Electrolyte combination, electrolyte injection method and battery

Abstract

The invention provides an electrolyte composition, a secondary liquid injection method and a battery. The electrolyte composition suitable for secondary liquid injection comprises a first electrolyte for primary liquid injection and a second electrolyte for secondary liquid injection, the first electrolyte comprises 0.01 to 5 weight percent of vinylene carbonate, 0.05 to 3 weight percent of a first additive, 0.01 to 5 weight percent of a second additive, 5 to 15 weight percent of lithium salt, 0.01 to 5 weight percent of a film-forming additive and the balance of a non-aqueous organic solvent; the second electrolyte comprises 5 to 30 weight percent of vinylene carbonate, 0.01 to 10 weight percent of first additive, 5 to 15 weight percent of lithium salt and the balance of non-aqueous organic solvent; wherein the first additive comprises a compound as shown in a formula 1; the second additive comprises a compound as shown in a formula 2. The electrolyte composition provided by the invention can enable the battery to present low gas yield, low initial DCR and normal-temperature and high-temperature cycle performance.

Description

Technical Field

[0001] The invention relates to an electrolyte combination, in particular to an electrolyte combination, a liquid injection method and a battery, belonging to the technical field of lithium ion batteries. Background Art

[0002] With the rapid development of pure electric vehicles, smart homes, power tools, smart transportation and other markets, consumers' requirements for battery performance are constantly increasing. Lithium-ion batteries are widely used in consumer electronics and energy storage and power batteries due to their high specific energy, long cycle life and low self-discharge.

[0003] Vinylene carbonate and sulfonate compounds (CAS: 2520352-94-5) are used as additives in the electrolyte, which can improve the electrochemical performance of the lithium iron cathode system. However, they can also lead to problems such as too high initial DCR, gas production during formation, and too fast DCR growth rate during the cycle, resulting in large gas production of the battery and poor room temperature cycle performance and high temperature cycle performance.

[0004] Therefore, how to achieve comprehensive improvement in initial DCR, gas production, and normal temperature and high temperature cycle performance is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0005] The present invention provides an electrolyte combination, which is suitable for secondary injection and can achieve comprehensive improvement of the initial DCR, gas production, and normal temperature and high temperature cycle performance of a battery.

[0006] The present invention provides a liquid injection method, which can give full play to the advantages of the electrolyte combination, so that the battery presents low initial DCR, low gas production, and excellent room temperature and high temperature cycle performance.

[0007] The present invention also provides a battery having low initial DCR, low gas generation, and excellent room temperature and high temperature cycle performance.

[0008] The present invention provides an electrolyte combination suitable for secondary liquid injection, which includes a first electrolyte for primary liquid injection and a second electrolyte for secondary liquid injection;

[0009] The first electrolyte comprises 0.01-5wt% of vinylene carbonate, 0.05-3wt% of a first additive, 0.01-5wt% of a second additive, 5-15wt% of a lithium salt, 0.01-5wt% of a film-forming additive, and the balance of a non-aqueous organic solvent;

[0010] The second electrolyte comprises 5-30wt% of vinylene carbonate, 0.01-10wt% of a first additive, 5-15wt% of a lithium salt, and the remainder of a non-aqueous organic solvent; wherein the first additive comprises a compound represented by Formula 1;

[0011] Wherein, the first additive includes a compound represented by Formula 1:

[0012]

[0013] The second additive includes a compound shown in Formula 2:

[0014]

[0015] R1, R2, and R3 are independently selected from substituted or unsubstituted C1-C3 alkyl groups, and the substituents of R1, R2, and R3 include at least one of halogen and hydroxyl groups.

[0016] In the electrolyte combination suitable for secondary injection as described above, the second additive includes at least one of trimethyl phosphate, triethyl phosphate, and tripropyl phosphate.

[0017] The electrolyte combination suitable for secondary injection as described above, wherein the ratio of the mass percentage of vinylene carbonate in the second electrolyte to the mass percentage of vinylene carbonate in the first electrolyte is 9-36;

[0018] And / or, the ratio of the mass percentage of the first additive in the second electrolyte to the mass percentage of the first additive in the first electrolyte is 5-16.7.

[0019] The electrolyte combination suitable for secondary injection as described above, wherein the film-forming additive includes at least one of fluoroethylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, 1,3-propane sultone, tris(trimethylsilyl)phosphate, hexamethylene diisocyanate, vinyl ethylene carbonate, methylene methanedisulfonate, lithium difluorooxalatophosphate, and lithium bis(oxalatoborate).

[0020] In the electrolyte combination suitable for secondary injection as described above, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide.

[0021] The electrolyte combination suitable for secondary injection as described above, wherein the non-aqueous organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, diethyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate.

[0022] The electrolyte combination suitable for secondary injection as described above, wherein the first electrolyte comprises 0.5-2wt% of vinylene carbonate, 0.3-1wt% of a first additive, 0.3-1wt% of a second additive, 10-15wt% of a lithium salt, 1-2wt% of a film-forming additive, and the remainder of a non-aqueous organic solvent;

[0023] The second electrolyte includes 10-20 wt % of vinylene carbonate, 3-5 wt % of a first additive, 10-15 wt % of a lithium salt and the balance of a non-aqueous organic solvent.

[0024] The present invention also provides a liquid injection method, wherein the liquid injection is performed using the electrolyte combination suitable for secondary liquid injection as described above, comprising the following steps:

[0025] 1) injecting the first electrolyte into the battery cell and performing a formation treatment to obtain a first battery cell;

[0026] 2) injecting the second electrolyte into the first battery cell and performing an aging treatment to obtain a battery.

[0027] The liquid injection method as described above, wherein the battery cell uses lithium iron phosphate as the positive electrode active material, and a lithium supplement is added to the positive electrode, wherein the lithium supplement includes at least one of Li3N, Li2S, Li5FeO4, Li2O2, and Li2NiO2;

[0028] And / or, the mass percentage of the lithium supplement agent in the positive electrode active material layer is 1-3%.

[0029] The present invention also provides a battery prepared by the above-mentioned liquid injection method.

[0030] The present invention applies an electrolyte combination to a lithium ion battery. When the battery is first injected, a low content of vinyl carbonate (VC), a low content of a first additive, and a second additive are used. The first electrolyte forms an SEI film and a CEI film on the surface of the positive and negative active materials. The SEI film is not thick and is uniform and dense, has good ion conductivity, low impedance, high elasticity, and good rate performance. The first additive promotes the improvement of the positive electrode CEI film, so that the high-temperature cycle performance is guaranteed. Since the amount of VC used in the first injection is not large, most of it participates in the film forming process, and the gas production caused by VC is not large. The low content of the first additive can not only avoid the initial DCR being too high, but also cooperate with the low content of VC to solve the problem of too fast decay of the cycle DCR caused by too low VC, and achieve the effect of low initial DCR and slow DCR decay during the cycle. Moreover, after adding an appropriate amount of the second additive, the second additive It can remove the oxygen generated during high-temperature storage. At the same time, the second additive also has a high antioxidant capacity, which can further inhibit the decomposition of the electrolyte, thereby further reducing the generation of gas. In addition, under the action of the first additive, the first additive and the second additive can cooperate with each other, which is not only beneficial to improve the film formation uniformity and stability of the SEI film and the CEI film, but also to improve the high-temperature cycle performance and electrochemical stability of the battery, and effectively inhibit the generation of gas. On the other hand, when the battery is filled with liquid for the second time, a high content of VC and a high content of the first additive are used. The main function is to improve the room temperature cycle and high-temperature storage performance. Because the SEI film will be consumed and damaged during high-temperature storage and room temperature circulation, and the decomposition of the electrolyte will be aggravated. The addition of VC and the first additive is mainly to repair the SEI film and prevent the electrolyte from decomposing at the damaged part of the membrane and causing gas production, thereby reducing the gas production and improving the room temperature and high temperature cycle performance of the battery.

[0031] The liquid injection method provided by the present invention can apply the electrolyte combination to the battery, so that the initial DCR of the battery is low, the gas production is low, and the normal temperature and high temperature cycle performance is high.

[0032] The battery provided by the present invention has low initial DCR, low gas production, and can present excellent normal temperature and high temperature cycle performance. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides an electrolyte combination suitable for secondary liquid injection, comprising a first electrolyte for primary liquid injection and a second electrolyte for secondary liquid injection;

[0035] The first electrolyte comprises 0.01-5wt% of vinylene carbonate, 0.05-3wt% of a first additive, 0.01-5wt% of a second additive, 5-15wt% of a lithium salt, 0.01-5wt% of a film-forming additive, and the balance of a non-aqueous organic solvent;

[0036] The second electrolyte comprises 5-30 wt % of vinylene carbonate, 0.01-10 wt % of a first additive, 5-15 wt % of a lithium salt, and the balance of a non-aqueous organic solvent;

[0037] Wherein, the first additive includes a compound shown in Formula 1:

[0038]

[0039] The second additive includes a compound shown in Formula 2:

[0040]

[0041] R1, R2, and R3 are independently selected from C1-C3 substituted or unsubstituted alkyl groups, and the substituents of R1, R2, and R3 include at least one of halogen and hydroxyl groups.

[0042] The electrolyte combination of the present invention comprises a first electrolyte and a second electrolyte, wherein the first electrolyte is used for primary injection and the second electrolyte is used for secondary injection. The primary injection of the present invention refers to the first injection, after which the electrolyte is infiltrated into the electrode through a formation treatment to participate in a chemical reaction and realize the conversion of chemical energy into electrical energy, and the secondary injection refers to the addition of an electrolyte after formation to supplement the electrolyte of the primary injection.

[0043] The first electrolyte of the present invention comprises 0.01-5wt% of vinylene carbonate, 0.05-3wt% of a first additive, 0.01-5wt% of a second additive, 5-15wt% of a lithium salt, 0.01-5wt% of a film-forming additive, and a balance of a non-aqueous organic solvent, that is, the mass percentage of vinylene carbonate in the first electrolyte is 0.01-5wt%, for example, 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt% , 4.5wt% or 5wt%, etc., the mass percentage of the first additive is 0.05-3wt%, for example, 0.05wt%, 0.08wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.1wt% %, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt% or 3wt%, etc., the mass percentage of the second additive is 0.01-5wt%, for example, 0.01wt%, 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc., the mass percentage of the lithium salt is The mass percentage is 5-15wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%, etc., the mass percentage of the film-forming additive is 0.01-5wt%, for example, 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%, etc., and the rest is non-aqueous organic solvent.

[0044] The second electrolyte of the present invention comprises 5-30wt% of vinylene carbonate, 0.01-10wt% of a first additive, 5-15wt% of a lithium salt and the remainder of a non-aqueous organic solvent, that is, the mass percentage of vinylene carbonate in the second electrolyte is 5-30wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, 52wt%, 53wt%, 54wt%, 55wt%, 56wt%, 57wt%, 58wt%, 59wt%, 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71 wt%, 28wt%, 29wt% or 30wt%, etc., the mass percentage of the first additive is 0.01-10wt%, for example, 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, etc., the mass percentage of the lithium salt is 5-15wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%, etc., and the rest is a non-aqueous organic solvent.

[0045] The first additive of the present invention includes a compound having a structural formula of Formula 1, and the second additive includes a compound having a structural formula of Formula 2, wherein R1, R2, and R3 are independently selected from substituted or unsubstituted C1-C3 alkyl groups, and the substituents of R1, R2, and R3 include at least one of halogen and hydroxyl groups. The substituted or unsubstituted C1-C3 alkyl group of the present invention refers to a substituted or unsubstituted chain alkyl group with 1-3 carbon atoms or a substituted or unsubstituted cycloalkyl group with 3 carbon atoms. The substituents of R1, R2, and R3 include at least one of halogen and hydroxyl groups. When specified as an alkyl group with a specific carbon number, all geometric isomers with the carbon number are included, that is, R1, R2, and R3 of the present invention can be independently selected from -CH3, -CH2CH3, -CH2CH2CH3, -CH2F, -CF3, -CH2Cl, -CCl3, -CBr3, -CH2CF 3、 -CH2CH2OH, etc.

[0046] The electrolyte of the present invention includes a lithium salt and a non-aqueous organic solvent. The present invention does not impose any special restrictions on the selection of the lithium salt, as long as a stable electrolyte with good lithium conductivity can be prepared. For example, the lithium salt can be selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide. Similarly, the present invention does not impose any special restrictions on the selection of the non-aqueous organic solvent, as long as the lithium salt can be completely dissolved to prepare a stable electrolyte. For example, the organic solvent can be selected from carbonates, carboxylates and ethers.

[0047] The film-forming additive of the present invention refers to an additive that adds a film layer to the surface of the positive and negative electrode materials of the battery to control the discharge and charge process of the battery, thereby improving the cycle stability, electrochemical performance and life of the electrode.

[0048] The first additive of the present invention has a strong polarity, a weak interaction with other non-polar molecules, less friction and collision between molecules, and better stability compared with other sulfate compounds; compared with other sulfate compounds, the first additive also has better thermal stability, not only can it be stored at room temperature without low-temperature storage, it can operate stably over a wide voltage range, and has good cycle life and capacity retention rate, and also has better high-temperature performance, and can maintain relatively stable electrochemical properties in a high-temperature environment, thereby extending the service life of the battery. Moreover, the oxidation and reduction potentials of the first additive are both before those of conventional electrolyte solvents. During the pre-charging process of the battery, it will be oxidized at the positive electrode and reduced at the negative electrode before the solvent, and then it is easy to form a dense CEI film at the positive electrode and a dense SEI film at the negative electrode. Among them, the first additive will form a small amount of inorganic salts (Li2SO4, Li2O) in the CEI film formed by the decomposition of the positive electrode, which improves the rigidity, flexibility and stability of the CEI film and inhibits the decomposition of the electrolyte. The CEI film formed by the first additive can also reduce the electrochemical impedance of the positive electrode, accelerate the transmission rate of lithium ions, and help form a more stable electrode-electrolyte interface, reduce the internal resistance and interface reaction of the battery, and protect the positive electrode. In addition, it can also inhibit the dissolution of transition metal elements in the active material of the positive electrode plate, thereby reducing the attenuation of high-temperature cycle capacity. Moreover, lithium carbonate will be generated in the SEI film formed by the first additive, and lithium carbonate helps to improve the film formation uniformity and stability of the SEI film. However, when the amount of the first additive added is too large, the initial DCR of the battery will increase, and the room temperature kinetics will be poor, resulting in a drop in the room temperature cycle performance of the battery; when the amount of the first additive added is too small, it is difficult for the battery to retain its basic performance, the cycle DCR decays too quickly, and the room temperature cycle performance is poor.

[0049] The second additive of the present invention can preheat and decompose phosphorus free radicals and oxygen free radicals, which will form phosphorus oxide compounds. The phosphorus oxide compounds can react with oxygen to remove the oxygen generated during high-temperature storage. Moreover, the second additive also has a high antioxidant capacity, which can further inhibit the decomposition of the electrolyte, thereby further reducing the generation of gas and reducing the gas production of the battery.

[0050] The present invention uses the above scheme to apply the electrolyte combination to the lithium ion battery, so that the initial DCR of the battery is low, the gas production is low, and the battery can exhibit excellent room temperature and high temperature cycle performance. The inventor believes that the reason may be that, on the one hand, when the battery is first filled with liquid, a low content of VC, a low content of the first additive, and a second additive are used. During the first charging process, under the action of the first additive, the electrolyte will form SEI films and CEI films on the surfaces of the positive and negative active materials. The low content of VC helps to form a thin and uniformly dense SEI film with good ion conductivity, low impedance, high elasticity, and good rate performance. The first additive promotes the improvement of the positive electrode CEI film, so that the high-temperature cycle performance is guaranteed. Since the amount of VC used in the first filling is not large, most of it participates in the film formation process, so during high-voltage formation, the gas production caused by VC is not large. More importantly, the low content of the first additive can not only avoid the initial DCR being too high, but also cooperate with the low content of VC to solve the problem of too fast decay of the cycle DCR caused by too low VC, and achieve the effect of low initial DCR and slow decay of DCR during the cycle. Moreover, when an appropriate amount of the second additive is added, the second additive can remove the gas generated during high-temperature storage. Oxygen, and the second additive also has a high antioxidant capacity, which can further inhibit the decomposition of the electrolyte, thereby further reducing the generation of gas; in addition, under the action of the first additive, the first additive and the second additive can cooperate with each other, which is not only beneficial to improve the film formation uniformity and stability of the SEI film and the CEI film, but also can improve the high-temperature cycle performance and electrochemical stability of the battery, and effectively inhibit the generation of gas; on the other hand, when the battery is injected for the second time, a high content of VC and a high content of the first additive are used, the main function is to improve the room temperature cycle and high temperature storage performance, because the SEI film will be consumed and damaged during high temperature storage and room temperature cycle and will aggravate the decomposition of the electrolyte. The addition of VC and the first additive is mainly to repair the SEI film and prevent the electrolyte from decomposing at the damaged part of the membrane to cause gas production, thereby reducing the gas production and improving the room temperature and high temperature cycle performance of the battery. In addition, most of the first additives in the second injection participate in the repair of the SEI film, which can avoid the increase of the DCR of the battery or the rapid decay of the cycle DCR, thereby improving the room temperature cycle performance of the battery.

[0051] In a specific embodiment, the second additive includes at least one of trimethyl phosphate, triethyl phosphate, and tripropyl phosphate. When the second additive is selected from the above compounds, the second additive can further remove the oxygen generated during high-temperature storage, and the second additive has a higher antioxidant capacity, which can further inhibit the decomposition of the electrolyte and reduce the generation of gas. At the same time, the second additive and the first additive have a better synergistic effect, which can improve the film formation uniformity and stability of the SEI film and the CEI film to a greater extent, thereby further improving the room temperature and high temperature cycle performance of the battery, and effectively inhibiting the generation of gas.

[0052] In a specific embodiment, the ratio of the mass percentage of vinylene carbonate in the second electrolyte to the mass percentage of vinylene carbonate in the first electrolyte is 9-36, for example, 9, 10, 15, 20, 25, 30, 35 or 36. When the ratio of the mass percentage of vinylene carbonate in the second electrolyte to the first electrolyte is within the above range, the first electrolyte and the second electrolyte can further cooperate, and the vinylene carbonate can form a thin, uniform and dense SEI film during the first charge and discharge, and the vinylene carbonate in the second electrolyte can better repair the SEI film during the second injection, so that the room temperature and high temperature cycle performance of the battery is better.

[0053] In a specific embodiment, the ratio of the mass percentage of the first additive in the second electrolyte to the mass percentage of the first additive in the first electrolyte is 5-16.7, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 16.7, etc. When the mass ratio of the second electrolyte to the first additive in the first electrolyte is within the above range, the first electrolyte and the second electrolyte can further cooperate with each other, and the first additive can further cooperate with vinylene carbonate during the first charge and discharge to construct a CEI film and SEI film with excellent lithium conductivity and low thickness, and the CEI film and SEI film can be further repaired after the second injection, so as to avoid the side reaction caused by the contact between the electrolyte and the positive and negative electrode materials due to the insufficient stability of the SEI film and the CEI film, thereby further reducing the gas production of the battery, and making the battery present higher room temperature and high temperature cycle performance.

[0054] In a specific embodiment, the film-forming additive includes at least one of fluoroethylene carbonate, vinyl sulfate, lithium difluorooxalate borate, 1,3-propane sultone, tris(trimethylsilyl) phosphate, hexamethylene diisocyanate, vinyl ethylene carbonate, methylene methane disulfonate, lithium difluorooxalate phosphate, and lithium bis(oxalate borate). When the film-forming additive is selected from the above compounds, the film-forming additive can better synergize with vinyl carbonate, the first additive, and the second additive to generate a SEI film and a CEI film with higher stability and better lithium conductivity, avoid oxidative decomposition of the electrolyte to a greater extent, reduce the gas production of the battery, and further improve the room temperature and high temperature cycle performance of the battery.

[0055] In a specific embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide. When the lithium salt is selected from the above compounds, the conductivity and stability of the electrolyte can be further improved, and it can be better matched with vinylene carbonate, the first additive and the film-forming additive, thereby further improving the room temperature and high temperature cycle performance of the battery.

[0056] In a specific embodiment, the non-aqueous organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, diethyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate. When the non-aqueous organic solvent is selected from the above solvents, the solubility of the lithium salt in the electrolyte can be increased, thereby improving the conductivity of the electrolyte, and the viscosity of the electrolyte is appropriate, which is conducive to improving the transmission rate of lithium ions, thereby further improving the room temperature and high temperature cycle performance of the battery.

[0057] In a specific embodiment, the first electrolyte includes 0.5-2wt% of vinylene carbonate, 0.3-1wt% of the first additive, 0.3-1wt% of the second additive, 10-15wt% of lithium salt, 1-2wt% of the film-forming additive and the balance of non-aqueous organic solvent; the second electrolyte includes 10-20wt% of vinylene carbonate, 3-5wt% of the first additive, 10-15wt% of lithium salt and the balance of non-aqueous organic solvent. When the combination and mass content of the first electrolyte and the second electrolyte are within the above range, the first electrolyte and the second electrolyte can be further matched, so that the battery can construct a SEI film and CEI film with high stability and excellent lithium conductivity during the first charge and discharge process, thereby reducing the initial DCR of the battery, reducing the gas production of the battery, and being able to supplement and repair the SEI film and CEI film of the battery after the second injection, avoiding the damage of the SEI film and CEI film leading to a decrease in battery performance, thereby further improving the normal temperature and high temperature cycle performance of the battery.

[0058] The present invention does not limit the preparation method of the first electrolyte. For example, vinylene carbonate, the first additive, the second additive, the lithium salt, the film-forming additive and the non-aqueous organic solvent may be mixed according to the mass percentage.

[0059] The present invention does not limit the preparation method of the second electrolyte. For example, vinylene carbonate, the first additive, the lithium salt and the non-aqueous organic solvent may be mixed according to the mass percentage.

[0060] The present invention also provides a liquid injection method, wherein the liquid injection is performed using the above-mentioned electrolyte combination suitable for secondary liquid injection, comprising the following steps:

[0061] 1) injecting a first electrolyte into a battery cell and performing a formation treatment to obtain a first battery cell;

[0062] 2) Injecting the second electrolyte into the first battery cell and performing an aging treatment to obtain a battery.

[0063] Specifically, in step 1), a battery cell is prepared, and a first electrolyte is injected into the battery cell. After the injection, the battery cell is left to stand for a period of time at a certain temperature to allow the first electrolyte to completely penetrate the battery cell, and then a formation treatment is performed. After the formation treatment, the first electrolyte forms a CEI film and a SEI film on the surface of the positive and negative electrodes to obtain a first battery cell.

[0064] The present invention uses lithium iron phosphate as the positive electrode active material, and not only can select lithium iron phosphate as the positive electrode active material, but also includes doping, coating and conductivity-increasing treatment of the lithium iron phosphate.

[0065] The present invention does not limit the negative electrode of the battery cell, and it can be selected according to actual needs. For example, the negative electrode active material can be selected from active materials such as graphite.

[0066] The present invention does not limit the temperature and time of standing still, which can be selected according to actual needs, for example, standing still at 45° C. for 2 hours.

[0067] The present invention does not limit the specific parameters of the formation, which can be selected according to actual needs. For example, the following operations can be performed in sequence: under a negative pressure of -60 KPa, 0.05C constant current charging for 5 minutes, 0.1C constant current charging for 10 minutes, breaking the vacuum and standing for 10 minutes, then, the negative pressure for the first 30 minutes is -80 KPa, and then it is reduced to -20 KPa at -20 KPa / 10 minutes, and maintained at -20 KPa. In this stage, 0.15C constant current charging is performed for 120 minutes. min; conventional formation, negative pressure -10KPa, constant current and constant voltage charging, 0.2C constant current to 3.65V, cut off current to 0.05C, break vacuum and let stand for 10min, negative pressure -30 to -40KPa (the formation gas can be removed in time to ensure the stability and consistency of the interface), constant current and constant voltage charging, 0.1C constant current 4.4V, cut off current to 0.05C, break vacuum and let stand for 0min, 0.5C constant current discharge to 50% SOC, to obtain the first battery cell.

[0068] Step 2), injecting the second electrolyte into the first battery cell, and then performing an aging treatment at a certain temperature to finally obtain a battery.

[0069] The present invention does not limit the aging temperature and aging time, which can be selected according to actual needs. For example, the aging can be performed at 45° C. for 24 hours and then at 25° C. for 14 hours.

[0070] The present invention does not limit the mass ratio of the first electrolyte to the second electrolyte, and can be selected according to actual needs. For example, the mass ratio of the first electrolyte to the second electrolyte can be controlled to be 85:15.

[0071] The present invention applies the first electrolyte and the second electrolyte to the battery through the above-mentioned injection method, so that the battery constructs a SEI film and a CEI film with excellent lithium conductivity and high stability in the formation stage after the first injection, and then repairs the damaged SEI film and CEI film in the aging stage after the second injection, thereby ensuring that the SEI film and the CEI film play their roles, thereby reducing the initial DCR of the battery, reducing the gas production, and improving the normal temperature and high temperature cycle performance of the battery.

[0072] In a specific embodiment, the battery core uses lithium iron phosphate as the positive electrode active material, and a lithium supplement is added to the positive electrode active material layer, and the lithium supplement includes at least one of Li3N, Li2S, Li5FeO4, Li2O2, and Li2NiO2. When the lithium supplement is added to the positive electrode active material layer, and the lithium supplement is selected from the above compounds, the lithium loss caused by the battery during the first charge and discharge process can be supplemented by the lithium supplement, thereby improving the lithium conductivity of the battery, and further improving the normal temperature and high temperature cycle performance of the battery.

[0073] In a specific embodiment, the mass percentage of the lithium supplement in the positive electrode active material layer is 1-3%, for example, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%. When the mass percentage of the lithium supplement is within the above range, the lithium consumed in the construction of the SEI film can be completely offset by the lithium supplement, so that the lithium conductivity of the battery is better, thereby making the battery's room temperature and high temperature cycle performance better.

[0074] The present invention also provides a battery prepared by the above-mentioned liquid injection method. The battery has low initial DCR, low gas production, and exhibits excellent normal temperature and high temperature cycle performance.

[0075] In a specific embodiment, the battery is a lithium-ion battery, and the positive electrode active material of the positive electrode plate includes: LiFePO4 and / or Li a Ni b Co c M1 d M2 e O f R g and / or LiMn x Fe 1－x PO4, wherein 1≤a≤1.2, 0.6≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤0.2, b+c+d+e=1, 1≤f≤2, 0≤g≤1, f+g=2; M1 includes Mn and / or Al, M2 includes at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and R includes at least one of N, F, S, and Cl; 0≤x≤1.

[0076] When the positive electrode active material is the above material, the interfacial stability between the positive electrode active material and the electrolyte is crucial to the cycle life and safety of the battery. Secondary injection can reduce the contact time between the electrolyte and the electrode material, thereby reducing the occurrence of interface side reactions and improving the stability of the battery; and secondary injection can improve the conductivity by optimizing the composition of the electrolyte, thereby improving the charge and discharge efficiency of the battery. Preferably, when the positive electrode active material is lithium iron phosphate, secondary injection can improve the cycle stability of the battery and extend the service life of the battery; and can reduce the risk of thermal runaway of the battery during the charge and discharge process and improve the safety of the battery.

[0077] The negative electrode active material in the negative electrode sheet includes at least one of graphite, silicon-based material, lithium metal and lithium titanate.

[0078] In a specific embodiment, the positive electrode sheet of the battery includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode current collector includes a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector includes a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] In a specific embodiment, the positive electrode active material layer further includes a binder, and the binder includes polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, and the like.

[0080] In a specific embodiment, the positive electrode active material layer further includes a conductive agent, for example, the conductive agent includes superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, etc.

[0081] In a specific embodiment, the negative electrode sheet of the battery includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector includes a metal foil, such as a copper foil. The negative electrode active material in the negative electrode sheet includes at least one of graphite, silicon-based materials, lithium metal and lithium titanate. The negative electrode active material layer also includes a binder, a conductive agent and other additives. For example, the binder may include styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylamide (PAM), etc.; the conductive agent includes superconducting carbon, acetylene black, carbon black, graphene, etc.; the additive includes a thickener, such as sodium carboxymethyl cellulose (CMC-Na), etc.

[0082] In a specific embodiment, the battery of the present invention further comprises a separator. The present invention has no particular limitation on the type of separator, and any porous separator with good chemical stability and mechanical stability can be selected. For example, the separator includes a polyethylene separator, a polypropylene separator, a PE ceramic coated separator, etc. The separator can be a single-layer film or a multi-layer composite film.

[0083] The battery of the present application may include a battery cell form, a battery module form and a battery pack form, which may be selected according to the application of the battery. Generally, a battery module may be formed by assembling battery cells, and a battery pack may be assembled by assembling battery modules.

[0084] The present invention is further described in detail through specific examples.

[0085] Example 1

[0086] The preparation process of the battery provided in this embodiment includes the following steps:

[0087] 1. Preparation of the first electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), the solvents ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed uniformly in a mass ratio of 3:5:2, and fully dried lithium hexafluorophosphate and lithium bisfluorosulfonyl imide are quickly added to the mixed solvent, and the electrolyte additive is added, and the electrolyte is fully mixed to obtain an electrolyte. Among them, the mass percentage of vinylene carbonate is 0.1%, the mass percentage of the first additive is 0.3%, the mass percentage of the second additive is 0.6%, the mass percentage of lithium hexafluorophosphate is 11%, the mass percentage of lithium bisfluorosulfonyl imide is 2%, the mass percentage of fluoroethylene carbonate is 1%, and the mass percentage of vinyl sulfate is 0.5%. Among them, the first additive is the compound shown in Formula 1 (CAS No.: 2520352-94-5), and the second additive is trimethyl phosphate (TMP, CAS No.: 512-56-1).

[0088] 2. Preparation of the second electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), the solvents of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed uniformly in a mass ratio of 3:5:2, and fully dried lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are quickly added to the mixed solvent, and an electrolyte additive is added, and the electrolyte is fully mixed to obtain an electrolyte. Among them, the mass percentage of vinylene carbonate is 18%, the mass percentage of the first additive is 5%, the mass percentage of lithium hexafluorophosphate is 11%, and the mass percentage of lithium bis(fluorosulfonyl)imide is 2%.

[0089] 3. Preparation of positive electrode sheet: Mix the positive electrode active material lithium iron phosphate, lithium supplement (Li5FeO4), binder polyvinylidene fluoride (PVDF), and conductive agent in a weight ratio of 92:3:3:2, add N-methylpyrrolidone (NMP), and stir under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; evenly coat the positive electrode slurry on the positive electrode current collector aluminum foil with a coating amount of 35g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and slitting are performed. After slitting, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the positive electrode sheet.

[0090] 4. Preparation of negative electrode sheet: Mix the negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber in a weight ratio of 95:1.5:1:2.5, add deionized water, and obtain negative electrode slurry under the action of a vacuum mixer; evenly coat the negative electrode slurry on the negative electrode current collector copper foil with a coating amount of 20g / m 2After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and slitting are performed. After slitting, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0091] 5. The positive electrode sheet, negative electrode sheet and separator (with 8 μm thick polyethylene porous film as separator) prepared according to the above process are made into a battery cell through a lamination process. After the battery cell is dried for 48 hours, the first electrolyte is injected, soaked at 45°C for 2 hours, and then left at room temperature for 24 hours; then a formation treatment is performed, which includes the following operations in sequence: under a negative pressure of -60KPa, 0.05C constant current charging for 5 minutes, 0.1C constant current charging for 10 minutes, breaking the vacuum and standing for 10 minutes, then, the negative pressure is -80KPa for the first 30 minutes, and then reduced to -2 at a rate of -20KPa / 10min. 0KPa, maintain -20KPa, at this stage, 0.15C constant current charging for 120min, conventional formation, negative pressure -10KPa, constant current and constant voltage charging, 0.2C constant current to 3.65V, cut-off current to 0.05C, break vacuum and let stand for 10min, positive electrode lithium supplement activation pre-lithiation, negative pressure -30 to -40KPa (formation gas can be removed in time to ensure stable and consistent interface), constant current and constant voltage charging, 0.1C constant current 4.4V, cut-off current to 0.05C, break vacuum and let stand for 10min, 0.5C constant current discharge to 50% SOC, to obtain the first battery cell;

[0092] Subsequently, the second electrolyte was injected into the first battery cell, and the battery cell was aged at 45° C. for 24 hours and then at 25° C. for 14 hours to obtain a battery; the weight ratio of the first electrolyte to the second electrolyte was 85:15.

[0093] The preparation process of the batteries of Examples 2-31 and Comparative Examples 1-10 is substantially the same as that of Example 3, and the specific parameters are shown in Table 1.

[0094] Embodiment 32

[0095] The preparation process of the battery provided in this embodiment is substantially the same as that of embodiment 3, except that the lithium supplement used is Li2O2.

[0096] Embodiment 33

[0097] The preparation process of the battery provided in this embodiment is substantially the same as that of embodiment 3, except that the lithium supplement agent used is Li2NiO.

[0098] Embodiment 34

[0099] The preparation process of the battery provided in this embodiment is substantially the same as that of embodiment 3, except that the positive electrode material used is LiNi 0.8 Co 0.1 Mn 0.1 .

[0100] Embodiment 35

[0101] The preparation process of the battery provided in this embodiment is substantially the same as that of embodiment 3, except that the positive electrode material used is LiNi 0.5 Co 0.2 Mn 0.3 .

[0102] Comparative Example 11

[0103] The preparation process of the battery provided in this comparative example comprises the following steps:

[0104] 1. Preparation of electrolyte: In a glove box filled with argon (water content <10ppm, oxygen content <1ppm), the solvents ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed uniformly in a mass ratio of 3:5:2, and fully dried lithium hexafluorophosphate and lithium bisfluorosulfonyl imide are quickly added to the mixed solvent, and the electrolyte additive is added, and the electrolyte is fully mixed to obtain an electrolyte. Among them, the mass percentage of vinylene carbonate is 3.6%, the mass percentage of the first additive is 1.0%, the mass percentage of the second additive is 0.6%, the mass percentage of lithium hexafluorophosphate is 12.5%, the mass percentage of lithium bisfluorosulfonyl imide is 2%, the mass percentage of fluoroethylene carbonate is 1%, and the mass percentage of vinyl sulfate is 0.5%. Among them, the first additive is the compound shown in Formula 1 (CAS No.: 2520352-94-5), and the second additive is trimethyl phosphate (TMP, CAS No.: 512-56-1).

[0105] 2. Preparation of positive electrode sheet: Mix the positive electrode active material lithium iron phosphate, lithium supplement (Li5FeO4), binder polyvinylidene fluoride (PVDF), and conductive agent in a weight ratio of 92:3:3:2, add N-methylpyrrolidone (NMP), and stir in a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; evenly coat the positive electrode slurry on the positive electrode current collector aluminum foil with a coating amount of 35g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and slitting are performed. After slitting, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the positive electrode sheet.

[0106] 4. Preparation of negative electrode sheet: Mix the negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber in a weight ratio of 95:1.5:1:2.5, add deionized water, and obtain negative electrode slurry under the action of a vacuum mixer; evenly coat the negative electrode slurry on the negative electrode current collector copper foil with a coating amount of 20g / m 2After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and slitting are performed. After slitting, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0107] 5. The positive electrode sheet, negative electrode sheet and separator (with 8 μm thick polyethylene porous film as separator) prepared according to the above process are made into battery cells through lamination process, and the battery cells are dried for 48 hours, and then injected with electrolyte, soaked at 45°C for 2 hours, and then left at room temperature for 24 hours; then chemical treatment is carried out, and the chemical treatment includes the following operations in sequence: negative pressure -60KPa, 0.05C constant current charging for 5 minutes, 0.1C constant current charging for 10 minutes, breaking vacuum and standing for 10 minutes, then, negative pressure -80KPa for the first 30 minutes, then reduced to -20KPa at -20KPa / 10min, and maintained at -20KPa. This stage The process was carried out by charging at a constant current of 0.15C for 120 min, conventional formation, constant current and constant voltage charging at a negative pressure of -10 KPa, constant current of 0.2C to 3.65V, current cutoff to 0.05C, breaking the vacuum and letting it stand for 10 min, positive electrode lithium replenishment activation and pre-lithiation, negative pressure of -30 to -40 KPa (formation gas can be removed in time to ensure stable and consistent interface), constant current and constant voltage charging, constant current of 0.1C to 4.4V, current cutoff to 0.05C, breaking the vacuum and letting it stand for 10 min, constant current discharge at 0.5C to 50% SOC, and obtaining a cell. The cell was aged at 45°C for 24 h, and then aged at 25°C for 14 h to obtain a battery.

[0108] Table 1

[0109]

[0110]

[0111]

[0112] Test example

[0113] The room temperature cycle performance and high temperature cycle performance of the batteries obtained in the examples and comparative examples were tested. The test method is as follows, and the test results are shown in Table 1.

[0114] Normal temperature cycle performance test: At 25°C, the lithium-ion battery is charged and discharged for 1000 times at 1C current, and the cycle capacity retention rate (%) = (1000th discharge capacity / 1st cycle discharge capacity) × 100%, see Table 2.

[0115] High temperature cycle performance test: At 45°C, the lithium-ion battery was charged and discharged 500 times at 1C current, and the cycle capacity retention rate (%) = (500th discharge capacity / 1st cycle discharge capacity) × 100%, see Table 2.

[0116] Gas production test: The gas production ΔV is measured by the water displacement method, ΔV = (m1-m2) / ρ, where m1 is the battery mass before formation, m2 is the battery mass after formation, and ρ is the density of liquid water, see Table 2.

[0117] DC impedance DCR test: Place the battery in a 25℃ environment, discharge at 1C constant current to a cut-off voltage of 2.5V, let stand for 5 minutes, charge at 1C constant current and constant voltage to an upper limit voltage of 4.2V, with a cut-off current of 0.05C, and then discharge at 1C constant current for 30 minutes. Place the battery adjusted to 50% SOC at 25℃, let stand for 5 minutes, and discharge at 2C constant current for 30 seconds. The discharge current during 2C discharge is I 2C Record the initial voltage V0 and the voltage V1 after 30s of discharge. The discharge DC internal resistance calculation formula at 50% SOC is as follows: DCR (mΩ) = (V0-V1) / I 2C ×1000, see Table 2.

[0118] Table 2

[0119]

[0120]

[0121]

[0122] According to Examples 1 to 35 and Comparative Examples 1 to 11, the above-mentioned embodiments of the present application use a secondary injection electrolyte combination for injection, the gas production of the battery in the formation stage is significantly reduced, the capacity retention rate of the battery after normal temperature and high temperature cycling is significantly improved, and the initial DCR of the battery is also reduced. After the electrolyte of the above-mentioned embodiments of the present application is used in the battery, the high temperature cycle performance and normal temperature performance of the battery are effectively improved, and the gas production after formation is also effectively reduced.

[0123] In addition, it can be seen from Examples 6, 7, 8, 9, 10 and Comparative Examples 3 and 4 that adding an appropriate amount of the first additive in combination with VC and the second additive (TMP) in the electrolyte can further improve the high temperature cycle performance and electrochemical stability of the battery and reduce the initial DCR of the battery. The main reason for this is that the first additive will form a small amount of inorganic salts (Li2SO4, Li2O) in the CEI film formed by decomposition of the positive electrode, which improves the rigidity and flexibility of the positive electrode interface layer, inhibits the decomposition of the electrolyte, and improves the stability of the positive electrode interface film. In addition, the CEI film formed by the first additive can also reduce the electrochemical impedance of the positive electrode, accelerate the transmission rate of lithium ions, and help form a more stable electrode-electrolyte interface, reducing the internal resistance and interface reaction of the battery.

[0124] Further, in combination with Examples 11, 12, 13, 14, 15 and Comparative Examples 5 and 6, it can be seen that the introduction of the second additive (TMP) into the first electrolyte can effectively improve the problem of gas production during battery formation. The reason for this is that the second additive can be preheated to decompose phosphorus free radicals P· and oxygen free radicals O·, and P· and O· will form phosphorus oxide compounds, which can react with oxygen to remove the oxygen generated during high-temperature storage. Moreover, the second additive also has a high antioxidant capacity, which can further inhibit the decomposition of the electrolyte, thereby further reducing gas generation.

[0125] Combining Examples 1, 2, 3, 4, 5 and Comparative Examples 1 and 2, it can be seen that when an appropriate amount of VC is added in combination with the first additive and the second additive, the high temperature cycle performance of the battery can be effectively improved, but too much VC will cause gas production and increase the initial DCR. Therefore, using a small amount of VC and a low content of the first additive in synergy can improve the problem of too fast decay of the cyclic DCR caused by low VC concentration and reduce the initial DCR.

[0126] Combining Example 3 and Examples 27-31, it can be seen that when an appropriate amount of FEC and DTD is added, the room temperature cycle performance and high temperature cycle performance of the battery can be effectively improved, but adding too much will cause gas production and increase the initial DCR. Therefore, controlling the addition amount of FEC and DTD within an appropriate range can make the battery have both room temperature cycle performance, high temperature cycle performance, low gas production and low impedance.

[0127] In combination with Example 3 and Examples 32 and 33, it can be seen that when the lithium supplement is Li2O2 and Li2NiO, the use of the first electrolyte and the second electrolyte provided by the present invention can also make the battery exhibit low initial DCR, low gas production, and excellent room temperature and high temperature cycle performance.

[0128] Combining Example 3 with Examples 34 and 35, it can be seen that the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 and LiNi 0.5 Co 0.2 Mn 0.3 By adding VC and the first additive and the second additive, a battery with good room temperature and high temperature cycle performance and low gas production is obtained.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte combination suitable for secondary injection, characterized in that: comprising a first electrolyte for primary injection and a second electrolyte for secondary injection; The first electrolyte comprises 0.01-5wt% of vinylene carbonate, 0.05-3wt% of a first additive, 0.01-5wt% of a second additive, 5-15wt% of a lithium salt, 0.01-5wt% of a film-forming additive, and the balance of a non-aqueous organic solvent; The second electrolyte comprises 5-30wt% of vinylene carbonate, 0.01-10wt% of a first additive, 5-15wt% of a lithium salt, and the balance of a non-aqueous organic solvent; Wherein, the first additive includes a compound represented by Formula 1: The second additive includes a compound shown in Formula 2: R1, R2, and R3 are independently selected from substituted or unsubstituted C1-C3 alkyl groups, and the substituents of R1, R2, and R3 include at least one of halogen and hydroxyl groups.

2. The electrolyte combination suitable for secondary injection according to claim 1, characterized in that: The second additive includes at least one of trimethyl phosphate, triethyl phosphate, and tripropyl phosphate.

3. The electrolyte combination suitable for secondary injection according to claim 1 or 2, characterized in that: The ratio of the mass percentage of vinylene carbonate in the second electrolyte to the mass percentage of vinylene carbonate in the first electrolyte is 9-36; And / or, the ratio of the mass percentage of the first additive in the second electrolyte to the mass percentage of the first additive in the first electrolyte is 5-16.

7.

4. The electrolyte combination suitable for secondary injection according to any one of claims 1 to 3, characterized in that: The film-forming additive includes at least one of fluoroethylene carbonate, vinyl sulfate, lithium difluorooxalatoborate, 1,3-propane sultone, tris(trimethylsilyl)phosphate, hexamethylene diisocyanate, vinyl ethylene carbonate, methylene methanedisulfonate, lithium difluorooxalatophosphate, and lithium bis(oxalatoborate).

5. The electrolyte combination suitable for secondary injection according to any one of claims 1 to 4, characterized in that: The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide.

6. The electrolyte combination suitable for secondary injection according to any one of claims 1 to 5, characterized in that: The non-aqueous organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, diethyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate.

7. The electrolyte combination suitable for secondary injection according to any one of claims 1 to 6, characterized in that: The first electrolyte comprises 0.5-2wt% of vinylene carbonate, 0.3-1wt% of a first additive, 0.3-1wt% of a second additive, 10-15wt% of a lithium salt, 1-2wt% of a film-forming additive, and the balance of a non-aqueous organic solvent; The second electrolyte includes 10-20 wt % of vinylene carbonate, 3-5 wt % of a first additive, 10-15 wt % of a lithium salt and the balance of a non-aqueous organic solvent.

8. A liquid injection method, characterized in that: The electrolyte combination suitable for secondary injection according to any one of claims 1 to 7 is used for injection, comprising the following steps: 1) injecting the first electrolyte into the battery cell and performing a formation treatment to obtain a first battery cell; 2) injecting the second electrolyte into the first battery cell and performing an aging treatment to obtain a battery.

9. The liquid injection method according to claim 8, characterized in that: The battery cell uses lithium iron phosphate as the positive electrode active material, and a lithium supplement is added to the positive electrode, and the lithium supplement includes at least one of Li3N, Li2S, Li5FeO4, Li2O2, and Li2NiO2; And / or, the mass percentage of the lithium supplement agent in the positive electrode active material layer is 1-3%.

10. A battery, characterized in that: The invention is prepared by the liquid injection method according to claim 8 or 9.

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