Secondary battery and electric equipment

Abstract

The invention provides a secondary battery and electric equipment. The secondary battery comprises a positive pole piece, a negative pole piece, an electrolyte and a diaphragm, and the secondary battery meets the following conditions: 200lt; a * N / (IG), A Ah is the discharge capacity of the secondary battery, N g / Ah is the liquid injection coefficient of the electrolyte, I is the OI value of the negative pole piece, and G mol / L is the concentration of the lithium salt in the electrolyte. By controlling the discharge capacity of the secondary battery, the liquid injection coefficient of the electrolyte, the OI value of the negative pole piece and the concentration of the lithium salt in the electrolyte to meet a certain relational expression, the long cycle performance, the energy efficiency and the storage performance of the secondary battery are improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, in particular to a secondary battery and an electrical device. Background Art

[0002] The lithium iron phosphate secondary battery has the advantages of high safety, low cost and good cycle performance, and is widely used in energy storage systems. However, the existing lithium iron phosphate secondary batteries for energy storage have small sizes and low capacities. When used in energy storage systems, a large number of batteries are often required, resulting in a complex system architecture, and thus higher costs and risks. Therefore, the development of large-sized batteries is beneficial to reducing costs and risks. However, the existing large-sized batteries have problems of low long-cycle performance, energy efficiency and storage performance. Summary of the Invention

[0003] The purpose of this application is to provide a secondary battery and an electrical device with excellent long-cycle performance, storage performance and energy efficiency.

[0004] To achieve the above purpose, in the first aspect of this application, a secondary battery is provided, including a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. The secondary battery satisfies: 200 < A × N / (I^G), where A Ah is the discharge capacity of the secondary battery, N g / Ah is the injection coefficient of the electrolyte, I is the OI value of the negative electrode sheet, and G mol / L is the concentration of the lithium salt in the electrolyte.

[0005] As an embodiment of this application, the secondary battery satisfies: 200 < A × N / (I^G) < 350.

[0006] As an embodiment of this application, the discharge capacity A Ah of the secondary battery satisfies: 280 Ah ≤ A Ah ≤ 800 Ah.

[0007] As an embodiment of this application, the injection coefficient N g / Ah of the secondary battery satisfies: 2 g / Ah ≤ N g / Ah ≤ 5 g / Ah.

[0008] As an embodiment of this application, the OI value I of the negative electrode sheet satisfies: 6 < I < 16. [[ID=3))

[0009] As an embodiment of this application, the concentration G mol / L of the lithium salt in the electrolyte satisfies: 0.8 mol / L ≤ G mol / L ≤ 1.5 mol / L.

[0010] As an embodiment of this application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium bis(oxalato)difluorophosphate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0011] As an embodiment of the present application, the area of the bottom surface of the secondary battery is S1 cm

[0018] ,

[0017] , ,

[0016] , , , , the area of the large surface of the secondary battery is S2 cm 2 , the area of the side surface of the secondary battery is S3 cm 2 , and it satisfies: S2 / S1 > 2.5, S2 / S3 > 4.5.

[0012] As an embodiment of the present application, the group margin of the secondary battery in the thickness direction is F, and it satisfies: 90% ≤ F ≤ 98%.

[0013] In the second aspect of the present application, an electrical device is provided, and the electrical device includes the secondary battery described in the first aspect of the present application.

[0014] Compared with the prior art, the beneficial effects of the present application are:

[0015] The secondary battery described in the present application includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The secondary battery satisfies: 200 < A×N / (I^G), where A Ah is the discharge capacity of the secondary battery, N g / Ah is the liquid injection coefficient of the electrolyte, I is the OI value of the negative electrode sheet, and G mol / L is the concentration of the lithium salt in the electrolyte. By controlling the discharge capacity of the secondary battery, the liquid injection coefficient of the electrolyte, the OI value of the negative electrode sheet, and the concentration of the lithium salt in the electrolyte to satisfy a certain relational expression, the long cycle performance and energy efficiency of the secondary battery are improved. Specific Embodiments

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0017] In the present application, for the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0018] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0019] For the reagents or instruments used in this application, if the manufacturer is not specified, they are all conventional products that can be obtained through commercial purchase.

[0020] An embodiment of this application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The secondary battery satisfies: 200 < A × N / (I^G), where A Ah is the discharge capacity of the secondary battery, N g / Ah is the liquid injection coefficient of the electrolyte, I is the OI value of the negative electrode sheet, and G mol / L is the concentration of the lithium salt in the electrolyte.

[0021] In this application, the discharge capacity of the secondary battery is obtained by the following method: The battery is left to stand in a constant temperature oven at 25°C for 1 h, charged at a constant power of 0.5P to 4.35V, left to stand for 1 h, and discharged at a constant power of 0.5P for 1 h, and the discharge capacity is recorded.

[0022] In some embodiments, the secondary battery satisfies: 200 < A × N / (I^G) < 350.

[0023] In some embodiments, the discharge capacity A Ah of the secondary battery satisfies: 280 Ah ≤ A Ah ≤ 800 Ah. Exemplarily, the discharge capacity A Ah of the secondary battery can be any value or the range value between any two values among 280 Ah, 314 Ah, 561 Ah, 580 Ah, 628 Ah, 655 Ah, 708 Ah, and 800 Ah.

[0024] In some embodiments, the liquid injection coefficient N g / Ah of the electrolyte satisfies: 2 g / Ah ≤ N g / Ah ≤ 5 g / Ah. Exemplarily, the liquid injection coefficient N g / Ah of the electrolyte can be 2 g / Ah, 2.3 g / Ah, 2.6 g / Ah, 2.9 g / Ah, 3.2 g / Ah, 3.5 g / Ah, 4.0 g / Ah, 4.5 g / Ah, 5.0 g / Ah or the range composed of any two of these numerical values. By controlling the liquid injection coefficient of the electrolyte within this range, the consumption rate of the additive during cycling and storage can be controlled, thereby ensuring the stable operation of the battery.

[0025] In some embodiments, the OI value I of the negative electrode sheet satisfies: 6 < I < 16. Exemplarily, the OI value I of the negative electrode sheet can be any value among 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5 or a range value between any two of these values.

[0026] In some embodiments, the concentration G mol / L of the lithium salt in the electrolyte satisfies: 0.8 mol / L ≤ G mol / L ≤ 1.5 mol / L. Exemplarily, the concentration G mol / L of the lithium salt in the electrolyte can be any value among 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L or a range value between any two of these values.

[0027] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium bis(oxalato)difluorophosphate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0028] In some embodiments, the area of the bottom surface of the secondary battery is S1 cm 2 and the area of the large surface of the secondary battery is S2 cm 2 and the area of the side surface of the secondary battery is S3 cm 2 satisfying: S2 / S1 > 2.5 and S2 / S3 > 4.5. Exemplarily, S2 / S1 can be any value among 2.8, 3.0, 3.5, 4, 4.5, 5, 6, 7 or a range value between any two of these values. Exemplarily, S2 / S3 can be any value among 5, 5.5, 6, 6.5, 7.0, 7.5, 8, 9, 10 or a range value between any two of these values. In this application, the area S1 of the bottom surface of the secondary battery = the length of the secondary battery × the width of the secondary battery, the area S2 of the large surface of the secondary battery = the length of the secondary battery × the height of the secondary battery, and the area S3 of the side surface of the secondary battery = the width of the secondary battery × the height of the secondary battery.

[0029] In some embodiments, the group margin F of the secondary battery in the thickness direction satisfies: 90% ≤ F ≤ 98%. For example, the group margin F of the secondary battery in the thickness direction can be any one of 90%, 92%, 94%, 96%, 98%, or a range between any two values. Reasonable group margin design can improve the performance of the battery throughout its life cycle and the safety of the battery during use. By controlling the battery group margin, the battery expansion force throughout its life cycle is controlled within a reasonable range, thereby improving the battery service life. The group margin of the secondary battery in the thickness direction is calculated by the core stacking height / the available space in the height direction of the secondary battery shell.

[0030] In some embodiments, in the secondary battery described in the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector and containing a positive electrode active material, wherein the positive electrode active material includes a lithium-containing phosphate containing Ti element and / or V element. Doping the positive electrode material with the Ti element can improve the electrochemical performance of the positive electrode material, help to increase the upper limit of the high voltage charge of the positive electrode material, improve the charge and discharge capacity of the positive electrode material, and increase the structural stability. Doping with Ti helps to improve the low temperature performance of the LiFePO4 / C battery. Doping the positive electrode material with the V element helps to improve the electrical conductivity of the material, helps to enhance the structural stability of the positive electrode material during the Li+ insertion and extraction process, effectively improves the rate performance of the positive electrode material, and improves the structural stability during the cycle.

[0031] In some embodiments, the positive electrode current collector includes aluminum foil or carbon-coated aluminum foil.

[0032] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and containing a negative electrode active material, wherein the negative electrode active material includes graphite.

[0033] In some embodiments, the negative electrode current collector comprises copper foil or carbon-coated copper foil.

[0034] In some embodiments, the electrolyte further includes an organic solvent and an additive, wherein the organic solvent includes a cyclic carbonate and a chain carbonate.

[0035] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0036] In some embodiments, the linear carbonate includes at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0037] In some embodiments, the additive includes at least one of 1,3-propylene sultone, vinyl sulfate, fluoroethylene carbonate, vinylene carbonate, and tris(trimethylsilyl)borate.

[0038] In a second aspect of the present application, an electrical device is provided, wherein the electrical device includes the secondary battery described in the first aspect of the present application.

[0039] Exemplarily, the electrical equipment may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0040] The following are specific examples of the present application, and the technical solutions of the present application are further described in conjunction with the examples, but the present application is not limited to these examples. The reagents, methods and equipment used in this application, unless otherwise specified, are conventional reagents, methods and equipment in the art.

[0041] Example 1

[0042] This embodiment provides a secondary battery, the preparation method of which includes the following steps:

[0043] Preparation of positive electrode

[0044] The LFP positive electrode material, conductive carbon, binder PVDF, and dispersant polyvinyl pyrrolidone were mixed in a ratio of 96.5%: 1%: 2%: 0.5%, and NMP was used as solvent through a wet stirring process to obtain the positive electrode slurry. The positive electrode slurry was coated at a density of 227.2 g / m 2 Coated on a 12μm aluminum foil current collector. Both sides of the 12μm aluminum foil current collector are coated with 1μm conductive carbon to increase the electronic conductivity between the positive electrode material and the current collector. The coated positive electrode sheet is dried in an oven and rolled, and then coated with 2.35g / cm 3 The compaction density is rolled by a roller press, and then the tabs are die-cut, striped and sliced ​​to obtain the positive electrode sheets;

[0045] Preparation of negative electrode sheet

[0046] Graphite negative electrode material, conductive carbon, binder SBR, dispersant CMC, plasticizer 1,2-butanediol were mixed in a ratio of 96%: 0.8%: 1.5%: 1.2%: 0.5%, and water was used as solvent to obtain negative electrode slurry through wet stirring process. The negative electrode slurry was coated at a density of 106.5 g / m 2 Coated on a 6μm copper foil current collector. The coated negative electrode sheet was dried in an oven and rolled up, and then coated with 1.45g / cm 3The compaction density is rolled by a roller press, and then the tab die-cutting, striping and slicing are carried out in sequence to obtain the negative electrode sheet. The CB value of the positive and negative electrode coating weight is designed to be 1.12, and the OI value of the negative electrode sheet after rolling is 6.49;

[0047] Assembly of secondary batteries

[0048] The positive and negative electrodes are passed through a laminating machine. The positive and negative electrodes are insulated by an insulating PE diaphragm. After hot pressing, the positive electrode, diaphragm, and negative electrode in the stack are tightly fitted. The tabs are ultrasonically welded, the connectors are laser welded, and the stack is wrapped with Mylar film to obtain a stack. The stack is assembled into a square aluminum shell with a length of 352mm, a width of 75mm, and a height of 215mm. The top cover is then welded around the core. After passing the internal resistance test and helium test, it enters the activation stage.

[0049] The assembled, unfilled secondary battery was oven-dried to remove any residual moisture. The electrolyte was then injected for the first time with an injection factor of 3.8. The electrolyte solvent was a mixture of ethylene carbonate and dimethyl carbonate, with a volume ratio of 1:1. The electrolyte lithium salt was a mixture of LiPF6 and LiFSI, with a lithium salt concentration of 1.2 mol / L. After injection, a low-current formation process was used to form an SEI film at the anode material interface. This film then underwent a high-temperature aging process, further densifying the SEI film on the anode electrode. This dense SEI prevents electrolyte corrosion and unwanted side reactions during use, and also inhibits the formation of lithium dendrites. After aging, the electrolyte was injected a second time to replenish the electrolyte consumed during activation. The sealing pins were then welded. After passing helium inspection, the battery was then capacity tested and binned. Dimensional testing and dielectric withstand voltage testing were then performed. Finally, the battery was coated with an insulating film, completing the production process. The resulting secondary battery had a standard discharge capacity of 725 Ah.

[0050] Examples 2 to 7 and Comparative Examples 1 to 3

[0051] A series of secondary batteries were provided, which were prepared according to the method of Example 1. By adjusting the coating surface density, compaction density, CB value, battery housing size, lithium salt concentration, and electrolyte injection amount of the positive and negative electrode active material layers, secondary batteries with different performances can be prepared. The parameters of the secondary batteries are detailed in Table 1.

[0052] Table 1 Parameters of secondary batteries

[0053]

[0054] Performance Testing

[0055] The electrochemical performance of the above examples and comparative examples was tested using the following test methods:

[0056] 1. The cycle test method is as follows: in a 25°C incubator, the battery is equipped with two 300kgf steel clamps; 1) the secondary battery is discharged at a constant power of 0.5 times the rated power (P) until the battery voltage drops to 2.5V; 2) it is left to stand for 30 minutes; 3) it is charged at a constant power of 0.5 times the rated power until the voltage reaches 3.65V; 4) it is left to stand for 30 minutes. (1) to (4) is one cycle. The capacity retention rate after 6000 cycles is calculated. The test results are shown in Table 2.

[0057] 2. Storage test method: The battery is equipped with two 300kgf steel fixtures, 1) 25℃, 0.5C, divided capacity three times at 2.5V~3.65V, and the average value is defined as the actual capacity C0 of the battery; 2) 25℃, 0.5C0 constant current charge to 3.65V, then 3.65V constant voltage charge to 0.05C0, rest 10min; 3) 0.5C0 constant current discharge to 2.5V, record the battery remaining capacity retention rate; 4) 0.5C0 is charged and discharged once, and the battery recovery capacity retention rate is recorded; 5) The battery is charged with 0.5C0 constant current to 3.65V, then 3.65V constant voltage charge to 0.05C0 full charge; 6) Place the battery in a 45℃ constant temperature box and let it stand. Every 30 days, move the battery to a 25℃ constant temperature box and let it stand for 120min; 7) Repeat steps 1 to 7 until the storage days reach 360 days.

[0058] 3. The energy efficiency test method is as follows: 1) the secondary battery is discharged at a constant power of 0.5 times the rated power (P) until the battery voltage drops to 2.5V; 2) it is allowed to stand for 30 minutes; 3) it is charged at a constant power of 0.5 times the rated power until the voltage reaches 3.65V; 4) it is allowed to stand for 30 minutes. This is one cycle, and the cycle is repeated three times. Energy efficiency = discharge energy / charge energy. The average of these three charge and discharge energy efficiencies is taken as the energy efficiency of the secondary battery. The test results are shown in Table 2.

[0059] Table 2 Performance test results

[0060]

[0061] From the above embodiments and comparative examples, the present application improves the long cycle performance, energy efficiency and storage performance of the secondary battery by controlling the discharge capacity of the secondary battery, the filling coefficient of the electrolyte, the OI value of the negative electrode plate and the concentration of the lithium salt in the electrolyte to satisfy a certain relationship.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, characterized in that: The secondary battery satisfies: 200 < A × N / (I^G), where A Ah is the discharge capacity of the secondary battery, N g / Ah is the liquid injection coefficient of the electrolyte, I is the OI value of the negative electrode sheet, and G mol / L is the concentration of the lithium salt in the electrolyte.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies: 200 < A × N / (I^G) < 350.

3. The secondary battery according to claim 1, wherein The discharge capacity A Ah of the secondary battery satisfies: 280 Ah ≤ A Ah ≤ 800 Ah.

4. The secondary battery according to claim 1, wherein The liquid injection coefficient N g / Ah of the secondary battery satisfies: 2 g / Ah ≤ N g / Ah ≤ 5 g / Ah.

5. The secondary battery according to claim 1, wherein The OI value I of the negative electrode sheet satisfies: 6 < I < 16.

6. The secondary battery according to claim 1, wherein The concentration G mol / L of the lithium salt in the electrolyte satisfies: 0.8 mol / L ≤ G mol / L ≤ 1.5 mol / L.

7. The secondary battery according to claim 1, wherein The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluorophosphate, lithium bis(oxalato)difluorophosphate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

8. The secondary battery according to claim 1, wherein The area of ​​the bottom surface of the secondary battery is S1 cm 2 The area of ​​the secondary battery's large surface is S2 cm 2 The area of ​​the side of the secondary battery is S3 cm 2 , satisfying: S2 / S1>2.5, S2 / S3>4.

5.

9. The secondary battery according to claim 1, wherein The group margin in the thickness direction of the secondary battery is F, which satisfies: 90% ≤ F ≤ 98%.

10. An electrical device, characterized in that: The electrical equipment includes the secondary battery according to any one of claims 1 to 9.

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