeneous bifunctional electrolyte combination of this invention simultaneously regulates the composition of the interface (SEI / CEI) between the lithium metal anode and the high-nickel ternary cathode, forming a highly stable, fast-conducting, and metalophilic inorganic interface composition that effectively suppresses dendrite growth. Furthermore, it passivates the cathode surface under high voltage, inhibiting transition metal dissolution. In practical commercial electrolytes, a true balance can be achieved between interface stability, ionic conductivity, and overall battery performance.

[0104] The above description is merely an embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

[0105] Table 1. Material differences and performance parameters of each embodiment and comparative example.

[0106]

[0107]

[0108] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A heterogeneous bifunctional electrolyte for lithium secondary batteries with a high-nickel layered positive electrode and a lithium metal negative electrode, characterized in that, The heterogeneous bifunctional electrolyte contains a solvent, a conductive lithium salt, and an additive. The additive contains one or more of the following: a fluorinated silver salt, a fluorinated film-forming agent and a silver salt, a film-forming agent and a fluorinated silver salt, a fluorinated lithium salt and a silver salt, and a lithium salt and a fluorinated silver salt. The heterogeneous bifunctional electrolyte is a suspension electrolyte exhibiting the Tyndall effect.

2. The heterogeneous bifunctional electrolyte according to claim 1, characterized in that, The total concentration of the additive in the electrolyte ranges from 0.005 to 0.05 mol / L.

3. The heterogeneous bifunctional electrolyte according to claim 1, characterized in that, The additive contains both fluorine and silver elements; through the synergistic effect of fluorine and silver elements, an interface film containing a lithium-silver alloy layer is induced to form on the surface of the lithium metal anode, while a heterostructure interface film rich in LiF is formed on the surface of the cathode.

4. The heterogeneous bifunctional electrolyte according to claim 1, characterized in that, The fluorinated film-forming agent and the film-forming agent are one or more of the following: vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, difluoroethylene carbonate, trifluoropropylene carbonate, propylene-1,3-sulfonyl lactone, tetravinylsilane, vinyl sulfite, propylene sulfite, cyclopentyl sulfite, tris(trimethylsilyl) phosphate, tris(trimethylsilane) borate, and triargyl phosphate.

5. The heterogeneous bifunctional electrolyte according to claim 1, characterized in that, The fluorinated silver salt and silver salt are one or more of the following: silver tetrafluoroborate, silver bis(trifluoromethanesulfonyl)imide, silver hexafluorophosphate, silver diphenyl phosphate, silver carbonate, silver succinimide, silver lactate, silver benzoate, silver sulfadiazine, silver acetate, silver p-toluenesulfonate, silver trifluoromethanesulfonate, silver trifluoroacetate, silver metaphosphate, silver pentafluoropropionate, silver methanesulfonate, silver fluorosulfonyl difluoroacetate, and silver heptafluorobutyrate.

6. The heterogeneous bifunctional electrolyte according to claim 1, characterized in that, The fluorinated lithium salt and lithium salt are one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorodioxazophosphate, lithium bis(oxazo)borate, lithium difluorooxazobate, lithium tetrafluoroborate, lithium 4-benzonitrile-1,3-bis(trimethylborate), and lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide.

7. The application of the heterogeneous bifunctional electrolyte according to any one of claims 1 to 6 in lithium batteries with high-nickel layered positive electrode and lithium metal negative electrode, characterized in that, The high-nickel layered cathode is Li[Ni] x Co y Mn 1-x-y O2, where x is greater than or equal to 0.

7.

8. A lithium secondary battery, characterized in that, include: The positive electrode is a high-nickel layered oxide with the general formula Li[Ni]. x Co y Mn 1-x-y O2, where x ≥ 0.7; The negative electrode is lithium metal or a lithium alloy; Diaphragm; And the heterogeneous bifunctional electrolyte according to any one of claims 1 to 6.

9. The lithium secondary battery according to claim 8, characterized in that, During cycling, the high-nickel layered oxide cathode can form a LiF-rich heterostructure cathode-electrolyte interface film in situ on its surface; during cycling, the lithium metal anode can form a solid electrolyte interface film containing a lithium-silver alloy phase on its surface.

10. The lithium secondary battery according to claim 8, characterized in that, Within a voltage range of 2.75 V–4.3 V, the first two activation cycles are performed using 0.1 C, and long-cycle testing is conducted at a 1 C rate. After 200 cycles, the capacity retention is not less than 85%, and the average coulombic efficiency is not less than 99%.

Images