A lithium ion battery based on in-situ lithium supplement of negative electrode and a preparation method thereof

Abstract

The application belongs to the technical field of batteries, and discloses a lithium ion battery based on in-situ lithium supplement of a negative electrode and a preparation method thereof. The lithium ion battery based on in-situ lithium supplement of the negative electrode comprises a positive electrode, a negative electrode, a separator and an electrolyte. The electrolyte comprises a lithium salt and a negative electrode lithium supplement additive. The negative electrode lithium supplement additive is capable of generating free radicals or positively charged functional groups under the condition that the charging voltage is above 4 V, and can be combined with anions in the lithium salt. The negative electrode lithium supplement additive in the lithium ion battery based on in-situ lithium supplement of the negative electrode is capable of generating free radicals or positively charged functional groups under the condition that the charging voltage is above 4 V, and can react to consume anions or be combined with anions in the lithium salt, so that part of lithium ions in the electrolyte are converted into active lithium ions. The active lithium ions are deposited on the negative electrode side or supplement part of lithium consumed in the process of forming an SEI film on the negative electrode side, so that the effect of in-situ lithium supplement of the negative electrode is achieved, and the cycle stability of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a lithium-ion battery based on in-situ lithium replenishment at the negative electrode and its preparation method. Background Technology

[0002] The limited theoretical specific capacity of the positive and negative electrodes in lithium-ion batteries restricts their energy density. For example, commonly used graphite anodes have limited specific capacity and low compaction density, significantly limiting the achievement of high-quality and volumetric energy density. Therefore, the development of more efficient anode materials is particularly urgent. Given its advantages of high specific capacity and low reaction potential, lithium metal anodes are an ideal choice for high-energy-density lithium-ion batteries. Lithium metal batteries are considered one of the most promising next-generation high-energy-density storage devices. They directly use metallic lithium as the anode, possessing a high theoretical specific capacity (3861 mAh / g, 10.4 times that of graphite) and the lowest electrode potential (-3.04 V vs. SHE). However, to achieve good cycle performance in lithium metal batteries, an excessive amount of lithium metal is often required as the anode (thickness greater than 250 μm), typically requiring an N / P ratio exceeding 50 to achieve a cycle life of several hundred cycles. Therefore, the high N / P ratio limits the actual energy density improvement of lithium metal batteries compared to traditional lithium-ion batteries. Electrodeless lithium metal batteries are a more ideal choice. Their negative electrode contains no active materials (such as graphite, Li, Si, Sn), but only uses a conductive current collector (such as copper foil). The positive electrode is a common lithium-containing material (such as lithium iron phosphate, ternary cathodes, lithium cobalt oxide, etc.). Compared to lithium metal batteries, electrodeless lithium metal batteries offer significant convenience and safety in battery assembly because the negative electrode uses a conductive current collector (such as copper foil) directly instead of the highly chemically active lithium metal. The working principle of electrodeless lithium metal batteries differs from traditional lithium-ion batteries. During charging, lithium ions combine with electrons on the surface of the conductive current collector at the negative electrode, resulting in lithium deposition. During discharging, the lithium metal deposited on the conductive current collector at the negative electrode is stripped off and returns to the positive electrode through the electrolyte. However, due to the high reactivity of lithium metal, it is prone to side reactions with the electrolyte, leading to irreversible loss of lithium metal. Simultaneously, the deposition / stripping process causes significant volume changes in the lithium metal anode, resulting in repeated formation and destruction of the SEI film in traditional electrolyte systems, consuming large amounts of lithium ions. Furthermore, the non-uniform deposition / stripping process easily induces the formation of lithium dendrites, and further dendrite growth can cause loss of electrical connection with the current collector, forming dead lithium. All these behaviors contribute to poor cycle stability and rapid battery failure.

[0003] To address the poor cycle stability of batteries due to interfacial side reactions and dendrite formation on the negative electrode side, research teams both domestically and internationally have investigated the failure mechanism and proposed various improvement strategies based on the main components of the battery. These strategies include electrolyte optimization, positive electrode modification, and negative electrode modification to improve the coulombic efficiency and cycle performance of negative electrode-free lithium metal batteries. For example, in electrolyte optimization, adding salts containing indium, tin, and bismuth as additives to the electrolyte forms a metal-containing SEI film on the negative electrode surface. These metals store lithium through alloy formation, improving the cycle stability of lithium metal batteries / negative electrode-free batteries (Patent CN112670574A). Regarding negative electrode modification, surface oxidation of the negative electrode current collector to generate Cu(OH)₂, followed by annealing, yields a copper foil with a lithium-loving nano-cuprous oxide surface layer. This helps form a stable SEI film, promotes uniform lithium deposition, inhibits dendrite growth, and improves battery performance (Patent CN115064700A). In addition, adding lithium-rich materials to the positive electrode active material, taking advantage of its high capacity for irreversible lithium removal, can compensate for the irreversible loss of lithium on the negative electrode side during subsequent cycles, thereby extending the battery cycle life (Patent CN114284567A).

[0004] However, all of the above methods have their limitations. For example, adding salts containing metals such as indium, tin, and bismuth, which have a higher electrode potential than lithium, can achieve lithium storage by forming an alloy at the negative electrode. However, the volume expansion of the negative electrode is more pronounced than in conventional lithium metal batteries without a negative electrode, leading to insufficient cycle stability. Modifying the surface of the negative electrode current collector improves the reversibility of lithium deposition / stripping, but the process is cumbersome and not conducive to large-scale application. Furthermore, during battery operation, some active lithium still needs to be sacrificed to form the SEI film at the interface. When the lithium metal is consumed to a certain extent, the battery will fail. Adding lithium-rich materials to the positive electrode can achieve lithium replenishment, but it is often difficult to be effectively compatible with the positive electrode production process, and the lithium replenishment effect is limited. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a lithium-ion battery based on in-situ lithium replenishment at the negative electrode, wherein the electrolyte inside the battery can provide additional active lithium to the lithium-ion battery system, thereby slowing down battery degradation and improving battery cycle stability.

[0006] A first aspect of the present invention provides a lithium-ion battery based on in-situ lithium replenishment at the negative electrode, the lithium-ion battery based on in-situ lithium replenishment at the negative electrode comprising a positive electrode, a negative electrode, and a separator and an electrolyte between the positive electrode and the negative electrode; the electrolyte comprises a lithium salt and a negative electrode lithium replenishment additive; the negative electrode lithium replenishment additive decomposes to generate free radicals or positively charged functional groups under a charging voltage of 4V or above; the free radicals or positively charged functional groups combine with anions in the lithium salt.

[0007] The free radicals mentioned in this invention refer to hydrogen free radicals, alkyl free radicals, alkoxy free radicals, etc.; the functional groups refer to positively charged ions centered on carbon or nitrogen. The combination of the free radicals or positively charged functional groups mentioned in this invention with the anions in the lithium salt includes two cases: one is that the positively charged functional group combines with the anion without destroying the anion, such as CH3H2C. + With FSI - Anions can combine; or free radicals can react with anions and consume them. For example, hydrogen free radicals react with hexafluorophosphate to generate HF and PF5, thereby consuming anions.

[0008] The main inventive concept of this invention lies in the fact that, as those skilled in the art know, the electrolyte system must maintain charge neutrality during charging, discharging, and battery resting processes. For example, if an electron-consuming reaction occurs at the negative electrode where lithium cations are consumed, the positive electrode must be forced to insert additional anions for charge compensation to ensure charge neutrality in the electrolyte. Based on this property, if the solvent or additives in the electrolyte decompose during charging, further combining with or reacting with anions in the lithium salt to consume anions, then, in order to ensure electron charge neutrality between the electrodes, the excess cations (i.e., lithium ions) will deposit on the surface of the negative electrode current collector, or compensate for the portion of lithium consumed by the formation of the SEI film on the negative electrode side. This invention adds a negative electrode lithium replenishing additive that is easily decomposed under high voltage (above 4V). This negative electrode lithium replenishing additive decomposes during charging to generate free radicals or positively charged functional groups, which combine with or react with anions of the lithium salt to consume anions, causing some lithium ions in the electrolyte to be converted into active lithium ions, thereby depositing on the negative electrode side or replenishing a portion of the lithium consumed by the formation of the SEI film on the negative electrode side. This approach ensures stable SEI film formation while simultaneously providing in-situ lithium replenishment to the negative electrode, enabling electrodeless lithium metal batteries to cycle stably for extended periods without failure. Compared to previous modification methods, the in-situ lithium replenishment technology of this invention only requires adjustment of the electrolyte composition and leverages the charge-neutral nature of the electrolyte to provide a large amount of active lithium, achieving long-cycle performance in electrodeless lithium metal batteries. Furthermore, the electrolyte of this invention is also applicable to other lithium-ion battery systems based on graphite, silicon-carbon, and alloyed negative electrodes, effectively compensating for the irreversible loss of active lithium ions during SEI formation on the negative electrode side, thereby improving battery cycle life.

[0009] The working mechanism of in-situ lithium replenishment at the negative electrode in this invention is as follows: During battery charging, when the voltage reaches a certain level (above 4V), the lithium replenishment additive in the electrolyte first decomposes to generate free radicals or positively charged functional groups, which react to consume or combine with anions in the lithium salt. Since the electrolyte needs to maintain electrical neutrality, some lithium ions in the electrolyte will be converted into active lithium ions and deposited on the negative electrode side or replenish some of the lithium consumed during the formation of the SEI film on the negative electrode side. Depending on the degree of lithium consumption in different electrolyte systems, the concentration or type of lithium replenishment additive can be changed to achieve different levels of lithium replenishment effect. Since different positive electrode materials have different charge and discharge platforms, for systems with low charge and discharge platforms, it is possible to charge to a high voltage (above 4V) in the first few cycles to allow the lithium replenishment additive to decompose and achieve a lithium replenishment effect. Then, charge and discharge within a suitable voltage range. The in-situ lithium replenishment method of this invention can effectively slow down battery degradation and extend battery failure time.

[0010] Preferably, the negative electrode lithium supplement additive is selected from one or more of ester compounds, ether compounds, olefin compounds, and lithium-containing compounds. The ester compounds mentioned in this invention refer to organic compounds formed by the reaction of acids (carboxylic acids or inorganic oxyacids) with alcohols, such as vinylene carbonate, ethylene ethylene carbonate, and vinyl acetate; the ether compounds refer to compounds containing ether bonds, such as ethylene glycol dimethyl ether, ethylene glycol phenyl ether, ethylene glycol diphenyl ether, and phenyl sulfide; the olefin compounds refer to hydrocarbons containing C=C bonds (carbon-carbon double bonds), such as 1,2-dichloroethoxyethane, 1,3-dioxocyclopentane, and 4-methyl-1,3-dioxocyclopentane.

[0011] Preferably, the negative electrode lithium supplement additive includes vinylene carbonate, ethylene carbonate, vinyl acetate, trimethylvinyl acetate, lithium difluorophosphate, lithium difluorooxalate borate, ethylene glycol dimethyl ether, ethylene glycol phenyl ether, ethylene glycol diphenyl ether, phenyl sulfide, tert-butylphenyl ether, chloromethylphenyl sulfide, glycidyl methyl ether, tetrahydrofuran, 2,3-dichlorotetrahydrofuran, tetrahydrofuran chloride, bis(2-chloroethoxy)methane, ethylpropyl ether, methyl butyl ether, dichloromethyl butyl ether, methyl propyl sulfide, methyl propyl ether, butylphenyl ether, 1,2-dichloroethoxyethane, chloromethyl isopropyl ether, 2-fluorophenyl allyl ether, 1- One or more of the following: chloromethyl ethyl ether, 2-chloroethyl methyl ether, 2-bromoethyl methyl ether, 2-chloroethyl chloromethyl ether, 2,2,2-trichloroethyl chloromethyl ether, 2-ethoxychloroethane, 2-chloro-1,1,2-trifluoroethyl methyl ether, 2-chloro-1,1,2-trifluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, 2-methyltetrahydrofuran, 1,3-dioxocyclopentane, 4-methyl diphenyl ether, 4-methyl-1,3-dioxocyclopentane, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, 1,2-dimethoxypropane, and triethylene glycol dimethyl ether.

[0012] Preferably, the negative electrode lithium supplementation additive has a mass percentage content of 0.1-10% in the electrolyte.

[0013] Preferably, the negative electrode lithium supplementation additive has a mass percentage content of 1-5% in the electrolyte.

[0014] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium sulfate, lithium nitrate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium perchlorate.

[0015] Preferably, the concentration of the lithium salt in the electrolyte is 0.1-10 mol / L.

[0016] Preferably, the concentration of the lithium salt in the electrolyte is 1-5 mol / L.

[0017] Preferably, the electrolyte further includes an organic solvent, which is selected from one or more of ester compounds, sulfone compounds, ether compounds, nitrile compounds, and carboxylic acid ester compounds. The nitrile compounds mentioned in this invention refer to organic compounds containing carbon atoms linked by hydrocarbon and cyano groups, such as succinic anionyl nitrile and adiponitrile.

[0018] Preferably, the organic solvent comprises one or more of the following: propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl formate, methyl acetate, N,N-dimethylacetamide, fluoroethylene carbonate, methyl propionate, ethyl propionate, ethyl acetate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, dipropylene glycol dimethyl ether, 1,2-dimethoxypropane, triethylene glycol dimethyl ether, dimethyl sulfone, sulfolane, dimethyl ether, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, and 12-crown ether-4.

[0019] Preferably, the electrolyte further includes an electrolyte additive, which is selected from one or more of ester compounds, sulfone compounds, ether compounds, nitrile compounds, and olefin compounds.

[0020] Preferably, the electrolyte additive includes one or more of the following: fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, propylene sulfate, ethylene sulfate, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, ethylene sulfite, methyl chloroformate, and tris(trimethylsilane) phosphate.

[0021] Preferably, the negative electrode is a negative electrode current collector, and the material of the negative electrode current collector is selected from copper foil, nickel foil, titanium foil, nickel mesh, foamed copper plate, porous copper skeleton, conductive carbon skeleton, carbon nanofiber scaffold or mesoporous carbon nanofiber.

[0022] Preferably, the negative electrode current collector is a negative electrode current collector that has undergone surface modification or three-dimensional current collector design. The surface modification includes, but is not limited to, coating the surface of the negative electrode current collector with a polymer coating or a fast ion conductor layer; or constructing an artificial SEI film on the surface of the negative electrode current collector before battery assembly. The three-dimensional current collector design includes, but is not limited to, three-dimensional structuring of the negative electrode current collector, such as copper foil, carbon substrate, porous foam copper plate, and polymer substrate.

[0023] Preferably, the surface of the negative electrode current collector is coated with a negative electrode active material. The negative electrode active material includes one or more of graphite, activated carbon, hard carbon, lithium titanate, graphene, carbon nanotubes, silicon carbide, metal oxides, aluminum, tin, bismuth, and antimony. The metal oxide includes one or more of manganese oxide, tin oxide, and nickel oxide.

[0024] Preferably, the positive electrode includes a positive electrode current collector, and the material of the positive electrode current collector is selected from one or more of aluminum, tin, copper, iron, nickel, titanium, magnesium, and zinc.

[0025] Preferably, the surface of the positive current collector is coated with a positive active material, which includes one or more of lithium cobalt oxide, lithium iron phosphate, ternary materials, lithium manganese oxide, lithium nickel manganese oxide, natural graphite, expanded graphite, conductive carbon black, graphene, carbon nanotubes, activated carbon fibers, and carbon molecular sieves.

[0026] Preferably, the diaphragm is made of glass fiber, polyethylene, polypropylene, or polypropylene / polyethylene / polypropylene.

[0027] Preferably, the lithium-ion battery based on in-situ lithium replenishment at the negative electrode is a lithium metal battery without a negative electrode.

[0028] A second aspect of the present invention provides a method for preparing a lithium-ion battery based on in-situ lithium replenishment at the negative electrode, comprising the following steps:

[0029] The positive electrode, the negative electrode, the separator, and the electrolyte are assembled to obtain the lithium-ion battery based on in-situ lithium replenishment at the negative electrode.

[0030] A third aspect of the present invention provides an application of an electrolyte in lithium-ion battery negative electrode lithium replenishment, the electrolyte comprising a lithium salt and a negative electrode lithium replenishment additive; the negative electrode lithium replenishment additive decomposes to generate free radicals or positively charged functional groups under a charging voltage of 4V or above, the free radicals or positively charged functional groups combining with anions in the lithium salt.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) The present invention is based on a lithium-ion battery with in-situ negative electrode lithium replenishment. By adding a negative electrode lithium replenishment additive to the electrolyte, the negative electrode lithium replenishment additive decomposes to generate free radicals or positively charged functional groups under the condition of charging voltage above 4V. These additives can react to consume anions or combine with anions in lithium salts, so that some lithium ions in the electrolyte are converted into active lithium ions. The active lithium ions are deposited on the negative electrode side or replenish some of the lithium consumed in the formation of the SEI film on the negative electrode side, thereby achieving the effect of in-situ negative electrode lithium replenishment and improving the cycle stability of the battery. The present invention is based on a lithium metal battery without a negative electrode with in-situ negative electrode lithium replenishment. After 50 cycles, the capacity retention rate can reach 78.5%.

[0033] (2) The electrolyte in the lithium-ion battery based on in-situ lithium replenishment at the negative electrode has good compatibility with existing battery processes and can be applied to different types of battery systems. In addition, different lithium replenishment additives can be selected according to different electrolyte systems, and the concentration or type of lithium replenishment additives can be changed to achieve different lithium replenishment effects, which has a certain degree of controllability. Attached Figure Description

[0034] Figure 1 The graphs show the three-electrode test curves of the first charge-discharge cycle at 0.2C rate for the dual-ion batteries of Example 83 and Comparative Example 2 at room temperature.

[0035] Figure 2 These are the cycling performance curves of Example 83 and Comparative Example 2 at room temperature and at a 1C rate. Detailed Implementation

[0036] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0037] Based on negative electrode-free lithium metal battery

[0038] Example 1

[0039] A method for preparing a negative electrode-free lithium metal battery

[0040] Preparation of electrolyte ①: The electrolyte consists of an organic solvent, a lithium salt, and a high-voltage, easily decomposed negative electrode lithium supplementation additive. The organic solvent is fluoroethylene carbonate, the lithium salt is lithium difluorosulfonyl imide, the molar concentration of the lithium salt in the electrolyte is 5 mol / L, and the negative electrode lithium supplementation additive is ethylene glycol dimethyl ether, the mass fraction of the negative electrode lithium supplementation additive in the electrolyte is 1 wt.%.

[0041] Preparation of positive electrode ①: Lithium iron phosphate (LFP) is used as the positive electrode material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder. The three are mixed evenly in N-methylpyrrolidone (NMP) in a ratio of 92%, 5%, and 3%, respectively. The mixture is coated on aluminum foil, dried, and then cut into 10mm round pieces. After vacuum drying, the positive electrode sheet is obtained.

[0042] Treatment of negative electrode ①: Immerse copper foil in 1 mol / L hydrochloric acid solution for 10 min, take it out and rinse it with deionized water and acetone respectively, vacuum dry it and transfer it to a glove box to obtain negative electrode sheet.

[0043] Assembly of a negative electrode-free lithium metal battery: Using the above-mentioned positive and negative electrode sheets as positive and negative electrodes, glass fiber as the separator, and the electrolyte ① prepared above, a CR2032 button cell battery is assembled.

[0044] Example 2

[0045] A method for preparing a negative electrode-free lithium metal battery

[0046] Preparation of electrolyte ②: The electrolyte is composed of an organic solvent, a lithium salt, and a negative electrode lithium supplementation additive that is easily decomposed under high voltage. The organic solvent is fluoroethylene carbonate, the lithium salt is lithium difluorosulfonyl imide, the molar concentration of the lithium salt in the electrolyte is 5 mol / L, and the negative electrode lithium supplementation additive is ethylene glycol dimethyl ether, the mass fraction of the negative electrode lithium supplementation additive in the electrolyte is 2 wt.%.

[0047] The preparation of the positive electrode, the treatment of the negative electrode, and the assembly method of the electrodeless lithium metal battery are the same as in Example 1, except that electrolyte ② is used for assembly in the electrodeless lithium metal battery assembly.

[0048] Example 3

[0049] A method for preparing a negative electrode-free lithium metal battery

[0050] Preparation of electrolyte ③: The electrolyte is composed of an organic solvent, a lithium salt, and a high-voltage, easily decomposed negative electrode lithium supplementation additive. The organic solvent is fluoroethylene carbonate, the lithium salt is lithium difluorosulfonyl imide, the molar concentration of the lithium salt in the electrolyte is 5 mol / L, and the negative electrode lithium supplementation additive is ethylene glycol dimethyl ether, the mass fraction of the negative electrode lithium supplementation additive in the electrolyte is 5 wt.%.

[0051] The preparation, processing and assembly methods of the positive electrode and negative electrode of the electrodeless lithium metal battery are the same as in Example 1, except that electrolyte ③ is used for assembly in the electrodeless lithium metal battery assembly.

[0052] Example 4

[0053] A method for preparing a negative electrode-free lithium metal battery

[0054] Preparation of electrolyte ④: The electrolyte consists of an organic solvent, lithium salt, conventional additives, and a high-voltage, easily decomposed negative electrode lithium supplementation additive. The organic solvent is ethylene carbonate:diethyl carbonate (1:1, v:v), the lithium salt is lithium hexafluorophosphate, and the molar concentration of the lithium salt in the electrolyte is 1.0 mol / L. The conventional additive is fluoroethylene carbonate with a mass fraction of 2 wt.%, and the negative electrode lithium supplementation additive is ethylene glycol dimethyl ether with a mass fraction of 2 wt.% in the electrolyte.

[0055] Preparation of positive electrode ②: Lithium manganese oxide is used as the positive electrode material, carbon black is used as the conductive agent, and polyvinylidene fluoride (PVDF) is used as the binder. The three are mixed evenly in N-methylpyrrolidone (NMP) in a ratio of 8:1:1, coated on aluminum foil, dried and cut into 10 mm round pieces, and vacuum dried to obtain the positive electrode sheet.

[0056] The processing and assembly method of the negative electrode of the negative electrode-free lithium metal battery is the same as that in Example 1, except that the positive electrode ② and electrolyte ④ are used for assembly in the assembly of the negative electrode-free lithium metal battery.

[0057] Example 5

[0058] A method for preparing a negative electrode-free lithium metal battery

[0059] Preparation of electrolyte ⑤: The electrolyte consists of an organic solvent, lithium salt, conventional additives, and a high-voltage, easily decomposed negative electrode lithium supplementation additive. The organic solvent is ethylene carbonate:diethyl carbonate (1:1, v:v), the lithium salt is lithium hexafluorophosphate, and the molar concentration of the lithium salt in the electrolyte is 1 mol / L. The conventional additive is vinylene carbonate, with a mass fraction of 2 wt.%, and the negative electrode lithium supplementation additive is ethylene glycol dimethyl ether, with a mass fraction of 2 wt.% in the electrolyte.

[0060] Preparation of positive electrode ③: Using NCM523 as the positive electrode material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder, the three are mixed evenly in N-methylpyrrolidone (NMP) in a ratio of 8:1:1, coated on aluminum foil, dried and cut into 10mm round pieces, and vacuum dried to obtain the positive electrode sheet.

[0061] The processing and assembly method of the negative electrode of the negative electrode-free lithium metal battery is the same as that in Example 1, except that the positive electrode ③ and electrolyte ⑤ are used for assembly in the assembly of the negative electrode-free lithium metal battery.

[0062] Example 6

[0063] A method for preparing a negative electrode-free lithium metal battery

[0064] Preparation of electrolyte ⑥: The electrolyte consists of an organic solvent, lithium salt, conventional additives, and a high-voltage, easily decomposed negative electrode lithium supplementation additive. The organic solvent is fluoroethylene carbonate: methyl ethyl carbonate (3:7, v:v), the lithium salt is lithium hexafluorophosphate, and the molar concentration of the lithium salt in the electrolyte is 1 mol / L. The conventional additive is vinylene carbonate, with a mass fraction of 2 wt.%, and the negative electrode lithium supplementation additive is ethylene glycol dimethyl ether, with a mass fraction of 2 wt.% in the electrolyte.

[0065] Preparation of positive electrode ④: Using NCM811 as the positive electrode material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder, the three are mixed evenly in N-methylpyrrolidone (NMP) in a ratio of 8:1:1, coated on aluminum foil, dried and cut into 10mm round pieces, and vacuum dried to obtain the positive electrode sheet.

[0066] The processing and assembly method of the negative electrode of the negative electrode-free lithium metal battery is the same as that in Example 1, except that the positive electrode ④ and electrolyte ⑥ are used for assembly in the assembly of the negative electrode-free lithium metal battery.

[0067] Example 7

[0068] A method for preparing a negative electrode-free lithium metal battery

[0069] Preparation of electrolyte ⑦: The electrolyte consists of an organic solvent, a lithium salt, and a high-voltage, easily decomposed negative electrode lithium supplementation additive. The organic solvent is fluoroethylene carbonate: 2,2,2-trifluoroethyl ether (2:1, v:v), the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the molar concentration of the lithium salt in the electrolyte is 2 mol / L, and the negative electrode lithium supplementation additive is lithium difluorophosphate, the mass fraction of the negative electrode lithium supplementation additive in the electrolyte is 2 wt.%.

[0070] The processing and assembly method of the negative electrode of the negative electrode-free lithium metal battery is the same as in Example 1, and the preparation of the positive electrode is the same as in Example 6. The difference is that in the assembly of the negative electrode-free lithium metal battery, the positive electrode ④ and the electrolyte ⑦ are used for assembly.

[0071] Comparative Example 1

[0072] A method for preparing a negative electrode-free lithium metal battery

[0073] Preparation of electrolyte ⑧: It consists of an organic solvent and a lithium salt. The organic solvent is fluoroethylene carbonate, and the lithium salt is lithium bis(fluorosulfonyl)imide. The molar concentration of the lithium salt in the electrolyte is 5 mol / L.

[0074] The preparation, processing and assembly methods of the positive electrode and negative electrode of the electrodeless lithium metal battery are the same as in Example 1, except that electrolyte ⑧ is used for assembly in the electrodeless lithium metal battery assembly.

[0075] Test Example 1

[0076] The electrochemical performance of the electrodeless lithium metal batteries assembled in Examples 1-7 and Comparative Example 1 was tested using the Newway testing system.

[0077] Test method:

[0078] At room temperature, the battery was first charged and discharged for the first five cycles at a rate of 0.2C and a voltage range of 3-5V (the charging cut-off voltage was higher than the decomposition voltage of the lithium additive on the negative electrode). Afterwards, it was charged and discharged at a constant current of 0.2C, with a voltage range of 2.5-4.2V. The test results are shown in Table 1.

[0079] Table 1. Performance parameters of the batteries assembled in Examples 1-7 and Comparative Example 1.

[0080]

[0081]

[0082] As shown in Table 1, based on Examples 1-3 and Comparative Example 1, this invention, by adding a high-voltage, easily decomposed negative electrode lithium replenishing additive to the electrolyte, provides additional active lithium to the battery system by consuming anions in the electrolyte, thereby slowing down battery degradation and improving battery cycle stability. In Examples 1-7, the addition of the negative electrode lithium replenishing additive effectively improved the cycle performance of the negative electrode-less lithium metal battery. After 50 cycles, the capacity retention rate was approximately 72%. In contrast, the negative electrode-less lithium metal battery assembled using Comparative Example 1 experienced rapid capacity degradation after 50 cycles, with a capacity retention rate of only about 51%. Therefore, the negative electrode lithium replenishing additive of Examples 1-7 can improve the cycle performance of the negative electrode-less lithium metal battery.

[0083] Examples 8-55

[0084] The only difference between Examples 8-55 and Example 1 is the type or concentration of the negative electrode lithium supplementation additive, as shown in Table 2. The electrochemical performance of the negative electrode-free lithium metal batteries prepared in Examples 8-55 was tested, and the test results are shown in Table 2.

[0085] Table 2 Performance parameters of the batteries assembled in Examples 8-55

[0086]

[0087]

[0088]

[0089] As shown in Table 2, different negative electrode lithium replenishment additives were selected in Examples 8-55. Among them, Example 24, with the addition of 2 wt.% dipropylene glycol dimethyl ether, showed better first-cycle efficiency and capacity retention. Compared with the battery assembled with electrolyte without the addition of negative electrode lithium replenishment additive, the lithium replenishment effect was obvious.

[0090] Examples 56-62

[0091] The only difference between Examples 56-62 and Example 5 is the type or concentration of conventional additives added to the prepared electrolyte, as shown in Table 3. The electrochemical performance of the batteries assembled in Examples 56-62 was tested, and the test results are shown in Table 3.

[0092] Table 3 Performance parameters of the batteries assembled in Examples 56-62

[0093]

[0094]

[0095] As shown in Table 3, by adding a negative electrode lithium replenishment additive and changing the type and concentration of conventional additives, the battery can not only have a lithium replenishment effect, but also further maintain the stability of the battery.

[0096] Examples 63-82

[0097] The only difference between Examples 63-82 and Example 1 is the type or concentration of organic solvent in the prepared electrolyte, as shown in Table 4. The electrochemical performance of the batteries assembled in Examples 63-82 was tested, and the test results are shown in Table 4.

[0098] Table 4 Performance parameters of the batteries assembled in Examples 63-82

[0099]

[0100]

[0101] The ratios between the organic solvents in Table 4 are by volume.

[0102] As shown in Table 4, Examples 63-82 added a negative electrode lithium replenishing additive that is easily decomposed under high voltage. This additive can achieve a certain effect of lithium replenishment in different electrolyte organic solvents, thereby improving the cycle stability of the battery.

[0103] Lithium-ion / dual-ion batteries based on traditional anode materials

[0104] Example 83

[0105] A method for preparing a lithium dual-ion battery

[0106] Preparation of electrolyte ⑨: The electrolyte is composed of an organic solvent, a lithium salt, and a negative electrode lithium supplementation additive. The organic solvent is ethyl methyl carbonate, the lithium salt is lithium hexafluorophosphate, the molar concentration of the lithium salt in the electrolyte is 4 mol / L, and the negative electrode lithium supplementation additive is vinylene carbonate, the mass fraction of the negative electrode lithium supplementation additive in the electrolyte is 2 wt.%.

[0107] Preparation of the positive electrode: Expanded graphite (EG) is used as the positive electrode material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder. The three are mixed evenly in N-methylpyrrolidone (NMP) in a ratio of 92%, 5%, and 3%, respectively. The mixture is coated on aluminum foil, dried, and then cut into 10mm round pieces. After vacuum drying, the positive electrode sheet is obtained.

[0108] Preparation of negative electrode ②: Graphite is used as the negative electrode material, conductive carbon black is used as the conductive agent, and LA133 is used as the binder. The three are mixed evenly in N-methylpyrrolidone (NMP) in a ratio of 92%, 5%, and 3%, respectively. The mixture is coated on copper foil, dried, and then cut into 12mm round pieces. After vacuum drying, the negative electrode sheet is obtained.

[0109] Assembly of dual-ion batteries: Using the above-mentioned positive and negative electrode sheets as positive and negative electrodes, glass fiber as the separator, and the electrolyte prepared above, a CR2032 button cell is assembled.

[0110] Example 84

[0111] A lithium-ion battery based on graphite anode and lithium iron phosphate cathode

[0112] Preparation of electrolyte ⑩: The electrolyte consists of an organic solvent, a lithium salt, and a negative electrode lithium supplementation additive. The organic solvent is ethyl methyl carbonate: ethylene carbonate: dimethyl carbonate (1:1:1, v:v:v), the lithium salt is lithium hexafluorophosphate, and the molar concentration of the lithium salt in the electrolyte is 1 mol / L. The negative electrode lithium supplementation additive is vinylene carbonate, and the mass fraction of the negative electrode lithium supplementation additive in the electrolyte is 2 wt.%.

[0113] Assembly of lithium-ion batteries: Using the above-mentioned positive electrode ① and negative electrode ② as positive and negative electrodes, glass fiber as the separator, and the electrolyte ⑩ prepared above, CR2032 button batteries are assembled.

[0114] Example 85

[0115] A lithium-ion battery based on graphite anode-ternary cathode

[0116] Assembly of lithium-ion batteries: Using the above-mentioned positive electrode ④ and negative electrode ② as positive and negative electrodes, glass fiber as the separator, and the electrolyte ⑩ prepared above, CR2032 button batteries are assembled.

[0117] Example 86

[0118] A lithium-ion battery based on silicon-carbon anode and lithium iron phosphate cathode

[0119] Preparation of negative electrode ③: Silicon-carbon alloy powder is used as negative electrode material, conductive carbon black is used as conductive agent, and CMC and SBR are used as binders. The four are mixed evenly in pure water at a ratio of 70%, 10%, 10%, and 10%, respectively. The mixture is coated on copper foil, dried, and then cut into 12mm round pieces. After vacuum drying, the negative electrode sheet is obtained.

[0120] Assembly of lithium-ion batteries: Using the above-mentioned positive electrode ① and negative electrode ③ as positive and negative electrodes, glass fiber as the separator, and the electrolyte ⑩ prepared above, CR2032 button batteries are assembled.

[0121] Example 87

[0122] A lithium-ion battery based on silicon-carbon anode-ternary cathode

[0123] Assembly of lithium-ion batteries: Using the above-mentioned positive electrode ④ and negative electrode ③ as positive and negative electrodes, glass fiber as the separator, and the electrolyte ⑩ prepared above, CR2032 button batteries are assembled.

[0124] Comparative Example 2

[0125] A method for preparing a lithium dual-ion battery

[0126] electrolyte Preparation: The electrolyte is composed of an organic solvent and a lithium salt. The organic solvent is methyl ethyl carbonate, and the lithium salt is lithium hexafluorophosphate. The molar concentration of the lithium salt in the electrolyte is 4 mol / L.

[0127] The preparation and assembly methods of the positive and negative electrodes of the dual-ion battery are the same as in Example 83, except that an electrolyte is used in the assembly of the lithium dual-ion battery. Assembly is carried out.

[0128] Comparative Example 3

[0129] A lithium-ion battery based on graphite anode and lithium iron phosphate cathode

[0130] electrolyte Preparation: The electrolyte is composed of an organic solvent and a lithium salt. The organic solvent is ethyl methyl carbonate: ethylene carbonate: dimethyl carbonate (1:1:1, v:v:v), and the lithium salt is lithium hexafluorophosphate. The molar concentration of the lithium salt in the electrolyte is 1 mol / L.

[0131] The preparation and assembly methods of the positive and negative electrodes of the lithium-ion battery are the same as in Example 84, the only difference being that an electrolyte is used in the assembly of the lithium-ion battery. Assembly is carried out.

[0132] Comparative Example 4

[0133] A lithium-ion battery based on silicon-carbon anode and lithium iron phosphate cathode

[0134] electrolyte Preparation: The electrolyte is composed of an organic solvent and a lithium salt. The organic solvent is ethyl methyl carbonate: ethylene carbonate: dimethyl carbonate (1:1:1, v:v:v), and the lithium salt is lithium hexafluorophosphate. The molar concentration of the lithium salt in the electrolyte is 1 mol / L.

[0135] The preparation and assembly methods of the positive and negative electrodes of the lithium-ion battery are the same as in Example 86, the only difference being that an electrolyte is used in the assembly of the lithium-ion battery. Assembly is carried out.

[0136] Test Example 2

[0137] The electrochemical performance of the dual-ion batteries assembled in Example 83 and Comparative Example 2 was tested using the Newway testing system.

[0138] Test method:

[0139] At room temperature, the first charge-discharge cycle was activated with a constant current of 0.2C, followed by a constant charge-discharge cycle of 1C, with a voltage range of 3-5V. The test results are as follows: Figure 1 , Figure 2 As shown. Figure 1 These are the three-electrode test curves of the dual-ion batteries of Embodiment 83 and Comparative Example 2 at room temperature (approximately 25°C) and a 0.2C rate during the first charge-discharge cycle. Figure 1 (a) is the three-electrode test curve of the first charge-discharge cycle of Comparative Example 2. Figure 1 (b) is the three-electrode test curve of the first charge-discharge cycle of Example 83. Figure 2 These are the cycling performance curves of Example 83 and Comparative Example 2 at room temperature and 1C rate.

[0140] from Figure 1 and Figure 2 As can be seen, in Example 83, after adding vinylene carbonate (VC) as a lithium supplement additive for the negative electrode, VC decomposes under high voltage during the first charge and discharge cycle. After decomposition, it combines with or consumes anions, causing some lithium ions in the electrolyte to be converted into active lithium ions and deposited on the negative electrode side, forming a stable and robust SEI film, thereby improving the cycle performance of the dual-ion battery.

[0141] Test Example 3

[0142] The electrochemical performance of the lithium-ion batteries assembled in Examples 84-87 and Comparative Examples 3-4 was tested using the Newway testing system.

[0143] Test method:

[0144] At room temperature, the batteries assembled in Examples 84 and 86 were first subjected to five charge-discharge cycles at a rate of 0.2C and a charge-discharge voltage range of 3-4.6V, while the batteries assembled in Examples 85 and 87 were subjected to a rate of 0.2C and a charge-discharge voltage range of 3-4.8V (the charging cut-off voltage was higher than the decomposition voltage of the lithium additive on the negative electrode). Afterward, a constant current of 0.2C was used for charging and discharging, with a charge-discharge voltage range of 2.5-4.2V. The test results are shown in Table 5.

[0145] Table 5. Performance parameters of the batteries assembled in Examples 84-87 and Comparative Examples 3-4.

[0146] Group Discharge specific capacity (mAh / g) First-efficacy (%) Capacity retention rate (%) after 50 cycles Example 84 155.7 73.6 75.5 Example 85 182.3 79.2 76.1 Example 86 158.2 78.1 78.3 Example 87 183.5 71.2 79.6 Comparative Example 3 151.9 76.3 52.4 Comparative Example 4 152.4 72.5 53.2

[0147] As shown in Table 5, Examples 84-87, using different negative and positive electrodes, can still achieve the effect of in-situ lithium replenishment of the negative electrode under the condition of adding a negative electrode lithium replenishment additive that is easily decomposed under high voltage, thereby increasing the cycle stability and capacity retention of the battery.

[0148] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A lithium-ion battery based on in-situ lithium replenishment at the negative electrode, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte; the electrolyte is composed of an organic solvent, a lithium salt, and a negative electrode lithium replenishing additive, or the electrolyte is composed of an organic solvent, a lithium salt, an electrolyte additive, and a negative electrode lithium replenishing additive; the negative electrode lithium replenishing additive decomposes to generate free radicals or positively charged functional groups under a charging voltage of 4V or higher; the free radicals or positively charged functional groups combine with anions in the lithium salt; The negative electrode lithium supplementation additive is one or more of 2,3-dichlorotetrahydrofuran, tetrahydrofuran chloride, bis(2-chloroethoxy)methane, ethylpropyl ether, and dipropylene glycol dimethyl ether; The negative electrode lithium supplementation additive has a mass percentage content of 1-5% in the electrolyte; The organic solvent is selected from one or more of ester compounds, sulfone compounds, ether compounds, nitrile compounds, and carboxylic acid ester compounds; When the electrolyte is composed of an organic solvent, a lithium salt, an electrolyte additive, and a negative electrode lithium supplementation additive, the electrolyte additive is one or more of the following: fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, propylene sulfate, ethylene sulfate, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, ethylene sulfite, methyl chloroformate, and tris(trimethylsilane) phosphate.

2. The lithium-ion battery based on in-situ lithium replenishment at the negative electrode according to claim 1, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium sulfate, lithium nitrate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium perchlorate.

3. The lithium-ion battery based on in-situ lithium replenishment at the negative electrode according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 0.1-10 mol / L.

4. The lithium-ion battery based on in-situ lithium replenishment at the negative electrode according to claim 3, characterized in that, The concentration of the lithium salt in the electrolyte is 1-5 mol / L.

5. The lithium-ion battery based on in-situ lithium replenishment at the negative electrode according to claim 1, characterized in that, The negative electrode uses a negative electrode current collector, and the material of the negative electrode current collector is selected from copper foil, nickel foil, titanium foil, nickel mesh, foamed copper plate, porous copper skeleton, conductive carbon skeleton, carbon nanofiber scaffold or mesoporous carbon nanofiber.

6. The method for preparing a lithium-ion battery based on in-situ lithium replenishment at the negative electrode according to any one of claims 1-5, characterized in that, Includes the following steps: The positive electrode, the negative electrode, the separator, and the electrolyte are assembled to obtain the lithium-ion battery based on in-situ lithium replenishment at the negative electrode.

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