Battery and preparation method thereof, and electric device

Abstract

The present application relates to the field of battery technology, and specifically discloses a battery and its preparation method, and electrical equipment. The battery includes a positive electrode sheet, a negative electrode sheet, a diaphragm, and an electrolyte; wherein the positive electrode sheet includes a positive electrode active layer and a current collector, the positive electrode active layer is arranged on the surface of the current collector, and the positive electrode active layer includes lithium supplement particles; the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet; the electrolyte includes a non-free electrolyte and a free electrolyte, the non-free electrolyte includes an electrolyte in the pores of the positive electrode sheet, an electrolyte in the pores of the negative electrode sheet, and an electrolyte in the pores of the diaphragm; the non-free electrolyte includes an ionic additive, and the mass proportion m of the ionic additive in the non-free electrolyte is: 0.001%≤m≤2%; the R value R of the free electrolyte at the lithium potential is e =0<R e <1. Therefore, the battery of the present application has excellent energy efficiency and a long cycle life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery and a preparation method thereof, and an electric device. BACKGROUND

[0002] Lithium ion batteries with lithium iron phosphate (LiFePO4) positive electrode and graphite negative electrode system have the characteristics of low cost and high safety, and are suitable for electrochemical energy storage field. The formation of SEI film (negative electrode / electrolyte interface film) on the anode side consumes active lithium of the cathode during the first charging process, resulting in a decrease in battery capacity and a low charging and discharging efficiency. In order to further optimize the efficient use of resources, promote sustainable development, and improve the energy efficiency of lithium iron phosphate batteries, the addition of lithium supplementing materials in the positive electrode material can effectively compensate for the first irreversible capacity loss of lithium batteries.

[0003] One of the most practically valuable pre-lithiation reagents is Li5FeO4 (LFO), which has broad application prospects due to its high theoretical specific capacity (867 mAh / g) and low cost. In addition, LFO is suitable for current lithium ion battery systems. By mixing an appropriate amount of LFO with conventional positive electrode materials, the initial charge capacity of the related positive electrode materials can be improved, thereby achieving the effect of lithium supplement. However, during the delithiation process of the pre-lithiation agent LFO, iron and oxygen oxidation reactions occur simultaneously, leading to the decomposition of electrolyte and the accumulation of by-products at the electrode sheet, which reduces the service life and energy efficiency of the battery.

[0004] Therefore, how to inhibit the electrolyte decomposition in the LFO activation lithium release reaction is a technical problem for improving the energy efficiency of lithium iron phosphate batteries. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art.

[0006] In a first aspect of the present application, a battery is provided. According to an embodiment of the present application, the battery comprises: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; wherein the positive electrode sheet comprises a positive electrode active layer and a current collector, the positive electrode active layer is arranged on the surface of the current collector, and the positive electrode active layer comprises lithium supplementing particles; the separator is arranged between the positive electrode sheet and the negative electrode sheet; the electrolyte comprises non-free electrolyte and free electrolyte, the non-free electrolyte comprises electrolyte in positive electrode sheet pores, electrolyte in negative electrode sheet pores, and electrolyte in separator pores; the non-free electrolyte comprises an ionic additive, the mass fraction m of the ionic additive in the non-free electrolyte is: 0.001%≤m≤2%; and the R value R of the free electrolyte at the lithium potential is: 0 e e

[0007] ​​The applicant can improve the cycle capacity retention rate and energy efficiency of the battery by designing the localized distribution characteristics of the free-state electrolyte and the non-free-state electrolyte. Among them, the non-free-state electrolyte contains an ionic additive, and the reduction product of the anion in the ionic additive after charging can react with the oxygen radicals / oxygen released by the lithium supplement particles to reduce the oxygen content in the system. When the mass ratio of the ionic additive in the non-free-state electrolyte is controlled to be 0.001%-2%, the ionic additive can be enriched in the electrode pores, and its reduction product can fully combine with the lithium supplement particles during the formation process, without causing insufficient oxygen capture due to insufficient addition, or excessive CEI (positive electrode / electrolyte interface film) impedance and cycle deterioration due to excessive addition. When the R value of the free-state electrolyte at the lithium potential is controlled to be in the range of 0-1 (not 0 or 1), the accumulation of by-products on the surface of the electrode can be avoided. Therefore, by simultaneously controlling the mass ratio of the ionic additive in the non-free-state electrolyte and the R value of the free-state electrolyte at the lithium potential, the overflow of gases such as methane, ethylene, and carbon dioxide, as well as the generation of by-products such as alkylated lithium and lithium carbonate, can be reduced, thereby effectively improving the energy efficiency of the battery and prolonging the cycle life of the battery.

[0008] According to an embodiment of the present application, the battery can further include at least one of the following additional technical features:

[0009] According to an embodiment of the present application, the battery satisfies the following condition: 0 e ≤ 2.5%, wherein m is the mass ratio of the ionic additive in the non-free-state electrolyte, and R e is the R value of the free-state electrolyte at the lithium potential.

[0010] According to an embodiment of the present application, the mass ratio of the lithium supplement particles in the positive active layer is 0.3%-3%.

[0011] According to an embodiment of the present application, the lithium supplement particles include a matrix and a coating layer, and the coating layer is arranged on the outer periphery of the matrix.

[0012] According to an embodiment of the present application, the ionic additive includes at least one of bisoxalate borate, difluoro bisoxalate borate, trisoxalate phosphate, difluoro bisoxalate phosphate, and tetrafluoro oxalate phosphate.

[0013] According to an embodiment of the present application, the matrix is Li5FeO4.

[0014] According to an embodiment of the present application, the coating layer includes an oxide and carbon, and the chemical formula of the oxide is Z x O y, Z is selected from at least one of iron, cobalt, nickel, titanium, zinc, magnesium, aluminum, manganese, vanadium, chromium, zirconium, copper, niobium, tantalum, tungsten, yttrium and lanthanum, 1≤x≤3, 1≤y≤5.

[0015] According to an embodiment of the present application, the thickness of the coating layer is 0.001 μm-1 μm.

[0016] In a second aspect, the present application provides a method for preparing the battery described in the first aspect. According to an embodiment of the present application, the method includes the following steps of injecting an electrolyte: performing a first injection treatment using a first electrolyte; performing a formation treatment after the first injection treatment; and performing a second injection treatment after the formation treatment using a second electrolyte, wherein the first electrolyte includes an ionic additive.

[0017] Therefore, the present application adopts a secondary injection method to prepare the electrolyte, that is, by separating the electrolyte components required for the battery formation stage and the electrolyte components required for the circulation stage, it is possible to achieve the local distribution characteristics of non-free electrolyte and free electrolyte. Among them, the first electrolyte is used to generate the initial SEI and CEI. The part of the first electrolyte remaining in the pores of the electrode and the diaphragm after the formation reaction, that is, the non-free electrolyte in the initial state, is closest to the active material. Therefore, the ionic additives in the first electrolyte are conducive to the negative polarization to form the initial SEI, and the remaining ionic additives are enriched in the pores of the positive electrode, which can capture the oxygen released by the lithium-supplementing particles in time. The second electrolyte is used to supplement the electrolyte required for long circulation. When the first electrolyte is excessive, the part that has not been consumed or entered into the pores of the diaphragm and the electrode merges with the second electrolyte to form the free electrolyte in the initial state.

[0018] According to an embodiment of the present application, the method may further include at least one of the following additional technical features:

[0019] According to an embodiment of the present application, the method satisfies the following conditions: 0.7≤(1-m) / M≤0.95, wherein m is the mass proportion of the ionic additive in the non-free electrolyte, and M is the mass proportion of the ionic additive in the first electrolyte.

[0020] According to an embodiment of the present application, the R value R of the second electrolyte at the lithium potential is z 0.1≤R z ≤3.

[0021] According to an embodiment of the present application, the maximum charging voltage of the formation treatment is 3.9V-4.6V.

[0022] According to an embodiment of the present application, the mass ratio of the first electrolyte to the second electrolyte is (6:4)-(9:1).

[0023] According to embodiments of the present application, the injection coefficient of the first electrolyte and the second electrolyte is 2.5 g / Ah-5 g / Ah.

[0024] In a third aspect of the present application, a power consuming device is provided. According to embodiments of the present application, the power consuming device comprises the battery of the first aspect, or the battery prepared by the method of the second aspect. As described above, the battery of the present application has excellent energy efficiency and cycle capacity retention rate, thus the power consuming device of the present application also has good energy density and cycle service life. Those skilled in the art can understand that the application has all the features and advantages of the battery described above, which will not be described in detail here.

[0025] Additional aspects and advantages of the present application will be in part apparent and in part pointed out below. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings.

[0027] Figure 1 A flow chart of a method for preparing an electrolyte in a battery is shown according to an embodiment of the present application. DETAILED DESCRIPTION

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application; unless otherwise specified, the values of the parameters mentioned in the present application can be measured by various measuring methods commonly used in the art (for example, the methods given in the embodiments of the present application can be used for testing).

[0029] The endpoints of the ranges and any values described in the present application are not limited to the precise values stated. The ranges and values should be construed to be roughly about the ranges or values stated to encompass amounts in close proximity to the exact values stated. For numerical ranges having an upper and lower limit, the endpoints of the ranges are included in the range. For ranges having an upper limit only, the upper limit is included in the range. For ranges having a lower limit only, the lower limit is included in the range. For ranges having no upper or lower limit, the range is inclusive of values less than or greater than the range. The ranges and values are also inclusive of individual points within the ranges.

[0030] The terms "comprising" and "having" and any variations thereof in the specification and claims of the present application are open-ended, that is, they mean including, but not limited to, the contents of the present application.

[0031] In the description of the present application, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature", "second feature" can include one or more of the features.

[0032] In the description of the present application, the meaning of "multiple" is two or more.

[0033] In the description of the present application, "A and / or B" can include any one of the cases of A alone, the case of B alone, the case of A and B, where A and B are only for example, which can be any technical feature connected by "and / or" in the present application.

[0034] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0035] By adding lithium supplement particles in the positive active layer, the lithium supplement particles release lithium ions as "sacrificial agent" during the first charging process of the lithium-rich positive electrode sheet, to supplement the irreversible lithium consumed by the formation of SEI film in the negative electrode, thereby improving the energy density of the battery. However, the lithium supplement particles release lithium ions while also releasing oxygen, which will accelerate the decomposition reaction of the components in the electrolyte at high voltage, especially in high-temperature formation or high-temperature standing aging, the reduction and oxidation decomposition of the electrolyte is more serious. As a result, a large amount of methane, ethylene, carbon dioxide and other gases overflow, a large amount of alkylated lithium and lithium carbonate accumulate on the surface of the electrode, thereby causing energy efficiency to decrease and shortening the cycle life.

[0036] Generally, the methods to inhibit the decomposition of electrolyte in the LFO activation lithium release reaction are: modification of lithium supplement material by doping, morphology control, surface coating, etc.; using phosphoric acid ester compounds, nitrogen-containing compounds, sulfonic acid ester compounds, etc. as electrolyte additives to inhibit the oxidation reaction gas production. However, the above measures will cause the positive electrode protection layer to be greatly thickened, the impedance to be increased, and the ion conductivity to be decreased, which worsens the energy efficiency of the battery.

[0037] Therefore, the applicant has developed a new battery, which has non-free electrolyte and free electrolyte in the battery cell by localizing and differentially designing the electrolyte according to the specific delithiation reaction platform potential of the lithium supplement particles. Among them, the non-free electrolyte contains an ionic additive, the anion of which can be enriched in the pores under the action of the electric field during the charging process, capturing the oxygen released by the lithium supplement particles in time, inhibiting its diffusion into the free electrolyte to accelerate the decomposition reaction of the electrolyte, and thereby improving the energy efficiency and cycle capacity retention rate of the battery. The battery and its preparation method will be described in detail below.

[0038] Battery

[0039] In a first aspect, the present application provides a battery. According to an embodiment of the present application, the battery comprises: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; wherein the positive electrode sheet comprises a positive electrode active layer and a current collector, the positive electrode active layer is arranged on the surface of the current collector, and the positive electrode active layer comprises lithium supplement particles; the separator is arranged between the positive electrode sheet and the negative electrode sheet; the electrolyte comprises a non-free electrolyte and a free electrolyte, the non-free electrolyte comprises electrolyte in pores of the positive electrode sheet, electrolyte in pores of the negative electrode sheet, and electrolyte in pores of the separator; the non-free electrolyte comprises an ionic additive, and the mass fraction m of the ionic additive in the non-free electrolyte is: 0.001%≤m≤2%; the R value of the free electrolyte at the lithium potential is: 0 e e

[0040] By designing the localized distribution characteristics of the free electrolyte and the non-free electrolyte, the applicant can improve the cycle capacity retention rate and the energy efficiency of the battery. The non-free electrolyte contains an ionic additive, the oxidation reactant of the ionic additive is rich in organic components, and the ionic additive has a non-linear three-dimensional structure. The component is attached to the lithium supplement particles to form a CEI with high conductivity and to block the further oxidation and decomposition of solvent molecules. The applicant found in the experiment that the addition amount of the ionic additive and the R value (R e ) of the free electrolyte have important effects on the performance of the battery. When the addition amount of the ionic additive is controlled, the ionic additive can be enriched in the pores of the electrode sheet, and the reduction product of the ionic additive can be fully combined with the lithium supplement particles during the formation process. The ionic additive can not have insufficient oxygen capture ability due to insufficient addition amount, or the CEI impedance can be too large due to excessive addition amount. When the R value (R e ) of the free electrolyte is controlled, the oxidation window of the free electrolyte is improved, and the accumulation of by-products is avoided. Therefore, by simultaneously controlling the mass fraction of the ionic additive in the non-free electrolyte and the R value of the free electrolyte at the lithium potential, the overflow of methane, ethylene, carbon dioxide, and other gases, and the generation of alkylated lithium, lithium carbonate, and other by-products can be reduced, thereby effectively improving the energy efficiency of the battery and prolonging the cycle life of the battery.

[0041] ​​Specifically, when the mass proportion m of the ionic additive in the non-free electrolyte is 0.001%≤m≤2%, the ionic additive can be enriched in the pores of the electrode, and its reduction product can be fully combined with the lithium supplement particles during the formation process, without causing insufficient oxygen capture capacity due to insufficient addition, or excessive addition causing excessive CEI impedance and cycle deterioration. Specifically, the mass proportion of the ionic additive in the non-free electrolyte can be 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, etc., or can be a range composed of any of the above values.

[0042] Specifically, when the R value of the free electrolyte at the lithium potential is R e 0<R e When R<1, the accumulation of by-products on the electrode surface can be avoided. e The value represents the electrochemical stability of the ionic medium in the battery cell, R e is the R value of the free electrolyte at the lithium potential. In addition, the voltage value set during the formation process is U max +0.1V, where U max The potential of the lithium supplement particles should not be lower than the highest delithiation reaction platform potential, so that the lithium supplement particles in the positive electrode active layer can be effectively activated and delithiated during the battery manufacturing process to provide the required energy. The lithium potential value is U max , for R under lithium potential e The upper limit indicates that the free electrolyte will not decompose seriously when the lithium replenishment reaction occurs, R e The closer to 0, the better the electrochemical stability of the free electrolyte at this voltage. Specifically, the R value R of the free electrolyte at the lithium potential is e It may be 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, etc., or may be a range consisting of any of the above values.

[0043] It should be noted that U max Greater than or equal to the highest delithiation reaction platform potential of the lithium supplement particle. If the lithium supplement particle has two or more delithiation reaction platform potentials, the highest delithiation reaction platform potential shall prevail.

[0044] In some embodiments of the present application, the battery satisfies the following conditions: 0<m / R e ≤2.5%; wherein, m is the mass ratio of the ionic additive in the non-free electrolyte, R e is the R value of the free electrolyte at the lithium potential. For example, m / R emay be 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, etc., or may be a range composed of any of the above values. The applicant found that when the non-free electrolyte does not contain ionic additives, i.e., m / R e 0, the function of capturing the oxygen released by the lithium supplement particles and inhibiting its diffusion into the free electrolyte to accelerate the electrolyte decomposition reaction cannot be achieved; when the amount of ionic additives is too high or the free electrolyte is too large, i.e., m / R e 2.5%, the lithium ion deintercalation will be affected, thereby causing the impedance to rise and the energy efficiency to deteriorate. Therefore, by making m / R e satisfy the above range, the lithium ion deintercalation can be ensured, and the oxygen released by the lithium supplement particles can be effectively captured to inhibit the decomposition of the electrolyte.

[0045] In some embodiments of the present application, the non-free electrolyte includes electrolyte in the pores of the positive electrode sheet, electrolyte in the pores of the negative electrode sheet, and electrolyte in the pores of the separator, and the rest is free electrolyte. The non-free electrolyte is in direct contact with the electrode sheet and the separator, dominates the formation and repair process of the SEI, participates in the desolvation effect of lithium ions, and directly determines the SEI film impedance R SEI and the charge transfer impedance R ct ; the free electrolyte exists in the cell cavity outside the material pores and is not absolutely physically separated from the non-free electrolyte. When the non-free electrolyte is insufficient, the free electrolyte is automatically absorbed by the capillary action of the electrode sheet and the separator to supplement it. When the content of a component in the non-free electrolyte is higher than that in the free electrolyte, the content of the component decreases after the non-free electrolyte absorbs the free electrolyte. When the content of a component in the non-free electrolyte is lower than that in the free electrolyte, the content of the component increases after the non-free electrolyte absorbs the free electrolyte. The electrolyte compositions in the two regions are dynamically different in the cycle consumption process, so the component content of the battery is also dynamically changing during use.

[0046] In some embodiments of the present application, the ionic additive includes, but is not limited to, at least one of bisoxalate borate, difluoro bisoxalate borate, trisoxalate phosphate, difluoro bisoxalate phosphate, and tetrafluoro bisoxalate phosphate. Thus, the reduction products generated by the anions of the above-mentioned ionic additives after charging can react with oxygen radicals / oxygen, and the intermediate reaction products of the anions and the remaining anions that have not been consumed will tend to be enriched in the positive electrode due to the electric field effect, thereby further playing a role in quickly capturing oxygen.

[0047] It should be noted that the cation in the ionic additive described in the present application has no particular limitation as long as it does not impair the technical effects of the present application, and as a specific embodiment of the present application, the cation can include metal cations such as lithium, sodium, potassium, magnesium, calcium, and the like, onium cations such as tetraalkylammonium, tetraalkylphosphonium, imidazolium derivatives, and the like, and preferably lithium ions.

[0048] In some embodiments of the present application, the mass percentage of the lithium supplement particles in the positive active layer is 0.3%-3%. For example, it can be 0.3%, 0.5%, 0.7%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.7%, 3%, or the like, or a range composed of any of the above values. Thus, by setting the mass percentage of the lithium supplement particles in the above range, on the one hand, it can release sufficient lithium ions as a "sacrificial agent" to supplement the irreversible lithium consumed by the formation of SEI film in the negative electrode, thereby improving the energy density of the battery; on the other hand, it can reduce the oxygen content released, thereby avoiding the generation of too much gas and by-products, and thus avoiding the reduction of energy efficiency and the shortening of cycle life.

[0049] In some embodiments of the present application, the lithium supplement particles include a substrate and a coating layer, and the coating layer is arranged on the outer periphery of the substrate. The substrate can release lithium ions, thereby improving the energy density of the battery. The coating layer can prevent the substrate from being oxidized by reacting with air, thereby improving the stability of the substrate. On the other hand, the coating layer has electrical conductivity, which reduces the lithium ion deintercalation impedance and polarization reaction, thereby improving the energy efficiency of the battery.

[0050] In some embodiments of the present application, the substrate is Li5FeO4. Thus, the Li5FeO4 can release more lithium ions, thereby improving the energy density of the battery.

[0051] In some embodiments of the present application, the coating layer includes an oxide and carbon, wherein the chemical formula of the oxide is Z x O y , Z is selected from at least one of iron, cobalt, nickel, titanium, zinc, magnesium, aluminum, manganese, vanadium, chromium, zirconium, copper, niobium, tantalum, tungsten, yttrium, and lanthanum, 1≤x≤3, and 1≤y≤5. The oxide can prevent the inner core from being oxidized and corroded by the outside world; the carbon is used to improve the electrical conductivity of the coating layer. It should be noted that the oxide in the coating layer can be one or multiple, and the chemical formula of the multiple oxides is Z x O y .

[0052] In some embodiments of the present application, the oxide has a mass of 0.1 wt% to 20 wt% of the coating layer. For example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, etc., or a range consisting of any of the above values.

[0053] In some embodiments of the present application, the thickness of the coating layer is 0.001 μm to 1 μm. For example, it can be 0.001 μm, 0.005 μm, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, etc., or a range consisting of any of the above values. In this way, by having the thickness of the coating layer in the above range, the stability of the substrate can be improved while ensuring the normal release of lithium ions from the substrate, avoiding oxidation and corrosion by the outside world. If the thickness of the coating layer is too thick, it will result in a too high deintercalation potential of the active material, and if the thickness of the coating layer is too thin, it will not be able to guarantee the integrity of the coating.

[0054] In some embodiments of the present application, the positive electrode active layer further comprises a positive electrode active material.

[0055] By way of example, when the positive electrode sheet is used in a lithium ion battery, the positive electrode active material can employ a positive electrode active material known in the art for use in lithium ion batteries. By way of example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphate of olivine structure, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination with two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to as NCM622 LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 LiNi 0.8 Co 0.15 Al 0.05 O2) or modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, or a composite of lithium manganese iron phosphate and carbon.

[0056] In some embodiments of the application, the positive current collector can include a metal foil or a composite positive current collector. For example, the metal foil can employ an aluminum foil. The composite positive current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite positive current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material).

[0057] In some embodiments of the application, the positive active layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0058] In some embodiments of the application, the positive active layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic resin.

[0059] In some embodiments of the application, the negative electrode tab includes a negative active layer and a negative current collector, the negative active layer including a negative active material.

[0060] In some embodiments of the application, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, etc. The silicon-based material can include at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can include at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0061] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite negative electrode current collector. For example, copper foil may be used as the metal foil. The composite negative electrode current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite negative electrode current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0062] In some embodiments of the present application, the negative electrode active layer may further include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0063] In some embodiments of the present application, the negative electrode active layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0064] In some embodiments of the present application, the negative electrode active layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0065] The present invention has no particular restrictions on the type of separator. Any known porous separator with good chemical and mechanical stability can be used. According to an embodiment of the present application, the separator can be made of at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0066] In some embodiments of the present application, the battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0067] In some embodiments of the present application, the outer packaging may include a housing and a cover. The housing may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates enclosing a receiving cavity. The housing may have an opening communicating with the receiving cavity, and the cover may be positioned over the opening to seal the receiving cavity.

[0068] In some embodiments of the present application, the outer packaging of the battery may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0069] The outer packaging of the battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0070] The batteries of the present application may include battery cells, battery modules, and battery packs. In some embodiments, battery cells may be assembled into a battery module, which may contain one or more battery cells, with the specific number selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, which may contain one or more battery modules, with the specific number selected by those skilled in the art based on the application and capacity of the battery pack.

[0071] Method for preparing battery

[0072] In the second aspect of the present application, the present application proposes a method for preparing the battery described in the first aspect. According to the embodiments of the present application, referring to Figure 1 , the method comprising:

[0073] S100: First injection process

[0074] In this step, the first electrolyte is injected for the first time, and the first electrolyte includes an ionic additive. The first electrolyte is used to generate the initial SEI and CEI. The portion of the first electrolyte remaining in the pores of the electrode and diaphragm after the reaction—the initial non-free electrolyte—is closest to the active material. Therefore, adding the ionic additive to the first electrolyte facilitates the formation of the initial SEI during negative polarization. The remaining ionic additive is enriched in the pores of the positive electrode, which can promptly capture the oxygen released by the lithium supplement particles.

[0075] In some embodiments of the present application, the method satisfies the following conditions: 0.7≤(1-m) / M≤0.95, wherein m is the mass proportion of the ionic additive in the non-free electrolyte, and M is the mass proportion of the ionic additive in the first electrolyte. The applicant has established a relationship between the manufacturing process parameters (the mass proportion of the ionic additive in the first electrolyte) and the battery characteristic parameters (the mass proportion of the ionic additive in the non-free electrolyte). This formula can ensure that the mass percentage of the ionic additive consumed during the manufacturing process is 50% or more and is not completely consumed, thereby indicating that the ionic additive participates in the negative polarization to form the initial SEI, and there is still residual ionic additive that can be used to capture the oxygen released by the lithium-supplementing particles.

[0076] S200: Chemical treatment

[0077] In this step, the first liquid injection treated battery cell is subjected to formation treatment. Thus, the part of electrolyte remaining in the pole piece and the diaphragm gap after the formation treatment forms the initial state of the non-free electrolyte.

[0078] In some embodiments of the present application, the maximum charging voltage value of the formation treatment is (U max +0.1V), and the (U max +0.1V) is 3.9V-4.6V. As some specific examples, the (U max +0.1V) can be 3.9V, 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, etc., or can be a range consisting of any of the above values. Wherein the U max value is not less than the maximum delithiation reaction platform potential of the lithium supplement particles, so in the actual manufacturing of the full battery of LiFePO4 and graphite negative electrode, the maximum charging voltage is set to U max +0.1V. Thus, by setting the maximum charging voltage (U max +0.1V) in the above range, the lithium supplement particles can be fully activated to achieve the lithium supplement effect, and the over-delithiation of the positive electrode LiFePO4 can be avoided to cause irreversible damage to the active material.

[0079] S300: Second liquid injection treatment

[0080] In this step, the second electrolyte is used to supplement the electrolyte required for long cycle, and when the first electrolyte is excessive, the part of the first electrolyte that is not consumed by the formation or enters the diaphragm and pole piece pores will be fused with the second electrolyte to form the initial state of the free electrolyte.

[0081] In some embodiments of the present application, the second electrolyte has a R value R z at the lithium potential of 0.1≤R z ≤3. As some specific examples, the R z can be 0.1, 0.2, 0.5, 0.7, 1, 1.2, 1.5, 1.7, 2, 2.2, 2.5, 2.7, 3, etc., or can be a range consisting of any of the above values. Thus, by setting the R value of the second electrolyte at the lithium potential in the above range, the R e value of the free electrolyte can satisfy 0 e <1, so that the free electrolyte has high electrochemical stability and ensures the role of the fast ion channel. The R z value of the second electrolyte is slightly higher than the R e value of the free electrolyte because the second electrolyte may have a reaction current generated by the additive of the advanced oxidation solvent, and the reaction current will cause the R zThe value is larger, however, this part of the additive will be slightly consumed in the liquid injection process and the capacity test process, which reduces this part of the additive, thereby reducing the R e value in the formed free electrolyte.

[0082] In some embodiments of the present application, the mass ratio of the first electrolyte to the second electrolyte is (6:4)-(9:1). As some specific examples, the mass ratio of the first electrolyte to the second electrolyte can be 6:4, 7:3, 8:2, 9:1, etc., or can be a range composed of any of the above values. During the experiments, the applicants proportionally divided the total electrolyte demand of the battery into the first injection demand and the second injection demand, and obtained the above ratio range capable of achieving the effects of the present application through testing. When exceeding this range, the effect of improving overcharge thermal runaway will no longer be achieved. This can be due to the fact that the ratio of the injection amount of the first injection process to the injection amount of the second injection process is too low, i.e., less than 6:4, so that the injection amount of the first injection is not sufficient to fully soak, the SEI protective layer obtained by the processing of Changsen is not uniform and has poor thermal stability, the area without SEI after the second injection (the second injection process) and the electrolyte electronic conduction cause the electrolyte to decompose and accumulate by-products; the ratio of the injection amount of the first injection process to the injection amount of the second injection process is too high, i.e., greater than 9:1, so that the second injection accounts for a low proportion, the free electrolyte composition mainly comes from the electrolyte composition that is not consumed in the first injection process, and the non-free electrolyte composition is basically the same. Under such a ratio, there is basically no difference between the secondary injection and the traditional primary injection, and it is difficult to achieve the design of localized electrolyte.

[0083] It should be noted that the absolute mass of the second electrolyte during the second injection process will be adjusted according to the capacity of different batteries, and the present application is applicable to battery systems of various capacities, so the present application does not limit the specific injection amount of the electrolyte.

[0084] In some embodiments of the present application, the sum of the injection coefficients of the first electrolyte and the second electrolyte is 2.5 g / Ah-5 g / Ah. As some specific examples, the sum of the injection coefficients of the first electrolyte and the second electrolyte is 2.5 g / Ah, 2.7 g / Ah, 3 g / Ah, 3.2 g / Ah, 3.5 g / Ah, 3.7 g / Ah, 4 g / Ah, 4.2 g / Ah, 4.5 g / Ah, 4.7 g / Ah, 5 g / Ah, etc., or can be a range consisting of any of the above values. According to embodiments of the present application, the sum of the injection coefficients of the first electrolyte and the second electrolyte is 3.5 g / Ah-5 g / Ah. Specifically, the injection coefficient (injection amount / cell capacity) represents the amount of electrolyte required, and for energy storage lithium ion batteries, a higher injection coefficient can maintain a long cycle life. Thus, by having the sum of the injection coefficients in the above range, sufficient wetting of the separator and the electrode sheet can be achieved, and excessive electrolyte swelling or local lithium precipitation caused by electrolyte accumulation at the bottom of the battery can be avoided.

[0085] In some embodiments of the present application, the method for preparing the battery can be performed by the following steps: first injection treatment, standing treatment, formation treatment, second injection treatment, high-temperature aging treatment, and capacity distribution treatment, to obtain the battery. The standing treatment and the high-temperature aging treatment are not particularly limited, as long as they can ensure sufficient wetting and uniform film formation during the formation treatment. The battery can be disassembled after the second injection treatment and before the capacity distribution treatment, and the positive and negative electrodes and the separator in the battery are distributed with visible electrolyte, and the negative electrode has no abnormal spots or dark marks, i.e., it meets the requirements. The full charge process can be constant current charging at 0.2C to 3.65V.

[0086] In some embodiments of the present application, the first electrolyte further includes: a first solvent, a first lithium salt, and a first additive.

[0087] In some embodiments of the present application, the second electrolyte includes: a second solvent, a second lithium salt, and a second additive.

[0088] In some embodiments of the present application, the first solvent and the second solvent are each independently selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, vinylene carbonate (VC), methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, ethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, propyl vinylene carbonate, 1,2-dipropyl vinylene carbonate, vinyl ethylene carbonate (VEC), divinyl ethylene carbonate (DVEC), methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate. In the above compounds, some of the hydrogen atoms can be substituted with fluorine atoms.

[0089] In some embodiments of the present application, the first lithium salt and the second lithium salt are each independently selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonimide, lithium bis-trifluoromethylsulfonimide, lithium trifluoromethanesulfonate, lithium bis(trifluoromethylsulfonyl)methide, lithium tris(trifluoromethylsulfonyl)methide. According to embodiments of the present application, the first lithium salt and the second lithium salt are each independently selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonimide.

[0090] In some embodiments of the present application, the first additive and the second additive are each independently selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4-butane sultone (BS), ethylene sulfate (DTD), tris(trimethylsilyl)phosphate (TMSP), adiponitrile (AND), succinonitrile (SN), etc., as long as the type and content of the additive used do not affect the realization of the effects of the present application and can achieve the expected technical effects, all are considered within the scope of technical protection.

[0091] The application adopts a method of twice electrolyte injection, that is, separating electrolyte components required in the cell formation stage and electrolyte components required in the circulation stage, so as to realize the local distribution characteristics of the non-free electrolyte and the free electrolyte in the initial state of the battery. The applicant has found that the local distribution characteristics of the initial state of the electrolyte determine the local distribution characteristics of the electrolyte in the subsequent working state: under the premise that the total amount of electrolyte is sufficient and the transmission is unobstructed, the local distribution proportion of the solvent in the initial state of the electrolyte can qualitatively determine the local distribution proportion of the solvent in the subsequent working state. Therefore, the applicant adopts two kinds of electrolytes for injection, among which the first electrolyte is used to generate the initial SEI and CEI, and the part of the first electrolyte remaining in the pores of the pole piece and the separator after the first electrolyte formation reaction, that is, the non-free electrolyte in the initial state, is closest to the active material, so that the ionic additive in the first electrolyte is beneficial to the formation of the initial SEI of the negative electrode, and the remaining ionic additive is enriched in the pores of the positive electrode, which can timely capture the oxygen released by the lithium supplement particles. The second electrolyte is used to supplement the electrolyte required for long cycle, and when the first electrolyte is excessive, the part that is not consumed or enters the pores of the separator and the pole piece is fused with the second electrolyte to form the initial state of the free electrolyte.

[0092] Electric device

[0093] The third aspect of the application provides an electric device. According to the embodiments of the application, the electric device comprises the battery of the first aspect or the battery prepared by the method of the second aspect. Thus, the electric device of the application has high efficiency of energy output and excellent service life and safety performance.

[0094] The battery cell, the battery module and the battery pack can be used as the power supply of the electric device or the energy storage unit of the electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0095] As the electric device, the battery cell, the battery module or the battery pack can be selected according to the use requirement thereof.

[0096] As an embodiment of the electric device, it can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the battery for the electric device, the battery pack or the battery module can be used.

[0097] As another embodiment of the electric device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as the power supply.

[0098] The scheme of the present application will be explained below in conjunction with examples. Those skilled in the art will understand that the examples below are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If no specific technique or condition is specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained commercially.

[0099] Example 1

[0100] 1. Preparation of positive electrode tab:

[0101] The positive electrode active material lithium iron phosphate (LiFePO4), lithium supplementing particles (may be referred to as lithium supplementing agent, which is purchased, wherein the substrate is Li5FeO4, the coating layer contains Fe2O3, FeO and carbon, and the total mass ratio of Fe2O3 and FeO in the coating layer is 12%), conductive carbon black (SP), and polyvinylidene fluoride (PVDF) are dispersed in a solvent N-methyl pyrrolidone (NMP) in a mass ratio of (97-w):w:2.5:0.5 (w=2) to mix uniformly to obtain a positive electrode slurry. The positive electrode slurry is coated on a positive electrode current collector aluminum foil, and the unit area coating weight of the positive electrode slurry is 33 mg / cm 2 After drying, cold pressing, slitting, and cutting, a positive electrode tab is obtained.

[0102] 2. Preparation of negative electrode tab:

[0103] The negative electrode active material artificial graphite, conductive carbon black (SP), thickening agent (CMC), and binder (SBR) are dispersed in deionized water in a mass ratio of 96.5:0.5:1:2 to mix uniformly to obtain a negative electrode slurry. The negative electrode slurry is coated on a negative electrode current collector 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, a negative electrode tab is obtained.

[0104] 3. Preparation of electrolyte:

[0105] In an argon atmosphere glove box with water and oxygen content ≤0.1 ppm, the solvent and lithium salt are mixed in a certain proportion, and the ionic additive (lithium difluorooxalate borate) and other additives are added and stirred until completely dissolved.

[0106] One note electrolyte:

[0107] Lithium salt: lithium hexafluorophosphate with a mass ratio of 8%, and lithium bisfluorosulfonylimide with a mass ratio of 4%;

[0108] Other additives: 3% vinylene carbonate, 1% fluoroethylene carbonate, 1% vinyl sulfate by mass;

[0109] Ionic additive A: 0.5% lithium difluoro(oxalato)borate by mass;

[0110] Solvent: EC: EMC: DMC is first mixed according to a mass ratio of 1:1:1, and the remaining components are supplemented;

[0111] Two-injection electrolyte:

[0112] Lithium salt: 8% lithium hexafluorophosphate, 4% lithium bisfluorosulfonylimide by mass;

[0113] Other additives: 3% vinylene carbonate, 1% fluoroethylene carbonate, 1% vinyl sulfate by mass;

[0114] Solvent: EC: EMC: DMC is first mixed according to a mass ratio of 1:1:1, and the remaining components are supplemented.

[0115] 4. Preparation of the separator film: a 16 μm polyethylene film is used.

[0116] 5. Assembly of the battery:

[0117] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator in the middle of the positive and negative electrode sheets, and wound into a bare cell. After welding the tabs, the cell is assembled into an outer package, heat-pressed, and then vacuum-dried. Subsequently, a secondary injection process is performed: first, electrolyte is injected, and the cell is packaged, left to stand, and formed. Second, electrolyte is injected, and the cell is left to stand at high temperature, and tested for capacity, etc. Finally, a soft-pack lithium ion battery with a capacity of 3.2 Ah is prepared.

[0118] The formation step is performed at a pressure of 0.3 MPa and a temperature of 45°C, according to the following specified process:

[0119] Step 1: constant-rate charging at 0.1 C to 3 V;

[0120] Step 2: constant-rate charging at 0.2 C to 3.5 V, constant-voltage charging to 0.05 C, and standing for 5 minutes;

[0121] Step 3: constant-rate charging at 0.05 C to (Umax+0.1 V).

[0122] The fixed injection coefficient is 4.0g / Ah; the injection ratio of the first and second injections is 7:3; the static condition after the first injection is 45±5℃ for 24 hours, and the formation temperature is 45℃. The static condition after the second injection (high temperature aging) is 45±5℃ for 24 hours. Umax = 3.9V, that is, the maximum voltage of the above battery formation step is 4.0V.

[0123] Example 2-18

[0124] 1. The positive electrode sheet was prepared according to the method described in Example 1. The specific value of w is shown in Table 1;

[0125] 2. Preparation of electrolyte:

[0126] The difference between Examples 2-8 and 13-17 and Example 1 is that the type and amount of the ionic additive A in one injection of the electrolyte are different, as shown in Table 1; the components of the two injections of the electrolyte are the same.

[0127] In Examples 9-12, the composition of the first injection of electrolyte is the same as that of Example 2, and the composition of the lithium salt in the second injection of electrode solution is different from that of Example 2, wherein:

[0128] Example 9: 6% by weight of lithium hexafluorophosphate and 4% by weight of lithium bis(fluorosulfonyl)imide;

[0129] Example 10: 10% by weight of lithium hexafluorophosphate and 2% by weight of lithium bis(fluorosulfonyl)imide;

[0130] Example 11: 12% by mass of lithium hexafluorophosphate;

[0131] Example 12: 11% by weight of lithium hexafluorophosphate and 3% by weight of lithium bis(fluorosulfonyl)imide.

[0132] In Example 18, the type and amount of the ionic additive A in the first injection of the electrolyte are as listed in Table 1; the lithium salt in the second injection of the electrolyte is 10% by weight of lithium hexafluorophosphate and 2% by weight of lithium bis(fluorosulfonyl)imide, and the solvents EC:EMC:DMC are first mixed in a weight ratio of 1:1:1 and then supplemented as the remaining components.

[0133] Comparative Examples 1-9

[0134] Comparative Example 1 is a one-time injection process, and the electrolyte components and proportions are consistent with those of the one-time injection of electrolyte in Example 2.

[0135] Comparative Example 2-3 is a two-step injection process, wherein the one-step electrolyte of Comparative Examples 2 and 3 both contains lithium salt with a mass ratio of 8% lithium hexafluorophosphate and 4% lithium bisfluorosulfonylimide, and other additives with a mass ratio of 3% vinylene carbonate, 1% fluoroethylene carbonate and 1% vinylsulfate, and the solvent EC: EMC: DMC is first mixed according to a mass ratio of 1:1:1, and then supplemented with the remaining components; the two-step electrolyte of Comparative Example 2 contains lithium salt with a mass ratio of 8% lithium hexafluorophosphate and 4% lithium bisfluorosulfonylimide, and other additives with a mass ratio of 3% vinylene carbonate, 1% fluoroethylene carbonate and 1% vinylsulfate, and the solvent EC: EMC: DMC is first mixed according to a mass ratio of 1:1:1, and then supplemented with the remaining components; the two-step electrolyte of Comparative Example 3 contains the same components and mass ratio as the one-step electrolyte of Example 2;

[0136] Comparative Example 4 is a two-step injection process, wherein the one-step electrolyte and the two-step electrolyte of Comparative Example 4 are the same as Example 2, and the difference is that Comparative Example 4 does not contain a lithium supplement agent;

[0137] Comparative Examples 5-7 are two-step injection processes, wherein the two-step electrolyte of Comparative Examples 5-7 is the same as Example 1, and the one-step electrolyte is different from Example 1, and the specific difference is that the content of ionic additive A is different, and the specific content of ionic additive A in Comparative Examples 5-7 is shown in Table 1;

[0138] Comparative Example 8 is a two-step injection process, wherein the one-step electrolyte of Comparative Example 8 is the same as Example 2, and the lithium salt in the two-step electrolyte is different from Example 2, and the specific difference is that the mass ratio of lithium hexafluorophosphate is 6% and the mass ratio of lithium bisfluorosulfonylimide is 2%;

[0139] Comparative Example 9 is a two-step injection process, wherein the one-step electrolyte and the two-step electrolyte of Comparative Example 9 are the same as Example 1, and the specific difference is that the content of the lithium supplement agent is different, and the content of the lithium supplement agent in Comparative Example 9 is shown in Table 1;

[0140] The specific parameters in Examples 1-18 and Comparative Examples 1-9 are shown in Table 1.

[0141] Table 1

[0142]

[0143]

[0144] Performance test:

[0145] 1. Test of positive electrode lithium supplement particles:

[0146] The matrix, coating and composition of the lithium supplement particles in the positive active layer can be easily observed by scanning electron microscope (SEM).

[0147] 2. Test of free electrolyte components:

[0148] Discharge the battery with the outer package to 0% SOC (2.0V) at a current of 0.05C, cut a gap of about 0.5 cm on the right side of the battery facing the positive pole, and cut a gap of the same size on the right side facing the negative pole, ensuring that the two gaps are on the diagonal. Pour the free electrolyte from the small opening on the positive pole side into a fluorinated bottle until intermittent droplets flow down for 30 seconds.

[0149] Use GC-MS and GC to test the types and relative mass contents of Formula I and other organic components in the collected electrolyte.

[0150] Use IC to test the types and relative mass contents of additive A and salt in the collected electrolyte.

[0151] 3. Test of non-free (pore) electrolyte:

[0152] Remove the outer package and take out the single bare cell. Quickly peel off the pole piece and put it into an aluminum plastic bag. Add enough acetonitrile solvent to completely soak the pole piece. Seal the aluminum plastic bag containing the acetonitrile solvent and the pole piece, and let it stand at 35±10°C for 3 days.

[0153] Use GC-MS and GC to test the types and relative mass contents of organic components in the collected electrolyte.

[0154] Use IC to test the types and relative mass contents of additive A and salt in the collected electrolyte.

[0155] 4. Test of free electrolyte R value:

[0156] According to the test method disclosed in the reference "Reliable Values of Electrochemical Stability Limits for Electrolytes", assemble a LiFePO4 positive electrode (without lithium supplement particles) and a lithium sheet into a half-cell. Charge the half-cell at 25°C at a constant current of 0.5C to 5.4V and stand for 30 minutes. Take the open circuit voltage of the overcharged battery as the initial point, and perform cyclic voltammetry (CV) scanning at a scan rate of 5mV / s. Set the cutoff voltage to 3.8V, 4V, 4.2V, 4.4V and 4.6V in turn for each cycle. Obtain the reversible reaction electric quantity QF and the irreversible reaction electric quantity QnF for each cycle in the CV process by integrating the CV current sum, and obtain the R value. Plot the R value and take the R value at Umax as R e (or R z ).

[0157] 5. Cycle performance test

[0158] Charge at 0.5P constant power to 3.65V, then discharge at 0.5P constant power to 2.5V, record the energy of the Xth cycle as CEx, DEx, until X = 1000, record the capacity and energy value of each cycle.

[0159] The energy efficiency of the battery after cycling is evaluated by the energy efficiency η, η = DE 1000 / CE 1000 .

[0160] Experimental results:

[0161] Examples 1-18 and Comparative Examples 1-9 evaluate the effect of free electrolyte and non-free electrolyte design parameters on the 45°C, 0.5P cycle capacity retention and energy efficiency after 1000 cycles, the results are shown in Table 1. Comparative Example 1 is a conventional one-time injection process, the electrolyte contains ionic additive A, and the positive electrode introduces a lithium supplement, the cycle capacity retention and energy efficiency after 1000 cycles of the application of this technology are less than 90%, which has a great room for improvement. Comparative Example 2 uses a two-time injection process, but the electrolyte does not contain ionic additive A, and the positive electrode introduces a lithium supplement, the cycle capacity retention and energy efficiency after 1000 cycles of the application of this technology are not as good as Comparative Example 1, which shows that without the introduction of ionic additive A, simply using a two-time injection process cannot significantly improve the cycle performance. Comparative Example 3 also uses a two-time injection process, but ionic additive A is only introduced in the second injection, and the positive electrode introduces a lithium supplement, the cycle is slightly improved compared to Comparative Example 2, but the cycle capacity retention is not as good as Comparative Example 1, which shows that ionic additive A can help improve the cycle to a certain extent, which is consistent with the previously disclosed technology, but when combined with the two-time injection process, if the appropriate addition method is not used, the cycle capacity retention and energy efficiency cannot be improved at the same time, and the cycle capacity retention may be worse than the one-time injection process. Comparative Example 4 uses a two-time injection process and optimizes the addition method of ionic additive A, but the positive electrode does not contain a lithium supplement, it can be seen that such electrolyte adjustment improves the energy efficiency, but the cycle capacity retention is not as good as Comparative Example 1. By analyzing the comparative examples, it can be concluded that in order to improve the cycle capacity retention and energy efficiency, the two-time injection process, ionic additive A in the electrolyte, and the positive electrode lithium supplement need to be designed in correlation.

[0162] Based on the design technology of localized electrolyte expected to be achieved by the two-time injection, the correlation between the oxidation reaction stability of the free electrolyte and the m / R of the ionic additive A in the non-free electrolyte is given e , the correlation between the amount of ionic additive A in the non-free electrolyte and the demand degree 1-m / M of the design amount of the positive electrode lithium supplement.

[0163] Examples 1-8, Comparative Examples 5-7, by regulating the type of ionic additive A in the first injection electrolyte and the designed amount M, cause the change of R e , m and the designed parameters, Examples 9-12, Comparative Example 8, by regulating the proportion of lithium salt and other components in the second injection electrolyte, cause the change of R e , m and the designed parameters, Examples 13-17, Comparative Example 9, by regulating the designed amount of the positive electrode lithium supplement agent, cause the change of R e , m and the designed parameters. By comparing the experimental results of the above examples and comparative examples respectively, it can be known that: ① Controlling the first amount of additive A can make additive A enriched in the electrode sheet pores, and its reduction product can fully combine with the lithium supplement particles during the formation process, without causing insufficient oxygen capture ability due to insufficient amount, such as Comparative Example 5, or causing excessive CEI impedance and cycle deterioration due to excessive amount, such as Comparative Example 7. ② The R value (R z ) of the second injection electrolyte is low, the oxidation window of the free electrolyte is wide, and R e is also low, which can avoid the accumulation of a large amount of by-products; if the R value (R z ) of the second injection electrolyte is too high, more by-products will be produced, which will affect the capacity retention rate and energy efficiency after cycling. The reason why the R z value of the second injection is slightly higher than the R e value of the free electrolyte is that there may be a reaction current generated by the additive that is oxidized in advance in the second injection, and this part of the additive is slightly consumed during the injection and capacity test process. ③ Adding lithium supplement particles to the positive active layer, the lithium-rich positive electrode sheet releases lithium ions during the first charging process, using lithium supplement particles as "sacrificial agents" to supplement the irreversible lithium consumed by the formation of SEI film in the negative electrode, thereby improving the energy density of the battery. However, the release of lithium ions by lithium supplement particles also releases oxygen, which will accelerate the decomposition reaction of the components in the electrolyte at high voltage, especially during high-temperature formation or high-temperature standing aging, the reduction and oxidation decomposition of the electrolyte is more serious. This causes a large amount of methane, ethylene, carbon dioxide and other gases to overflow, a large amount of alkylated lithium and lithium carbonate to accumulate on the surface of the electrode, thereby causing energy efficiency to decline and shortening the cycle life. The content w of lithium supplement particles in the positive active layer has a suitable interval [0.3, 3], so that both the cycle life advantage and the energy efficiency can be achieved without serious deterioration.

[0164] Example 18 comprehensively adjusts the additive A of the first injection electrolyte, the composition of the second injection electrolyte, and the content of the positive electrode lithium supplement agent, and when the design parameters of the localized electrolyte are met, the cycle capacity retention rate and the energy efficiency after 1000 cycles are further improved at the same time, both of which exceed 90%, which is significantly improved compared with the comparative examples. It can be seen that the design requirements disclosed in the present application are universal for the interaction effects of injection process, electrolyte composition, and positive electrode lithium supplement.

[0165] Examples 19-24

[0166] The batteries were prepared according to the method described in Example 1, except that:

[0167] In Examples 19-23, the one- and two- injection electrolytes were consistent with Example 2.

[0168] In Example 24, the one- and two- injection electrolytes were consistent with Example 18.

[0169] The maximum voltage of the battery formation step was controlled according to the design value in Table 2, i.e., the control of Umax variation. In addition to the maximum voltage of the battery formation step, changes in other formation conditions during production, as long as they do not affect the implementation of the claims and can achieve the expected technical effects, are considered within the scope of technical protection.

[0170] Table 2

[0171]

[0172] Examples 19-24 evaluated the effects of the maximum formation voltage on the characteristics of the localized electrolyte, design parameters, and cycles in the two-injection process. The performance of Example 19, in which the formation voltage was too low to fully activate the lithium supplement, was only slightly different from that of Comparative Example 4, and was significantly different from the experimental results of Example 3, which had the same positive electrode design and electrolyte design. The cycle performance of Example 23 was poor because the high formation voltage caused the positive active material to be over-lithiated, resulting in irreversible damage; the severe oxidative decomposition of the electrolyte also consumed a large amount of active lithium source and produced electrochemically unstable products, which were dispersed in the free electrolyte. The test results of Examples 20 to 22 showed that the consumption of the ionic additive A and the oxidation stability of the electrolyte also changed with the variation of the formation voltage, mainly manifested as changes in the content of the ionic additive A in the non-free electrolyte and the Re of the free electrolyte, which mainly affected the changes in the design parameters m / R e , 1-m / M. When the design parameters exceed the protection range, it indicates that the ionic additive A in the non-free electrolyte cannot play its role of capturing oxygen radicals / oxygen, and / or the free electrolyte cannot maintain a fast ion channel. Example 24, which fine-tuned the formation voltage based on Example 18, can slightly improve the energy efficiency after cycling while maintaining the cycle capacity retention rate, with a maximum of 96%.

[0173] Although the embodiments of the present application have been shown and described above, it will be understood by those skilled in the art that the above embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements, and variations to the above embodiments within the scope of the present application.

Claims

1. A battery, characterized in that: include: Positive electrode sheet, negative electrode sheet, separator and electrolyte; wherein, The positive electrode plate includes a positive electrode active layer and a current collector, wherein the positive electrode active layer is arranged on the surface of the current collector, and the positive electrode active layer includes lithium supplement particles; The separator is arranged between the positive electrode sheet and the negative electrode sheet; The electrolyte includes a non-free electrolyte and a free electrolyte, and the non-free electrolyte includes the electrolyte in the pores of the positive electrode sheet, the electrolyte in the pores of the negative electrode sheet, and the electrolyte in the pores of the diaphragm; The non-free electrolyte includes an ionic additive, and the mass proportion m of the ionic additive in the non-free electrolyte is: 0.001%≤m≤2%; The R value R of the free electrolyte at the lithium potential e =0<R e <1; The ionic additive includes at least one of bis(oxalatoborate), difluorooxalatoborate, trioxalatophosphate, difluorobis(oxalatophosphate), and tetrafluorooxalatophosphate; During the preparation of the battery, the highest charging voltage of the formation treatment is 3.9V-4.6V.

2. The battery according to claim 1, characterized in that The battery meets the following conditions: 0<m / R e ≤2.5%; Wherein, m is the mass ratio of the ionic additive in the non-free electrolyte, R e is the R value of the free electrolyte at the potential relative to lithium.

3. The battery according to claim 1, characterized in that The mass proportion of the lithium supplement particles in the positive electrode active layer is 0.3%-3%.

4. The battery according to claim 3, characterized in that The lithium supplement particles include a matrix and a coating layer, wherein the coating layer is arranged on the periphery of the matrix.

5. The battery according to claim 4, characterized in that The matrix is ​​Li5FeO4; And / or, the coating layer comprises oxide and carbon, wherein the chemical formula of the oxide is Z x O y , Z is at least one selected from the group consisting of iron, cobalt, nickel, titanium, zinc, magnesium, aluminum, manganese, vanadium, chromium, zirconium, copper, niobium, tantalum, tungsten, yttrium and lanthanum, 1≤x≤3, 1≤y≤5; And / or, the coating layer has a thickness of 0.001 μm-1 μm.

6. A method for preparing the battery according to any one of claims 1 to 5, characterized in that: The steps of injecting electrolyte include: Performing a first electrolyte injection process; After the first liquid injection treatment, a chemical formation treatment is performed; After the chemical formation treatment, a second electrolyte injection treatment is performed. Wherein, the first electrolyte includes ionic additives.

7. The method according to claim 6, characterized in that The method satisfies the following conditions: 0.7≤(1-m) / M≤0.95, Wherein, m is the mass ratio of the ionic additive in the non-free electrolyte, and M is the mass ratio of the ionic additive in the first electrolyte; And / or, the R value R of the second electrolyte at the lithium potential is z 0.1≤R z ≤3; And / or, the maximum charging voltage of the formation treatment is 3.9V-4.6V.

8. The method according to claim 7, characterized in that The mass ratio of the first electrolyte to the second electrolyte is (6:4)-(9:1); And / or, the sum of the injection coefficients of the first electrolyte and the second electrolyte is 2.5g / Ah-5g / Ah.

9. An electrical device, characterized in that: A battery comprising the battery according to any one of claims 1 to 5, or a battery prepared by the method according to any one of claims 6 to 8.

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