Electrolyte, energy storage device and electric equipment

Abstract

The application provides an electrolyte, an energy storage device and an electric equipment. An electrolyte provided by a first aspect of the application comprises an electrolyte salt, an organic solvent and a film-forming additive. The organic solvent comprises an ether compound. The film-forming additive comprises a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group. By adding the ether compound and the nitrogen-containing heterocyclic compound with the strong electron-withdrawing group into the electrolyte, the electrolyte has good wettability, can quickly wet a thick electrode plate, and can form a stable interface film on the surface of the electrode plate, so that the energy storage device has high energy density and good cycle performance.

Description

TECHNICAL FIELD

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

[0002] With the continuous development of battery technology, whether it is a consumer battery, a power battery, or an energy storage battery, the battery needs to have lower cost and higher energy density. An important way to reduce cost or increase battery energy density is to increase the coating weight per unit area of the pole piece, the pole piece coating thickness and the pole piece compaction density, to reduce the amount of non-active materials such as aluminum foil and copper foil under the condition that the capacity of the active material remains unchanged, thereby increasing the energy density of the battery and reducing the cost. However, while increasing the pole piece coating thickness and the pole piece compaction density, a series of problems also arise. The electrolyte has insufficient wettability to the active material, and in the cycle process, due to the expansion and contraction of the SEI film, the electrolyte on the surface of the active material is continuously consumed. However, due to the insufficient wettability of the conventional carbonate solvent in the electrolyte, the active material near the foil part inside the active material layer cannot be effectively wetted in time, resulting in the inability of lithium ions to be smoothly transmitted to the surface of the internal active material. In the charging process, there is a lack of lithium ions inside the negative active material layer and an excess of lithium ions on the surface, which further leads to lithium precipitation, resulting in rapid decay of the capacity retention rate. SUMMARY

[0003] To solve the above problems, the present application provides an electrolyte which can ensure good wettability and form a stable interface film on the surface of the pole piece, so that the energy storage device has high energy density and good cycle performance.

[0004] The first aspect of the present application provides an electrolyte, which comprises: an electrolyte salt, an organic solvent and a film-forming additive, the organic solvent comprises an ether compound; and the film-forming additive comprises a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group.

[0005] The nitrogen-containing heterocyclic compound with a strong electron-withdrawing group is a fluorine-substituted nitrogen-containing heterocyclic compound.

[0006] The nitrogen-containing heterocyclic compound with a strong electron-withdrawing group includes at least one of a fluorine-substituted pyrazine, a fluorine-substituted pyridine and a fluorine-substituted pyridazine.

[0007] The ratio of the mass m1 of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group to the mass m2 of the ether compound is in the range of 0.01≤m1 / m2≤0.06.

[0008] The mass fraction a of the ether compound in the electrolyte ranges from 10% to 50%; the mass fraction b of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte ranges from 0.1% to 3%.

[0009] The electrolyte further comprises a sulfur-containing additive, and the ratio of the mass m3 of the sulfur-containing additive to the mass m1 of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group ranges from 0.1 to 10.

[0010] The sulfur-containing additive comprises at least one of vinyl sulfate, 1,3-propane sulfonate lactone, 1,3-propylene sulfonate lactone, methyl disulfonate methylene, 1,4-butane sulfonate lactone, 2,4-butane sulfonate lactone, 1,3-propanediol sulfate, ethylene sulfite, and pentaerythritol bis-cyclic sulfate.

[0011] The fluorine-substituted pyrazine comprises at least one of 2-fluoropyrazine and 2,5-difluoropyrazine; the fluorine-substituted pyridine comprises at least one of 2-fluoropyridine, 3-fluoropyridine, 4-fluoropyridine, 2,3-fluoropyridine, and 3,4-fluoropyridine; and the fluorine-substituted pyridazine comprises at least one of 2-fluoropyridazine and 3-fluoropyridazine.

[0012] The second aspect of the application provides an energy storage device, comprising: the electrolyte, a negative electrode sheet, a separator, and a positive electrode sheet according to the embodiments of the application; the negative electrode sheet is at least partially immersed in the electrolyte; the separator is located on one side of the negative electrode sheet and is at least partially immersed in the electrolyte; and the positive electrode sheet is arranged on the side of the separator away from the negative electrode sheet and is at least partially immersed in the electrolyte.

[0013] The positive electrode sheet comprises a current collector and an active material layer, and the weight t of the active material layer ranges from 0.16 mg / mm 2 to 0.39 mg / mm 2 .

[0014] The electrolyte further comprises a sulfur-containing additive, and the energy storage device satisfies the relationship 6 < t*(b+c) / a < 240, where a is the mass fraction of the ether compound in the electrolyte, b is the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte, and c is the mass fraction of the sulfur-containing additive in the electrolyte.

[0015] The third aspect of the application provides an electronic device, comprising: a power-consuming device body and an energy storage device according to the embodiments of the application, wherein the energy storage device supplies power to the power-consuming device body.

[0016] The electrolyte of the present application contains an ether compound, which has low viscosity and can solve the problem of insufficient infiltration as an organic solvent of the electrolyte, so that the electrolyte can well infiltrate the active material. However, the interface film formed on the surface of the positive and negative electrode sheets by the ether compound has poor quality, which cannot effectively inhibit the further reaction of the electrode sheet and the electrolyte, resulting in rapid consumption of the organic solvent and affecting the service life of the energy storage device. By further adding a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group to the electrolyte, the nitrogen-containing heterocyclic compound has a strong electron-withdrawing group, and the presence of the strong electron-withdrawing group causes the overall charge of the nitrogen-containing heterocyclic compound to be biased, which makes the nitrogen-containing heterocyclic compound more easily ring-opening, oxidizing and polymerizing at the positive electrode to protect the positive active material, thereby avoiding further contact between the positive active material and the electrolyte. At the negative electrode, the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group can be reduced by electron at a high potential to form a dense and thick SEI film wrapped on the surface of the negative electrode sheet, effectively inhibiting the side reaction of the electrolyte on the surface of the negative electrode, thereby improving the cycle life of the energy storage device. During the process of infiltrating the inner layer of active material layer close to the current collector by the electrolyte, if there are many side reactions on the surface of the electrode sheet, it may cause the path of the electrolyte into the inner layer to be blocked, while the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group can generate a stable interface film to effectively prevent the side reaction on the surface of the electrode sheet, so that the ether compound can better exert its low viscosity advantage; the low viscosity and high conductivity of the ether compound can also help the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group to reach the surface of the active material layer more uniformly, thereby forming a uniform and stable interface film on the surface of the thick electrode sheet, so that the energy storage device has better cycle performance. By adding the ether compound and the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group to the electrolyte, the electrolyte can have good infiltration capacity, can quickly infiltrate the thick electrode sheet, and can also form a stable interface film on the surface of the electrode sheet, so that the energy storage device has high energy density and good cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0018] Figure 1 is a structural schematic diagram of an energy storage device of an embodiment of the present application.

[0019] Figure 2 is a structural schematic diagram of an energy storage device of an embodiment of the present application along Figure 1 the A-A direction.

[0020] Figure 3is a structural schematic diagram of a positive electrode tab according to an embodiment of the present application.

[0021] Figure 4 is a structural schematic diagram of a positive electrode tab according to an embodiment of the present application. Figure 3 is a structural schematic diagram of a positive electrode tab according to an embodiment of the present application.

[0022] Figure 5 is a structural schematic diagram of an electrical device according to an embodiment of the present application, wherein the energy storage device and the electrical device body are in a separated state.

[0023] Legend of reference signs:

[0024] 100-energy storage device, 120-negative electrode tab, 130-separator, 140-positive electrode tab, 141-active material layer, 142-current collector, 200-electrical device, 210-electrical device body. DETAILED DESCRIPTION

[0025] In order to enable persons skilled in the art to better understand the schemes of the present application, the technical schemes in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by persons skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] The terms "first", "second", and the like in the specification and claims of the present application and the above drawings are used to distinguish different objects, and are not used to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but can optionally further include steps or units not listed, or can optionally further include other steps or units inherent to the process, method, product or device.

[0027] The technical schemes in the embodiments of the present application will be described below in combination with the drawings.

[0028] It should be noted that, for the sake of illustration, in the embodiments of the present application, the same reference signs represent the same components, and for the sake of brevity, detailed description of the same components is omitted in different embodiments.

[0029] With the continuous development of battery technology, whether it is a consumer battery, a power battery, or an energy storage battery, the battery needs to have lower cost and higher energy density. An important way to reduce the cost or increase the energy density of the battery is to increase the coating weight per unit area of the pole piece, the coating thickness of the pole piece, and the compaction density of the pole piece, to reduce the amount of non-active material such as aluminum foil and copper foil under the condition that the capacity of the active material remains unchanged, thereby increasing the energy density of the battery and reducing the cost. However, while increasing the coating thickness of the pole piece and the compaction density of the pole piece, a series of problems also occur. The electrolyte is insufficiently infiltrated into the active material, and in the cycle process, due to the expansion and contraction of the SEI film, the electrolyte on the surface of the active material is continuously consumed. However, due to the insufficient infiltration of the conventional carbonate solvent in the electrolyte, the active material near the foil in the internal active material layer cannot be infiltrated in time and effectively, resulting in the inability of lithium ions to be smoothly transmitted to the surface of the internal active material. In the charging process, there is a lack of lithium ions in the internal active material layer of the negative electrode active material layer and an excess of lithium ions on the surface, which leads to lithium precipitation, resulting in rapid decay of the capacity retention rate.

[0030] The first aspect of the present application provides an electrolyte, comprising: an electrolyte salt, an organic solvent, and a film-forming additive, wherein the organic solvent comprises an ether compound; and the film-forming additive comprises a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group.

[0031] It can be understood that the electrolyte salt can be, but is not limited to, at least one of a lithium salt and a sodium salt.

[0032] The electrolyte of the present application contains ether compounds, which have low viscosity and can solve the problem of insufficient infiltration as an organic solvent of the electrolyte, so that the electrolyte can well infiltrate the active material. However, the interface film formed on the surface of the positive electrode plate 140 and the negative electrode plate 120 by the ether compound has poor quality, which cannot effectively inhibit the further reaction of the positive electrode plate 140 and the negative electrode plate 120 with the electrolyte, resulting in rapid consumption of the organic solvent and affecting the service life of the energy storage device 100. By further adding a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group to the electrolyte, the nitrogen-containing heterocyclic compound has a strong electron-withdrawing group, and the presence of the strong electron-withdrawing group causes the overall charge of the nitrogen-containing heterocyclic compound to be biased, which makes the nitrogen-containing heterocyclic compound more easily ring-opening, oxidizing and polymerizing on the positive electrode, protecting the positive electrode active material, thereby avoiding further contact of the positive electrode active material with the electrolyte. At the negative electrode, the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group can be reduced by electron at a high potential to form a dense and thick SEI film wrapped on the surface of the negative electrode plate 120, effectively inhibiting the side reaction of the electrolyte on the surface of the negative electrode, thereby improving the cycle life of the energy storage device 100. During the process of infiltrating the inner layer of active material layer 141 close to the current collector 142, if the positive electrode plate 140 and the negative electrode plate 120 surface have more side reactions, it may cause the path of the electrolyte into the inner layer to be blocked, while the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group can generate a stable interface film, effectively preventing the side reaction on the surface of the positive electrode plate 140 and the negative electrode plate 120, so that the ether compound can better exert its low viscosity advantage; the low viscosity and high conductivity characteristics of the ether compound can also help the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group to reach the surface of the active material layer 141 more uniformly, thereby forming a uniform and stable interface film on the surface of the relatively thick positive electrode plate 140 and negative electrode plate 120, so that the energy storage device 100 has better cycle performance. By adding ether compounds and nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups to the electrolyte, the electrolyte can have good infiltration ability, can quickly infiltrate the relatively thick positive electrode plate 140 and negative electrode plate 120, and can also form a stable interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120, so that the energy storage device 100 has high energy density and good cycle performance.

[0033] In some embodiments, the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group is a fluorine-substituted nitrogen-containing heterocyclic compound.

[0034] When the nitrogen-containing heterocyclic compound with strong electron-withdrawing group is a fluorine-substituted nitrogen-containing heterocyclic compound, the fluorine-substituted group generates some organic fluorinated phosphorus products in the process of forming a film on the surface of the positive electrode sheet 140 and the negative electrode sheet 120, and the organic fluorinated phosphorus products can balance the high impedance generated by the ring-opening polymerization of the nitrogen-containing heterocyclic compound to form a film, so that the energy storage device 100 has smaller impedance, and the cycle performance of the energy storage device 100 is further improved.

[0035] In some embodiments, the nitrogen-containing heterocyclic compound with strong electron-withdrawing group includes at least one of a fluorine-substituted pyrazine, a fluorine-substituted pyridine, and a fluorine-substituted pyridazine.

[0036] When the nitrogen-containing heterocyclic compound with strong electron-withdrawing group includes a fluorine-substituted pyrazine, a fluorine-substituted pyridine, and a fluorine-substituted pyridazine, it is easier to generate a reduction reaction by electron transfer at a higher potential, and a dense and thick SEI film is formed to wrap the surface of the negative electrode sheet 120, effectively inhibiting side reactions of the electrolyte on the surface of the negative electrode, thereby improving the cycle life of the energy storage device 100.

[0037] In some embodiments, the fluorine-substituted pyrazine includes at least one of 2-fluoropyrazine and 2,5-difluoropyrazine; the fluorine-substituted pyridine includes at least one of 2-fluoropyridine, 3-fluoropyridine, 4-fluoropyridine, 2,3-difluoropyridine, and 3,4-difluoropyridine; and the fluorine-substituted pyridazine includes at least one of 2-fluoropyridazine and 3-fluoropyridazine.

[0038] In some embodiments, the ratio of the mass m1 of the nitrogen-containing heterocyclic compound with strong electron-withdrawing group to the mass m2 of the ether compound ranges from 0.01 to 0.06. Specifically, the mass ratio m1 / m2 of the nitrogen-containing heterocyclic compound with strong electron-withdrawing group to the ether compound can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, and any value between the above values.

[0039] When the mass ratio m1 / m2 of the nitrogen-containing heterocyclic compound with strong electron-withdrawing group to the ether compound is less than 0.01, the interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120 has poor quality, which causes the positive electrode plate 140 and the negative electrode plate 120 to further react with the electrolyte, leading to rapid consumption of organic solvents and affecting the service life of the energy storage device 100. When the mass ratio m1 / m2 of the nitrogen-containing heterocyclic compound with strong electron-withdrawing group to the ether compound is greater than 0.06, the wettability of the electrolyte is insufficient, and the interface film formed on the surface of the positive electrode plate 140 and the negative electrode plate 120 is too thick, leading to increased impedance of the positive electrode plate 140 and the negative electrode plate 120 and affecting the cycle performance of the energy storage device 100. When the mass ratio m1 / m2 of the nitrogen-containing heterocyclic compound with strong electron-withdrawing group to the ether compound is between 0.01 and 0.06, the electrolyte can have good wettability, and a stable and appropriately thick interface film can be formed on the surface of the positive electrode plate 140 and the negative electrode plate 120, improving the cycle performance of the energy storage device 100.

[0040] In some embodiments, the fluorine-substituted pyrazine includes at least one of 2-fluoropyrazine and 2,5-difluoropyrazine; the fluorine-substituted pyridine includes at least one of 2-fluoropyridine, 3-fluoropyridine, 4-fluoropyridine, 2,3-fluoropyridine, and 3,4-fluoropyridine; and the fluorine-substituted pyridazine includes at least one of 2-fluoropyridazine and 3-fluoropyridazine.

[0041] In some embodiments, the ether compound includes at least one of the compounds shown in the following chemical structural formula:

[0042] Chemical formula (I-1): Chemical formula (I-2):

[0043] Chemical formula (I-3): Chemical formula (I-4):

[0044] Chemical formula (I-5): Chemical formula (I-6):

[0045] Chemical formula (I-7): Chemical formula (I-8):

[0046] Chemical formula (I-9): Chemical formula (I-10):

[0047] Chemical formula (I-11): Chemical formula (I-12):

[0048] Formula (I-13): Formula (I-14):

[0049] Formula (I-15): Formula (I-16):

[0050] Formula (I-17): Formula (I-18): Formula (I-19): Formula (I-20):

[0051] Formula (I-21): Formula (I-22):

[0052] Formula (I-23): Formula (I-24):

[0053] Formula (I-25): Formula (I-26):

[0054] Formula (I-27): Formula (I-28):

[0055] Formula (I-29): Formula (I-30):

[0056] Formula (I-31): Formula (I-32): Formula (I-33): Formula (I-34):

[0057] Formula (I-35): Formula (I-36):

[0058] In some embodiments, the mass fraction a of the ether compound in the electrolyte is in the range of 10%≤a≤50%. Specifically, the mass fraction of the ether compound in the electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any value between the above-mentioned values.

[0059] When the mass fraction of the ether compound in the electrolyte is less than 10%, the electrolyte has poor wettability, which affects the cycle performance of the energy storage device 100. When the mass fraction of the ether compound in the electrolyte is greater than 50%, it is easy to form an interface film with poor quality on the surface of the positive electrode plate 140 and the negative electrode plate 120, which cannot effectively inhibit the further reaction of the positive electrode plate 140 and the negative electrode plate 120 with the electrolyte, and will cause rapid consumption of organic solvents, affecting the service life of the energy storage device 100. When the mass fraction of the ether compound in the electrolyte is between 10% and 50%, the electrolyte has good wettability and does not make the interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120 deteriorate, so that the energy storage device 100 has both high energy density and good cycle performance.

[0060] Further, the mass fraction a of the ether compound in the electrolyte is in the range of 10%≤a≤30%. When the mass fraction of the ether compound in the electrolyte is between 10% and 30%, the electrolyte has good wettability and does not affect the quality of the interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120, so that the energy storage device 100 further has both high energy density and good cycle performance.

[0061] In some embodiments, the mass fraction b of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte is in the range of 0.1%≤b≤3%. Specifically, the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3.0%, and any value between the above values.

[0062] When the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte is less than 0.1%, the electrolyte cannot form a stable interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120, and cannot effectively inhibit the further reaction of the positive electrode plate 140 and the negative electrode plate 120 with the electrolyte, which will cause rapid consumption of organic solvents, affecting the service life of the energy storage device 100. When the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte is greater than 3%, the electrolyte forms an interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120, which is too thick, resulting in increased impedance of the positive electrode plate 140 and the negative electrode plate 120, affecting the cycle performance of the energy storage device 100. When the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte is between 0.1% and 3%, the electrolyte can form a stable and appropriately thick interface film on the surface of the positive electrode plate 140 and the negative electrode plate 120, improving the cycle performance of the energy storage device 100.

[0063] Further, the mass fraction b of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte is in the range of 0.3%≤b≤1%. Specifically, the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte can be 0.3%, 0.5%, 0.7%, 1.0%, and any value between the above values.

[0064] When the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte is between 0.3% and 1%, the electrolyte can form a more stable and appropriately thick interface film on the surface of the positive electrode sheet 140 and the negative electrode sheet 120, further improving the cycle performance of the energy storage device 100.

[0065] In some embodiments, the electrolyte further comprises a sulfur-containing additive, and the ratio of the mass m3 of the sulfur-containing additive to the mass m1 of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group is in the range of 0.1≤m3 / m1≤10. Specifically, the mass ratio m1 / m2 of the mass of the sulfur-containing additive to the mass of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group can be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and any value between the above values.

[0066] When the ratio of the mass m3 of the sulfur-containing additive to the mass m1 of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group is less than 0.1, the electrolyte cannot sufficiently oxidize to form a film on the surface of the positive electrode sheet 140, cannot inhibit the dissolution of transition metals of the positive electrode, and affects the high-temperature performance of the energy storage device 100. When the ratio of the mass m3 of the sulfur-containing additive to the mass m1 of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group is greater than 10, the interface film formed on the surface of the positive electrode sheet 140 and the negative electrode sheet 120 is too thick, affecting the cycle performance of the energy storage device 100. When the ratio of the mass m3 of the sulfur-containing additive to the mass m1 of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group is between 0.1 and 10, the electrolyte can both oxidize to form a film on the surface of the positive electrode sheet 140, inhibit the dissolution of transition metals of the active material, and form an appropriately thick interface film on the surface of the positive electrode sheet 140 and the negative electrode sheet 120, further improving the cycle performance of the energy storage device 100.

[0067] In some embodiments, the sulfur-containing additive includes at least one of vinyl sulfonate, 1,3-propane sulfonate lactone, 1,3-propylene sulfonate lactone, methyl disulfonate methylene, 1,4-butane sulfonate lactone, 2,4-butane sulfonate lactone, 1,3-propanediol sulfate, ethylene sulfite, and pentaerythritol bis-cyclic sulfate.

[0068] When the sulfur-containing additive is at least one of vinyl sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, methylene disulfonate, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1,3-propanediol sulfate, ethylene sulfite, and pentaerythritol bicyclic sulfate, the electrolyte can better form a stable and appropriately thick interfacial film on the surfaces of the positive electrode 140 and the negative electrode 120, thereby improving the cycle performance of the energy storage device 100.

[0069] In some embodiments, the mass fraction c of the sulfur-containing additive in the electrolyte ranges from 0.5% to 3%. Specifically, the mass fraction of the sulfur-containing additive in the electrolyte can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3.0%, or any value between these values.

[0070] When the mass fraction of the sulfur-containing additive in the electrolyte is less than 0.5%, the sulfur-containing additive cannot be sufficiently oxidized to form a film on the surface of the positive electrode 140, thus failing to inhibit the dissolution of transition metals from the positive electrode and affecting the high-temperature performance of the energy storage device 100. When the mass fraction of the sulfur-containing additive in the electrolyte is greater than 3%, a thicker interfacial film is formed on the surfaces of the positive electrode 140 and the negative electrode 120, affecting the cycle performance of the energy storage device 100. When the mass fraction of the sulfur-containing additive in the electrolyte is between 0.5% and 3%, the electrolyte can both oxidize to form a film on the surface of the positive electrode 140, inhibiting the dissolution of transition metals from the active material, and simultaneously form an interfacial film of suitable thickness on the surfaces of the positive electrode 140 and the negative electrode 120, further improving the cycle performance of the energy storage device 100.

[0071] Please see Figure 1 and Figure 2 This application also provides an energy storage device 100, which includes: an electrolyte, a negative electrode 120, a separator 130, and a positive electrode 140 as described in the embodiments of this application; the negative electrode 120 is at least partially immersed in the electrolyte; the separator 130 is located on one side of the negative electrode 120 and is at least partially immersed in the electrolyte, and the positive electrode 140 is disposed on the side of the separator 130 away from the negative electrode 120 and is at least partially immersed in the electrolyte.

[0072] Please see Figure 3 and Figure 4 In some embodiments, the positive electrode 140 includes a current collector 142 and an active material layer 141, wherein the weight t of the active material layer 141 ranges from 0.16 mg / mm² to 0.39 mg / mm². 2 Specifically, the weight of the active material layer 141 can be 0.16 mg / mm². 20.2 mg / mm 2 0.25 mg / mm 2 0.3 mg / mm 2 0.35 mg / mm 2 0.39 mg / mm 2 and any value between the above values.

[0073] When the weight of the active material layer 141 is less than 0.16 mg / mm 2 , the active material layer 141 is thinner, and the energy density of the energy storage device 100 is lower. When the weight of the active material layer 141 is greater than 0.39 mg / mm 2 , the active material layer 141 is prone to cracking, the processing difficulty is greater, and the electrolyte is difficult to infiltrate the active material layer 141, which affects the cycle performance of the energy storage device 100. When the weight of the active material layer 141 is between 0.16 mg / mm 2 and 0.39 mg / mm 2 , the electrolyte can better infiltrate the active material layer 141 and form a good interface layer on the surface, so that the energy storage device 100 has both high energy density and good cycle performance.

[0074] In some embodiments, the energy storage device 100 satisfies the relationship: 6 < t*(b+c) / a < 240, where a is the mass fraction of the ether compound in the electrolyte, b is the mass fraction of the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte, and c is the mass fraction of the sulfur-containing additive in the electrolyte. Specifically, the value of t*(b+c) / a can be 6, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, and any value between the above values.

[0075] When the value of t*(b+c) / a is less than 6, the sulfur-containing additive and the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group cannot effectively inhibit the reaction of the ether compound on the positive electrode plate 140 and the negative electrode plate 120, resulting in the cycle performance degradation and high-temperature storage gas production of the energy storage device 100. When the value of t*(b+c) / a is greater than 240, the content of the ether compound is less, the active material layer 141 is thicker, resulting in insufficient infiltration of the electrolyte to the active material layer 141, or the sulfur-containing additive and the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group are too much, resulting in too high interface film resistance on the surface of the positive electrode plate 140 and the negative electrode plate 120, affecting the internal resistance of the energy storage device 100. When the value of t*(b+c) / a is between 6 and 240, the electrolyte is better infiltrated to the active material layer 141, the sulfur-containing additive and the nitrogen-containing heterocyclic compound with a strong electron-withdrawing group can effectively inhibit the reaction of the ether compound on the positive electrode plate 140 and the negative electrode plate 120, and the interface film resistance on the surface of the positive electrode plate 140 and the negative electrode plate 120 is low, and the energy storage device 100 has good cycle performance and high-temperature storage performance.

[0076] Further, the energy storage device 100 satisfies the relationship: 6 < t*(b+c) / a < 100. Specifically, the value of t*(b+c) / a can be 6, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, and any value between the above-mentioned values. When the value of t*(b+c) / a is between 6 and 100, the energy storage device 100 has better cycle performance and high-temperature storage performance.

[0077] The energy storage device 100 of the embodiments of the present application can be, but is not limited to, a lithium ion secondary energy storage device 100, a lithium ion primary energy storage device 100, a sodium ion energy storage device 100, a lithium-sulfur energy storage device 100, etc.

[0078] It can be understood that the energy storage device 100 can be, but is not limited to, a battery monomer, a battery module, a battery pack, etc.

[0079] Optionally, the separator 130 can be, but is not limited to, at least one of a polypropylene film (PP) and a polyethylene film (PE).

[0080] The embodiments provided by the present application are further described below in conjunction with the embodiments. It should be understood that the embodiments provided by the present application are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0081] For the convenience of understanding, the present application lists the following embodiments. Those skilled in the art should understand that the specific conditions not mentioned in the embodiments are carried out according to the conventional conditions.

[0082] Embodiment 1

[0083] 1) Preparation of the positive electrode sheet 140: the positive electrode active material lithium iron phosphate, conductive carbon black SP, and the binder PVDF were mixed in a mass ratio of 97:0.7:2.3 and dispersed in the solvent NMP to obtain a positive electrode slurry; the positive electrode slurry was coated on the positive electrode current collector 142 aluminum foil. After drying, cold pressing, slitting, and cutting, the positive electrode sheet 140 was obtained. The weight of the active material layer 141 of the positive electrode sheet 140 is shown in Table 1:

[0084] 2) Preparation of the negative electrode sheet 120: the negative electrode active material graphite, conductive carbon SP, thickening agent CMC, and binder SBR were mixed in a mass ratio of 96.5:0.5:1:2 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil. After drying, rolling, slitting, and cutting, the negative electrode sheet 120 was obtained.

[0085] 3) Preparation of the separator 130:

[0086] A 16-μm polyethylene film was used as the separator 130.

[0087] 4) Preparation of the electrolyte:

[0088] In an argon atmosphere glove box with a water content of ≤1 ppm, ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate were mixed in a mass ratio of 1:1:1. Then, the dry electrolyte lithium salt lithium hexafluorophosphate was dissolved in the solvent, stirred until completely dissolved and uniform, and mixed with fluoroethylene carbonate to obtain the electrolyte. The composition of the obtained electrolyte was as follows: the solvent composition was ethylene carbonate:dimethyl carbonate:methyl ethyl carbonate = 1:1:1 (mass ratio), the lithium salt concentration was 1 mol / L, and the content of fluoroethylene carbonate was 3%. The types and contents of the ether compounds, nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups, and sulfur-containing additives in Examples 1-17 and Comparative Examples 1-11 are shown in Tables 1 and 2. When there are two ether compounds in the examples and comparative examples, the mass ratio of the two ether compounds is 1:1.

[0089] 5) Preparation of the energy storage device 100: the above-mentioned positive electrode sheet 140, separator 130, and negative electrode sheet 120 were stacked in order, with the separator 130 between the positive and negative electrodes to act as a barrier, then wound to obtain a bare cell, the bare cell was assembled into an outer package, electrolyte was injected, and the cell was packaged, rested, formed, shaped, and tested for capacity, etc. to obtain the energy storage device 100 described in Examples 1-17 and Comparative Examples 1-11.

[0090] Performance test of the energy storage device 100

[0091] 1) Cycle performance test

[0092] The energy storage device 100 obtained in the above examples is subjected to charge-discharge cycle test on a charge-discharge instrument, the test temperature is 25°C, the cycle rate is 1C (i.e. the charge rate and the discharge rate are both 1C), the charge voltage is 2.5V to 3.65V, and the capacity retention rate after cycling is calculated. The capacity retention rate calculation formula for 25°C cycling is: capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) * 100%.

[0093] It can be understood that the term "number of cycles" in the present application refers to the number of times the energy storage device 100 is charged at a predetermined rate and discharged at a predetermined rate. One complete charge-discharge process of the energy storage device 100 is referred to as one cycle, and the 25°C 1C / 1C cycle 3000 cycle capacity retention rate refers to the capacity retention rate of the energy storage device 100 after 3000 charge-discharge processes at 1C charge rate and 1C discharge rate at a test temperature of 25°C.

[0094] 2) 50% SOC direct current impedance (DCR) test

[0095] The energy storage device 100 obtained in the above examples is placed in a 25°C constant temperature box, discharged at 0.5C constant current to a voltage of 2.5V, and then charged at 0.5C constant current to a voltage of 3.65V, and constant voltage charged to a current of 0.025C. After 5 minutes of standing, discharge at 0.1C constant current to 2.5V, and record the discharge capacity at this time as C1. Charge at 0.5C constant current to 3.65V, constant voltage to a current of 0.025C, stand for 5 minutes, and discharge at 0.1C constant current for 5 hours, and record the voltage V1 at this time. Then, discharge at 1C constant current for 1s, and record the voltage V2 at this time. The 50% SOC direct current impedance of the energy storage device 100 is: (V1-V2) / C1.

[0096] It can be understood that the term "SOC" in the present application refers to the remaining capacity of the energy storage device 100, i.e. the remaining amount of electricity of the energy storage device 100.

[0097] 3) 60°C storage for 90 days cell remaining capacity retention rate

[0098] The energy storage device 100 obtained in the above examples is subjected to test on a charge-discharge instrument, the test temperature is 25°C, and the discharge rate is 1C (i.e. the charge rate and the discharge rate are both 1C) for 3 cycles, and the discharge capacity of the 3rd cycle is recorded as C1. Then the energy storage device 100 is stored at 60°C for 90 days, and then discharged at a test temperature of 25°C at a rate of 1C, and the discharge capacity is recorded as C2. The 60°C storage for 90 days cell remaining capacity retention rate is C2 / C1.

[0099] The relevant test data of the energy storage device 100 described in Examples 1-17 and Comparative Examples 1-11 are shown in Table 2:

[0100] Table 1:

[0101]

[0102]

[0103] Table 2:

[0104]

[0105]

[0106] As shown in Tables 1 and 2, from the data of Comparative Example 1 and Comparative Example 2, Example 1 and Example 8, when ether compounds and nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups are added to the electrolyte, the cycle performance of the energy storage device 100 is better, and when the active material layer 141 of the positive electrode sheet 140 is thicker, the addition of ether compounds and nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups in the electrolyte greatly improves the cycle performance of the energy storage device 100. This is because when the electrolyte adds ether compounds and nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups, the ether compounds can well infiltrate the active material, and the nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups can be reduced at a higher potential to form a dense and thick SEI film wrapped on the surface of the negative electrode sheet 120, effectively inhibiting the side reaction of the electrolyte on the surface of the negative electrode, thereby improving the cycle life of the energy storage device 100.

[0107] From the data of Comparative Examples 3-5 and Comparative Example 7 and Example 1, it can be seen that when only ether compounds are added to the electrolyte, the cycle performance of the energy storage device 100 is poorer, and the capacity retention rate after 3000 cycles at 25°C is more than 8% lower than that of the group of simultaneously adding ether compounds and nitrogen-containing heterocyclic compounds with strong electron-withdrawing groups. This is because the interface film formed by the ether compounds on the surface of the positive electrode sheet 140 and the negative electrode sheet 120 has poor quality, which cannot effectively inhibit the further reaction of the positive electrode sheet 140 and the negative electrode sheet 120 with the electrolyte, which will lead to rapid consumption of organic solvents and affect the service life of the energy storage device 100.

[0108] From the data of Comparative Example 6 to Comparative Example 9 and Example 1, it can be seen that, in the case of adding only an ether compound in the electrolyte, the cycle capacity retention rate of the energy storage device 100 first increases and then decreases with the increase of the mass fraction of the ether compound. This is because, with the increase of the mass fraction of the ether compound, the electrolyte wets better, so that the cycle capacity retention rate of the energy storage device 100 increases, and when the mass fraction of the ether compound increases to a certain value, the ether compound is easy to form an interface film with poor quality on the surface of the positive electrode plate 140 and the negative electrode plate 120, which cannot effectively inhibit the further reaction of the positive electrode plate 140 and the negative electrode plate 120 with the electrolyte, and will cause the rapid consumption of organic solvents, affecting the service life of the energy storage device 100.

[0109] From the data of Comparative Example 10 and Comparative Example 11 and Example 2, it can be seen that, when the nitrogen-containing heterocyclic compound in the electrolyte has a strong electron-withdrawing group, the cycle performance of the energy storage device 100 is better, and the capacity retention rate after 3000 cycles at 25°C is more than 5%. This is because the nitrogen-containing heterocyclic compound has a strong electron-withdrawing group, and the presence of the strong electron-withdrawing group causes the overall charge of the nitrogen-containing heterocyclic compound to be biased, which makes the nitrogen-containing heterocyclic compound more prone to ring opening, and the oxidation polymerization occurs in the positive electrode, protecting the positive electrode active material and improving the cycle performance of the energy storage device 100.

[0110] As shown in Tables 1 and 2, from the data of Example 1 to Example 4, in the case of simultaneously adding an ether compound and a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group (i.e. 2-fluoropyrazine) in the electrolyte, the cycle retention rate of the energy storage device 100 first increases and then decreases with the gradual increase of the mass ratio of 2-fluoropyrazine to the ether compound, and the 50% SOC DCR of the energy storage device 100 continuously increases. This is because, with the increase of the mass ratio of 2-fluoropyrazine to the ether compound, a more stable interface film is formed on the surface of the positive electrode plate 140 and the negative electrode plate 120, which improves the cycle performance of the energy storage device 100, and with the continuous increase of the mass ratio of 2-fluoropyrazine to the ether compound, the interface film formed on the surface of the positive electrode plate 140 and the negative electrode plate 120 is too thick, which causes the impedance of the positive electrode plate 140 and the negative electrode plate 120 to be too high, affecting the cycle performance of the energy storage device 100.

[0111] From the data of Example 2, Example 5 and Example 6, it can be seen that, in the case of simultaneously adding an ether compound and a nitrogen-containing heterocyclic compound with a strong electron-withdrawing group in the electrolyte, the cycle data of the energy storage device 100 are all good no matter whether the nitrogen-containing heterocyclic compound is 2-fluoropyrazine, 2-fluoropyridine or 4,4-bipyridine.

[0112] From the data of Example 2, Example 7 to Example 9, it can be seen that when the ether compound and the nitrogen-containing heterocyclic compound with strong electron-withdrawing group are added in the electrolyte at the same time, the cycle performance of the energy storage device 100 gradually deteriorates with the increase of the weight of the active material layer 141 of the positive electrode plate 140. This is because with the increase of the weight of the active material layer 141, the electrolyte is more difficult to infiltrate the active material layer 141, thereby affecting the cycle capacity retention rate of the energy storage device 100.

[0113] From the data of Example 2, Example 10 to Example 13, it can be seen that when the ether compound and the nitrogen-containing heterocyclic compound with strong electron-withdrawing group (i.e. 2-fluoropyrazine) are added in the electrolyte at the same time, the 60°C storage 90-day remaining capacity retention rate of the energy storage device 100 is higher when the sulfur-containing additive (1,3-propane sulfone lactone) is added in the electrolyte, the cycle capacity retention rate of the energy storage device 100 first remains unchanged and then decreases with the increase of the mass fraction of the sulfur-containing additive, and the 60°C storage 90-day remaining capacity retention rate of the energy storage device 100 becomes higher. This is because the addition of 1,3-propane sulfone lactone forms a film on the surface of the positive electrode plate 140, inhibits the dissolution of transition metals of the active material, and improves the high-temperature performance and cycle performance of the energy storage device 100. When the 1,3-propane sulfone lactone increases to a certain value, the interfacial film on the surface of the positive electrode plate 140 and the negative electrode plate 120 is too thick, resulting in the deterioration of the cycle of the energy storage device 100.

[0114] From the data of Example 11, Example 14 and Example 15, it can be seen that when the ether compound and 2-fluoropyrazine and the sulfur-containing additive are added in the electrolyte at the same time, the cycle performance and high-temperature performance of the energy storage device 100 do not differ much no matter whether the sulfur-containing additive is 1,3-propane sulfone lactone, 2,4-butane sulfone lactone or 1,3-propylene sulfone lactone.

[0115] From the data of Example 14, Example 16 and Example 17, it can be seen that when the ether compound and 2-fluoropyrazine and 2,4-butane sulfone lactone are added in the electrolyte at the same time, the energy storage device 100 has a higher cycle capacity retention rate and 60°C storage 90-day remaining capacity retention rate when the energy storage device 100 satisfies the relationship: 6 < t*(b+c) / a < 240. This is because the electrolyte is well infiltrated into the active material layer 141, the sulfur-containing additive and the nitrogen-containing heterocyclic compound with strong electron-withdrawing group can effectively inhibit the reaction of the ether compound on the positive electrode plate 140 and the negative electrode plate 120, and the interfacial film on the surface of the positive electrode plate 140 and the negative electrode plate 120 has low impedance, so that the energy storage device 100 has good cycle performance and high-temperature storage performance.

[0116] Please refer to Figure 5The application also provides a power-using device 200, comprising a power-using device body 210 and the energy storage device 100 described in the embodiments of the application, wherein the energy storage device 100 supplies power to the power-using device body 210. It can be understood that, for the convenience of illustration, the energy storage device 100 is placed outside the power-using device body 210, and in the normal use state, the energy storage device 100 is inside the power-using device body 210.

[0117] The power-using device 200 of the embodiments of the application can be, but is not limited to, a mobile phone, a tablet computer, a notebook computer, a desktop computer, a smart bracelet, a smart watch, an electronic reader, a game console, a toy, and the like. In addition, the power-using device 200 can also be a car, a household appliance, and the like.

[0118] It can be understood that the power-using device 200 described in the embodiments of the application is only one form of the power-using device 200 to which the energy storage device 100 is applied, and should not be understood as a limitation on the power-using device 200 provided by the application, nor should it be understood as a limitation on the energy storage device 100 provided by the embodiments of the application.

[0119] In the present application, the phrase "embodiment" or "embodiments" means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment that is not mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments. In addition, it should also be understood that the features, structures or characteristics described in the embodiments of the present application can be combined with each other without contradiction, to form another embodiment of the present application without departing from the spirit and scope of the present application.

[0120] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

1. An electrolyte, characterized by, The electrolyte comprises an electrolyte salt, an organic solvent comprising an ether compound, and a film-forming additive comprising a nitrogen-containing heterocyclic compound having a strong electron-withdrawing group; the nitrogen-containing heterocyclic compound having a strong electron-withdrawing group comprises at least one of a fluorine-substituted pyrazine, a fluorine-substituted pyridine, and a fluorine-substituted pyridazine; a ratio of a mass m1 of the nitrogen-containing heterocyclic compound having a strong electron-withdrawing group to a mass m2 of the ether compound ranges from 0.01 to 0.06; a mass fraction a of the ether compound in the electrolyte ranges from 10% to 50%; and a mass fraction b of the nitrogen-containing heterocyclic compound having a strong electron-withdrawing group in the electrolyte ranges from 0.1% to 3%.

2. The electrolyte according to claim 1, characterized in that, The ether compound comprises at least one of the following compounds: 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 。 3. The electrolyte according to claim 1 or 2, characterized in that, The electrolyte further comprises a sulfur-containing additive, and a ratio of a mass m3 of the sulfur-containing additive to the mass m1 of the nitrogen-containing heterocyclic compound having a strong electron-withdrawing group ranges from 0.1 to 10.

4. The electrolyte according to claim 3, characterized in that, The sulfur-containing additive comprises at least one of vinyl sulfonate, 1,3-propane sultone, 1,3-propene sultone, methyl bisulfonate methylene, 1,4-butane sultone, 2,4-butane sulfite, 1,3-propanediol sulfate, ethylene sulfite, and pentaerythritol bis-cyclic sulfate.

5. The electrolyte according to any one of claims 1, 2, 4, characterized in that, The fluorine-substituted pyrazine comprises at least one of 2-fluoropyrazine and 2,5-difluoropyrazine; the fluorine-substituted pyridine comprises at least one of 2-fluoropyridine, 3-fluoropyridine, 4-fluoropyridine, 2,3-difluoropyridine, and 3,4-difluoropyridine; and the fluorine-substituted pyridazine comprises at least one of 2-fluoropyridazine and 3-fluoropyridazine.

6. An energy storage device, characterized by, The electrolyte comprises: The electrolyte of any one of claims 1-5; A negative electrode tab at least partially immersed in the electrolyte; A separator located on one side of the negative electrode tab and at least partially immersed in the electrolyte, and A positive electrode tab disposed on a side of the separator away from the negative electrode tab and at least partially immersed in the electrolyte.

7. The energy storage device of claim 6, wherein, The positive electrode tab comprises a current collector and an active material layer, and a weight t of the active material layer ranges from 0.16 mg / mm2 to 0.39 mg / mm2.

8. The energy storage device of claim 7, wherein, The electrolyte further comprises a sulfur-containing additive, and the energy storage device satisfies a relationship: 6 < t x (b + c) / a < 240, where a is a mass fraction of the ether compound in the electrolyte, b is a mass fraction of the nitrogen-containing heterocyclic compound having a strong electron-withdrawing group in the electrolyte, and c is a mass fraction of the sulfur-containing additive in the electrolyte.

9. An electric device, characterized by The electrolyte comprises: A use device body, and The energy storage device of any one of claims 6-8, wherein the energy storage device supplies power to the use device body.

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