Electrolyte, lithium battery and energy storage device

Abstract

The invention provides an electrolyte, a lithium battery and an energy storage device. The electrolyte comprises recycled lithium salt and a modified additive, the mass fraction of the recycled lithium salt in the electrolyte is w1, the modified additive is tris (trimethylsilane) phosphate, the mass fraction of the tris (trimethylsilane) phosphate in the electrolyte is w2, and the electrolyte meets the relational expression that w2 / w1 is larger than or equal to 0.008 and smaller than or equal to 0.3.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte, a lithium battery and an energy storage device. BACKGROUND

[0002] The electrolyte of a lithium ion battery is considered as the "blood" of the lithium ion battery. In recent years, the shipment volume of electrolyte in China has been increasing year by year. It can be predicted that in the near future, the amount of waste electrolyte generated from waste batteries and manufacturing redundancy will be very large, and the recycling and high-value utilization of electrolyte are imminent. At the same time, the green recycling and high-value utilization of waste electrolyte are also the key to realizing the sustainable development of the country. However, compared with the electrolyte prepared from non-recycled lithium salt, the electrolyte prepared from recycled lithium salt contains more impurities, which affects the cycle performance of the lithium ion battery and is not conducive to the reuse of recycled lithium salt. SUMMARY

[0003] The embodiments of the present application provide an electrolyte which uses recycled lithium salt as electrolyte salt, and the lithium salt can be reused. When the electrolyte is applied to a lithium battery, the lithium battery has a high cycle life.

[0004] In a first aspect, the embodiments of the present application provide an electrolyte, the electrolyte comprising recycled lithium salt and a modified additive, the mass fraction of the recycled lithium salt in the electrolyte being w1, the modified additive being tris(trimethylsilyl) phosphate, the mass fraction of the tris(trimethylsilyl) phosphate in the electrolyte being w2, and the electrolyte satisfying the relationship: 0.008≤w2 / w1≤0.3.

[0005] In some embodiments, the mass fraction w1 of the recycled lithium salt in the electrolyte ranges from 3% to 18%.

[0006] In some embodiments, the mass fraction w2 of the tris(trimethylsilyl) phosphate in the electrolyte ranges from 0.01% to 5%.

[0007] In some embodiments, the platinum-cobalt colority of the electrolyte after high-temperature storage at 45℃ for 2 days ranges from 50 Hazen to 450 Hazen.

[0008] In some embodiments, the recycled lithium salt comprises impurities, and the impurities comprise at least one of alcohol, water, dimethyl sulfoxide, N-methyl pyrrolidone and acetonitrile.

[0009] In some embodiments, the electrolyte further comprises non-recycled lithium salt, the mass fraction of the non-recycled lithium salt in the electrolyte being w3, and the total mass fraction of the recycled lithium salt and the non-recycled lithium salt in the electrolyte ranging from 10% to 18%.

[0010] In some embodiments, the recovered lithium salt comprises at least one of recovered lithium hexafluorophosphate, recovered lithium tetrafluoroborate, recovered lithium perchlorate, recovered lithium hexafluoroarsenate, recovered lithium bisfluorosulfonimide, recovered lithium bis-trifluoromethanesulfonimide, recovered lithium bisoxalateborate, and recovered lithium bisfluorooxalateborate.

[0011] In some embodiments, the non-recovered lithium salt comprises at least one of non-recovered lithium hexafluorophosphate, non-recovered lithium tetrafluoroborate, non-recovered lithium perchlorate, non-recovered lithium hexafluoroarsenate, non-recovered lithium bisfluorosulfonimide, non-recovered lithium bis-trifluoromethanesulfonimide, non-recovered lithium bisoxalateborate, and non-recovered lithium bisfluorooxalateborate.

[0012] In a second aspect, the embodiments of the present application further provide a lithium battery, comprising a positive electrode sheet, a separator, a negative electrode sheet, and the electrolyte of the first aspect of the present application.

[0013] In a third aspect, the embodiments of the present application further provide an energy storage device, comprising at least one lithium battery of the second aspect of the embodiments of the present application.

[0014] The electrolyte of the present application adopts recycled lithium salt as electrolyte salt, and adds tris(trimethylsilyl) phosphate as a modified additive. The methyl and trimethylsilyl groups in the tris(trimethylsilyl) phosphate molecule can convert the hydroxyl, carboxyl, alcohol group and the like in the electrolyte into the corresponding trimethylsilyl ether, thereby realizing the protective effect of shielding the hydroxyl-containing impurities. In other words, tris(trimethylsilyl) phosphate can effectively adsorb alcohol, water and other molecules with active hydrogen. Compared with other water removal additives or modified additives, tris(trimethylsilyl) phosphate is more targeted to the impurities in the recycled lithium salt, so the impurity removal function is more prominent. In addition, the characteristics of high HOMO energy level and low LUMO energy level of tris(trimethylsilyl) phosphate make it reduce and oxidize before organic solvents, and the HOMO energy level and LUMO energy level of the organic solvent impurities in the recycled lithium salt, such as dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP), acetonitrile (AN) and the like, are studied to select the optimal additive. Compared with other film-forming additives such as vinyl carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD) and the like, tris(trimethylsilyl) phosphate can more effectively inhibit the deterioration of these impurity solvents on the stability of the solid electrolyte interface film (SEI film) and the cathode electrolyte interface film (CEI film), and better lithium battery performance is realized in long cycle. The present application uses recycled lithium salt as the electrolyte salt of lithium battery, which can be well reused in lithium battery, reduces the pollution and harm of waste battery electrolyte to the environment, is a green and environmentally friendly electrolyte, and can better reduce the production cost of lithium battery. In addition, by adding tris(trimethylsilyl) phosphate to the electrolyte containing recycled lithium salt, tris(trimethylsilyl) phosphate can well remove alcohol, water, dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile and other solvent impurities in the recycled lithium salt, reduce the deterioration of these impurities on the cycle performance of lithium battery, and improve the cycle life of lithium battery. For example, tris(trimethylsilyl) phosphate has the functions of water and acid removal, and can react with hydrofluoric acid to generate (Me3SiO)2POH and Me3SiF, thereby consuming the hydrofluoric acid (HF) in the electrolyte, preventing the hydrofluoric acid from damaging the SEI film and the CEI film, and avoiding the deterioration of the cycle life, kinetic performance and safety performance of the lithium battery. Furthermore, tris(trimethylsilyl) phosphate can preferentially react with the positive electrode sheet and the negative electrode sheet to form the CEI film and the SEI film, respectively, and block the reduction and oxidation of dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile and other organic solvents, thereby improving the cycle life of the lithium battery. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0016] Figure 1 A structural schematic diagram of a storage energy system according to an embodiment of the present application.

[0017] Figure 2 A structural schematic diagram of a storage energy system according to another embodiment of the present application.

[0018] Figure 3 A structural schematic diagram of a storage energy system according to still another embodiment of the present application.

[0019] Figure 4 A structural schematic diagram of a storage energy device according to an embodiment of the present application.

[0020] Figure 5 A structural schematic diagram of a lithium battery according to an embodiment of the present application.

[0021] Figure 6 A structural schematic diagram of a lithium battery according to an embodiment of the present application along the A-A direction. Figure 5

[0022] A structural schematic diagram of a lithium battery according to an embodiment of the present application along the A-A direction. Figure 7

[0023] Figure 8 A structural schematic diagram of a lithium battery according to an embodiment of the present application along the A-A direction.

[0024] Legend of reference signs:

[0025] 100 - storage energy system, 110 - first electric energy conversion device, 120 - first user load, 130 - second user load, 140 - high-voltage cable, 150 - second electric energy conversion device, 160 - light storage and charging station, 170 - automobile, 200 - storage energy device, 210 - single battery, 300 - lithium battery, 310 - positive electrode sheet, 311 - positive electrode current collector, 312 - positive electrode active layer, 320 - separator, 330 - negative electrode sheet, 331 - negative electrode current collector, 332 - negative electrode active layer, 340 - shell, 350 - end cover assembly. DETAILED DESCRIPTION

[0026] ​In the following, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0027] The terms “first”, “second”, and the like in the specification and claims of the present application and the above drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms “include” and “have” and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device including a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product, or device.

[0028] The technical solutions in the embodiments of the present application will be described in conjunction with the drawings.

[0029] It should be noted that, for the sake of illustration, the same reference signs represent the same components in the embodiments of the present application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0030] Since the energy required by people has strong time and space characteristics, in order to reasonably use energy and improve the utilization rate of energy, it is necessary to store one form of energy in the same form or convert it into another form of energy through a medium or device, and release it in a specific energy form based on future application needs. At present, the main way to generate green electricity is to develop green energy such as photovoltaic and wind power to replace fossil energy.

[0031] At present, the generation of green electricity generally depends on photovoltaic, wind power, and water potential. However, wind energy and solar energy have strong intermittency and large fluctuation, which can cause instability of the power grid. During the peak of electricity consumption, there is not enough electricity, and during the valley of electricity consumption, there is too much electricity. Unstable voltage can also cause damage to electricity. Therefore, due to insufficient electricity demand or insufficient grid acceptance capacity, the problem of “abandoning wind and light” may occur. To solve these problems, it is necessary to rely on energy storage. That is, the electricity is converted into other forms of energy through physical or chemical means and stored, and the energy is converted into electricity and released when needed. In simple terms, energy storage is similar to a large “power bank”, which stores electricity when photovoltaic and wind energy are sufficient, and releases the electricity stored when needed.

[0032] Taking electrochemical energy storage as an example, the scheme provides an energy storage device, which is applied to an energy storage system, and is internally provided with a group of chemical batteries, mainly using chemical elements in the batteries as energy storage medium. The charging and discharging process is accompanied by chemical reaction or change of the energy storage medium. In simple terms, the wind energy and solar energy generated are stored in the chemical batteries, and the stored power is released for use when the external power use reaches the peak, or is transferred to a place where the power is in short supply for use.

[0033] At present, the energy storage (i.e. energy storage) application scenarios are relatively wide, including power generation side energy storage, power grid side energy storage and power consumption side energy storage, and the corresponding types of energy storage devices include:

[0034] (1) Large-scale energy storage power station (composed of multiple energy storage prefabricated cabins) applied in wind power and photovoltaic power station side, which can assist renewable energy power generation to meet the grid connection requirements and improve the utilization rate of renewable energy; as a high-quality active / reactive power regulation power source in the power supply side, the energy storage power station realizes the load matching of power in time and space, enhances the renewable energy consumption capacity, reduces the instantaneous power change, reduces the impact on the power grid, improves the new energy power generation consumption problem and has great significance in power grid system backup, relieving peak load power supply pressure and peak regulation;

[0035] (2) Energy storage prefabricated cabin applied in the power grid side, the main functions of which are peak regulation, frequency regulation and peak regulation for relieving power grid congestion, which can realize the peak clipping and valley filling of power consumption load, i.e. charging the energy storage battery when the power consumption load is low, and releasing the stored power when the power consumption load is high, so as to realize the balance between power production and consumption;

[0036] (3) Small energy storage cabinet applied in the power consumption side, the main functions of which are power self-generation and self-use, peak-valley price difference arbitrage, capacity cost management and improvement of power supply reliability. According to different application scenarios, the power consumption side energy storage can be divided into industrial and commercial energy storage cabinet, household energy storage device and energy storage charging pile, etc., which is generally used with distributed photovoltaic power supply. Industrial and commercial users can use energy storage for peak-valley price difference arbitrage and capacity cost management. In the electricity market implementing peak-valley electricity price, the energy storage system is charged at low price and discharged at high price, realizing peak-valley price difference arbitrage and reducing power consumption cost. In addition, industrial enterprises applying two-part electricity price can use the energy storage system to store energy at low power consumption and discharge at high peak load, so as to reduce the sharp peak power and the maximum demand amount reported, achieving the purpose of reducing capacity electricity cost. Household photovoltaic power supply with storage can improve the level of power self-generation and self-use. Due to high electricity price and poor power supply stability, the demand for household photovoltaic power supply is increased. Considering that photovoltaic power is generated during the day and users generally have high load at night, through the configuration of energy storage, photovoltaic power can be better utilized, the level of self-generation and self-use can be improved, and the power consumption cost can be reduced. In addition, communication base stations, data centers and other fields need to configure energy storage for backup power supply.

[0037] In some embodiments, please refer to Figure 1 , Figure 1 The structure diagram of the energy storage system 100 of an embodiment of the present application is shown in FIG. 1. The present application Figure 1 The present application takes the home energy storage scenario in the user side energy storage as an example for illustration, and the energy storage device 200 of the present application is not limited to the home energy storage scenario.

[0038] The present application provides an energy storage system 100, which comprises a first electric energy conversion device 110 (a photovoltaic panel), a first user load 120 (a home lamp), a second user load 130 (for example, a home appliance such as an air conditioner), and an energy storage device 200. The energy storage device 200 is a small energy storage box, which can be installed on an outdoor wall by a wall hanging manner. The energy storage device 200 of the present application is not limited to the wall hanging manner, but can also be placed in a user's residence by other manners. Specifically, the photovoltaic panel can convert solar energy into electric energy during the low valley period of electricity price. The energy storage device 200 is used to store the electric energy and supply the lamp and the home appliance for use during the peak period of electricity price, or supply electricity during the power grid outage.

[0039] In some embodiments, please refer to Figure 2 , Figure 2 The structure diagram of the energy storage system 100 of another embodiment of the present application is shown in FIG. 2. The present application Figure 2 The present application takes the generation / distribution side shared energy storage scenario as an example for illustration, and the energy storage device 200 of the present application is not limited to the generation / distribution side energy storage scenario.

[0040] The application provides a kind of energy storage system 100, the energy storage system 100 includes: high voltage cable 140, first electric energy conversion device 110, second electric energy conversion device 150 and the energy storage device 200 provided by the application, in some embodiments of power generation side scene, second electric energy conversion device 150 can be wind power electric energy conversion device, since the fluctuation, randomness and intermittence of wind power electric energy conversion generated electric energy, can be stored to energy storage device 200 by grid connection first unstable electric energy exported by wind power electric energy conversion device, energy storage device 200 is connected with high voltage cable and exports smooth electric energy to supply distribution network for power consumption side, realizes peak shaving and frequency modulation, and grid stable operation;Or, wind power electric energy conversion device is always connected with high voltage cable, and the electric energy exported by wind power electric energy conversion device is supplied to distribution network for power consumption side by high voltage cable in ordinary power generation, and when current power consumption load is low, wind power electric energy conversion device generates excess, first store the electric quantity of overproduction to energy storage device 200, reduce the rate of abandoned wind and light, improve new energy power generation consumption problem;And when power consumption load is high, grid issues instructions, and the electric quantity stored in energy storage device 200 is transmitted to power consumption side by high voltage cable 140 in grid connection mode, provides peak shaving, frequency modulation, backup and other services for grid operation, fully plays the role of grid peak shaving, promotes grid peak clipping, and relieves grid power supply pressure.

[0041] In some embodiments of distribution network side, first electric energy conversion device 110 can be photovoltaic panel, energy storage device 200 is connected with high voltage cable 140 and is installed between high voltage cable 140 downstream and user load, and the electric energy exported by photovoltaic electric energy conversion device is stored in energy storage device 200, which can be used as backup power source in response to grid / distribution network failure;Or, when high voltage cable 140 transmission line appears line congestion, provide power support to delay economic pressure generated by grid / distribution expansion.

[0042] In some embodiments, please refer to Figure 3 , Figure 3 The structure diagram of the energy storage system 100 of another embodiment of the application, and the energy storage device 200 of the application Figure 3 Embodiments are illustrated by taking industrial and commercial side energy storage scene as an example, and the energy storage device 200 of the application is not limited to industrial and commercial side energy storage scene.

[0043] The application provides a kind of energy storage system 100, the energy storage system 100 includes: energy storage device 200, high voltage cable 140, factory with first electric energy conversion device 110 and light storage charging station 160 and automobile 170 are equipped;In some embodiments of factory and business side scene, first electric energy conversion device 110 can be photovoltaic panel, solar energy is converted into electric energy and is stored in the energy storage device 200 of factory, when power grid outage failure, power supply is ensured by energy storage device 200 to ensure that factory is safe and stable and does not stop production;Or when the high load of factory electricity load, grid issues instructions, the electric quantity stored in energy storage device 200 is transmitted to the power supply of factory by high voltage cable 140 in grid-connected mode, to provide peak shaving / frequency modulation, backup and other services for grid operation;In addition, first electric energy conversion device 110 can also convert solar energy into electric energy and store in the energy storage device 200 of light storage charging station 160, directly charge automobile 170 by light storage charging station 160, fast and convenient.

[0044] Optionally, first electric energy conversion device 110 can include but is not limited to photovoltaic panel, and second electric energy conversion device 150 can include but is not limited to wind power conversion device, and first electric energy conversion device 110 and second electric energy conversion device 150 can convert at least one of solar energy, light energy, wind energy, heat energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0045] Please see Figure 4 , Figure 4 It is the structure schematic view of energy storage device 200 of an embodiment of the application.

[0046] Optionally, energy storage device 200 includes one or more single batteries 210.

[0047] The term "a plurality of" refers to greater than or equal to two, for example, can be but not limited to 2, 5, 10, 30, 50, 100, 200, 300, 400, 800, 1000, etc.The number of single batteries 210 included in energy storage device 200 can be determined according to the rated capacity of single battery 210 and the rated capacity to be achieved by the energy storage device 200.

[0048] Optionally, energy storage device 200 can be used but is not limited to energy storage power station, hydraulic power / thermal power / wind power generation system, solar power generation system, mobile power system, smart home system or temporary power supply system and other energy storage application scenarios, and is also applied to data center, military equipment, aerospace, charging pile, electric vehicle and other fields.

[0049] Optionally, the energy storage device 200 can include, but is not limited to, a battery integrated system including or consisting of a single battery cell 210, a battery module, a battery pack, a battery cluster, a mobile power supply, an energy storage cabinet / energy storage prefabricated cabin, etc. In other words, when the energy storage device 200 includes one single battery cell 210, the energy storage device 200 can exist in the form of the single battery cell 210. When the energy storage device 200 includes a plurality of single battery cells 210, the plurality of single battery cells 210 can be arranged, assembled, etc. to form a battery integrated system such as a battery module, a battery pack, a battery cluster, a mobile power supply, an energy storage cabinet / energy storage container, etc. That is, the energy storage device 200 exists in the form of a battery integrated system such as a battery module, a battery pack, a battery cluster, a mobile power supply, an energy storage cabinet / energy storage container, etc. The actual application form of the energy storage device 200 provided by the embodiments of the present application can be, but is not limited to, the listed products, and can also be other application forms. The embodiments of the present application do not strictly limit the application form of the energy storage device 200. The embodiments of the present application only take the energy storage device 200 as an example of a multi-core battery (i.e. a plurality of single battery cells 210).

[0050] Optionally, the single battery cell 210 can be, but is not limited to, at least one of a cylindrical battery, a square battery, a prismatic battery, or other shaped batteries.

[0051] Optionally, the single battery cell 210 can be a secondary battery, which means that after the single battery cell 210 is discharged, the active material can be activated by charging to continue to be used. The single battery cell 210 can be a lithium ion battery, a sodium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, a lithium sulfur battery, a magnesium ion battery, a nickel-hydrogen battery, a nickel-cadmium battery, a lead-acid battery, etc. The present application does not make specific limitations.

[0052] It can be understood that the single battery cell 210 can be, but is not limited to, a sodium battery, a lithium battery, a magnesium battery, a hydrogen-nickel battery, a nickel-cadmium battery, a lead-acid battery, etc. In the following embodiments of the present application, the single battery cell 210 is taken as a lithium battery 300 for illustration and demonstration.

[0053] Figure 5 Structure schematic diagram of the lithium battery 300 according to an embodiment of the present application. Figure 6 Structure schematic diagram of the lithium battery 300 according to an embodiment of the present application along the direction of A-A. Figure 5 Structure schematic diagram of the lithium battery 300 according to an embodiment of the present application along the direction of A-A.

[0054] Please refer to Figure 5 and Figure 6 The embodiments of the present application provide a lithium battery 300, which includes a positive electrode sheet 310, a separator 320, a negative electrode sheet 330, and an electrolyte.

[0055] It can be understood that the positive electrode sheet 310 and the negative electrode sheet 330 are respectively located on opposite sides of the diaphragm 320, that is, the diaphragm 320 is located between the positive electrode sheet 310 and the negative electrode sheet 330, and separates the positive electrode sheet 310 and the negative electrode sheet 330.

[0056] It should be noted that the positive electrode sheet 310, the diaphragm 320 and the negative electrode sheet 330 are at least partially immersed in the electrolyte.

[0057] Figure 7 A cross-sectional view of the positive electrode sheet 310 of an embodiment of the present application.

[0058] Please refer to Figure 7 Optionally, the positive electrode sheet 310 further comprises a positive electrode current collector 311, and the positive electrode active layer 312 is arranged on the surface of the positive electrode current collector 311.

[0059] It should be noted that the positive electrode active layer 312 can be arranged on one surface or more surfaces (greater than or equal to two surfaces) of the positive electrode current collector 311. In the schematic diagram of the drawings of the present application, the positive electrode active layer 312 is arranged on the opposite two surfaces of the positive electrode current collector 311 as an example, which should not be understood as a limitation of the positive electrode active layer 312 and the positive electrode sheet 310 of the embodiments of the present application.

[0060] Optionally, the positive electrode current collector 311 can be, but is not limited to, an aluminum sheet, an aluminum foil, etc.

[0061] Optionally, the positive electrode active layer 312 further comprises a positive electrode conductive agent and a positive electrode binder.

[0062] Optionally, the positive electrode conductive agent can be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0063] Optionally, the positive electrode binder can be, but is not limited to, at least one of polyvinylidene fluoride (PVDF for short), polyamide (PA for short), polyacrylonitrile (PAN for short), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA for short), polyhexafluoropropylene, polymerized styrene butadiene rubber (SBR for short), etc.

[0064] Figure 8 A cross-sectional view of the negative electrode sheet 330 of an embodiment of the present application.

[0065] Please refer to Figure 8 Optionally, the negative electrode tab 330 comprises a negative current collector 331 and a negative active layer 332, and the negative active layer 332 is arranged on the surface of the negative current collector 331.

[0066] It should be noted that the negative active layer 332 can be arranged on one surface or more surfaces (greater than or equal to two surfaces) of the negative current collector 331. In the schematic diagram of the drawings of the present application, the negative active layer 332 is arranged on the opposite two surfaces of the negative current collector 331 as an example, which should not be understood as a limitation of the negative active layer 332 and the negative electrode tab 330 of the embodiments of the present application.

[0067] Optionally, the negative current collector 331 can be, but is not limited to, at least one of a copper foil, a copper sheet, an aluminum foil, and an aluminum sheet.

[0068] Optionally, the negative active layer 332 comprises a negative active material, a negative conductive agent, a negative binder, and a negative thickening agent, etc.

[0069] Optionally, the negative active material can be, but is not limited to, graphite.

[0070] Optionally, the negative conductive agent can be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotubes, carbon fibers, graphene, etc.

[0071] Optionally, the negative binder can be, but is not limited to, at least one of polyvinylidene fluoride, polyamide, polyacrylonitrile, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, sodium carboxymethyl cellulose (CMC for short), butadiene-styrene rubber, etc.

[0072] Optionally, the negative thickening agent can be, but is not limited to, at least one of polyacrylamide (PAM) and polymethyl acrylate (PMA), etc.

[0073] Optionally, the separator 320 can be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic separator, a glass fiber film, etc.

[0074] Please refer to Figure 5 and Figure 6Optionally, the lithium battery 300 further comprises a shell 340 and an end cover assembly 350, the shell 340 and the end cover assembly 350 enclose a closed receiving cavity (not shown in the figure) for accommodating the electrolyte, the positive electrode sheet 310, the separator 320 and the negative electrode sheet 330. It can be understood that the end cover assembly 350 is electrically connected to the positive electrode sheet 310 and the negative electrode sheet 330 respectively, and leads out the positive electrode sheet 310 and the negative electrode sheet 330 to electrically connect external devices or other lithium batteries 300.

[0075] The electrolyte of the lithium ion battery is considered as the "blood" of the lithium ion battery. In recent years, the shipment volume of electrolyte in China has been increasing year by year. It can be predicted that in the near future, the amount of waste electrolyte generated from waste batteries and manufacturing redundancy will be very large, and the recycling and high-value utilization of electrolyte are imminent. At the same time, the green recycling and high-value utilization of waste electrolyte is also the key to realizing the sustainable development of the country. However, compared with the electrolyte prepared from non-recycled lithium salt, the electrolyte prepared from recycled lithium salt contains more unavoidable impurities, which affects the cycle performance of the lithium ion battery and is not conducive to the reuse of recycled lithium salt.

[0076] In view of this, the embodiments of the present application also provide an electrolyte.

[0077] The embodiments of the present application also provide an electrolyte, which comprises a recycled lithium salt (also referred to as a recycled lithium salt) and a modified additive, the mass fraction of the recycled lithium salt in the electrolyte is w1, the modified additive is tris(trimethylsilyl) phosphate (abbreviated as TMSP), the mass fraction of the tris(trimethylsilyl) phosphate in the electrolyte is w2, and the electrolyte satisfies the relationship: 0.008≤w2 / w1≤0.3.

[0078] The term "recycled lithium salt" refers to being mainly extracted from waste batteries (such as positive electrode materials, electrolyte), and being obtained by pyrometallurgy, hydrometallurgy or direct regeneration technology (such as molten salt, deep eutectic solvent, etc.).

[0079] The term "non-recycled lithium salt" refers to being usually extracted from lithium ore (such as spodumene) or salt lake brine, and being prepared by chemical purification (such as lithium carbonate precipitation, electrolysis), which has a complex process and high energy consumption.

[0080] It can be understood that the electrolyte comprises an electrolyte salt, and the electrolyte salt comprises a recycled lithium salt.

[0081] It can be understood that the mass ratio of the modified additive to the recycled lithium salt in the electrolyte ranges from 0.008 to 0.3.

[0082] In the embodiments of the present application, when a numerical range a to b is involved, if not specifically indicated, it means that the numerical value can be any numerical value between a and b, including the endpoint numerical value a and the endpoint numerical value b.

[0083] Specifically, the mass ratio w2 / w1 of the tris(trimethylsilyl) phosphate ester to the recycled lithium salt in the electrolyte can be, but is not limited to, 0.008, 0.01, 0.02, 0.02, 0.04, 0.06, 0.08, 0.12, 0.12, 0.14, 0.16, 0.18, 0.22, 0.22, 0.24, 0.26, 0.28, 0.3, etc. If the mass ratio w2 / w1 of the tris(trimethylsilyl) phosphate ester to the recycled lithium salt in the electrolyte is too small, the content of the tris(trimethylsilyl) phosphate ester in the electrolyte is too low, and the content of the recycled lithium salt is too high. The tris(trimethylsilyl) phosphate ester is not sufficient to remove the impurities introduced by the recycled lithium salt, the impurities in the electrolyte are not completely removed, and the cycle life of the lithium battery 300 is reduced. In addition, before the electrolyte is configured and before it is injected into the lithium battery 300, the tris(trimethylsilyl) phosphate ester has reacted with the alcohol and other impurities in the electrolyte, and cannot play a role in consolidating the interface film (CEI) of the positive electrode plate 310 and the interface film (SEI) of the negative electrode plate 330 in the formation and film reaction after the lithium battery 300 is injected, which has limited improvement in the cycle performance of the lithium battery 300. Moreover, even if the recycled lithium salt is purified to a high degree, it will still have more impurities than non-recycled lithium salt. When the content of the recycled lithium salt in the electrolyte is too high, the cycle life of the lithium battery 300 is reduced. If the mass ratio w2 / w1 of the tris(trimethylsilyl) phosphate ester to the recycled lithium salt in the electrolyte is too large, the content of the tris(trimethylsilyl) phosphate ester in the electrolyte is too high, and the content of the recycled lithium salt is too low. If the content of the tris(trimethylsilyl) phosphate ester in the electrolyte is too high, the viscosity of the electrolyte is too large, the dissociation performance and transport capacity of lithium ions are reduced, and the kinetic performance of the lithium battery 300 is reduced. In addition, the tris(trimethylsilyl) phosphate ester not only removes impurities from the electrolyte, but also participates in the formation of the CEI film of the positive electrode plate 310 and the SEI film of the negative electrode plate 330. If the content of the tris(trimethylsilyl) phosphate ester in the electrolyte is too high, the thickness of the SEI film and the CEI film of the lithium battery 300 is too thick, the impedance of the SEI film and the CEI film is increased, and the kinetic performance of the lithium battery 300 is further reduced.

[0084] In the electrolyte containing the recycled lithium salt, even if the purity of the recycled lithium salt is high, alcohol (such as methanol, ethanol), dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile and other inevitable solvent impurities will be introduced, and the presence of these impurities will have a great influence on the cycle performance of the lithium battery 300.

[0085] The electrolyte of the present application adopts recycled lithium salt as electrolyte salt, and adds tris(trimethylsilyl) phosphate as a modified additive. The methyl and trimethylsilyl groups in the tris(trimethylsilyl) phosphate molecule can convert the hydroxyl, carboxyl, alcohol group and the like in the electrolyte into the corresponding trimethylsilyl ether, thereby realizing the protective effect of shielding the hydroxyl-containing impurities. In other words, tris(trimethylsilyl) phosphate can effectively adsorb alcohol, water and other molecules with active hydrogen. Compared with other water removal additives or modified additives, tris(trimethylsilyl) phosphate is more targeted to the impurities in the recycled lithium salt, so the impurity removal function is more prominent. In addition, the characteristics of high HOMO energy level and low LUMO energy level of tris(trimethylsilyl) phosphate make it reduce and oxidize before organic solvents, and the HOMO energy level and LUMO energy level of the organic solvent impurities in the recycled lithium salt, such as dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP), acetonitrile (AN) and the like, are studied to select the optimal additive. Compared with other film-forming additives such as vinyl carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD) and the like, tris(trimethylsilyl) phosphate can more effectively inhibit the deterioration of these impurity solvents on the stability of the solid electrolyte interface film (SEI film) and the cathode electrolyte interface film (CEI film), and better performance of the lithium battery 300 in long cycle. The present application uses recycled lithium salt as the electrolyte salt of the lithium battery 300, which is applied to the lithium battery 300, can well recycle the lithium salt, reduce the pollution and harm of the electrolyte of the waste battery to the environment, is a green and environmentally friendly electrolyte, and can better reduce the production cost of the lithium battery 300; in addition, by adding tris(trimethylsilyl) phosphate to the electrolyte containing recycled lithium salt, tris(trimethylsilyl) phosphate can well remove alcohol, water, dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile and other solvent impurities in the recycled lithium salt, reduce the deterioration of these impurities on the cycle performance of the lithium battery 300, and improve the cycle life of the lithium battery 300; for example, tris(trimethylsilyl) phosphate has the functions of water and acid removal, can react with hydrofluoric acid to generate (Me3SiO)2POH and Me3SiF, thereby consuming the hydrofluoric acid (HF) in the electrolyte, preventing the hydrofluoric acid from damaging the SEI film and the CEI film, and avoiding the deterioration of the cycle life, kinetic performance and safety performance of the lithium battery 300; furthermore, tris(trimethylsilyl) phosphate can preferentially react with the positive electrode plate 310 and the negative electrode plate 330 to form the CEI film and the SEI film, respectively, and block the reduction and oxidation of dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile and other organic solvents, thereby improving the cycle life of the lithium battery 300.

[0086] In some embodiments, the mass fraction of the recovered lithium salt in the electrolyte is w1 in the range of 3%≤w1≤18%.

[0087] Specifically, the mass fraction of the recovered lithium salt in the electrolyte w1 can be, but is not limited to, 3%, 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, etc.

[0088] In the present embodiment, if the mass fraction of the recovered lithium salt in the electrolyte w1 is too low, the increase in the cost of the process of recovering the electrolyte and extracting the lithium salt from the retired waste battery is not sufficient to cover the decrease in the cost of the lithium battery 300 due to the reuse of the recovered lithium salt. If the mass fraction of the recovered lithium salt in the electrolyte w1 is too high, the performance of the electrolyte is extremely poor, and even if the recovered lithium salt is further refined, impurities are strictly removed, and high-efficiency additives are used in combination, the cycle performance of the lithium battery 300, i.e., the cycle life of the lithium battery 300, is still too low. When the mass fraction of the recovered lithium salt in the electrolyte w1 is in the range of 3%≤w1≤18%, the lithium battery 300 can have a lower cost and a higher cycle life.

[0089] In some embodiments, the mass fraction of the tris(trimethylsilyl) phosphate in the electrolyte w2 is in the range of 0.01%≤w2≤5%.

[0090] Specifically, the mass fraction of the tris(trimethylsilyl) phosphate in the electrolyte w2 can be, but is not limited to, 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8%, 1.1%, 1.3%, 1.5%, 1.8%, 2.1%, 2.3%, 2.5%, 2.8%, 3.1%, 3.3%, 3.5%, 3.8%, 4.1%, 4.3%, 4.5%, 4.8%, 5%, etc.

[0091] In the present embodiment, if the mass fraction w2 of tris(trimethylsilyl) phosphate in the electrolyte is too low, the tris(trimethylsilyl) phosphate in the electrolyte is insufficient to remove the impurities introduced by the recovered lithium salt, the impurities in the electrolyte are not removed completely, and the electrolyte cannot prevent the impurities introduced by the recovered lithium salt from intensifying the decomposition of the electrolyte salt, thereby reducing the cycle life of the lithium battery 300. In addition, before the electrolyte is configured and before the lithium battery 300 is injected, the tris(trimethylsilyl) phosphate has reacted with the impurities such as alcohols in the electrolyte, and cannot play a role in consolidating the interface film (CEI) of the positive electrode plate 310 and the interface film (SEI) of the negative electrode plate 330 in the formation and film reaction after the lithium battery 300 is injected, and the improvement of the cycle performance of the lithium battery 300 is limited. If the mass fraction w2 of tris(trimethylsilyl) phosphate in the electrolyte is too high, the viscosity of the electrolyte is too large, the dissociation performance and the transmission capacity of lithium ions are reduced, and the kinetic performance of the lithium battery 300 is reduced. In addition, tris(trimethylsilyl) phosphate not only removes impurities from the electrolyte, but also participates in the formation of the CEI film of the positive electrode plate 310 and the SEI film of the negative electrode plate 330. If the content of tris(trimethylsilyl) phosphate in the electrolyte is too high, the thickness of the SEI film and the CEI film of the lithium battery 300 is too thick, the impedance of the SEI film and the CEI film is increased, and the kinetic performance of the lithium battery 300 is further reduced. When the mass fraction w2 of tris(trimethylsilyl) phosphate in the electrolyte is 0.01%≤w2≤5%, the cycle life of the lithium battery 300 can be better improved, and the lithium battery 300 has high kinetic performance and rate performance.

[0092] In some embodiments, the platinum-cobalt color of the electrolyte after 2 days of high-temperature storage at 45°C is in the range of 50 Hazen to 450 Hazen.

[0093] Specifically, the platinum-cobalt color of the electrolyte after 2 days of high-temperature storage at 45°C can be, but is not limited to, 50 Hazen, 80 Hazen, 100 Hazen, 130 Hazen, 150 Hazen, 180 Hazen, 200 Hazen, 230 Hazen, 250 Hazen, 280 Hazen, 300 Hazen, 330 Hazen, 350 Hazen, 380 Hazen, 400 Hazen, 430 Hazen, 450 Hazen, and the like.

[0094] In the present embodiment, if the platinum-cobalt colority of the electrolyte after high-temperature storage at 45°C for 2 days is too high, it indicates that the electrolyte salt in the electrolyte decomposes too much and / or the organic solvent such as ethylene carbonate in the electrolyte polymerizes, which greatly reduces the cycle life and kinetic performance of the lithium battery 300. When the platinum-cobalt colority of the electrolyte after high-temperature storage at 45°C for 2 days ranges from 50 Hazen to 450 Hazen, the lithium battery 300 has higher cycle life and kinetic performance.

[0095] In some embodiments, the recycled lithium salt includes impurities, and the impurities include at least one of alcohol, water, dimethyl sulfoxide, N-methyl pyrrolidone, and acetonitrile. In the present embodiment, compared with non-recycled lithium salt, the recycled lithium salt has unavoidable impurities, and the electrolyte of the present application has excellent impurity removal effect on alcohol, water, dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile and other impurities in the recycled lithium salt by adding tris(trimethylsilyl) phosphate, in addition, it can also improve the stability of the SEI film and the CEI film of the lithium battery 300, and improve the cycle life of the lithium battery 300.

[0096] In some embodiments, the electrolyte further includes non-recycled lithium salt, and the mass fraction of the non-recycled lithium salt in the electrolyte is w3, and the total mass fraction of the recycled lithium salt and the non-recycled lithium salt in the electrolyte ranges from 10% to 18%.

[0097] It can be understood that in some embodiments, the electrolyte salt includes recycled lithium salt and non-recycled lithium salt. The mass fraction of the electrolyte salt in the electrolyte ranges from 10% to 18%.

[0098] Specifically, the total mass fraction of the recycled lithium salt and the non-recycled lithium salt in the electrolyte can be, but is not limited to, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, and the like.

[0099] In the present embodiment, if the total mass fraction of the recycled lithium salt and the non-recycled lithium salt in the electrolyte is too low, the ionic conductivity of the electrolyte is too low, which reduces the kinetic performance of the lithium battery 300, and also makes the SEI film and the CEI film of the lithium battery 300 unstable, which reduces the cycle life of the lithium battery 300. If the total mass fraction of the recycled lithium salt and the non-recycled lithium salt in the electrolyte is too high, the viscosity of the electrolyte increases, which reduces the diffusion rate of lithium ions and reduces the wettability of the electrolyte to the positive electrode plate 310 and the negative electrode plate 330, thereby reducing the kinetic performance and cycle performance of the lithium battery 300.

[0100] In some embodiments, the recycled lithium salt includes at least one of recycled lithium hexafluorophosphate (LiPF6), recycled lithium tetrafluoroborate (LiBF4), recycled lithium perchlorate (LiClO4), recycled lithium hexafluoroarsenate (LiAsF6), recycled lithium bis(fluorosulfonyl)imide (LiFSI), recycled lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), recycled lithium bis(oxalato)borate (LiBOB), and recycled lithium bis(fluorooxalato)borate (LiODFB).

[0101] In the present embodiment, the use of these recycled lithium salts as electrolyte salts can enable the lithium battery 300 to have a longer cycle life and better kinetic performance.

[0102] In some embodiments, the non-recycled lithium salt includes at least one of non-recycled lithium hexafluorophosphate (LiPF6), non-recycled lithium tetrafluoroborate (LiBF4), non-recycled lithium perchlorate (LiClO4), non-recycled lithium hexafluoroarsenate (LiAsF6), non-recycled lithium bis(fluorosulfonyl)imide (LiFSI), non-recycled lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), non-recycled lithium bis(oxalato)borate (LiBOB), and non-recycled lithium bis(fluorooxalato)borate (LiODFB).

[0103] In the present embodiment, the use of these non-recycled lithium salts as electrolyte salts can enable the lithium battery 300 to have a longer cycle life and better kinetic performance.

[0104] Optionally, the electrolyte further includes an organic solvent and a film-forming additive.

[0105] Optionally, the organic solvent can include at least one of a cyclic carbonate and a chain carbonate. Optionally, the cyclic carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), and the like. The dielectric constant of ethylene carbonate is much larger than that of propylene carbonate, and ethylene carbonate can better promote the formation of a solid electrolyte interface film (SEI). Optionally, the chain carbonate can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and the like. Optionally, the organic solvent further includes at least one of ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, and 2,2-difluoroethyl acetate.

[0106] Optionally, the film-forming additive can include, but is not limited to, at least one of propargyl benzene sulfonic acid, vinylene carbonate (VC), fluoroethylene carbonate (FEC), diethyl sulfite (DTD), methane methylene disulfonate (MMDS), butyl sulfonic acid lactone (BS), 3,3-propylene sulfonic acid lactone (PST), and the like.

[0107] The lithium battery 300 of the present application is further described below through specific examples.

[0108] Examples 1 to 12, Comparative Examples 1 to 16

[0109] The lithium battery 300 of each example and comparative example is prepared by the following steps:

[0110] (1) Preparation of the positive electrode sheet 310: commercially available lithium iron phosphate (positive active material, LFP), conductive carbon black (positive conductive agent, SP), and polyvinylidene fluoride (positive binder, PVDF) are mixed in a preset ratio of 97:2.5:0.5, dispersed in a solvent N-methyl pyrrolidone (NMP), and stirred uniformly to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive current collector 311 aluminum foil, and the unit area coating weight of the positive electrode slurry is 33 mg / cm 2 , after embossing, drying, cold pressing, slitting, and cutting, the positive electrode sheet 310 is obtained;

[0111] (2) Preparation of the negative electrode sheet 330: artificial graphite (negative active material), conductive carbon black (negative conductive agent, SP), thickening agent (CMC), and negative binder (SBR) are mixed in a ratio of 96.5:0.5:1:2 in deionized water to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative current collector 331 copper foil, and the unit area coating weight of the negative electrode slurry is 16 mg / cm 2 , after drying, cold pressing, slitting, and cutting, the negative electrode sheet 330 is obtained;

[0112] (3) Preparation of the electrolyte: in an argon atmosphere glove box with water and oxygen content ≤0.1 ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a mass ratio of 2:3:5, and recycled lithium salt, non-recycled lithium salt, modified additive, and film-forming additive are added and stirred until completely dissolved to obtain the electrolyte; the film-forming additive includes vinylene carbonate (VC), fluoroethylene carbonate (FEC), and diethyl sulfite (DTD), and the electrolyte includes 4% vinylene carbonate, 1% fluoroethylene carbonate (FEC), and 1% diethyl sulfite by mass fraction; the recycled lithium salt, non-recycled lithium salt, modified additive, platinum-cobalt color, and other parameters in each example and comparative example are shown in Table 1 and Table 2 as follows:

[0113] (4) Isolation film: a 16-μm polyethylene film was used.

[0114] (5) Assembly of the lithium battery 300: the positive electrode sheet 310, the isolation film 320, and the negative electrode sheet 330 were stacked in order with the isolation film 320 between the positive electrode sheet 310 and the negative electrode sheet 330 to separate the positive electrode sheet 310 and the negative electrode sheet 330, and were wound into a bare cell. After the tabs were welded, the bare cell was assembled into an outer package, and after hot pressing, vacuum drying treatment was performed. Subsequently, liquid injection, packaging, standing, formation, capacity testing, and the like were performed, and finally, a soft-pack lithium battery 300 with a capacity of 3 Ah was prepared. The formation process included: standing the lithium battery 300 in a 45°C formation cabinet for 10 min, charging at a 0.1C rate for 7 min to 1.17% SOC, and standing for 3 min, and charging at a 0.2C rate to 30% SOC.

[0115] SOC (State of Charge) is a percentage that describes the current remaining capacity of a battery relative to its maximum available capacity, and is used to quantify the charge and discharge state of the battery.

[0116] The lithium battery 300 of each example and comparative example was subjected to various performance tests:

[0117] (1) Electrolyte composition test: GC-MS and IC were used for testing.

[0118] (2) Electrolyte platinum-cobalt colorimetric test: The environmentally friendly electrolyte (which can be a newly obtained regenerated electrolyte or an electrolyte obtained by centrifugation from the lithium battery 300) using recycled lithium salt was sealed and stored in a 45°C high-temperature vacuum environment for 48±2h. After cooling to room temperature, the electrolyte platinum-cobalt colorimetric test was performed. The test method referred to the national standard liquid chemical product colorimetric method. When the result exceeded 500 Hazen degrees, only the color was recorded.

[0119] (3) Cycle life test: the lithium battery 300 was charged at 1P constant power to 3.65V at 45°C, and then discharged at 1P constant power to 2.5V. The cycle was repeated, and the capacity of the 3rd cycle was recorded as the initial capacity DC3, and the capacity of the nth cycle was recorded as DCn. Until the cycle capacity retention rate λ (λ = DCn / DC3) decayed to less than 85%, the cycle number n at this time was recorded. At this time, the cycle number of the lithium battery 300 was the cycle life of the lithium battery 300. The test results of the cycle life of each example and comparative example are shown in Tables 1 and 2.

[0120] Table 1 Performance parameters of the lithium battery 300 of Examples 1 to 9 and Comparative Examples 1 to 13

[0121]

[0122]

[0123] As can be seen from Comparative Example 1 to Comparative Example 3 in Table 1, in a conventional non-recycled lithium battery 300 (also referred to as a non-regenerative lithium battery 300 or a conventional lithium battery 300) without the introduction of a recycled lithium salt, Comparative Example 1 uses TMSP as a modification additive, Comparative Example 2 uses trimethylsilyl triflate as a modification additive, and Comparative Example 3 uses N-trimethylsilyl-bis(trifluoromethanesulfonate) imide. Compared with Comparative Examples 2 and 3, the electrolyte of Comparative Example 1 has a smaller platinum-cobalt color after 2 days of high-temperature storage at 45°C, and a lower cycle life. This is because when the electrolyte is subjected to high temperature, the trimethylsilyl functional group actively combines with PF6 - to generate PF5, which easily causes the polymerization of solvents such as ethylene carbonate (EC) to generate oligomers similar to polyethylene carbonate, and the π-π* absorption of the oligomers causes the electrolyte to turn yellow. The trimethylsilyl group in trimethylsilyl triflate and N-trimethylsilyl-bis(trifluoromethanesulfonate) imide of Comparative Examples 2 and 3 is more prone to breakage and participate in the reaction, thus causing the platinum-cobalt color to deteriorate more severely than TMSP. Therefore, in order to control the platinum-cobalt color of the electrolyte within a suitable range, the electrolyte added with trimethylsilyl triflate and N-trimethylsilyl-bis(trifluoromethanesulfonate) imide needs to be strictly controlled in the storage temperature environment, which increases the production cost. In addition to the trimethylsilyl group in trimethylsilyl triflate and N-trimethylsilyl-bis(trifluoromethanesulfonate) imide of Comparative Examples 2 and 3, the triflate group also has the effect of constructing a SEI film. Therefore, the high-temperature (45°C) cycle life of the lithium battery 300 is slightly better than that of Comparative Example 1.

[0124] From the test results of Comparative Example 4 and Comparative Example 5 in Table 1, it can be seen that although the lithium battery 300 (also referred to as a regenerated lithium battery 300 or a recycled lithium battery 300) introduced with the recycled lithium salt achieves the initial intention of lithium recycling and recycling from the material, due to the high impurity content of the recycled lithium salt itself, the poor stability of the electrolyte (also referred to as a regenerated electrolyte or a recycled electrolyte, i.e., an electrolyte containing a recycled lithium salt), and the high-temperature cycle of the lithium battery 300 far from the realistic limitations of commercial promotion, the regenerated lithium battery 300 can only be limited to conceptual design. And with the increase of the amount of recycled lithium salt introduced, the defect problem of the electrolyte introduced with the recycled lithium salt becomes more and more obvious. Through Comparative Examples 4 to 6, it is shown that the additives developed from the perspective of the cast SEI film disclosed previously do not help the pathogen of the regenerated lithium battery 300. From Comparative Example 7, it can be seen that tris(trimethylsilyl) phosphite (abbreviated as TMSPi) with similar structure and functional groups as TMSP has a certain effect on improving the cycle performance of the lithium battery 300, but it has little effect on the discoloration problem of the electrolyte after high-temperature storage. This is because TMSPi, like TMSP, has the effect of capturing hydroxyl impurities in the regenerated electrolyte, and alleviating the negative effects of hydroxyl in high-temperature cycle, but TMSPi is extremely easy to react with LiPF6, which occurs rapidly at room temperature. Compared with the slow reaction of TMSP with LiPF6 at high temperature, the effect of TMSPi on electrolyte discoloration is more rapid and obvious.

[0125] From the test results of Example 1, Comparative Examples 4 to 7, it can be seen that compared with other modified additives such as trimethylsilyl triflate, N-trimethylsilyl-bis(trifluoromethanesulfonic acid) imide and tris(trimethylsilyl) phosphite, TMSP has better impurity removal effect on the impurities introduced by the recycled lithium salt in the electrolyte. In the electrolyte using recycled lithium salt, TMSP reacts with impurities such as alcohols (such as methanol, ethanol), dimethyl sulfoxide, N-methyl pyrrolidone, acetonitrile, etc. instead, and has less effect on the platinum-cobalt color of the electrolyte after high-temperature storage than the electrolyte prepared by using non-recycled lithium salt in Comparative Example 4, which shows that TMSP can improve the high-temperature storage stability of the electrolyte introduced with the recycled lithium salt.

[0126] As can be seen from the test results of Examples 1 to 5, Comparative Example 8 and Comparative Example 9, when the mass fraction of the recovered lithium salt in the electrolyte is too low (such as Comparative Example 8), although the lithium battery 300 has a higher high-temperature cycle life, the increase in the process input cost of recovering the electrolyte and extracting the lithium salt from the retired waste battery is not sufficient to cover the decrease in the cost of the lithium battery 300 due to the reuse of the recovered lithium salt, thereby increasing the preparation cost of the lithium battery 300; moreover, at this time, there is still a large amount of residue after the reaction of TMSP with the impurities in the electrolyte, which will significantly deteriorate the platinum-cobalt color of the electrolyte after high-temperature storage (i.e., deteriorate the high-temperature storage stability of the electrolyte). With the increase of the mass fraction w1 of the recovered lithium salt in the electrolyte, w2 / w1 gradually decreases, the platinum-cobalt color of the electrolyte gradually decreases first and then gradually increases (i.e., the high-temperature storage stability first increases and then decreases); the high-temperature cycle life of the lithium battery 300 gradually decreases. When the mass fraction of the recovered lithium salt in the electrolyte is too high (such as Comparative Example 9), the platinum-cobalt color of the electrolyte is too high, and the high-temperature cycle life of the lithium battery 300 is too low, which indicates that when the mass fraction of the recovered lithium salt in the electrolyte is too high, the performance of the electrolyte is extremely poor, and even if the recovered lithium salt is further refined, impurities are strictly removed, and TMSP is used, the cycle performance of the lithium battery 300 cannot be saved.

[0127] As can be seen from the test results of Example 1, Example 6 to Example 9, Comparative Example 10 and Comparative Example 12, when the mass fraction of TMSP in the electrolyte is too low (such as Comparative Example 10), the tris(trimethylsilyl) phosphate in the electrolyte is not enough to remove the impurities introduced by the recovered lithium salt, the impurities in the electrolyte are not removed completely, and the electrolyte cannot prevent the impurities introduced by the recovered lithium salt from accelerating the decomposition of the electrolyte salt and reducing the high-temperature cycle life of the lithium battery 300. In addition, before the electrolyte is configured and before the lithium battery 300 is injected, the tris(trimethylsilyl) phosphate and the impurities such as alcohol in the electrolyte have been almost completely reacted, and the tris(trimethylsilyl) phosphate cannot play a role in consolidating the interface film (CEI) of the positive electrode plate 310 and the interface film (SEI) of the negative electrode plate 330 in the formation and film forming reaction after the lithium battery 300 is injected, and the improvement of the cycle performance of the lithium battery 300 is limited. Therefore, when the mass fraction of TMSP in the electrolyte is too low, the high-temperature storage stability and the high-temperature cycle life of the electrolyte cannot be improved. With the increase of the mass fraction of TMSP in the electrolyte, the color of the electrolyte after high-temperature storage first gradually decreases and then gradually increases (i.e., the high-temperature storage stability of the electrolyte first increases and then decreases), and the high-temperature cycle life of the lithium battery 300 first gradually increases and then gradually decreases. When the mass fraction of TMSP in the electrolyte is too high (such as Comparative Example 12), the viscosity of the electrolyte is too high, which seriously reduces the dissociation and transport capacity of lithium ions, and reduces the kinetic performance and the high-temperature cycle life of the lithium battery 300. In addition, when the mass fraction of TMSP in the electrolyte is too high, the redundant TMSP not only accelerates the discoloration of the electrolyte after combining with LiPF6, but also is reduced too much on the negative electrode plate 330, consumes more lithium source to generate a product layer that hinders the smooth deintercalation of lithium ions, causes lithium precipitation and cycle deterioration of the lithium battery 300, and further reduces the high-temperature cycle life of the lithium battery 300.

[0128] In addition, as can be seen from the test results of Example 1, Example 6 to Example 9, Comparative Example 11 and Comparative Example 13, when w2 / w1 is too small (such as Comparative Example 11), the high-temperature storage color of the electrolyte is too high, the high-temperature storage stability of the electrolyte is reduced, and the high-temperature cycle life of the lithium battery 300 is reduced. With the increase of w2 / w1 (such as Example 1, Example 6 to Example 9), the color of the electrolyte after high-temperature storage first gradually decreases and then gradually increases (i.e., the high-temperature storage stability of the electrolyte first increases and then decreases), and the high-temperature cycle life of the lithium battery 300 first gradually increases and then gradually decreases. When w2 / w1 is too large (such as Comparative Example 13), the high-temperature storage stability of the electrolyte is low, and the high-temperature cycle life of the lithium battery 300 is greatly reduced.

[0129] The test results of Example 2 and Example 3 show that when the electrolyte includes both recycled lithium salt and non-recycled lithium salt, the total mass fraction of electrolyte salt in the electrolyte is constant, the high-temperature storage stability of the electrolyte and the high-temperature cycle life of the lithium battery 300 can be improved, and the recycling of lithium salt can be realized.

[0130] The test results of Example 1 and Example 7 show that when 10% of recycled lithium salt is used in the electrolyte, combined with TMSP, the cycle performance level of the lithium battery 300 (i.e., the lithium battery 300 using non-recycled lithium salt, such as Comparative Example 1) can be basically close to that of the lithium battery 300 without using recycled lithium salt, and at this time the high-temperature storage stability of the electrolyte itself is significantly improved.

[0131] Table 2 Performance parameters of the lithium battery 300 of Example 1, Example 10 to Example 11, Comparative Example 14 to Comparative Example 16

[0132]

[0133]

[0134] Table 2 shows the applicability of different types of recycled lithium salt in the principles and design parameters disclosed in the present technology.

[0135] The test results of Comparative Example 14 to Comparative Example 16 show that for different types of recycled lithium salt, the inevitable impurity introduction is a common problem, which directly leads to poor high-temperature storage stability of the electrolyte and serious non-compliance of the high-temperature cycle life of the lithium battery 300 with application requirements. Among them, LiPF6 is sensitive to moisture and high temperature, and the defects of the electrolyte are more obvious when using a lithium salt system containing recycled LiPF6 (such as Comparative Example 14). The test results of Example 10 to Example 12 show that in different lithium salt systems, the addition of TMSP can effectively improve the high-temperature storage stability of the electrolyte and the high-temperature cycle performance of the battery. Combined with adjusting the combination system of lithium salt, even if a high content of recycled lithium salt is used in the electrolyte, the color after high-temperature storage of the electrolyte and the high-temperature cycle life can even exceed that of the lithium battery 300 using non-recycled lithium salt.

[0136] In this application, the phrase "embodiment" or "implementation" means that a particular feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive of other embodiments. It will be explicitly understood by one of ordinary skill in the art that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the embodiments of this application can be combined with each other without contradiction, forming another embodiment of the technical solution of this application without departing from the spirit and scope of the technical solution of this application.

[0137] Finally, it should be noted that the above implementations are only used to illustrate the technical solutions of the application and are not limited. Although the application has been described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the application can be modified or replaced without departing from the spirit and scope of the technical solutions of the application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises a recycled lithium salt and a modified additive, the mass fraction of the recycled lithium salt in the electrolyte is w1, the modified additive is tris(trimethylsilyl) phosphate, the mass fraction of the tris(trimethylsilyl) phosphate in the electrolyte is w2, and the electrolyte satisfies the relationship: 0.008≤w2 / w1≤0.

3.

2. The electrolyte according to claim 1, characterized in that, The mass fraction of the recycled lithium salt in the electrolyte is w1, and the range of w1 is 3%≤w1≤18%.

3. The electrolyte of claim 1, wherein, The mass fraction of the tris(trimethylsilyl) phosphate in the electrolyte is w2, and the range of w2 is 0.01%≤w2≤5%.

4. The electrolyte of claim 1, wherein, The platinum-cobalt colority of the electrolyte after high-temperature storage at 45℃ for 2 days ranges from 50 Hazen to 450 Hazen.

5. The electrolyte of claim 1, wherein The recycled lithium salt comprises impurities, and the impurities comprise at least one of alcohol, water, dimethyl sulfoxide, N-methyl pyrrolidone, and acetonitrile.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte further comprises a non-recycled lithium salt, the mass fraction of the non-recycled lithium salt in the electrolyte is w3, and the total mass fraction of the recycled lithium salt and the non-recycled lithium salt in the electrolyte ranges from 10%≤w1+w3≤18%.

7. The electrolyte according to any one of claims 1 to 5, characterized in that, The recycled lithium salt comprises at least one of recycled lithium hexafluorophosphate, recycled lithium tetrafluoroborate, recycled lithium perchlorate, recycled lithium hexafluoroarsenate, recycled lithium bisfluorosulfonimide, recycled lithium bis-trifluoromethanesulfonimide, recycled lithium bisoxalato borate, and recycled lithium bisfluorooxalato borate.

8. The electrolyte of claim 6, wherein, The non-recycled lithium salt comprises at least one of non-recycled lithium hexafluorophosphate, non-recycled lithium tetrafluoroborate, non-recycled lithium perchlorate, non-recycled lithium hexafluoroarsenate, non-recycled lithium bisfluorosulfonimide, non-recycled lithium bis-trifluoromethanesulfonimide, non-recycled lithium bisoxalato borate, and non-recycled lithium bisfluorooxalato borate.

9. A lithium battery, characterized by The lithium battery comprises a positive electrode sheet, a separator, a negative electrode sheet, and the electrolyte of any one of claims 1-8.

10. An energy storage device, characterized by, The energy storage device comprises at least one lithium battery of claim 9.

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