Secondary battery and electric equipment

Abstract

The invention provides a secondary battery and electric equipment. The secondary battery provided by the invention comprises a positive pole piece, a negative pole piece, an electrolyte and a diaphragm, and meets: # imgabs0 #, CB being a capacity excess coefficient of the secondary battery; aP g / cm < 3 > is the compaction density of the negative pole piece in the secondary battery; a Ah is the standard discharge capacity of the secondary battery; l mm is the length of the secondary battery; w mm is the width of the secondary battery; and H mm is the height of the secondary battery. By reasonably designing the parameters of the secondary battery, the capacity excess coefficient of the secondary battery, the compaction density of the negative pole piece, the standard discharge capacity of the secondary battery and the sizes (including length, width and height) of the secondary battery are controlled to meet a certain relationship, so that the energy density and the cycle life of the secondary battery can be remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, in particular to a secondary battery and an electrical device. Background Art

[0002] In order to better meet the needs of the user side, the grid side, and the power supply side, energy storage batteries need to further improve their volume energy density, long cycle performance, long storage performance, and high energy efficiency. Studies have found that the size of energy storage batteries is closely related to battery electrical performance and battery volume energy density, as well as battery design. Therefore, in order to further improve the volume energy density and cycle performance of secondary batteries, more reasonable battery design is needed. Summary of the invention

[0003] The purpose of the present application is to provide a secondary battery and an electrical device with long cycle performance.

[0004] To achieve the above-mentioned object, in a first aspect of the present application, a secondary battery is provided, wherein the secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, and satisfies:

[0005]

[0006] Wherein, CB is the excess capacity factor of the secondary battery;

[0007] AP g / cm 3 is the compaction density of the negative electrode sheet in the secondary battery;

[0008] A Ah is the standard discharge capacity of the secondary battery;

[0009] L mm is the length of the secondary battery;

[0010] W mm is the width of the secondary battery;

[0011] H mm is the height of the secondary battery.

[0012] As an embodiment of the present application, the capacity excess coefficient CB of the secondary battery satisfies: 1.1 <CB<1.2。

[0013] As an embodiment of the present application, the compaction density AP of the negative electrode sheet of the secondary battery satisfies: 1.45 g / cm 3 ≤AP≤1.7g / cm 3 .

[0014] As an embodiment of the present application, the secondary battery satisfies: (L×W×H) / (A×1000)<7.5.

[0015] As an implementation scheme of the present application, the length of the secondary battery satisfies: 250 mm ≤ L ≤ 550 mm.

[0016] As an embodiment of the present application, the width of the secondary battery satisfies: 50 mm ≤ W ≤ 80 mm.

[0017] As an embodiment of the present application, the height of the secondary battery satisfies: 170 mm ≤ H ≤ 220 mm.

[0018] As an embodiment of the present application, the group margin F of the secondary battery in the height direction T Satisfied: 100% ≥ F T ≥88%.

[0019] As an embodiment of the present application, the group margin F of the secondary battery in the width direction is W Satisfaction: F W ≥98%.

[0020] As an embodiment of the present application, the standard discharge capacity of the secondary battery satisfies: 280Ah≤A≤800Ah.

[0021] As an embodiment of the present application, the secondary battery positive electrode plate includes a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode 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.

[0022] A second aspect of the present application provides an electrical device, wherein the electrical device comprises the secondary battery described in the first aspect of the present application.

[0023] Compared with the prior art, the beneficial effects of this application are:

[0024] The present application reasonably designs the parameters of the secondary battery, controls the excess capacity coefficient of the secondary battery, the compaction density of the negative electrode plate, the standard discharge capacity of the secondary battery, and the size of the secondary battery (including length, width and height) to meet certain requirements, thereby significantly improving the energy density and cycle life of the secondary battery. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0026] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, as well as an open technical solution including the listed features.

[0027] In this application, regarding 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, these 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.

[0028] For the reagents or instruments used in this application that are not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0029] The embodiments of this application provide a secondary battery, which includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. It is characterized in that the secondary battery satisfies:

[0030]

[0031] wherein, CB is the capacity excess coefficient of the secondary battery;

[0032] AP g / cm 3 is the compaction density of the negative electrode plate in the secondary battery;

[0033] A Ah is the standard discharge capacity of the secondary battery;

[0034] L mm is the length of the secondary battery;

[0035] W mm is the width of the secondary battery;

[0036] H mm is the height of the secondary battery.

[0037] In this application, the standard discharge capacity of the secondary battery is obtained through the following method: The battery is left standing in a constant temperature oven at 25°C for 1 h, charged at a constant power of 0.5P to 4.35V, left standing for 1 h, and discharged at a constant power of 0.5P for 1 h, and the discharge capacity is recorded.

[0038] Through a large number of experimental studies, it is found in this application that when the secondary battery satisfies: 300 < V * CB / AP < 325, the secondary battery can have both a high energy density and a long cycle life.

[0039] In some embodiments, the capacity excess coefficient CB of the secondary battery satisfies: 1.1 < CB < 1.2. The capacity excess coefficient CB of the secondary battery = the gram capacity per unit area of the negative electrode / the gram capacity per unit area of the positive electrode. When the battery is charged and discharged, the active ions of the positive electrode are released and inserted into the negative electrode. The capacity excess coefficient represents the relationship between the capacitance that the negative electrode can receive and the capacitance released by the positive electrode. On the one hand, the active ions released from the positive electrode will form a SEI film on the surface of the negative electrode. On the other hand, the remaining active ions will be inserted into the negative electrode material. For batteries designed with different excess coefficients, when fully charged, the negative electrode plate will be in different SOC states. The larger the excess coefficient, the lower the SOC state of the negative electrode. When the negative electrode plate is in a lower SOC state, its swelling and side reactions are both smaller, which will contribute to the long cycle life of the battery. However, if the capacity excess coefficient is too large, the energy density of the battery will be too small. At the same time, when other conditions remain unchanged, the thickness of the negative electrode plate increases, which is not conducive to the charge and discharge of the battery. Therefore, when CB is within the above appropriate range, the obtained secondary battery has both excellent energy density and cycle life. For example, the value of CB can be any value among 1.12, 1.13, 1.14, 1.15, 1.16, 1.17 or the range value between any two values.

[0040] In the secondary battery, by adjusting the coating surface density ρ 正 (unit: g / m 2 ) and the compaction density CP of the positive electrode plate (unit: g / cm 3 ), different gram capacities of the positive electrode can be obtained; similarly, by adjusting the coating surface density ρ 负 (unit: g / m 2 ) and the compaction density AP of the negative electrode plate (unit: g / cm 3 ), different gram capacities of the negative electrode can be obtained.

[0041] In some embodiments, the coating surface density ρ of the positive electrode active material layer 正 > 190 g / m 2 , and the compaction density CP of the positive electrode plate ≥ 2.5 g / cm 3 .

[0042] In some embodiments, the coating surface density ρ of the negative electrode active material layer 负 > 90 g / m 2 ; the compaction density AP of the negative electrode plate ≥ 1.45 g / cm 3 .

[0043] In some embodiments, the compaction density AP of the negative electrode plate satisfies: 1.45 g / cm 3 ≤ AP ≤ 1.7 g / cm 3 , specifically, it can be 1.45 g / cm3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 The compaction density of the negative electrode sheet is within the appropriate value range, which can ensure that the negative electrode active material in the negative electrode sheet will not fall off and precipitate lithium, and has a relatively developed pore structure, which is conducive to the conduction of active ions in the secondary battery, and further improves the cycle life of the secondary battery.

[0044] In some embodiments, in the secondary battery, the standard discharge capacity and the size of the secondary battery (including length, width, height) further satisfy the relationship: (L×W×H) / (A×1000)≤7.5, which can further simultaneously satisfy the high energy density and excellent long cycle performance of the secondary battery.

[0045] In some embodiments, the length of the secondary battery satisfies: 250 mm ≤ L ≤ 550 mm.

[0046] In some embodiments, the width of the secondary battery satisfies: 50 mm ≤ W ≤ 80 mm.

[0047] In some embodiments, the height of the secondary battery satisfies: 170 mm ≤ H ≤ 220 mm.

[0048] In some embodiments, the secondary battery has a stacked structure.

[0049] In some embodiments, the group margin F of the secondary battery in the height (also referred to as thickness) direction is T Satisfied: 100% ≥ F T ≥88%. 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 increasing the battery life. The group margin of the secondary battery in the height direction is calculated by the stacking core height / the available space of the secondary battery shell in the height direction.

[0050] In some embodiments, the group margin F of the secondary battery in the width direction is W Satisfaction: F W ≥98%. High group margin design significantly increases the active lithium content of the battery, improves the charge and discharge capacity and storage performance of the battery while ensuring battery safety and performance throughout the battery life cycle. Extends battery life and improves battery cycle life. At the same time, high group margin can optimize module and pack structure. The group margin of the secondary battery in the width direction is calculated by the stacking width / the available space of the secondary battery shell in the width direction.

[0051] In some embodiments, the standard discharge capacity of the secondary battery satisfies: 280Ah≤A≤800Ah, and specifically can be any one of 280Ah, 314Ah, 561Ah, 580Ah, 628Ah, 655Ah, 708Ah, 800Ah, or a range value between any two values.

[0052] 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 disposed 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 properties of the positive electrode material, help increase the upper limit of the high voltage charging of the positive electrode material, increase 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 and helps to enhance the positive electrode material in Li + The structural stability during the insertion and extraction process effectively improves the rate performance of the positive electrode material and enhances the structural stability during the cycle.

[0053] In some embodiments, the negative electrode plate 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, the negative electrode active material includes a silicon-carbon composite material formed by a silicon-based material and a carbon-based material, the silicon-based material includes at least one of silicon element, silicon oxide material and silicon-carbon material; the carbon-based material includes graphite.

[0054] Electrolytes and diaphragms commonly used in this field can also be used in this application.

[0055] In a second aspect of the present application, there is also provided an electric device, which includes the secondary battery described in the first aspect of the present application; the electric device includes but is not limited to electric vehicles and energy storage equipment.

[0056] The following are specific embodiments of the present application, and the technical scheme of the present application is further described in conjunction with the embodiments, but the present application is not limited to these embodiments. The reagents, methods and equipment used in the present application, unless otherwise specified, are conventional reagents, methods and equipment in the art.

[0057] Example 1

[0058] This embodiment prepares a secondary battery, and the preparation method of the secondary battery includes the following steps:

[0059] Preparation of positive electrode

[0060] The positive electrode active material LFP (lithium iron phosphate) and the Ti-containing compound TiO2 are ground and mixed evenly, and calcined at 900°C in an air atmosphere to obtain a Ti-doped LiFePO4 material to obtain a positive electrode active material, wherein the Ti element accounts for 2wt% of the LFP; then the positive electrode active material, conductive carbon, binder PVDF, and dispersant PVP (polyvinyl pyrrolidone) are mixed in a weight ratio of 90:5:4:1 and added to a solvent NMP, and a uniform positive electrode active slurry is prepared by a wet stirring process;

[0061] The positive electrode active slurry is coated on the positive electrode collector, and then rolled, rolled, slit and sliced ​​after oven drying to obtain the positive electrode sheet. The relevant parameters of the positive electrode sheet are detailed in Table 1; wherein, the positive electrode collector is a 12 μm aluminum foil, and 1 μm of conductive carbon is coated on both sides of the aluminum foil current collector to increase the electronic conductivity between the positive electrode material and the current collector.

[0062] Preparation of negative electrode

[0063] The negative electrode active material graphite, conductive carbon, binder SBR, dispersant CMC, and plasticizer butanediol were mixed in a mass ratio of 90:5:3.8:1:0.2, and deionized water was added as a solvent. The mixture was stirred under a vacuum mixer until the system was uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on both surfaces of the negative electrode current collector copper foil (the thickness of the copper foil was 6 μm), dried at room temperature, and then transferred to a 120°C oven for further drying. The negative electrode sheet was then obtained by cold pressing and slitting. The relevant parameters of the negative electrode sheet are shown in Table 1.

[0064] Preparation of electrolyte

[0065] The electrolyte includes the following components:

[0066] Solvent: a mixture of chain carbonate dimethyl carbonate and cyclic carbonate ethylene carbonate in a volume ratio of 1:1;

[0067] Lithium salt: LiPF6 and LiFSI are mixed in a mass ratio of 1:0.02. The concentration of lithium in the electrolyte is 1 mol / L.

[0068] Based on the total weight of the electrolyte, the following additives were added: 3 wt % of 1,3 propene sultone.

[0069] Assembly of secondary batteries

[0070] After the positive electrode sheet, separator (PE), and negative electrode sheet are stacked in sequence, they are assembled into a stacked core through a stacking process on a stacking machine. After hot pressing, the positive electrode sheet, separator, and negative electrode sheet in the stacked core are tightly fitted;

[0071] After the tabs are ultrasonically welded, the connecting pieces are laser welded, and the battery is wrapped with mylar film. The battery is assembled into a square aluminum shell with a length of 517mm, a width of 51mm, and a height of 177mm. The top cover is then welded around the periphery. After the internal resistance and helium inspection are tested and qualified, the battery activation stage is entered:

[0072] (1) First, the assembled battery is dried in an oven to remove residual moisture, and then the electrolyte is injected for the first time. After the injection, the SEI film is formed on the interface of the negative electrode material through formation, and then the SEI film of the negative electrode sheet becomes more dense after a high-temperature aging process (the dense SEI can prevent the electrolyte from corroding the negative electrode during the use of the battery and cause unnecessary side reactions, and can inhibit the formation of lithium dendrites);

[0073] (2) After aging, the electrolyte is injected for the second time to replenish the electrolyte consumed in the activation film formation;

[0074] (3) The battery is sealed with pins and welded. After the helium test is passed, the capacity test is carried out for grading;

[0075] (4) Finally, the battery size test and insulation withstand voltage test are carried out, and the battery preparation is completed after wrapping with an insulating film.

[0076] The test yielded a secondary battery with a standard discharge capacity of 655Ah.

[0077] The test method for standard discharge capacity is as follows: the secondary battery is placed in a 25°C constant temperature box for 1 hour, charged to 3.65V at 0.5P constant current, placed for 1 hour, discharged at 0.5P constant current for 1 hour, and the discharge capacity is recorded.

[0078] Example 2-11, Comparative Example 1-2

[0079] A series of secondary batteries are provided, which are prepared according to the method of Example 1. Secondary batteries with different performances can be prepared by adjusting the coating surface density, compaction density, CB value of the positive and negative electrode active material layers and the size of the battery shell. The parameters of the secondary batteries are detailed in Table 1.

[0080] The electrochemical performance of the above embodiments and comparative examples was tested, and the testing method was as follows:

[0081] 1. The cycle test method is as follows: in a 25°C incubator; 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.

[0082] 2. The test method for energy efficiency is: 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; this is one cycle, and the cycle is repeated three times. Energy efficiency = discharge energy / charge energy. The average value of the three charge and discharge energy efficiencies is taken as the energy efficiency of the secondary battery. The test results are shown in Table 2.

[0083] Table 1

[0084]

[0085]

[0086] Table 2

[0087]

[0088] Energy efficiency is an important criterion for measuring the performance indicators of energy storage batteries. As shown in Table 2, the secondary batteries meet the relationship of the present application, and the energy efficiency of the batteries is greater than 94%, which is significantly better than the comparative example; the cycle performance is also above 85%, which is significantly better than the comparative example.

[0089] In this application, the standard discharge capacity and volume energy density of the secondary battery are linked to the size of the secondary battery through an empirical formula. Only by reasonably designing the capacity of the secondary battery according to the size of the existing secondary battery can a square aluminum shell secondary battery product with ideal performance be obtained.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than 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, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution 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 meets the following requirements: Wherein, CB is the excess capacity factor of the secondary battery; AP g / cm 3 is the compaction density of the negative electrode sheet in the secondary battery; A Ah is the standard discharge capacity of the secondary battery; L mm is the length of the secondary battery; W mm is the width of the secondary battery; H mm is the height of the secondary battery.

2. The secondary battery according to claim 1, characterized in that: The excess capacity factor CB of the secondary battery satisfies: 1.1 <CB<1.2。 3. The secondary battery according to claim 1, characterized in that: The compaction density AP of the negative electrode sheet of the secondary battery satisfies: 1.45 g / cm 3 ≤AP≤1.7g / cm 3 .

4. The secondary battery according to claim 1, characterized in that: Satisfies: (L×W×H) / (A×1000)<7.

5.

5. The secondary battery according to claim 1, characterized in that: The secondary battery meets at least one of the following characteristics: (1) 250mm≤L≤550mm; (2) 50mm≤W≤80mm; (3)170mm≤H≤220mm.

6. The secondary battery according to claim 1, characterized in that: The group margin F of the secondary battery in the height direction T Satisfied: 100% ≥ F T ≥88%.

7. The secondary battery according to claim 1, characterized in that: The group margin F of the secondary battery in the width direction W Satisfaction: F W ≥98%.

8. The secondary battery according to claim 1, characterized in that: The standard discharge capacity of the secondary battery satisfies: 280Ah≤A≤800Ah.

9. The secondary battery according to claim 1, characterized in that: The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed 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.

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

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