Method and device for improving energy efficiency of aged lithium ion battery

Abstract

The invention relates to a method and device for improving the energy efficiency of an aged lithium ion battery, and belongs to the technical field of lithium ion batteries. The method comprises the following steps: acquiring an aged lithium ion battery, and measuring the aging state of the aged lithium ion battery; determining a load to be applied according to the aging state of the aged lithium ion battery; the aged lithium ion battery is fixed between a movable clamping plate and a fixed clamping plate in the loading device, a spring is fixed on the other surface of the movable clamping plate, and stress is applied to the movable clamping plate by compressing the spring, so that a load is applied to the aged lithium ion battery, and the energy efficiency of the aged lithium ion battery is improved. Wherein the stress applied to the movable clamping plate is a load to be applied. The device provided by the invention is simple in structure and low in cost, the use method is simple and easy to understand, the energy efficiency of the aged lithium ion battery can be improved, the performance of the aged lithium ion battery in secondary utilization is improved, the service life of the aged lithium ion battery in secondary utilization is prolonged, and energy waste is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and relates to a method and device for improving the energy efficiency of aged lithium-ion batteries. Background Art

[0002] With the popularization of electric vehicles and the continuous expansion of the energy storage field, lithium-ion batteries, as an important energy storage device, have been widely used unprecedentedly. This trend has not only promoted the rapid development of the electric vehicle industry but also provided a new power source for various energy storage systems. However, as the usage time of lithium-ion batteries increases, their performance gradually deteriorates. Especially in the application of electric vehicles, due to frequent charge-discharge cycles and complex and changeable energy output environments, the performance degradation of lithium-ion batteries is more significant.

[0003] Among the performance indicators of lithium-ion batteries, SOH is an important one. When the SOH of the battery drops to 80% of the initial value, the lithium-ion battery often fails to meet the power performance, cruising range, and safe operation requirements of electric vehicles, so it needs to be replaced. In addition, battery energy efficiency is another important indicator. Energy efficiency refers to the ability of the battery to convert stored chemical energy into electrical energy, usually expressed as the ratio of output electrical energy to input electrical energy, which describes how much of the electrical energy input during charging can be effectively converted into energy available during discharge. Energy efficiency is extremely important in the field of electric vehicles because it directly affects the driving distance, energy consumption, and overall economy of electric vehicles.

[0004] The reduction of SOH and energy efficiency has led to the emergence of a large number of scrapped batteries from electric vehicles. However, these power batteries actually still have a relatively high remaining capacity, and direct elimination will cause serious waste of resources. To make full use of these replaced lithium batteries, the industry has carried out a series of research and practices. After processes such as testing, screening, and recombination, these batteries can be reapplied to fields with relatively low requirements for battery performance, such as low-speed electric vehicles, backup power supplies, and power energy storage. However, as the batteries further age, the internal resistance of lithium-ion batteries increases, the electrochemical performance deteriorates significantly, and the energy efficiency is low, which not only causes serious waste of energy but also limits the performance and lifespan of these batteries in secondary applications.

[0005] In response to the problem of low energy efficiency of aged lithium-ion batteries, the industry has been exploring effective solutions. Traditional methods often involve repairing or improving the batteries through chemical methods or physical means, but these methods are usually costly, complex to operate, and have limited effects. Therefore, there is an urgent need for a simple, effective, and low-cost method to improve the energy efficiency of aged lithium-ion batteries. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide a simple and low-cost method and device for improving the energy efficiency of aged lithium-ion batteries, which can improve their electrochemical performance and energy efficiency by applying a load to the aged lithium-ion batteries.

[0007] To achieve the above object, one aspect of the present invention provides a method for improving the energy efficiency of aged lithium-ion batteries, which includes:

[0008] Step 1: Obtain an aged lithium-ion battery and measure its state of health (SOH);

[0009] Step 2: Determine the load to be applied according to the state of health of the aged lithium-ion battery;

[0010] Step 3: Fix the aged lithium-ion battery between a movable clamping plate and a fixed clamping plate in a loading device, and apply a stress to the movable clamping plate, thereby applying a load to the aged lithium-ion battery to improve the energy efficiency of the aged lithium-ion battery. Wherein, the stress applied to the movable clamping plate is the load to be applied.

[0011] Further, in Step 2, determining the load to be applied according to the state of health of the aged lithium-ion battery includes: incrementally applying a load to the aged lithium-ion battery; performing charge and discharge on the aged lithium-ion battery each time a load is applied, and calculating the energy efficiency according to the charge and discharge results; when the increase rate of the energy efficiency is less than 5%, determine the minimum load that satisfies this condition as the load to be applied.

[0012] Further, in Step 3, applying a stress to the movable clamping plate, thereby applying a load to the aged lithium-ion battery, includes: setting a spring at one end of the movable clamping plate where the aged lithium-ion battery is not fixed, and applying a stress to the movable clamping plate by compressing the spring, thereby applying a load to the aged lithium-ion battery. Specifically, calculate the deformation amount that the spring should reach according to the stress that should be applied to the movable clamping plate, where the stress applied to the movable clamping plate is equal to the load to be applied determined according to the state of health of the aged lithium-ion battery. The deformation amount that the spring should reach can be calculated according to the following formula: In the formula, l represents the deformation amount of the spring, F represents the load to be applied, k represents the spring stiffness, and n represents the number of springs.

[0013] Another aspect of the present invention provides a device for improving the energy efficiency of aged lithium-ion batteries. The device applies a load to the aged lithium-ion batteries through the above method, thereby improving the energy efficiency of the aged lithium-ion batteries.

[0014] The device includes a fixed clamping plate, a first movable clamping plate, a spring, a second movable clamping plate, and a displacement measuring device.

[0015] Among them, the first movable clamp plate is located between the fixed clamp plate and the second movable clamp plate, and the aged lithium-ion battery is fixed between the first movable clamp plate and the fixed clamp plate; the spring is fixed between the first movable clamp plate and the second movable clamp plate; the displacement measuring device is fixed on the second movable clamp plate and is used to measure the distance between the first movable clamp plate and the second movable clamp plate.

[0016] In addition, the device further includes guiding bolts which are arranged at the four corners of each clamp plate and pass through the fixed clamp plate, the first movable clamp plate and the second movable clamp plate. The spring is sleeved on the guiding bolts located between the first movable clamp plate and the second movable clamp plate. Among them, nuts are arranged on the parts of the guiding bolts protruding from the second movable clamp plate, and the spring is compressed by rotating the nuts.

[0017] The beneficial effects of the present invention are as follows: According to the correlation between the energy efficiency of lithium-ion batteries and the loads borne by the batteries, the present invention proposes a method of applying loads to lithium-ion batteries to improve the battery energy efficiency, and at the same time proposes a device for applying loads to lithium-ion batteries. The device proposed by the present invention has a simple structure, low cost, an easy-to-understand usage method, allows the batteries to be placed vertically, is applicable to the loading of multiple batteries, and can increase the load range by replacing the spring. This device can improve the energy efficiency of aged lithium-ion batteries, improve the performance and lifespan of aged lithium-ion batteries in secondary utilization, and reduce energy waste.

[0018] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Description of the Drawings

[0019] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0020] Figure 1 is a top view of the loading device provided by the present invention.

[0021] Figure 2 is a front view of the loading device provided by the present invention.

[0022] Figure 3 is a three-dimensional structure diagram of the loading device provided by the present invention.

[0023] Figure 4 are the capacity and voltage information of lithium iron phosphate batteries in different aging states under a load of 0N.

[0024] Figure 5Capacity and voltage information of lithium iron phosphate batteries in different aging states under a load of 15 kN.

[0025] Figure 6 Energy efficiency of lithium iron phosphate batteries in different aging states under different loads and charging rates.

[0026] Reference numerals: 1 - fixed clamping plate; 2 - guiding bolt; 3 - aged lithium-ion battery; 4 - first movable clamping plate; 5 - spring; 6 - second movable clamping plate; 7 - nut; 8 - displacement measuring device. Detailed implementation manners

[0027] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0028] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as a limitation to the present invention; for better illustrating the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual products; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0029] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and should not be construed as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0030] Embodiment 1

[0031] This embodiment provides a method for improving the energy efficiency of aged lithium-ion batteries, and the method is as follows:

[0032] (1) Vertically place the aged battery as shown in Figures 1 to 3In the loading device shown, specifically, the aged battery is placed between the fixed clamping plate 1 and the first movable clamping plate 4 of the loading device.

[0033] (2) Select a suitable load according to the aging state of the battery. Specifically, apply an increasing load to the battery, obtain the results of cyclic charge and discharge of the battery under different stresses, and calculate the energy efficiency. When the increase rate of the battery energy efficiency is less than 5%, the minimum load that meets this condition can be considered as the load required for the optimal state of the battery.

[0034] (3) Select a spring with a suitable stiffness according to the required load.

[0035] (4) Calculate the loading displacement through the load, the number of springs, and the spring stiffness Where F is the load, k is the spring stiffness, and n is the number of springs. Here, the loading displacement is the deformation of the spring. In this embodiment, the load required for the optimal state of the battery is 15000 N, the spring stiffness is 37.5 N / mm, and the number of springs is 4. The loading displacement can be calculated to be 100 mm.

[0036] (5) Load the lithium-ion battery by tightening the bolts, and measure the loading displacement through the displacement measuring device 8.

[0037] (6) Connect the battery to the battery test system, and charge and discharge the aged battery according to the actual use conditions.

[0038] Taking the test of square lithium iron phosphate batteries in different aging states as an example, the effectiveness of the method proposed in this embodiment is verified.

[0039] First, place lithium-ion batteries with SOH of 100%, 88%, and 82% respectively in the loading device, and apply loads of 0 N, 1000 N, 2000 N, 8000 N, and 15000 N to the batteries through the loading device respectively. Under different loading states, charge and discharge the batteries at 0.2C and 1C rates respectively to obtain information such as their capacity and voltage, as Figure 4 Shown are the capacity and voltage information of the battery under the unloaded state and at a 0.2C charge rate, Figure 5 Shown are the capacity and voltage information of the battery under a 15 kN loading state and at a 0.2C charge rate. Figure 6 Shown is the energy efficiency of lithium iron phosphate batteries in different aging states under different loads. From Figure 6 It can be seen that compared with the case without loading, the energy efficiency of the aged lithium-ion battery after loading is significantly improved, and with the increase of the charge and discharge rate, the increase of the energy efficiency of the aged lithium-ion battery after loading is more significant. Thus, it can be seen that the method proposed in this embodiment can effectively improve the energy efficiency of the aged lithium-ion battery.

[0040] Embodiment 2

[0041] This embodiment provides a loading device for improving the energy efficiency of aged lithium-ion batteries, as Figures 1 to 3 shown. The loading device includes a fixed clamping plate 1, a guiding bolt 2, a first movable clamping plate 4, a spring 5, a second movable clamping plate 6, and a displacement measuring device 8. Among them, the lithium-ion battery is clamped between the fixed clamping plate 1 and the first movable clamping plate 4; the spring 5 is arranged between the first movable clamping plate 4 and the second movable clamping plate 6; the guiding bolt 2 is used to connect the fixed clamping plate 1, the first movable clamping plate 4, and the second movable clamping plate 6, and protrudes from the surface of the second movable clamping plate 6. A nut 7 is arranged on the protruding part. By means of the nut 7, each clamping plate is fixed and a pressure is applied to the spring 5, so as to apply a load to the lithium-ion battery; the displacement measuring device 8 is fixed on the second movable clamping plate 6 and is used to measure the loading displacement.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the energy efficiency of an aged lithium-ion battery, characterized in that: The method includes: Obtain aged lithium-ion batteries and measure their aging state; Determine the load to be applied based on the aging state of the aged lithium-ion battery; The aged lithium-ion battery is fixed between a movable clamp and a fixed clamp in a loading device, and a load is applied to the aged lithium-ion battery by applying stress to the movable clamp, so as to improve the energy efficiency of the aged lithium-ion battery; wherein the stress applied to the movable clamp is the load to be applied.

2. The method for improving the energy efficiency of an aged lithium-ion battery according to claim 1, characterized in that: Determining the load to be applied according to the aging state of the aged lithium-ion battery includes: incrementally applying the load to the aged lithium-ion battery; charging and discharging the aged lithium-ion battery each time the load is applied, and calculating energy efficiency according to the charging and discharging results; when the increase rate of the energy efficiency is less than 5%, determining the minimum load that meets this condition as the load to be applied.

3. The method for improving the energy efficiency of an aged lithium-ion battery according to claim 1, characterized in that: Applying stress to the movable clamp to apply load to the aged lithium-ion battery includes: arranging a spring at one end of the movable clamp where the aged lithium-ion battery is not fixed, and applying stress to the movable clamp by compressing the spring to apply load to the aged lithium-ion battery.

4. The method for improving the energy efficiency of an aged lithium-ion battery according to claim 3, characterized in that: The deformation amount that the spring should reach is calculated according to the stress that should be applied to the movable clamp, wherein the stress applied to the movable clamp is equal to the load that should be applied determined according to the aging state of the aged lithium-ion battery; the deformation amount that the spring should reach is calculated according to the following formula: Wherein, l represents the spring deformation, F represents the load to be applied, k represents the spring stiffness, and n represents the number of springs.

5. A device for improving the energy efficiency of aged lithium-ion batteries applicable to the method according to any one of claims 1 to 4, characterized in that: The device comprises a fixed clamp, a first movable clamp, a spring, a second movable clamp and a displacement measuring device; the first movable clamp is located between the fixed clamp and the second movable clamp, and the aged lithium-ion battery is fixed between the first movable clamp and the fixed clamp; the spring is fixed between the first movable clamp and the second movable clamp; the displacement measuring device is fixed on the second movable clamp and is used to measure the distance between the first movable clamp and the second movable clamp.

6. The device according to claim 5, characterized in that It also includes guide bolts, which are arranged at the four corners of each clamp plate and pass through the fixed clamp plate, the first movable clamp plate and the second movable clamp plate; the spring is sleeved on the guide bolts located between the first movable clamp plate and the second movable clamp plate; wherein the part of the guide bolt protruding from the second movable clamp plate is provided with a nut, and the spring is compressed by rotating the nut.

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