A secondary battery and an electric device

Abstract

The application provides a secondary battery and a power consumption device. The secondary battery of the application comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, and satisfies: wherein CB is a capacity excess coefficient of the secondary battery; AP g / cm 3 is a compactness of the negative electrode sheet in the secondary battery; A Ah is a standard discharge capacity of the secondary battery; L mm is a length of the secondary battery; W mm is a width of the secondary battery; and H mm is a height of the secondary battery. By reasonably designing the parameters of the secondary battery, the capacity excess coefficient of the secondary battery, the compactness of the negative electrode sheet, the standard discharge capacity of the secondary battery and the size (including the length, the width and the height) of the secondary battery satisfy certain relationships, so that the energy density and the cycle life of the secondary battery can be significantly improved.

Description

Technical Field

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

[0002] To better meet the needs of users, the grid, and the power source, energy storage batteries need to further improve their volumetric energy density, long-cycle performance, long-storage performance, and high energy efficiency. Research has found a close relationship between battery size, electrical performance, volumetric energy density, and battery design. Therefore, to further improve the volumetric energy density and cycle performance of secondary energy storage batteries, a more rational battery design is required. Summary of the Invention

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

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery, the secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, satisfying the following:

[0005]

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

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

[0008] A Ah represents 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 represents the height of the secondary battery.

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

[0013] As an embodiment of this application, the compaction density AP of the negative electrode sheet of the secondary battery satisfies: 1.45 g / cm³. 3 ≤AP≤1.7g / cm 3 .

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

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

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

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

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

[0019] As an embodiment of this application, the secondary battery has a group margin F in the width direction. W Satisfy: F W ≥98%.

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

[0021] As an embodiment of this application, the positive electrode sheet of the secondary battery includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector and containing a positive active material, wherein the positive active material includes a lithium phosphate containing Ti and / or V elements.

[0022] A second aspect of this application provides an electrical device comprising the secondary battery described in the first aspect of this application.

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

[0024] This application, through the rational design of secondary battery parameters, controls the secondary battery's capacity excess coefficient, negative electrode compaction density, standard discharge capacity, and dimensions (including length, width, and height) to meet certain requirements, which can significantly improve the energy density and cycle life of the secondary battery. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] In this application, among the technical features described in an open manner, it includes both closed technical solutions composed of the listed features and open technical solutions comprising the listed features.

[0027] 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 every value between the minimum and maximum values. Further, when the range refers to integers, it includes every integer between the minimum and maximum values of the range. In addition, when multiple ranges describing features or characteristics are provided, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein are to be understood as including any and all sub-ranges subsumed therein.

[0028] Reagents or instruments used in this application without manufacturer specifications are all conventional products commercially available.

[0029] An embodiment of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator, 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 tested by the following method: the battery is left standing for 1 hour in a 25°C thermostat, charged at a constant power of 0.5P to 4.35V, left standing for 1 hour, discharged at a constant power of 0.5P for 1 hour, and the discharge capacity is recorded.

[0038] Through a large number of experimental studies, the present application found that when the secondary battery satisfies 300 < V*CB / AP < 325, the secondary battery can have both high energy density and 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 = gram capacity of negative electrode per unit area / gram capacity of positive electrode per unit area. During charging and discharging of the battery, active ions are delithiated from the positive electrode and intercalated into the negative electrode. The capacity excess coefficient represents the relationship between the capacitance receivable by the negative electrode and the capacitance delithiated from the positive electrode. On one hand, active ions delithiated from the positive electrode form an SEI film on the surface of the negative electrode, and on the other hand, remaining active ions are intercalated into the negative electrode material. For batteries designed with different excess coefficients, the negative electrode plate will be in different SOC states when fully charged. A larger excess coefficient leads to a lower SOC state of the negative electrode. When the negative electrode plate is at a lower SOC state, its expansion and side reactions are both smaller, which contributes to the long cycle life of the battery. However, an excessively large capacity excess coefficient results in too low energy density of the battery. Meanwhile, under the condition that other parameters remain unchanged, the increased thickness of the negative electrode plate is unfavorable for the charging and discharging of the battery. Therefore, when CB is within the above suitable range, the obtained secondary battery has both excellent energy density and cycle life. For example, the value of CB can be any one of 1.12, 1.13, 1.14, 1.15, 1.16, 1.17 or a range between any two of the values.

[0040] In a secondary battery, by adjusting the coating areal density ρ of the positive electrode active material layer 正 (unit: g / m 2 ), and the compacted 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 areal density ρ of the negative electrode active material layer 负 (unit: g / m 2 ), and the compacted 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 areal density ρ of the positive electrode active material layer 正 >190g / m 2 , and the compacted density CP of the positive electrode plate ≥ 2.5g / cm 3 .

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

[0043] In some embodiments, the compacted density AP of the negative electrode plate satisfies: 1.45g / cm 3 ≤AP≤1.7g / cm 3 , specifically can be 1.45g / 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 any one or any two values ​​in the range. Within this suitable range, the compaction density ensures that the negative electrode active material in the negative electrode sheet will not shed powder or deposit lithium, and also possesses a relatively well-developed porous structure, which is beneficial for the conduction of active ions in the secondary battery, further improving the cycle life of the secondary battery.

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

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

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

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

[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 known as thickness) direction T Satisfy: 100% ≥ F T ≥88%. A reasonable group margin design can improve the battery's overall lifespan performance and safety during use. By controlling the battery group margin, the battery expansion force throughout its lifespan is kept within a reasonable range, thus extending battery life. The group margin of the secondary battery in the height direction is calculated by dividing the stacked core height by the available space in the height direction of the secondary battery casing.

[0050] In some embodiments, the group margin F of the secondary battery in the width direction W Satisfy: F W ≥98%. The high group margin design significantly increases the active lithium content of the battery, improving charge / discharge capacity and storage performance while ensuring battery safety and performance throughout its entire lifespan. This extends battery life and increases cycle life. Simultaneously, the high group margin optimizes module and pack structures. The group margin of the secondary battery in the width direction is calculated by dividing the stack width by the available space in the width direction of the secondary battery casing.

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

[0052] In some embodiments, the secondary battery described in this application includes a positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector and containing a positive active material, wherein the positive active material comprises a lithium phosphate containing Ti and / or V. Doping the positive electrode material with Ti can improve its electrochemical performance, helping to increase the upper limit of the charging high voltage, increase the charge-discharge capacity, and enhance structural stability. Doping with Ti helps improve the low-temperature performance of LiFePO4 / C batteries. Doping the positive electrode material with V helps to improve the material's conductivity and enhance the positive electrode material's performance in Li... + The structural stability during the insertion / deintercalation process effectively improves the rate performance of the cathode material and enhances the structural stability during cycling.

[0053] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector and containing a negative active material. The negative active material includes a silicon-carbon composite material formed by silicon-based materials and carbon-based materials. The silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. The carbon-based material includes graphite.

[0054] Commonly used electrolytes and diaphragms in this field can also be used in this application.

[0055] A second aspect of this application also provides an electrical device, which includes the secondary battery described in the first aspect of this application; the electrical device includes, but is not limited to, electric vehicles and energy storage devices.

[0056] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[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 sheet

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

[0061] The positive electrode active slurry is coated onto the positive electrode current collector, and then dried in an oven before being rolled, rolled, slit, and sliced ​​to obtain the positive electrode sheet. The relevant parameters of the positive electrode sheet are detailed in Table 1. The positive electrode current collector is a 12μm aluminum foil, and 1μm 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 sheet

[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. Deionized water was added as a solvent, and the mixture was stirred under vacuum until the system was homogeneous to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on both surfaces of the negative electrode current collector copper foil (copper foil thickness was 6μm). After drying at room temperature, it was transferred to a 120℃ oven for further drying. Then, it was cold-pressed and slit to obtain the negative electrode sheet. The relevant parameters of the negative electrode sheet are detailed in Table 1.

[0064] Preparation of electrolyte

[0065] The electrolyte comprises the following components:

[0066] Solvent: Dimethyl carbonate (a chain carbonate) and ethylene carbonate (a cyclic carbonate) are mixed in a volume ratio of 1:1.

[0067] Lithium salt: LiPF6 and LiFSI are mixed at 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 are also added in weight percentage: 3 wt% of 1,3-propenesulfonate lactone.

[0069] Assembly of secondary batteries

[0070] After the positive electrode, separator (PE) and negative electrode are stacked in sequence, they are assembled into a stack core by stacking process on a stacking machine. The positive electrode, separator and negative electrode in the stack core are tightly bonded by hot pressing.

[0071] After ultrasonic welding of the tabs, laser welding of the connecting pieces, and wrapping with a Mylar film, the battery is obtained. The battery is then assembled into a square aluminum shell with dimensions of 517mm in length, 51mm in width, and 177mm in height. Next, the top cover is welded around the perimeter. After internal resistance and helium content are tested and found to be within acceptable limits, the battery enters the activation stage.

[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 electrolyte is injected, the battery forms an SEI film at the interface of the negative electrode material through formation. Then, after a high-temperature aging process, the SEI film of the negative electrode becomes denser (a dense SEI can prevent the electrolyte from eroding the negative electrode and causing unnecessary side reactions during battery use, and can inhibit the formation of lithium dendrites).

[0073] (2) After aging, electrolyte is injected a second time to replenish the electrolyte consumed during the activation and film formation process;

[0074] (3) The battery is sealed with a nail and after passing the helium test, it is tested for capacity and graded.

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

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

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

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

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

[0080] The electrochemical performance of the above embodiments and comparative examples was tested using the following methods:

[0081] 1. Cyclic test method: in a 25℃ incubator; 1) the secondary battery is discharged at 0.5 times the rated power (P) until the battery voltage drops to 2.5V; 2) let stand for 30 minutes; 3) charge at 0.5 times the rated power until the voltage reaches 3.65V; 4) let stand for 30 minutes, (1) to (4) is one cycle, calculate the capacity retention rate after 6000 cycles, and the test results are shown in Table 2;

[0082] 2. The energy efficiency test method is as follows: 1) The secondary battery is discharged at 0.5 times the rated power (P) until the battery voltage drops to 2.5V; 2) Let it stand for 30 minutes; 3) Charge it at 0.5 times the rated power until the voltage reaches 3.65V; 4) Let it 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 energy efficiency of these three charge and discharge cycles 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 standard for measuring the performance of energy storage batteries. As shown in Table 2, the secondary batteries meet the relationship of this 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 greater than 85%, which is significantly better than the comparative example.

[0089] In this application, the standard discharge capacity and volumetric energy density of a secondary battery are linked to its size using empirical formulas. Only by rationally designing the capacity of a secondary battery based on its existing size can a square aluminum-cased 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 solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, characterized in that, The secondary battery satisfies: ， ； Wherein, CB is the capacity excess factor of the secondary battery, 1.1 <CB<1.2; AP g / cm 3 The compaction density of the negative electrode sheet in the secondary battery is 1.45 g / cm³. 3 ≤AP g / cm 3 ≤1.7 g / cm 3 ; AAh is the standard discharge capacity of the secondary battery, 280Ah≤Ah≤800Ah; L mm is the length of the secondary battery, 250 mm ≤ L mm ≤ 550 mm; W mm is the width of the secondary battery, 50mm≤W mm≤80mm; H mm is the height of the secondary battery, where 170 mm ≤ H mm ≤ 220 mm.

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

5.

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

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

5. The secondary battery according to claim 1, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector and containing a positive active material, wherein the positive active material includes a lithium phosphate containing Ti and / or V elements.

6. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in any one of claims 1-5.

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