Battery and preparation method thereof

Abstract

The invention provides a battery and a preparation method thereof, and aims to improve the cycle performance of the battery under a low-temperature condition. The battery comprises an electrode assembly and an electrolyte, wherein the electrolyte comprises a primary injection electrolyte; the primary liquid injection electrolyte comprises an organic solvent, a lithium salt and an additive, the organic solvent comprises a carboxylic ester solvent and a carbonic ester solvent, and the additive comprises VC; the battery is configured in a manner that after formation, at a first temperature, the conductivity of a primary injection electrolyte is a mS / cm, and the viscosity is b mPa.s; based on the total mass of the electrolyte, the mass contents of the carboxylic ester solvent and the carbonic ester solvent are x and y respectively, and x and y meet the following relations: a / 50 < = x < = a / 20, and b / 15 < = y < = b / 5; based on the total mass of the primary injection electrolyte, the mass content of the additive is z0, 0.01 < = z0 < = 0.15, the mass content of VC is z1, and z0 / 10 < = z1 < = z0 / 1.2.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery and a method for preparing the same. Background Art

[0002] With the growing demand for wide-temperature-range power batteries for electric vehicles, developing batteries for all-scenario applications has become a key R&D direction for major battery manufacturers. However, at low temperatures, electrolyte viscosity increases significantly, conductivity decreases, and batteries may even freeze. This slows interfacial redox kinetics and significantly reduces battery cycle life. Summary of the Invention

[0003] The embodiments of the present application provide a battery and a method for preparing the same, which can improve the technical problem of poor cycle performance of the battery under low temperature conditions.

[0004] In a first aspect, an embodiment of the present application provides a battery, comprising an electrode assembly and an electrolyte that impregnates the electrode assembly, wherein the electrolyte comprises a primary injection electrolyte, wherein the primary injection electrolyte is injected into the battery before formation;

[0005] The primary injection electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises a carboxylate solvent and a carbonate solvent, and the additive comprises vinylene carbonate;

[0006] The battery is configured such that, after formation, at a first temperature, the conductivity of the primary electrolyte is amS / cm and the viscosity is b mPa·s; based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, wherein x and y satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5; based on the total mass of the primary electrolyte, the mass content of the additive is z0, wherein 0.01≤z0≤0.15, the mass content of the vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.2.

[0007] In one embodiment, the electrolyte further comprises a secondary injection electrolyte, and the secondary injection electrolyte is injected into the battery after formation;

[0008] The secondary injection electrolyte comprises a carbonate solvent, a lithium salt and vinylene carbonate, wherein the mass content of the vinylene carbonate is 0.1 to 0.2 based on the total mass of the secondary injection electrolyte;

[0009] The battery is further configured such that after 100 cycles, based on the total mass of the electrolyte, the total mass content of the vinylene carbonate is z2, and z1 / 10≤z2≤z1 / 1.2.

[0010] In one embodiment, the volume ratio of the injection amount of the primary injection electrolyte to the injection amount of the secondary injection electrolyte is (8-9):(1-2).

[0011] In one embodiment, the first temperature is -30°C to 30°C, a is 5 to 20, and / or b is 2 to 10.

[0012] In one embodiment, the battery is configured such that after formation, based on the total mass of the primary electrolyte, the mass content of the lithium salt is w, 0.05≤w≤0.18; optionally, 0.08≤w≤0.15.

[0013] In one embodiment, the additive further includes at least one of vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite and methane disulfide sulfonate.

[0014] In one embodiment, the carboxylate solvent includes at least one of ethyl acetate, propyl acetate, methyl acetate, propyl propionate, and methyl propionate; and / or,

[0015] The carbonate solvent includes at least one of ethylene carbonate, ethyl methyl carbonate, propylene carbonate, and dimethyl carbonate; and / or,

[0016] The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(difluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0017] In one embodiment, the electrode assembly includes a positive electrode and a negative electrode arranged opposite to each other: the negative electrode contains a negative electrode active material, and the negative electrode active material is a carbon-based material; and / or the positive electrode contains a positive electrode active material, and the positive electrode active material includes lithium iron phosphate.

[0018] In one embodiment, the electrode assembly includes a positive electrode and a negative electrode disposed opposite to each other: the compaction density of the positive electrode is greater than or equal to 2.5 g / cm 3 ; and / or, the surface density of the positive electrode is greater than or equal to 230g / m 2 ; and / or, the compaction density of the negative electrode is greater than or equal to 1.6 g / cm 3 ; and / or, the surface density of the negative electrode is greater than or equal to 105g / m 2 .

[0019] In a second aspect, an embodiment of the present application provides a method for preparing a battery, comprising:

[0020] Providing an initial battery cell, wherein the initial battery cell includes an electrode assembly;

[0021] Injecting a primary injection electrolyte into the initial battery cell to obtain a battery; the primary injection electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the organic solvent comprises a carboxylate solvent and a carbonate solvent, and the additive comprises vinylene carbonate;

[0022] The battery is subjected to a formation treatment. After the formation treatment, at a first temperature, the conductivity of the primary injection electrolyte is a mS / cm, and the viscosity is b mPa·s. Based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, wherein x and y satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5. Based on the total mass of the primary injection electrolyte, the mass content of the lithium salt is w, the mass content of the additive is z0, wherein 0.01≤z0≤0.15, the mass content of the vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.2.

[0023] In one embodiment, the battery preparation method further includes: after the formation treatment is completed, injecting a secondary injection electrolyte into the initial battery cell, wherein the secondary injection electrolyte includes a carbonate solvent, a lithium salt and vinylene carbonate, and the mass content of the vinylene carbonate is 0.1 to 0.2 based on the total mass of the secondary injection electrolyte;

[0024] The battery is further configured such that after 100 cycles, based on the total mass of the electrolyte, the total mass content of the vinylene carbonate is z2, and z1 / 10≤z2≤z1 / 1.2.

[0025] Beneficial effects of the embodiments of the present application:

[0026] In the battery provided in the embodiment of the present application, a carboxylate solvent is introduced into the primary injection electrolyte. Since the carboxylate solvent itself has a relatively low melting point and viscosity, combined with the carbonate solvent with a higher dielectric constant, the primary injection electrolyte can maintain a high lithium ion migration rate at a lower temperature, thereby improving the performance of the battery in a low temperature environment; however, the introduction of the carboxylate solvent will aggravate the consumption of vinylene carbonate, especially in the formation process, vinylene carbonate is easily consumed in large quantities, which will cause the cycle performance of the battery to deteriorate. For this reason, by controlling the amount of carboxylate solvent, carbonate solvent, additive and vinylene carbonate in the electrolyte of the battery, the x, y, z0 and z1 of the battery after formation meet the above relationship, so that in the subsequent cycle process of the battery, the carboxylate solvent, carbonate solvent, additive and vinylene carbonate in the electrolyte can effectively cooperate to improve the cycle performance of the battery, especially the cycle stability in a low temperature environment. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0028] In this application, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to the upper and lower parts of a device during actual use or operation; whereas "inner" and "outer" refer to the outline of a device. Furthermore, in the description of this application, the term "including" means "including but not limited to." Terms such as first, second, and third are used merely as labels and do not impose numerical requirements or establish a sequence.

[0029] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0030] In this application, "at least one" means one or more, and "plurality" means two or more. "One or several", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0031] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0032] In a first aspect, an embodiment of the present application provides a battery, comprising an electrode assembly and an electrolyte that impregnates the electrode assembly, the electrolyte comprising a primary injection electrolyte, which is injected into the battery before formation; the primary injection electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the organic solvent comprises a carboxylate solvent and a carbonate solvent, and the additive comprises at least vinylene carbonate; the battery is configured such that after formation, at a first temperature, the conductivity of the primary injection electrolyte is a mS / cm, and the viscosity is b mPa·s; based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, wherein x and y satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5; based on the total mass of the primary injection electrolyte, the mass content of the additive is z0, wherein 0.01≤z0≤0.15, the mass content of vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.2.

[0033] A battery is a device that converts chemical energy into electrical energy. Optionally, the battery is specifically a battery cell. A battery cell is the basic unit that converts chemical energy into electrical energy. Optionally, the battery cell is a rechargeable battery cell, which can convert chemical energy into electrical energy and vice versa. Furthermore, the battery is a lithium-ion battery.

[0034] A battery includes an electrode assembly, also referred to herein as a core pack, which is the core component of the battery. Specifically, the electrode assembly includes a positive electrode and a negative electrode disposed opposite each other, and also includes a separator, wherein the separator is located between the positive electrode and the negative electrode to separate the positive electrode and the negative electrode, preventing direct contact between the positive and negative electrodes and causing a short circuit. The electrode assembly can be a laminated structure or a wound structure. As an example, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material. Optionally, the positive electrode active material includes lithium iron phosphate. As an example, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material. Optionally, the negative electrode active material is a carbon-based material, which expands relatively less during battery cycling compared to silicon-based materials. Optionally, the carbon-based material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon (such as coke), carbon nanotubes, graphene, and carbon fibers.

[0035] The battery also includes an electrolyte, which soaks into the electrode assembly and provides a pathway for ion transport. Specifically, the electrolyte includes a primary injection electrolyte, which is injected into the battery prior to formation. The primary injection electrolyte comprises an organic solvent, a lithium salt, and additives, wherein the lithium salt and additives are dissolved in the organic solvent.

[0036] More specifically, the organic solvent is a mixed solvent including a carboxylate solvent and a carbonate solvent. Carbonate solvents have good solubility for lithium salts and additives, and the dielectric constant of carbonate solvents is relatively high. For example, the dielectric constant of ethylene carbonate EC is 89.78, and the dielectric constant of propylene carbonate PC is 64.92, which is beneficial to improving the conductive properties of the single-injection electrolyte; while the melting point and viscosity of carboxylate solvents are relatively low. For example, the melting point of ethyl acetate (EA) is -84°C, which makes the carboxylate solvent have good fluidity under low temperature conditions, thereby helping to improve the low-temperature performance of the electrolyte. In this way, the conductivity of the single-injection electrolyte can be improved but the viscosity can be reduced by combining carboxylate solvents and carbonate solvents. As an example, the carboxylate solvent includes at least one of ethyl acetate (EA), propyl acetate (EP), methyl acetate (MA), propyl propionate (PP), and methyl propionate (MP); the carbonate solvent includes at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and dimethyl carbonate (DMC).

[0037] The lithium salt may include at least one of an inorganic lithium salt and an organic lithium salt. Optionally, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(difluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Wherein LiFP6 is an inorganic lithium salt, and LiFSI and LiTFSI are both organic lithium salts. As an example, the lithium salt includes at least an organic lithium salt, such as LiFSI and LiTFSI. Since the boiling point of carboxylic acid ester solvents is relatively low, the addition of such lithium salts can promote the improvement of the thermal stability of the electrolyte and the stability of the SEI film.

[0038] The additive includes at least vinylene carbonate (VC), which undergoes an electrochemical reaction on the surface of the negative electrode of the lithium battery to form a dense solid electrolyte interface film (SEI film). This film can effectively inhibit the embedding of solvent molecules and the decomposition of the electrolyte, thereby protecting the electrode material and improving the safety and stability of the battery. Optionally, the additive also includes at least one of vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES) and methane disulfide methyl ester (MMDS). The above substances can be used as film-forming agents to promote the formation of SEI film. In particular, fluoroethylene carbonate can form a SEI film with a compact structure and excellent performance on the surface of the negative electrode. This film not only improves the cycle stability of the battery, but also reduces the impedance of the battery interface.

[0039] Since the primary injection electrolyte is injected into the battery before the battery is formed, the electrolyte in the battery after formation is also mainly the primary injection electrolyte injected during the primary injection. Formation refers to the process of activating the internal electrode material when the battery is first charged, with the purpose of forming a solid electrolyte interface (SEI) film. During the formation process, part of the primary injection electrolyte will be consumed. Here, the formation conditions can be set according to the specific battery and are not limited here.

[0040] After battery formation, at a first temperature, the conductivity of the primary electrolyte is a mS / cm, and the viscosity is b mPa·s. Optionally, the first temperature is between -30°C and 30°C, a is 5 to 20, and b is 2 to 10. That is, at a temperature between -30°C and 30°C, after battery formation, the conductivity of the primary electrolyte is 5 mS / cm to 20 mS / cm, and the viscosity is 2 mPa·s to 10 mPa·s.

[0041] After battery formation, based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, where x and y satisfy the following relationship: a / 50 ≤ x ≤ a / 20, b / 15 ≤ y ≤ b / 5. It should be noted that x and y are both numbers less than 1 and greater than 0.

[0042] After the battery is formed, based on the total mass of the electrolyte in the first injection (i.e., the total mass of the electrolyte after the battery is formed), the mass content of the additive is z0, where 0.01≤z0≤0.15, the mass content of vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.2. That is to say, after the battery is formed, the mass content of the additive in the electrolyte in the first injection is 1wt% to 15wt%, and the mass content z1 of vinylene carbonate is one tenth to five sixths of the mass content z0 of the additive. As an example, z0 is 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13 or 0.15.

[0043] In the battery provided in the embodiment of the present application, a carboxylate solvent is introduced into the primary injection electrolyte. Since the carboxylate solvent itself has a relatively low melting point and viscosity, combined with the carbonate solvent with a higher dielectric constant, the primary injection electrolyte can maintain a high lithium ion migration rate at a lower temperature, thereby improving the performance of the battery in a low temperature environment; however, the introduction of the carboxylate solvent will aggravate the consumption of vinylene carbonate, especially in the formation process, vinylene carbonate is easily consumed in large quantities, which will cause the cycle performance of the battery to deteriorate. For this reason, by further controlling the amount of carboxylate solvent, carbonate solvent, additive and vinylene carbonate in the electrolyte of the battery, the x, y, z0 and z1 of the battery after formation meet the above relationship. In this way, the carboxylate solvent, carbonate solvent, additive and vinylene carbonate in the electrolyte can effectively cooperate with each other in the subsequent cycle process of the battery, thereby improving the cycle performance of the battery, especially the cycle stability in a low temperature environment.

[0044] In addition, thanks to the introduction of carboxylic acid ester solvents, the wettability of the primary electrolyte injection will also be improved, thereby accelerating the ion transport of the electrolyte in the electrodes (including the positive and negative electrodes) and improving the kinetic performance of the electrolyte on the electrodes. Based on this, the electrode assembly in the battery can use thick electrodes with thicker active material layers, which is conducive to improving the energy density of the battery.

[0045] In some embodiments, the electrode assembly includes a positive electrode and a negative electrode disposed opposite each other, wherein the compaction density of the positive electrode is greater than or equal to 2.5 g / cm 3 ; The surface density of the positive electrode is greater than or equal to 230g / m 2 ; The compaction density of the negative electrode is greater than or equal to 1.6g / cm 3 ; The surface density of the negative electrode is greater than or equal to 105g / m 2 Combined with the improvement of the electrolyte infiltration ability, the energy density of the battery can be improved through the above settings.

[0046] In some embodiments, the battery is configured such that after formation, the mass content of the lithium salt is w, based on the total mass of the primary injection electrolyte, 0.05≤w≤0.18. By controlling the mass content of the lithium salt in the primary injection electrolyte after formation, the viscosity and conductivity of the electrolyte under low temperature conditions can be effectively controlled, thereby improving the low temperature cycle performance of the battery. As an example, w is 0.05, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16 or 0.18. Optionally, 0.08≤w≤0.15.

[0047] In some embodiments, the electrolyte further includes a secondary injection electrolyte, which is injected into the battery after formation; the secondary injection electrolyte includes a carbonate solvent, a lithium salt and vinylene carbonate, and the mass content of vinylene carbonate is 0.1 to 0.2 based on the total mass of the secondary injection electrolyte; the battery is further configured so that after 100 cycles, the total mass content of vinylene carbonate is z2 based on the total mass of the electrolyte, and z1 / 10≤z2≤z1 / 1.2.

[0048] The secondary injection electrolyte can replenish the electrolyte consumed by the battery during formation. It can be understood that when the secondary injection electrolyte is injected into the battery, the electrolyte of the battery includes the primary injection electrolyte and the secondary injection electrolyte. Since carboxylic acid ester solvents easily consume vinylene carbonate, the solvent of the secondary injection electrolyte is mainly carbonate solvent, which can alleviate the further consumption of vinylene carbonate; at the same time, vinylene carbonate continues to be added to the secondary injection electrolyte, and the mass content of vinylene carbonate is 0.1 to 0.2 to achieve the replenishment of vinylene carbonate. As an example, the mass content of vinylene carbonate in the secondary injection electrolyte is 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2. By combining the above-mentioned primary injection electrolyte and secondary injection electrolyte, the total mass content of vinylene carbonate in the battery's electrolyte (including the primary injection electrolyte and the secondary injection electrolyte) after the battery has been cycled 100 times is z2, and z1 / 10≤z2≤z1 / 1.2, that is, the mass content of vinylene carbonate z2 after the battery has been injected twice and cycled 100 times is one-tenth to five-sixths of the mass content of vinylene carbonate z1 after the battery has been formed and before the secondary injection. By setting up as above, it can be ensured that the battery has a sufficient amount of vinylene carbonate during subsequent cycles. The presence of vinylene carbonate can effectively promote the formation of the SEI film, especially when the SEI film ruptures due to the change in volume of the negative electrode during the cycle, the presence of the SEI film is beneficial to reduce the interface side reactions between the electrolyte and the negative electrode, thereby improving the battery's low-temperature, room-temperature and high-temperature cycle performance.

[0049] Here, the condition of circulating 100 times can be set according to the specific battery and is not limited here. The mass content of the lithium salt in the secondary injection electrolyte and the type of lithium salt can be the same as or different from those in the primary injection electrolyte. The secondary injection electrolyte may also further include at least one of vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES) and methane disulfide methyl ester (MMDS). Optionally, the secondary injection electrolyte does not contain a carboxylic acid ester solvent.

[0050] In some embodiments, the volume ratio of the first injection amount of the electrolyte to the second injection amount of the electrolyte is (8-9):(1-2). As an example, the volume ratio of the two injection amounts is 8:2, 8.5:1.5 or 9:1.

[0051] In a second aspect, an embodiment of the present application provides a method for preparing a battery, comprising:

[0052] S1. Providing an initial battery cell, the initial battery cell including an electrode assembly;

[0053] S2. Injecting a primary injection electrolyte into the initial battery cell to obtain a battery; the primary injection electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the organic solvent comprises a carboxylate solvent and a carbonate solvent, and the additive comprises at least vinylene carbonate;

[0054] S3. Perform a formation treatment on the battery. After the formation treatment, at the first temperature, the conductivity of the primary injection electrolyte is a mS / cm, and the viscosity is b mPa·s; based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, wherein x and y satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5; based on the total mass of the primary injection electrolyte, the mass content of the lithium salt is w, the mass content of the additive is z0, wherein 0.01≤z0≤0.15, the mass content of the vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.2.

[0055] Optionally, the initial battery cell includes a shell having a receiving cavity, and the electrode assembly is arranged in the receiving cavity; injecting the primary injection electrolyte into the initial battery cell is specifically injecting the electrolyte into the receiving cavity, and the electrolyte infiltrates the electrode assembly located in the receiving cavity.

[0056] In some embodiments, the method for preparing a battery further comprises:

[0057] S4. After the formation treatment is completed, a secondary injection electrolyte is injected into the initial battery cell, where the secondary injection electrolyte includes a carbonate solvent, a lithium salt and vinylene carbonate. The mass content of vinylene carbonate is 0.1 to 0.2 based on the total mass of the secondary injection electrolyte. The battery is also configured so that after 100 cycles, the total mass content of vinylene carbonate is z2 based on the total mass of the electrolyte, and z1 / 10≤z2≤z1 / 1.2.

[0058] In some embodiments, the method for preparing a battery is used to prepare the battery provided in the first aspect.

[0059] The following describes the method in conjunction with specific embodiments.

[0060] Example 1

[0061] This embodiment provides a battery, and the preparation process of the battery includes:

[0062] S1. Preparation of primary injection electrolyte: In a glove box with an oxygen content of <10ppm and a moisture content of <1ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and ethyl acetate (EA) are prepared into an organic solvent, and a mixed lithium salt of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6) is dissolved in the organic solvent. Then, vinylene carbonate (VC), ethylene sulfite (ES), fluoroethylene carbonate (FEC) and methylene methanedisulfonate (MMDS) are added to the organic solvent, stirred with a magnetic stirrer overnight until they are completely dissolved, and stored in a high-purity argon glove box for use.

[0063] S2. Preparation of secondary liquid injection electrolyte: In a glove box with an oxygen content of <10ppm and a moisture content of <1ppm, prepare an organic solvent according to the ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 3:3:4 (v:v:v), take lithium hexafluorophosphate (LiPF6) and dissolve it in the organic solvent at a molar concentration of 1 mol / L, then add vinylene carbonate (VC) to the organic solvent at a mass content of 0.15, stir with a magnetic stirrer overnight until it is completely dissolved, and store in a high-purity argon glove box for use.

[0064] S3. Preparation of positive electrode sheet: first prepare a polyvinylidene fluoride (PVDF) positive electrode glue with a solid content of 1.327wt%; add lithium iron phosphate and conductive agent Super-P to N-methylpyrrolidone (NMP) and rotate at 25r / min, disperse at 500r / min, stir for 10min, then rotate at 25r / min, disperse at 1000r / min, and stir at 45℃ for 90min; then add conductive agent carbon nanotubes, rotate at 25r / min, disperse at 1000r / min, vacuum at 0.080KPa, and stir at 45℃ for 60min; then add positive electrode glue, rotate at 25r / min, disperse at 2500r / min, and stir at 45℃ for 60min. min, vacuum degree 0.080KPa, stirring at 45℃ for 90min; then adding NMP to adjust the slurry viscosity; finally, slowly stirring and revolving at 15r / min, dispersing at 500r / min, vacuum degree 0.080KPa, stirring for 0.5h to cool down, ensuring that the positive electrode discharge viscosity is 15000mPa·s and the fineness is ≤15μm. The deposited material on the stirring cylinder wall and the stirring rod is scraped in time at each step. The positive electrode sheet is obtained through screening, coating, cold pressing and slitting, wherein the mass ratio of lithium iron phosphate, conductive agent Super-P, carbon nanotubes and binder polyvinylidene fluoride is 95.0:2.0:0.5:2.5; the positive electrode compaction density is 2.55g / cm 3 ; Surface density: 230g / m2 .

[0065] S4. Preparation of negative electrode sheets: first prepare a sodium carboxymethyl cellulose (CMC) negative electrode glue with a solid content of 8wt%; dry-mix graphite and conductive agent Super-P, rotate at 20r / min, disperse at 1000r / min, and stir for 1h; then add 50% negative electrode glue, rotate at 20r / min, disperse at 1000r / min, and stir for 1.5h; then add another 50% negative electrode glue, rotate at 25r / min, disperse at 2000r / min, vacuum at 0.085KPa, and stir for 1h; then add deionized water to adjust the slurry viscosity; finally add water-based dispersant styrene-butadiene latex, rotate at 25r / min, disperse at 800r / min, vacuum at 0.085KPa, and stir for 1h. The negative electrode discharge viscosity is guaranteed to be 4000mPa·s and the fineness is ≤20μm. The deposited material on the stirring cylinder wall and stirring rod is scraped promptly at each step. After screening, coating, cold pressing and slitting, the negative electrode sheet is produced. The mass ratio of the negative electrode active material graphite, conductive agent Super-P, thickener sodium carboxymethyl cellulose, and adhesive styrene-butadiene latex is 95.5:1.5:1.2:1.8; the negative electrode compaction density is 1.6g / cm 3 , surface density: 105g / m 2 .

[0066] S5. Preparation of lithium-ion batteries: The prepared positive electrode sheet, negative electrode sheet and separator (specifically, a wet double-sided sprayed ceramic film) are subjected to a lamination process to obtain a bare battery cell. After the bare battery cell is placed in an aluminum-plastic film packaging shell, the above-mentioned primary injection electrolyte is injected, and then the shell is sealed, allowed to stand, hot and cold pressed, and formed. After the formation is completed, the composition and related physical properties of the electrolyte are tested, and the results are shown in Table 1; then the above-mentioned secondary injection electrolyte is injected, and the volume ratio of the injection amount of the primary injection electrolyte to the injection amount of the secondary injection electrolyte is 85:15. The capacity division and other processes are carried out to obtain a lithium-ion battery.

[0067] S6. Cycle 100: After the battery cycle is completed 100 times, the composition of the electrolyte is tested. The results are shown in Table 1.

[0068] It should be noted here that the test method for the electrolyte composition after the battery is formed and after 100 cycles is the same: the battery is discharged to 2.5V with a constant current of 0.33C (that is, the battery is discharged), the battery is disassembled and the free electrolyte is squeezed out, and the content of each component is tested using a gas chromatograph (GC).

[0069] Example 2

[0070] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0071] The content of the carboxylic acid ester solvent EA in the organic solvent of the primary injection electrolyte was increased, and the content of the organic solvent in the electrolyte remained unchanged. The composition of the electrolyte obtained by testing after formation is shown in Table 1. Others are the same as in Example 1.

[0072] Example 3

[0073] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0074] The content of the carboxylic acid ester solvent EA in the organic solvent of the primary injection electrolyte was reduced, and the content of the organic solvent in the electrolyte remained unchanged. The composition of the electrolyte obtained by testing after formation is shown in Table 1. Others are the same as in Example 1.

[0075] Example 4

[0076] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0077] In the organic solvent of the primary injection electrolyte, other carboxylic acid ester solvent EP was used instead of EA, and the content of the organic solvent in the electrolyte remained unchanged. The composition of the electrolyte obtained by testing after formation is shown in Table 1. Others are the same as in Example 1.

[0078] Example 5

[0079] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0080] The lithium salt LiFSI in the primary injection electrolyte was replaced with LiPF6 (i.e., all the lithium salts were LiPF6), and the content of lithium salt in the electrolyte remained unchanged. The composition of the electrolyte obtained after formation and testing was shown in Table 1, and the rest was the same as in Example 1.

[0081] Example 6

[0082] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0083] The content of VC in the additive was increased, while the content of the additive in the primary injection electrolyte remained unchanged. The composition of the electrolyte obtained after formation was shown in Table 1. Other aspects were the same as in Example 1.

[0084] Example 7

[0085] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0086] The content of VC in the additive was reduced, while the content of the additive in the primary injection electrolyte remained unchanged. The composition of the electrolyte obtained after formation was shown in Table 1. Other parameters were the same as those in Example 1.

[0087] Example 8

[0088] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0089] The additive only contains VC, and the content of the additive in the primary injection electrolyte remains unchanged. The composition of the electrolyte obtained by testing after formation is shown in Table 1. Others are the same as in Example 1.

[0090] Example 9

[0091] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0092] There was no secondary injection. After 100 cycles, the composition of the electrolyte obtained by testing was shown in Table 1. Other aspects were the same as those in Example 1.

[0093] Example 10

[0094] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0095] The mass content of vinylene carbonate in the secondary injection electrolyte is 0.05 (ie 5 wt %). The composition of the electrolyte obtained after 100 cycles is shown in Table 1. Other components are the same as those in Example 1.

[0096] Example 11

[0097] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0098] The mass content of vinylene carbonate in the secondary injection electrolyte is 0.1 (ie 10 wt %). The composition of the electrolyte obtained after 100 cycles is shown in Table 1. Other components are the same as those in Example 1.

[0099] Example 12

[0100] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0101] The mass content of vinylene carbonate in the secondary injection electrolyte is 0.2 (ie 20 wt %). The composition of the electrolyte obtained after 100 cycles is shown in Table 1. Other components are the same as those in Example 1.

[0102] Example 13

[0103] This embodiment provides a battery. The preparation process of the battery is different from that of Example 1 in that:

[0104] The mass content of vinylene carbonate in the secondary injection electrolyte is 0.3 (ie 30 wt %). The composition of the electrolyte obtained after 100 cycles is shown in Table 1. Other components are the same as those in Example 1.

[0105] Comparative Example 1

[0106] This comparative example provides a battery, the preparation process of which is different from that of Example 9 in that:

[0107] In the organic solvent of the primary injection electrolyte, the carbonate solvent DMC was used instead of EA (i.e., there was no carboxylate solvent in the organic solvent), and the content of the organic solvent in the electrolyte remained unchanged. The composition of the electrolyte obtained by testing after formation is shown in Table 1, and the rest is the same as Example 9.

[0108] Comparative Example 2

[0109] This comparative example provides a battery, the preparation process of which is different from that of Example 9 in that:

[0110] The composition of the organic solvent in the primary injection electrolyte was adjusted so that x and y did not satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5; the rest was the same as in Example 9.

[0111] Comparative Example 3

[0112] This comparative example provides a battery, the preparation process of which is different from that of Example 9 in that:

[0113] The composition of the additive in the primary injection electrolyte was adjusted so that VC was not contained in the additive. Other aspects were the same as those in Example 9.

[0114] Comparative Example 4

[0115] This comparative example provides a battery, the preparation process of which is different from that of Example 9 in that:

[0116] The composition of the additives in the primary injection electrolyte is adjusted so that z0 and z1 do not satisfy the following relationship: 0.01≤z0≤0.15, z0 / 10≤z1≤z0 / 1.2; the rest is the same as in Example 9.

[0117] Table 1

[0118]

[0119]

[0120] In Table 1, the unit of T is °C, the unit of a is mS / cm, the unit of b is mPa·s, and the unit of x, y, w, z0, z1, and z2 is 1.

[0121] Performance testing:

[0122] 1. Cyclic performance test at 25 and 45℃:

[0123] At 25℃ / 45℃, the battery was charged at a constant current and constant voltage of 0.5C, with a cut-off voltage of 3.75V and a cut-off current of 0.05C. The battery was discharged at a constant current of 0.5C to 2.5V for 5 cycles. The last discharge capacity was taken as the initial capacity and recorded as Q0.

[0124] The battery was then fully charged and discharged, and the capacity Q1 at 1500 cycles was recorded. The capacity retention rate = Q1 / Q0. The test results are shown in Table 2. Full charge: the battery is charged with a constant current and constant voltage of 1C, with a cut-off voltage of 3.75V and a cut-off current of 0.05C; full discharge: the battery is discharged with a constant current of 1C to 2.5V.

[0125] 2. -10℃ cycle performance test:

[0126] At -10°C, the battery was charged at a constant current and constant voltage of 0.5C, with a cut-off voltage of 3.75V and a cut-off current of 0.05C. The battery was discharged at a constant current of 0.5C to 2.5V for 5 cycles. The last discharge capacity was taken as the initial capacity and recorded as Q0.

[0127] The battery was then fully charged and discharged, and the capacity Q1 at 1500 cycles was recorded. The capacity retention rate = Q1 / Q0. The test results are shown in Table 2. Full charge: the battery was charged at a constant current and constant voltage of 0.5C, with a cut-off voltage of 3.75V and a cut-off current of 0.05C; full discharge: the battery was discharged at a constant current of 0.5C to 2.5V.

[0128] 3. Internal resistance test:

[0129] The battery was charged to 50% SOC at a current of 0.33C and directly tested with a voltage internal resistance meter. The value displayed by the instrument is the internal resistance value. The test results are shown in Table 2.

[0130] Table 2

[0131]

[0132] Compared with Example 1, Example 2 increases the carboxylate content, resulting in increased conductivity, improved electrolyte kinetics, and reduced battery internal resistance. However, its low boiling point causes poor high-temperature cycling, while its low melting point improves low-temperature cycling and increases VC consumption. Similarly, reducing the carboxylate content reduces conductivity, degrades kinetics, increases internal resistance, and causes attenuation in room-temperature and low-temperature cycling. However, the overall thermal stability of the electrolyte is improved, resulting in improved high-temperature cycling.

[0133] Compared with Example 1, in Example 4, EA was replaced with EP with a slightly smaller dielectric constant. Since its kinetic performance was slightly worse than that of EA, the internal resistance increased, and both room temperature and low temperature cycles decreased. However, the thermal stability of the electrolyte was improved, which improved the high temperature cycle.

[0134] Compared with Example 1, Example 5 replaces all lithium salts with lithium hexafluorophosphate. Due to the higher ion mobility of LiFSI and its inherent stability, it does not hydrolyze or produce acid, which reduces the thermal stability of the electrolyte, increases the viscosity, and reduces the kinetic performance, thereby worsening the cycle performance.

[0135] Compared with Example 1, Example 6 increases the VC content. Since the VC film is a macromolecular cross-linked polymer, although it is mechanically stable and has good flexibility, an excessively high content increases its internal resistance, making interfacial charge transfer difficult and causing cycle attenuation.

[0136] Compared with Example 1, in Example 8, only VC was used as an additive without other additives to assist in film modification, that is, to further increase the VC content, which was not conducive to the growth of the SEI film and further attenuated the cycle.

[0137] Compared with Example 1, Example 7 reduces the VC content, so that VC is completely consumed during the formation process. After 100 cycles, there is little residual VC, which makes it impossible to effectively utilize VC to self-repair the SEI film during the cycle, resulting in cycle attenuation.

[0138] Compared with Example 1, Example 9 to Example 13, Example 9 does not have a secondary injection, that is, the VC content is reduced, so that the VC cannot be effectively utilized to self-repair the SEI film during the cycle, causing the impedance to increase and the cycle performance to decay; Example 10, Example 11, Example 1, Example 12 and Example 13 all carried out a secondary injection, and the VC content in the secondary injection gradually increased, but the cycle performance of the battery first improved and then deteriorated, and the internal resistance of the battery gradually increased. This is because as the VC content increases, the film-forming effect of the SEI film is improved, which improves the battery cycle performance. However, if the secondary injection injects VC with too high a concentration, the SEI film will be too thick, which will increase the impedance and reduce the interface dynamics, which will also lead to cycle decay.

[0139] In Comparative Example 1, the solvent is only a carbonate solvent, and there is no second injection scheme. The kinetic performance of the electrolyte is insufficient to support thick electrode cycling.

[0140] In Comparative Example 2, the carboxylate content is too low and no longer satisfies the relationship. The kinetic performance of the electrolyte decreases, resulting in a significant deterioration in the cycle.

[0141] In Comparative Example 3, there is no VC additive in the first injection, and the battery cell cannot form a stable SEI film during the formation. In the later cycles, the SEI film continues to rupture, continuously consuming active lithium and deteriorating the cycle.

[0142] Comparative Example 4 has no VC after formation and cannot support subsequent cycle consumption, and the cycle is significantly deteriorated.

[0143] The above is a detailed introduction to the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A battery, characterized in that: The battery includes an electrode assembly and an electrolyte that impregnates the electrode assembly, wherein the electrolyte includes a primary injection electrolyte, and the primary injection electrolyte is injected into the battery before formation; The primary injection electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises a carboxylate solvent and a carbonate solvent, and the additive comprises vinylene carbonate; The battery is configured such that, after formation, at a first temperature, the conductivity of the primary electrolyte is a mS / cm, and the viscosity is b mPa·s; based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, wherein x and y satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5; based on the total mass of the primary electrolyte, the mass content of the additive is z0, wherein 0.01≤z0≤0.15, the mass content of the vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.

2.

2. The battery according to claim 1, characterized in that The electrolyte also includes a secondary injection electrolyte, which is injected into the battery after formation; The secondary injection electrolyte comprises a carbonate solvent, a lithium salt and vinylene carbonate, wherein the mass content of the vinylene carbonate is 0.1 to 0.2 based on the total mass of the secondary injection electrolyte; The battery is further configured such that after 100 cycles, based on the total mass of the electrolyte, the total mass content of the vinylene carbonate is z2, and z1 / 10≤z2≤z1 / 1.

2.

3. The battery according to claim 2, characterized in that The volume ratio of the injection amount of the primary injection electrolyte to the injection amount of the secondary injection electrolyte is (8-9):(1-2).

4. The battery according to any one of claims 1 to 3, characterized in that The first temperature is -30°C to 30°C, a is 5 to 20, and / or b is 2 to 10.

5. The battery according to any one of claims 1 to 3, characterized in that The battery is configured such that after formation, based on the total mass of the primary electrolyte, the mass content of the lithium salt is w, 0.05≤w≤0.18; optionally, 0.08≤w≤0.

15.

6. The battery according to any one of claims 1 to 3, characterized in that The additive further comprises at least one of vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite and methane disulfide sulfomethylene.

7. The battery according to any one of claims 1 to 3, characterized in that The carboxylate solvent includes at least one of ethyl acetate, propyl acetate, methyl acetate, propyl propionate, and methyl propionate; and / or, The carbonate solvent includes at least one of ethylene carbonate, ethyl methyl carbonate, propylene carbonate, and dimethyl carbonate; and / or, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(difluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

8. The battery according to any one of claims 1 to 3, characterized in that The electrode assembly includes a positive electrode and a negative electrode arranged opposite to each other: the negative electrode contains a negative electrode active material, and the negative electrode active material is a carbon-based material; and / or the positive electrode contains a positive electrode active material, and the positive electrode active material includes lithium iron phosphate.

9. The battery according to any one of claims 1 to 3, characterized in that The electrode assembly includes a positive electrode and a negative electrode arranged opposite to each other; the compaction density of the positive electrode is greater than or equal to 2.5 g / cm 3 ; and / or, the surface density of the positive electrode is greater than or equal to 230g / m 2 ; and / or, the compaction density of the negative electrode is greater than or equal to 1.6 g / cm 3 ; and / or, the surface density of the negative electrode is greater than or equal to 105g / m 2 .

10. A method for preparing a battery, characterized in that: include: Providing an initial battery cell, wherein the initial battery cell includes an electrode assembly; Injecting a primary injection electrolyte into the initial battery cell to obtain a battery; the primary injection electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the organic solvent comprises a carboxylate solvent and a carbonate solvent, and the additive comprises vinylene carbonate; The battery is subjected to a formation treatment. After the formation treatment, at a first temperature, the conductivity of the primary injection electrolyte is a mS / cm, and the viscosity is b mPa·s. Based on the total mass of the electrolyte, the mass content of the carboxylate solvent is x, and the mass content of the carbonate solvent is y, wherein x and y satisfy the following relationship: a / 50≤x≤a / 20, b / 15≤y≤b / 5. Based on the total mass of the primary injection electrolyte, the mass content of the lithium salt is w, the mass content of the additive is z0, wherein 0.01≤z0≤0.15, the mass content of the vinylene carbonate is z1, and z0 / 10≤z1≤z0 / 1.

2.

11. The method for preparing a battery according to claim 10, wherein: The preparation method of the battery also includes: after the formation treatment is completed, injecting a secondary injection electrolyte into the initial battery cell, the secondary injection electrolyte including a carbonate solvent, a lithium salt and vinylene carbonate, and based on the total mass of the secondary injection electrolyte, the mass content of the vinylene carbonate is 0.1 to 0.2; the battery is also configured so that after 100 cycles, based on the total mass of the electrolyte, the total mass content of the vinylene carbonate is z2, and z1 / 10≤z2≤z1 / 1.2.

Images