Batteries and their electrolyte filling methods, energy storage devices and power systems

Abstract

The present application belongs to the field of energy storage, and specifically discloses a battery and a liquid injection method thereof, an energy storage device and an electricity consumption system, wherein the battery comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet, the electrolyte comprises a free electrolyte and a non-free electrolyte, the non-free electrolyte comprises an electrolyte in the pores of the positive electrode sheet, an electrolyte in the pores of the negative electrode sheet and an electrolyte in the pores of the diaphragm; the non-free electrolyte comprises a carboxylate solvent, the mass proportion of the carboxylate solvent in the non-free electrolyte is m1, the free electrolyte comprises a carboxylate solvent, the mass proportion of the carboxylate solvent in the free electrolyte is m2, and 0.4≤m1 / m2≤1.2 is satisfied; the diaphragm has a PVDF coating, and the surface density of the PVDF in the PVDF coating on the diaphragm is fg / m 2 , satisfying 0.8≤f / m2≤4.

Description

Technical Field

[0001] The present application belongs to the field of energy storage, and specifically relates to a battery and a liquid injection method thereof, an energy storage device and an electricity consumption system. Background Art

[0002] With the development of the energy storage industry, lithium-ion battery technology has continued to develop. Whether it is the power generation side, the user energy storage side or other user scenarios, higher requirements are placed on the overcharge safety performance of lithium-ion batteries. For large-scale energy storage lithium-ion batteries (batteries with a capacity of more than 280Ah), the main means to improve overcharge safety performance is to reduce the oxidation reaction of the electrolyte during overcharge, or reduce the reaction of lithium graphite and electrolyte in the battery cell, thereby slowing down the reaction heat generated during overcharge.

[0003] During the overcharge test, as the overcharge progresses, the voltage of the lithium-ion battery increases, the electrolyte oxidizes at the positive electrode, and the heat generated by the battery cell increases rapidly. The heat generated by the battery cell causes the battery cell temperature to rise rapidly, and the rise in battery cell temperature further promotes the reaction of the electrolyte at the positive electrode / electrolyte interface and the negative electrode / electrolyte interface, thereby causing the battery cell to further accumulate heat. If the battery cell cannot quickly reach the overcharge cut-off condition at this time, the continuous heat accumulation under the condition of continuous charging can easily cause a chain reaction in the chemical system, and the reaction heat continues to accumulate, causing thermal runaway of the battery cell, and even fire, explosion, etc. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present application is to provide a battery and a liquid injection method thereof, an energy storage device and a power system, which effectively improve the overcharge safety performance of the battery.

[0005] The first aspect of the present application provides a battery. According to an embodiment of the present application, the battery includes: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, the electrolyte includes a free electrolyte and a non-free electrolyte, and the non-free electrolyte includes an electrolyte in the pores of the positive electrode sheet, an electrolyte in the pores of the negative electrode sheet and an electrolyte in the pores of the separator;

[0006] The non-free electrolyte includes a carboxylate solvent, the mass proportion of the carboxylate solvent in the non-free electrolyte is m1, the free electrolyte includes a carboxylate solvent, the mass proportion of the carboxylate solvent in the free electrolyte is m2, and 0.4≤m1 / m2≤1.2 is satisfied;

[0007] The diaphragm has a PVDF coating, and the surface density of PVDF in the PVDF coating on the diaphragm is fg / m 2, satisfying 0.8≤f / m2≤4.

[0008] According to the battery of the above embodiment of the present application, both the free electrolyte and the non-free electrolyte contain carboxylate solvents, which have the advantage of low viscosity, can improve the wettability of the electrolyte and realize the rapid transfer of lithium ions in the negative electrode pores. Moreover, when the temperature of the battery core rises, the carboxylate solvent in the free electrolyte easily causes the PVDF coating on the diaphragm to swell, thereby causing the PVDF to block the gaps in the diaphragm, increasing the battery impedance, and causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering the charging to stop, thereby effectively improving the overcharge safety performance of the battery.

[0009] At the same time, the present application adjusts the content m2 of the carboxylic acid ester solvent in the free electrolyte and the surface density f of the PVDF on the diaphragm coating to satisfy 0.8≤f / m2≤4, thereby achieving that during normal operation (circulation operation at room temperature), the free electrolyte does not swell the PVDF coating on the diaphragm. However, in the case of overcharge, as the temperature rises, the PVDF layer on the diaphragm swells, blocking the gaps in the diaphragm, causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering charging to stop.

[0010] In addition, the battery according to the above embodiment of the present application may also have the following additional technical features:

[0011] In some embodiments of the present application, the range of m1 is 20%≤m1≤30%; and / or the range of m2 is 25%≤m2≤50%.

[0012] In some embodiments of the present application, the range of f is 0.4≤f≤1.

[0013] In some embodiments of the present application, the carboxylate solvent includes at least one of methyl formate, ethyl formate, propyl formate, ethyl acetate, methyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate.

[0014] In some embodiments of the present application, the non-free electrolyte further includes a diisocyanate additive, and the mass proportion of the diisocyanate additive in the non-free electrolyte is a, satisfying 66≤m1 / a≤600.

[0015] In some embodiments of the present application, the range of a is 0.05%≤a≤0.3%.

[0016] In some embodiments of the present application, the diisocyanate additive includes at least one of toluene-2,5-diisocyanate, toluene-2,6-diisocyanate, toluene-2,4-diisocyanate, 1,4-cyclohexanedimethyl diisocyanate, and cyclohexane-1,4-diisocyanate.

[0017] The second aspect of the present application proposes a liquid injection method for a battery as described in the above embodiment. According to the embodiment of the present application, the liquid injection method includes:

[0018] Use one injection of electrolyte for the first injection, let it stand, and form;

[0019] Use two injections of electrolyte for the second injection, high temperature aging, and volume separation.

[0020] According to the injection method of the embodiment of the present application, the electrolyte required for the battery formation stage and the electrolyte required for the circulation stage are separated by secondary injection, and the local distribution characteristics of the non-free electrolyte and the free electrolyte in the initial state of the battery are flexibly controlled, thereby effectively improving the overcharge safety performance of the battery.

[0021] In addition, the liquid injection method according to the above embodiment of the present application may also have the following additional technical features:

[0022] In some embodiments of the present application, the first injection of electrolyte includes a carboxylate solvent, and the mass proportion of the carboxylate solvent in the first injection of electrolyte is M1. The second injection of electrolyte includes a carboxylate solvent, and the mass proportion of the carboxylate solvent in the second injection of electrolyte is M2, satisfying 15%≤M1≤25%, 30%≤M2≤60%.

[0023] In some embodiments of the present application, the one injection of electrolyte includes a diisocyanate additive, and the mass proportion of the diisocyanate additive in the one injection of electrolyte is M3, satisfying 0.1%≤M3≤0.5%.

[0024] In some embodiments of the present application, the mass ratio of the first injection of electrolyte to the second injection of electrolyte is (7:3) to (9:1).

[0025] In some embodiments of the present application, the injection coefficient of the sum of the first injection of electrolyte and the second injection of electrolyte is 2.5 g / Ah to 5 g / Ah.

[0026] The third aspect of the present application proposes an energy storage device. According to an embodiment of the present application, the above energy storage device includes a battery of the above embodiment or a battery obtained by the injection method of the above embodiment. As a result, the energy storage device has excellent safety performance and cycle performance. It should be noted that the above-described features and advantages for the battery are also applicable to the energy storage device and will not be repeated here.

[0027] The fourth aspect of the present application proposes an electric power system. According to an embodiment of the present application, the electric power system includes: electric equipment, and an energy storage device as in the above embodiment, and the energy storage device supplies power to the electric equipment. As a result, the electric power system has excellent safety performance and cycle performance. It should be noted that the features and advantages described above for the battery are also applicable to the electric power system and will not be repeated here.

[0028] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. DETAILED DESCRIPTION

[0029] The embodiments of the present application are described in detail below, which are intended to be used to explain the present application but should not be construed as limiting the present application.

[0030] In a first aspect, the present application proposes a battery. According to an embodiment of the present application, the battery includes: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, the electrolyte includes a free electrolyte and a non-free electrolyte, the non-free electrolyte includes the electrolyte in the pores of the positive electrode sheet, the electrolyte in the pores of the negative electrode sheet and the electrolyte in the pores of the separator, the free electrolyte includes the electrolyte in the gap between the positive electrode sheet and the separator, the electrolyte in the gap between the positive electrode sheet and the separator, and the electrolyte in the gap between the positive electrode sheet and the separator. The electrolyte in the gap between the pole piece and the diaphragm; the non-free electrolyte includes a carboxylate solvent, the mass proportion of the carboxylate solvent in the non-free electrolyte is m1, the free electrolyte includes a carboxylate solvent, the mass proportion of the carboxylate solvent in the free electrolyte is m2, satisfying 0.4≤m1 / m2≤1.2; the diaphragm has a PVDF coating, and the surface density of the PVDF in the PVDF coating on the diaphragm is fg / m 2 , satisfying 0.8≤f / m2≤4.

[0031] The principle of the beneficial effect of the battery proposed in this application is described in detail below:

[0032] In order to solve the problem that during the overcharging process of large batteries, the rapid accumulation of heat causes a chain chemical reaction inside the battery, which in turn causes thermal runaway of the battery and even fire and explosion, the present application forms two forms of free electrolyte and non-free electrolyte in the battery by injecting electrolyte twice. Specifically, the main function of one injection of electrolyte is to infiltrate into the electrode pores and the diaphragm pores, and to form an initial SEI film during the first charge and discharge process of the battery, which is the main component of the non-free electrolyte; the second injection of electrolyte is injected after the battery is formed, and it mainly exists outside the bare battery and in the gap between the electrode and the diaphragm, which is the main component of the free electrolyte. The free electrolyte and the non-free electrolyte play different functions and play a role in improving the overcharge safety performance. The inventors found that only by limiting 0.4≤m1 / m2≤1.2 within the above range can the overcharge safety performance of the battery be effectively improved. If m1 / m2 is too small or too large, the overcharge safety performance of the battery cannot be effectively improved.

[0033] In the present application, both the free electrolyte and the non-free electrolyte contain carboxylate solvents, which have the advantage of low viscosity, can improve the wettability of the electrolyte and realize the rapid transfer of lithium ions in the negative electrode pores. In addition, when the temperature of the battery core rises, the carboxylate solvent in the free electrolyte easily causes the PVDF coating on the diaphragm to swell, thereby causing the PVDF to block the gaps in the diaphragm, increasing the battery impedance, and causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering the charging to stop, thereby effectively improving the overcharge safety performance of the battery.

[0034] In addition, the characteristic of the PVDF swelling effect is that the higher the content of the carboxylate solvent in the free electrolyte, the more obvious the swelling degree of PVDF, and the higher the temperature, the higher the swelling degree. Therefore, the present application satisfies 0.8≤f / m2≤4 (for example, f / m2 can be 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, etc.) by regulating the content m2 of the carboxylate solvent in the free electrolyte and the surface density f of PVDF on the diaphragm coating, thereby achieving that the free electrolyte does not swell the PVDF coating on the diaphragm during normal operation (circulation operation at room temperature), but in the case of overcharge, as the temperature rises, the PVDF layer on the diaphragm swells, blocking the gaps in the diaphragm, causing the battery voltage to rise rapidly to the overcharge cut-off voltage, thereby triggering the stop of charging. The inventors found that only by satisfying 0.8≤f / m2≤4 can the overcharge safety performance of the battery be effectively improved, and f / m2 that is too small or too large cannot effectively improve the overcharge safety performance of the battery.

[0035] According to some specific embodiments of the present application, the range of m2 is 25%≤m2≤50%, for example, m2 can be 25%, 30%, 35%, 40%, 45%, 50%, etc., thereby further cooperating the free electrolyte with the PVDF coating of the diaphragm, so that when the battery cell is working normally, the free electrolyte will not swell the PVDF coating on the diaphragm, and during the overcharging process, the PVDF is swollen by the electrolyte, blocking the gaps in the diaphragm, causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering charging to stop, further improving the overcharge safety performance of the battery.

[0036] According to some specific embodiments of the present application, the range of f is 0.4≤f≤1, for example, the surface density of PVDF on the diaphragm coating can be 0.4 g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1.0g / m 2 Etc., which can further make the PVDF coating of the diaphragm cooperate with the free electrolyte, so that when the battery cell is working normally, the free electrolyte will not swell the PVDF coating on the diaphragm, and during the overcharge process, the PVDF is swollen by the electrolyte, blocking the diaphragm gap, causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering the charging to stop, further improving the overcharge safety performance of the battery.

[0037] According to some other specific embodiments of the present application, the above-mentioned non-free electrolyte also includes a diisocyanate additive. As mentioned above, the present application cooperates with the free electrolyte and the diaphragm PVDF coating so that the PVDF of the battery cell is swollen by the free electrolyte during the overcharging process, blocking the diaphragm gap, causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering the charging to stop. At this time, although the battery cell has stopped charging, if the heat generation of the battery cell in the early stage is too rapid, the heat generation may trigger a chain chemical reaction inside the battery cell, and the heat generation will continue to accumulate in a snowball-like manner, which may still cause thermal runaway of the battery cell. Therefore, the present application makes the SEI film more stable through the cooperation of the carboxylic acid ester solvent and the diisocyanate additive in the non-free electrolyte, and the SEI film will not rupture in large quantities during the overcharging process, avoiding the possibility of excessive heat generation in the early stage, thereby further avoiding the occurrence of overcharge thermal runaway and further improving the overcharge safety performance of the battery.

[0038] Specifically, carboxylate solvents can improve the wettability of non-free electrolytes and achieve rapid transfer of lithium ions in the pores of the negative electrode. Diisocyanate additives contain diisocyanate groups, which can effectively construct a stable SEI film on the surface of the negative electrode (such as a graphite negative electrode) and reduce the reaction between the negative electrode interface and the electrolyte. When a shot of electrolyte contains both carboxylate solvents and diisocyanate additives, due to the improved wettability brought by the carboxylate solvent, the diisocyanate additives can form a film more uniformly on the negative electrode, and the formed SEI film is more stable, avoiding a large number of ruptures of the SEI film during overcharging, thereby effectively avoiding a large amount of heat release caused by direct contact reaction between the lithiated negative electrode (such as lithiated graphite) and the electrolyte, and avoiding rapid chain reactions caused by excessive temperature rise, thereby further improving the overcharge safety performance of the battery. At the same time, due to the improvement of SEI film formation, the cycle performance of the battery cell is also improved.

[0039] At the same time, the mass proportion of the above-mentioned diisocyanate additive in the non-free electrolyte is a. The present application limits 66≤m1 / a≤600 (for example, m1 / a can be 66.7, 100, 200, 300, 400, 500, 600, etc.), which can further make the diisocyanate additive and the carboxylate solvent in the non-free electrolyte cooperate with each other, form a film more evenly at the negative electrode, and the formed SEI film is more stable, further avoiding a large number of SEI films from rupturing during overcharging.

[0040] According to some other specific embodiments of the present application, the range of m1 is 20%≤m1≤30%, for example, m1 can be 20%, 22%, 24%, 26%, 28%, 30%, etc., thereby further coordinating the carboxylic acid ester solvent in the non-free electrolyte with the diisocyanate additive, forming a more uniform film at the negative electrode, and the formed SEI film is more stable, further avoiding a large number of SEI film ruptures during overcharging.

[0041] According to some other specific embodiments of the present application, the range of a is 0.05%≤a≤0.3%, for example, it can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc., thereby further making the diisocyanate additives in the non-free electrolyte cooperate with the carboxylate solvent, forming a more uniform film at the negative electrode, and the formed SEI film is more stable, further avoiding a large number of SEI film ruptures during overcharging.

[0042] In the embodiments of the present application, the specific types of the above-mentioned carboxylate solvents are not particularly limited, and those skilled in the art can select them according to actual needs. As some preferred embodiments, the above-mentioned carboxylate solvents include at least one of methyl formate (MF for short), ethyl formate, propyl formate, ethyl acetate (EA for short), methyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate (n-Pr-Pr for short), and methyl butyrate. The above-mentioned types of carboxylate solvents are all easy to cause the PVDF coating on the diaphragm to swell, and the above-mentioned types of carboxylate solvents can also promote the diisocyanate additive to form a film more uniformly on the negative electrode.

[0043] In the embodiments of the present application, the specific types of the above-mentioned diisocyanate additives are not particularly limited, and those skilled in the art can select them according to actual needs. As some preferred embodiments, the diisocyanate additives include toluene-2,5-diisocyanate (2,5-TDI for short), toluene 2,6-diisocyanate, toluene-2,4-diisocyanate (2,4-TDI for short), 1,4-cyclohexane dimethyl diisocyanate, cyclohexane-1,4-diisocyanate (CHDI for short) at least one. The above-mentioned types of diisocyanate additives can be more uniformly filmed on the negative electrode in the combination of carboxylic acid ester solvents.

[0044] In the embodiments of the present application, the first electrolyte and the second electrolyte further include other organic solvents, lithium salts, and additives, respectively. The above-mentioned other organic solvents include but are not limited to at least one of cyclic carbonates and their fluorinated compounds, linear carbonates and their fluorinated compounds, carboxylates and their fluorinated compounds. The use of the above-mentioned ester solvents has the advantages of a wide electrochemical window, a wide stable operating temperature range, and good electrical conductivity.

[0045] In an embodiment of the present application, the above-mentioned diaphragm may include a diaphragm substrate and a PVDF coating, wherein the PVDF coating is disposed on at least a portion of the surface of the diaphragm substrate. Optionally, a ceramic layer or other functional layer may be disposed between the diaphragm substrate and the PVDF coating.

[0046] In the embodiments of the present application, the above-mentioned battery can be used for both lithium-ion batteries and sodium-ion batteries. The following takes lithium-ion batteries as an example for explanation:

[0047] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, and the positive active material layer includes a positive active material. The specific type of the positive active material is not particularly limited. As some specific embodiments, the positive active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium cobalt phosphate, lithium manganese phosphate, lithium nickel phosphate, lithium manganese oxide, binary materials, and ternary materials.

[0048] In some embodiments of the present application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material base and a metal layer formed on at least one side of the polymer material base. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and other substrates).

[0049] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0050] In some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene-butadiene rubber (SBR).

[0051] In some embodiments of the present application, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet (such as positive electrode active material, conductive agent, binder) are dispersed in an organic solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0052] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0053] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0054] In some embodiments of the present application, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. The silicon-based material may include at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin-oxygen compounds, and tin alloys.

[0055] In some embodiments of the present application, the negative electrode active material layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0056] In some embodiments of the present application, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] In some embodiments of the present application, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0058] In some embodiments of the present application, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet (such as negative electrode active material, conductive agent, binder and any other components) are dispersed in an organic solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0059] The second aspect of the present application proposes a method for injecting liquid in a battery of one or more embodiments. According to the embodiments of the present application, the above-mentioned injection method includes: using one injection of electrolyte for the first injection, standing, and forming; using two injections of electrolyte for the second injection, high temperature aging, and capacity separation.

[0060] Specifically, the above-mentioned injection method includes:

[0061] S100: Use one injection of electrolyte for the first injection, let it stand, and then

[0062] In this step, an electrolyte is injected for the first time, left to stand, and formed to form an initial SEI film on the surface of the positive electrode active material and the negative electrode active material respectively. The part of the electrolyte remaining in the positive electrode plate, the negative electrode plate and the pores of the diaphragm after the electrolyte formation reaction forms a non-free electrolyte in the initial state.

[0063] S200: Use two injections of electrolyte for the second injection, high temperature aging, and capacity division

[0064] In this step, two injections of electrolyte are used for the second injection, high temperature aging, and volume separation to form the initial state of free electrolyte. When one injection of electrolyte is excessive, the part that is not consumed or does not enter the pores of the diaphragm, positive electrode sheet, and negative electrode sheet merges with the second injection of electrolyte to form the initial state of free electrolyte.

[0065] According to the injection method of the embodiment of the present application, the electrolyte required for the battery formation stage and the electrolyte required for the circulation stage are separated by secondary injection, and the local distribution characteristics of the non-free electrolyte and the free electrolyte in the initial state of the battery are flexibly controlled, thereby effectively improving the overcharge safety performance of the battery.

[0066] According to some specific embodiments of the present application, the first injection of electrolyte includes a carboxylate solvent, and the mass proportion of the carboxylate solvent in the first injection of electrolyte is M1, and the second injection of electrolyte includes a carboxylate solvent, and the mass proportion of the carboxylate solvent in the second injection of electrolyte is M2, satisfying 15%≤M1≤25%, 30%≤M2≤60%. By controlling the content of the carboxylate solvent in the first injection of electrolyte and the second injection of electrolyte respectively, the content of the carboxylate solvent in the free electrolyte and the non-free electrolyte can be effectively controlled, so that the free electrolyte and the PVDF coating of the diaphragm can be matched, so that the PVDF of the battery cell is swollen by the free electrolyte during the overcharging process, blocking the gaps in the diaphragm, causing the battery voltage to quickly rise to the overcharge cut-off voltage, thereby triggering the charging to stop.

[0067] According to some further specific embodiments of the present application, the one injection of electrolyte includes a diisocyanate additive, and the mass proportion of the diisocyanate additive in the one injection of electrolyte is M3, satisfying 0.1%≤M3≤0.5%. By controlling the content of the diisocyanate additive in the one injection of electrolyte, the content of the diisocyanate additive in the non-free electrolyte can be effectively controlled, so that the diisocyanate additive in the one injection of electrolyte can be combined with the carboxylate solvent to form a film more evenly at the negative electrode, and the formed SEI film is more stable, further avoiding a large number of ruptures of the SEI film during overcharging.

[0068] In the embodiments of the present application, the electrolyte demand of the battery is related to the cell capacity, and the electrolyte demand can be represented by the injection coefficient (injection amount / cell capacity). According to some specific embodiments of the present application, the injection coefficient of the sum of the first injection of electrolyte and the second injection of electrolyte is 2.5g / Ah to 5g / Ah, and as an example, it can be 2.5g / Ah, 3g / Ah, 3.5g / Ah, 4g / Ah, 4.5g / Ah, 5g / Ah, etc. By limiting the injection coefficient within the above range, it can ensure that the diaphragm and the positive and negative electrode plates are fully infiltrated, and the electrolyte will not swell or accumulate at the bottom of the battery due to excessive amount of electrolyte, causing local lithium precipitation.

[0069] According to some further specific embodiments of the present application, the mass ratio of the first injection of electrolyte to the second injection of electrolyte is (7:3) to (9:1). By limiting the mass ratio of the first injection of electrolyte to the second injection of electrolyte within the above range, the local distribution characteristics of the non-free electrolyte and the free electrolyte can be further ensured, thereby effectively improving the overcharge safety performance of the battery.

[0070] The third aspect of the present application proposes an energy storage device. According to an embodiment of the present application, the above energy storage device includes a battery of the above embodiment or a battery obtained by the injection method of the above embodiment. As a result, the energy storage device has excellent safety performance and cycle performance. It should be noted that the above-described features and advantages for the battery are also applicable to the energy storage device and will not be repeated here.

[0071] Specifically, the energy storage device of the present application may include but is not limited to a battery module, a battery pack, a battery system, etc. In addition, the energy storage device of the present application may also include at least one of an electric energy storage device for the power generation side of the power system, an electric energy storage device for the power distribution side of the power system (such as an electrochemical energy storage device), and an electric energy storage device for the user side of the power system.

[0072] The fourth aspect of the present application proposes an electric power system. According to an embodiment of the present application, the electric power system includes: electric equipment, and an energy storage device as in the above embodiment, and the energy storage device supplies power to the electric equipment. As a result, the electric power system has excellent safety performance and cycle performance. It should be noted that the features and advantages described above for the battery are also applicable to the electric power system and will not be repeated here.

[0073] The above-mentioned power consumption system may include but is not limited to mobile phones, tablet computers, laptop computers, desktop computers, smart bracelets, smart watches, e-readers, game consoles and other portable electronic devices. It may also include but is not limited to vehicles such as cars, trucks, cars, vans, motor vehicles, high-speed trains, electric vehicles, etc. In addition, it may also be various household appliances, such as but not limited to refrigerators, electric lights, air conditioners, etc.

[0074] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. In addition, unless otherwise explicitly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to this article or known methods, and the reaction conditions not listed are also easily available to those skilled in the art.

[0075] Example 1

[0076] This embodiment provides a lithium ion battery, and the preparation method thereof includes:

[0077] 1) Preparation of positive electrode sheet:

[0078] The positive electrode active material lithium iron phosphate, conductive carbon black SP, and adhesive PVDF were dispersed in the solvent NMP according to the mass ratio of 97:0.7:2.3, and mixed evenly to obtain the positive electrode slurry; the positive electrode slurry was coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The surface density of the positive electrode active material layer on the positive electrode sheet was 0.01948 mg / cm 2 .

[0079] 2) Preparation of negative electrode sheet:

[0080] The negative electrode active material artificial graphite, conductive carbon SP, thickener CMC and binder SBR were dispersed in deionized water according to a mass ratio of 96.5:0.5:1:2, and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector aluminum foil, and after drying, cold pressing, slitting and cutting, a negative electrode sheet was obtained. The surface density of the negative electrode active material layer on the negative electrode sheet was 0.009349 mg / cm 2 .

[0081] 3) Preparation of electrolyte:

[0082] In an argon atmosphere glove box with a moisture content of ≤1ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a mass ratio of 1:1:1, and then the dried electrolyte lithium hexafluorophosphate is dissolved in the solvent and stirred until completely dissolved and uniform. The mass proportion of lithium hexafluorophosphate in the electrolyte is 12.5%. According to the design in Table 1, carboxylic acid ester solvents and diisocyanate additives are added to the electrolyte, and the electrolyte is obtained after mixing evenly. Except for the mass proportion of carboxylic acid ester solvents and diisocyanate additives in one shot and two shots of electrolyte, which changes according to the design in the table, the other components have no different designs in one shot and two shots of electrolyte.

[0083] 4) Preparation of isolation membrane:

[0084] A 16 μm polyethylene film is used as a diaphragm, and the diaphragm has a PVDF coating. The surface density f value of PVDF in the PVDF coating on the diaphragm is shown in Table 1.

[0085] 5) Battery assembly:

[0086] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order so that the separator is in the middle of the positive and negative electrodes to separate the positive and negative electrode sheets. After winding, a bare battery cell is obtained. After welding the pole ears, the battery cell is assembled into an outer package, injected with a shot of electrolyte and allowed to stand and formed, allowed to stand again and injected with a second shot of electrolyte, packaged, and capacity tested, etc., to finally prepare a lithium-ion battery.

[0087] The formation process adopts the following process: Step 1: the battery cell is allowed to stand in a 45°C formation cabinet for 10 minutes, and charged at a rate of 0.1C for 7 minutes to 1.17% SOC; Step 2: Stand for 3 minutes, and charge at a rate of 0.2C to 30% SOC.

[0088] Among them, the injection coefficient is 4.0g / Ah; the mass ratio of the first injection of electrolyte and the second injection of electrolyte is 85:15; the static conditions after the first injection are 45±5℃ for 24 hours, and the formation temperature is 45℃; the high temperature aging conditions after the second injection are 45±5℃ for 24 hours.

[0089] Embodiments 2 to 18

[0090] The preparation methods of Examples 2 to 18 are basically the same as those of Example 1, and the differences are detailed in Table 1.

[0091] Comparative Examples 1 to 6

[0092] The preparation methods of Comparative Examples 1 to 6 are substantially the same as those of Example 3, and the differences are detailed in Table 1.

[0093] Free electrolyte composition test:

[0094] Discharge the battery with outer packaging with a current of 0.05C to 0% SOC (2.5V), cut a notch of about 0.5cm on the right side facing the positive column of the battery, and cut the same notch on the right side facing the negative column, ensuring that the two notches are on the diagonal line, and pour the free electrolyte into the fluoride bottle from the small opening on the side of the positive column until intermittent dripping flows down and count for 30s.

[0095] Gas chromatography-mass spectrometry (GC-MS) was used to test the types and relative mass contents of organic components in the collected electrolyte.

[0096] Non-free (pore) electrolyte composition test:

[0097] Remove the outer packaging, take out a single bare cell, quickly peel off the electrode, put it into an aluminum-plastic bag, add enough acetonitrile solvent to completely immerse the electrode, seal the aluminum-plastic bag containing acetonitrile solvent and electrode, and let it stand at 35±10℃ for 3 days.

[0098] The types and relative mass contents of organic components in the collected electrolyte were tested using a gas chromatography-mass spectrometer (GC-MS). The results are shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] The lithium ion batteries of Examples 1 to 18 and Comparative Examples 1 to 6 were subjected to overcharge safety tests and cycle performance tests, respectively. The results are shown in Table 2.

[0103] Overcharge safety test:

[0104] The lithium-ion battery was tested on a charge and discharge instrument, and left at (25±2)℃ for 5h; 1P was discharged to 2.5V, 1P was charged to 3.65V, and left at rest for 10min. Then it was transferred to the overcharge test instrument for testing, and charged at a constant current of 0.5C until the battery voltage reached 5.475V or the charging time reached 1h. Observed for 1h, and recorded whether there was swelling, leakage, smoke, fire, or explosion. Rating: If the battery cell does not leak, it is the first level of compliance; if the battery cell leaks but does not have thermal runaway, it is the second level of compliance; if the battery cell leaks, smokes, and has thermal runaway, but does not catch fire or explode, it is the third level of compliance; if the battery cell catches fire or explodes, it is the fourth level, which means it does not meet the standard.

[0105] Conditions for determining whether thermal runaway has occurred: a temperature sensor is set up and arranged on the surface of the test sample, the temperature monitoring sampling frequency is 1s, and if the temperature rise rate at the monitoring point is ≥3℃ / s for three consecutive times or a fire or explosion occurs, it is considered to be thermal runaway.

[0106] Cycle performance test:

[0107] The lithium-ion battery is subjected to a charge and discharge cycle test on a charge and discharge instrument, the test temperature is 25°C, the cycle rate is 1C (i.e., both the charge rate and the discharge rate are 1C), the charging voltage is 2.5V to 3.65V, and the capacity retention rate after the cycle is calculated. The capacity retention rate calculation formula for the 25°C cycle is: Capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) * 100%.

[0108] Table 2

[0109]

[0110]

[0111] As can be seen from Table 1, the overcharge safety performance and the capacity retention rate of 3000 cycles at 25°C of Examples 1 to 18 are better than those of Comparative Example 1, and the overcharge safety performance and the capacity retention rate of 3000 cycles at 25°C of Examples 1 to 18 are better than those of Comparative Example 2. It can be seen that when the electrolyte does not contain the carboxylate solvent M, even if the diaphragm contains PVDF, the overcharge safety performance and capacity retention rate of the battery cannot be significantly improved; when the diaphragm does not contain PVDF, even if the carboxylate solvent M is added to the electrolyte, it cannot improve the overcharge safety performance and capacity retention rate of the battery. However, in the present application, when the diaphragm contains a PVDF coating, the free electrolyte carboxylate solvent M can be used to significantly improve the overcharge safety performance and capacity retention rate of the battery.

[0112] It can be seen from Table 1 that compared with Comparative Examples 3 and 4, the overcharge safety performance and the capacity retention rate of 3000 cycles at 25°C of Examples 1 to 18 are superior. It can be seen that only when 0.8≤f / m2≤4 is satisfied can the overcharge safety performance and capacity retention rate of the battery be effectively improved. If f / m2 is too small or too large, the overcharge safety performance and capacity retention rate of the battery cannot be effectively improved.

[0113] It can be seen from Table 1 that compared with Comparative Examples 5 and 6, the overcharge safety performance and the capacity retention rate of 3000 cycles at 25°C of Examples 1 to 18 are better. It can be seen that only when 0.4≤m1 / m2≤1.2 is satisfied can the overcharge safety performance and capacity retention rate of the battery be effectively improved. If m1 / m2 is too small or too large, the overcharge safety performance and capacity retention rate of the battery cannot be effectively improved.

[0114] As can be seen from Table 1, compared with Examples 1 to 9, the overcharge safety performance of Examples 10 to 18 is further improved, and the capacity retention rate of Examples 10 to 18 after 3000 cycles at 25°C is significantly improved. It can be seen that the carboxylic acid ester solvent M and the diisocyanate additive A cooperate to form a film more uniformly at the negative electrode, and the formed SEI film is more stable, thereby further improving the overcharge safety performance and capacity retention rate of the battery. In addition, compared with Examples 10 to 13 and Examples 15 to 18, the overcharge safety performance and capacity retention rate of Example 14 are relatively poor, which is due to the fact that the mass proportion m1 of M in the non-free electrolyte in Example 14 is too high and the mass proportion m2 of M in the free electrolyte is too high.

[0115] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0116] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet, the electrolyte comprises a free electrolyte and a non-free electrolyte, and the non-free electrolyte comprises an electrolyte in the pores of the positive electrode sheet, an electrolyte in the pores of the negative electrode sheet and an electrolyte in the pores of the separator; The non-free electrolyte includes a carboxylate solvent, the mass proportion of the carboxylate solvent in the non-free electrolyte is m1, the free electrolyte includes a carboxylate solvent, the mass proportion of the carboxylate solvent in the free electrolyte is m2, and 0.4≤m1 / m2≤1.2 is satisfied; The diaphragm has a PVDF coating, and the surface density of PVDF in the PVDF coating on the diaphragm is fg / m 2 , satisfying 0.8≤f / m2≤4.

2. The battery according to claim 1, characterized in that The range of m1 is 20%≤m1≤30%; And / or, the range of m2 is 25%≤m2≤50%.

3. The battery according to claim 1, characterized in that The range of f is 0.4≤f≤1.

4. The battery according to claim 1, characterized in that The carboxylate solvent includes at least one of methyl formate, ethyl formate, propyl formate, ethyl acetate, methyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and methyl butyrate.

5. The battery according to any one of claims 1 to 4, characterized in that The non-free electrolyte also includes a diisocyanate additive, and the mass proportion of the diisocyanate additive in the non-free electrolyte is a, satisfying 66≤m1 / a≤600.

6. The battery according to claim 5, characterized in that The range of a is 0.05%≤a≤0.3%.

7. The battery according to claim 5, characterized in that The diisocyanate additive includes at least one of toluene-2,5-diisocyanate, toluene-2,6-diisocyanate, toluene-2,4-diisocyanate, 1,4-cyclohexanedimethyl diisocyanate, and cyclohexane-1,4-diisocyanate.

8. A method for injecting liquid into a battery as claimed in any one of claims 1 to 7, characterized in that: include: Use one injection of electrolyte for the first injection, let it stand, and form; Use two injections of electrolyte for the second injection, high temperature aging, and volume separation.

9. The liquid injection method according to claim 8, characterized in that: The first injection of electrolyte includes a carboxylate solvent, and the mass proportion of the carboxylate solvent in the first injection of electrolyte is M1. The second injection of electrolyte includes a carboxylate solvent, and the mass proportion of the carboxylate solvent in the second injection of electrolyte is M2, satisfying 15%≤M1≤25%, 30%≤M2≤60%.

10. The liquid injection method according to claim 8, characterized in that: The one injection of electrolyte includes a diisocyanate additive, and the mass proportion of the diisocyanate additive in the one injection of electrolyte is M3, satisfying 0.1%≤M3≤0.5%.

11. The liquid injection method according to any one of claims 8 to 10, characterized in that: The mass ratio of the first injection of electrolyte to the second injection of electrolyte is (7:3) to (9:1).

12. The liquid injection method according to any one of claims 8 to 10, characterized in that: The total injection coefficient of the first injection of electrolyte and the second injection of electrolyte is 2.5 g / Ah to 5 g / Ah.

13. An energy storage device, characterized in that: A battery comprising the battery according to any one of claims 1 to 7 or a battery obtained by the injection method according to any one of claims 8 to 12.

14. An electricity system, characterized in that: include: Electrical equipment, and The energy storage device as claimed in claim 13, wherein the energy storage device supplies power to the electrical equipment.

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