Qualification judgment method of solid-state battery

Abstract

The invention relates to a qualification judgment method for a solid-state battery. Comprising the following steps: carrying out cycle performance test on a to-be-tested battery after capacity grading to obtain a coulombic efficiency curve and a capacity retention rate cycle curve; respectively comparing the coulombic efficiency curve and the capacity retention rate cycle curve of the battery to be detected with the coulombic efficiency curve and the capacity retention rate cycle curve of a standard battery; if the cycle curve of the to-be-detected battery is lower than that of the standard battery, but the coulombic efficiency curve of the to-be-detected battery is superior to that of the standard battery, if the capacity retention ratio of the to-be-detected battery is not lower than 85% after 100 cycles, the to-be-detected battery can be regarded as a qualified product, otherwise, the to-be-detected battery is an unqualified product. According to the method, whether the battery is a qualified product or not is judged based on the coulombic efficiency curve and the capacity retention rate cyclic curve, and development and application of the solid-state battery are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and in particular to a method for determining whether a solid-state battery is qualified. Background Art

[0002] Solid-state batteries are a new type of battery technology. Compared with traditional liquid batteries, they use solid electrolytes instead of liquid or gel electrolytes in traditional batteries. The cycle life of solid-state batteries is one of the important indicators of battery performance. Cycle life prediction can be used to determine whether the solid-state battery is qualified and its future working performance. The existing solid-state battery cycle life assessment method has a long test cycle, requiring several months or even years of testing time. This results in a large amount of time and site costs for solid-state battery cycle life assessment work, which in turn leads to a serious lack of test data for the full cycle life of solid-state batteries, which seriously hinders the development and application of solid-state batteries. Summary of the invention

[0003] Based on this, it is necessary to provide a method for judging the qualification of solid-state batteries, which can judge whether they are qualified based on the coulombic efficiency curve and capacity retention rate cycle curve of the battery to be tested and the standard battery.

[0004] A method for determining the quality of a solid-state battery comprises the following steps:

[0005] Perform cycle performance test on the battery to be tested after capacity division to obtain the coulomb efficiency curve and capacity retention rate cycle curve;

[0006] Comparing the coulombic efficiency curve and the capacity retention rate cycle curve of the battery to be tested with the coulombic efficiency curve and the capacity retention rate cycle curve of the standard battery respectively;

[0007] If the coulombic efficiency curve and capacity retention rate cycle curve of the battery to be tested are better than those of the standard battery, it is a qualified product;

[0008] If the coulombic efficiency curve and the cycle curve of the battery to be tested are both lower than those of the standard battery, it is a defective product;

[0009] If the cycle curve of the battery to be tested is better than that of the standard battery, but the coulomb efficiency curve of the battery to be tested is lower than that of the standard battery, then the battery to be tested is a defective product;

[0010] If the cycle curve of the battery to be tested is lower than that of the standard battery, but the coulomb efficiency curve of the battery to be tested is better than that of the standard battery, then if the capacity retention rate of the battery to be tested is not less than 85% after 100 cycles, it can be regarded as a qualified product, otherwise it is an unqualified product.

[0011] The present invention provides a method for judging the quality of solid-state batteries. The method judges whether a solid-state battery is a qualified product based on the coulomb efficiency curve and the capacity retention rate cycle curve of the battery to be tested and the standard battery, which is beneficial to the development and application of solid-state batteries.

[0012] In a feasible implementation, if the coulombic efficiency curve of the battery to be tested is better than that of the standard battery, if the cycle curve of the battery to be tested within n cycles is lower than that of the standard battery, and the cycle curve of the battery to be tested after n cycles is higher than that of the standard battery, where n≤100, then it can be regarded as a qualified product.

[0013] In a feasible implementation, the cycle performance test of the battery to be tested after capacity division is performed to obtain the coulombic efficiency curve and the capacity retention rate cycle curve. The operation is as follows: the cycle performance test of the battery to be tested after capacity division is performed under low rate charge and discharge conditions to obtain the coulombic efficiency curve; the cycle performance test of the battery to be tested after capacity division is performed under normal rate charge and discharge conditions to obtain the capacity retention rate cycle curve.

[0014] In a feasible implementation, the charge and discharge rate under the low-rate charge and discharge condition does not exceed 0.1C, and the charge and discharge rate under the conventional-rate charge and discharge condition is 1C to 2C.

[0015] In a feasible implementation, the capacity-divided battery to be tested is subjected to a cycle performance test under low-rate charge and discharge conditions. When the coulomb efficiency curve test is completed, the number of cycles of the cycle performance test is 15 to 20 cycles.

[0016] In a feasible implementation, the capacity-divided battery to be tested is subjected to a cycle performance test under conventional rate charge and discharge conditions until it cycles to 80% SOH, thereby obtaining a capacity retention rate cycle curve.

[0017] In one feasible implementation, the solid-state battery is a solid-state lithium-ion battery.

[0018] In a feasible implementation, the solid-state lithium-ion battery comprises a positive electrode, a solid electrolyte and a negative electrode; and / or

[0019] The positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder;

[0020] The solid electrolyte includes one of a halide, a sulfide and an oxide;

[0021] The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder.

[0022] In a feasible implementation, the solid-state lithium-ion battery includes a positive electrode, a solid electrolyte and a negative electrode current collector. The solid-state lithium-ion battery relies on the deposition of lithium ions on the negative electrode current collector to achieve a negative electrode reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of a method for determining the quality of a solid-state battery according to an embodiment of the present invention;

[0024] Figure 2 The Coulomb efficiency curve obtained in the qualified judgment method of the solid-state battery in Example 1 of the present invention;

[0025] Figure 3 This is a capacity retention rate cycle curve obtained in the qualification judgment method of the solid-state battery in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0028] See also Figure 1 A method for determining the quality of a solid-state battery according to an embodiment of the present invention comprises the following steps:

[0029] S10, performing a cycle performance test on the battery to be tested after capacity division to obtain a coulombic efficiency curve and a capacity retention rate cycle curve.

[0030] In the present invention, capacity classification refers to discharging the battery under certain conditions after fully charging it, and determining the capacity of the battery by measuring the amount of electricity discharged. This process can help distinguish qualified batteries from unqualified batteries, and classify and group the batteries.

[0031] In the present invention, coulombic efficiency (CE) refers to the ratio of discharge capacity to charge capacity in each cycle of a solid-state battery during the cycling process. In each cycle, the energy input from the outside cannot be fully used for the conversion of active substances, but part of it is used for side reactions. Therefore, coulombic efficiency can well characterize the degree of side reactions inside solid-state batteries, and thus reflect the stability and cycle life of solid-state batteries.

[0032] In step S10, unless otherwise specified, the Coulomb efficiency curve test is generally performed under the following environmental conditions:

[0033] 1) Temperature: 25℃±0.5℃;

[0034] 2) Relative humidity: not more than 90%;

[0035] 3) Air pressure: 86kPa~106kPa.

[0036] Specifically, at an ambient temperature of 25℃±0.5℃, charge at a constant current of 0.1C. When the battery terminal voltage reaches the charge limit voltage, change to constant voltage charging until the charging current is less than or equal to 0.05C, then stop charging. The maximum charging time should be no more than 15h. Discharge at a current of 0.1C to the discharge termination voltage at an ambient temperature of 25℃±0.5℃. The maximum discharge time should be no more than 15h. The specific test is to discharge at a constant current to the discharge termination voltage according to the recommended discharge current specified for different system batteries. The time interval between the charge and discharge procedures is the current multiple used in the previous charging process multiplied by 60min.

[0037] In step S10, the solid-state battery is charged and discharged for the first time, and the battery discharge capacity at this time is recorded as the initial discharge capacity (C0). The battery is repeatedly charged and discharged according to the set charge and discharge conditions. One cycle includes one charge and one discharge. After each cycle is completed, the battery discharge capacity (C0) is recorded. n ) until the battery reaches 80% SOH (full name: state of health, which reflects the health of the battery), and the capacity retention rate (%) is obtained as (C n / C0)×100%. Among them, C n is the battery discharge capacity at the nth cycle, and C0 is the initial discharge capacity.

[0038] In a feasible implementation, the cycle performance test of the battery to be tested after capacity division is performed to obtain the coulombic efficiency curve and the capacity retention rate cycle curve. The operation is as follows: the cycle performance test of the battery to be tested after capacity division is performed under low rate charge and discharge conditions to obtain the coulombic efficiency curve; the cycle performance test of the battery to be tested after capacity division is performed under normal rate charge and discharge conditions to obtain the capacity retention rate cycle curve.

[0039] In a feasible implementation, the charge and discharge rate under low-rate charge and discharge conditions does not exceed 0.1C, and the charge and discharge rate under conventional rate charge and discharge conditions is 1C to 2C. Among them, the charge and discharge rate under low-rate charge and discharge conditions does not exceed 0.1C, which can reduce the impact of concentration polarization so that the coulomb efficiency more truly reflects the side reaction. Furthermore, the charge and discharge rate under low-rate charge and discharge conditions can be, but is not limited to, 0.05C or 0.1C.

[0040] In a feasible implementation, the test conditions for obtaining the Coulomb efficiency curve are: voltage of 2.5V to 4.35V, current of 0.1C, and ambient temperature of 25℃±0.5℃. Under such test conditions, the accuracy of the Coulomb efficiency curve can be improved, the large fluctuations of the curve can be reduced, and a stable and smooth curve can be obtained. The polarization of solid-state batteries is the driving force for the smooth operation of the battery, and solid-state batteries have multiple polarizations during the charging and discharging process. The realization of this technology requires a certain degree of precision charging and discharging equipment in order to distinguish the relationship between the Coulomb efficiency and the cycle attenuation curve, and the output noise is small and the test environment temperature is stable (±0.5℃).

[0041] In a feasible implementation, the battery to be tested after capacity division is subjected to a cycle performance test under low rate charge and discharge conditions, and when the coulomb efficiency curve test is completed, the number of cycles of the cycle performance test is 15 to 20. Further, when the coulomb efficiency curve test is completed, the number of cycles of the cycle performance test may be, but is not limited to, 15, 16, 17, 18, 19 or 20.

[0042] In a feasible implementation, the capacity-divided battery to be tested is subjected to a cycle performance test under conventional rate charge and discharge conditions until it cycles to 80% SOH, thereby obtaining a capacity retention rate cycle curve.

[0043] In a feasible implementation, the test conditions for obtaining the capacity retention rate cycle curve are: voltage of 2.5V to 4.35V, current of 1C, and ambient temperature of 23°C ± 2°C.

[0044] S20, comparing the coulombic efficiency curve and the capacity retention rate cycle curve of the battery to be tested with the coulombic efficiency curve and the capacity retention rate cycle curve of the standard battery respectively.

[0045] S30. If the coulombic efficiency curve and the capacity retention rate cycle curve of the battery to be tested are better than those of the standard battery, it is a qualified product; if the coulombic efficiency curve and the cycle curve of the battery to be tested are both lower than those of the standard battery, it is an unqualified product; if the cycle curve of the battery to be tested is better than that of the standard battery, but the coulombic efficiency curve of the battery to be tested is lower than that of the standard battery, then the battery to be tested is an unqualified product; if the cycle curve of the battery to be tested is lower than that of the standard battery, but the coulombic efficiency curve of the battery to be tested is better than that of the standard battery, then if the capacity retention rate of the battery to be tested is not lower than 85% after 100 cycles, it can be regarded as a qualified product, otherwise it is an unqualified product.

[0046] In a feasible implementation, if the coulomb efficiency curve of the battery to be tested is better than that of the standard battery, if the cycle curve of the battery to be tested within n cycles is lower than that of the standard battery, and the cycle curve of the battery to be tested after n cycles is higher than that of the standard battery, where n≤100, it can be regarded as a qualified product. In this embodiment, the capacity retention rate cycle curves of the battery to be tested and the standard battery intersect, and the cycle performance results of the battery to be tested and the standard battery change. Before the intersection point appears, the relationship between the capacity retention rate cycle curves of the battery to be tested and the standard battery deviates from the relationship between the coulomb efficiency curve, and the curve after the intersection point in the capacity retention rate cycle curve can predict the cycle life of the battery to be tested.

[0047] In this embodiment, the cycle life of the battery to be tested is predicted based on the curve after the intersection point in the capacity retention rate cycle curve, which can ensure the accuracy of the predicted cycle life. However, if only the previous capacity retention rate points (i.e., the curve before the intersection point) are used for analysis, misjudgment may occur. Compared with the traditional cycle life evaluation method, this method has a shorter cycle number, and only more than 10 cycles are required to achieve judgment, which realizes the rapid and accurate prediction of the battery cycle life, which is conducive to wide application.

[0048] In one possible implementation, the solid-state battery is a solid-state lithium-ion battery.

[0049] In a feasible implementation, a solid-state lithium-ion battery includes a positive electrode, a solid electrolyte and a negative electrode. The raw materials of the positive / negative electrode materials are mixed, ground and processed to form positive / negative electrode slurries. The positive / negative electrode slurries are coated on the current collector to form positive / negative electrode sheets. The electrolyte materials are mixed, melted and processed to form electrolyte slurries or films. The electrolyte slurry is coated on the current collector to form an electrolyte layer. The positive electrode sheet, the electrolyte layer and the negative electrode sheet are stacked in order to form a battery cell, and the battery cell is packaged to form a solid-state lithium-ion battery.

[0050] Furthermore, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder. It should be noted that the present invention does not limit the positive electrode current collector, the positive electrode active material, the conductive agent and the binder.

[0051] Furthermore, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder. It should be noted that the present invention does not limit the negative electrode current collector, the negative electrode active material, the conductive agent and the binder.

[0052] In another feasible implementation, a solid-state lithium-ion battery includes a positive electrode, a solid electrolyte, and a negative electrode current collector, and the solid-state lithium-ion battery relies on the deposition of lithium ions on the negative electrode current collector to achieve a negative electrode reaction. In this embodiment, the solid-state lithium-ion battery only includes a positive electrode and a solid electrolyte, and has no negative electrode. Among them, no negative electrode means that the negative electrode has only a negative electrode current collector and no active layer, and only relies on the deposition of lithium ions on the current collector to achieve a negative electrode reaction.

[0053] The present invention provides a method for judging the quality of solid-state batteries. The method judges whether a solid-state battery is a qualified product based on the coulomb efficiency curve and the capacity retention rate cycle curve of the battery to be tested and the standard battery, which is beneficial to the development and application of solid-state batteries.

[0054] With reference to the above implementation contents, in order to make the technical solution of the present invention more specific, clear and easy to understand, the technical solution of the present invention is now exemplified. However, it should be noted that the contents to be protected by the present invention are not limited to the following embodiments.

[0055] Example 1

[0056] Example 1 The influence of two types of binders on the cycle performance is studied using a high nickel NCM ternary positive electrode & silicon-based negative electrode system (specifically NCM811 & silicon-oxygen negative electrode). Benchmark sample (i.e. standard battery): CMC+SBR type; comparative sample (i.e. battery to be tested): PAA type.

[0057] The qualification judgment method of the solid-state battery of Example 1 is as follows:

[0058] For this embodiment, the test conditions are based on the recommendations of this system. If a different battery system is used, the recommended test conditions specified by the manufacturer shall be followed. Under the condition of a stable test environment temperature of 25°C ± 0.5°C, charge with a current of 0.1C to a charging cut-off voltage of 4.2V, switch to constant voltage charging to a cut-off current of 0.05C, let stand for 0.5h, and then discharge with a current of 0.1C to a cut-off voltage of 2.5V, let stand for 0.5h. For multiple lithium-ion batteries to be tested in the same electrochemical system (i.e., reference sample 1, reference sample 2, comparison sample 1, and comparison sample 2), cycle performance tests were performed under 20 cycles of constant current charge and discharge, and the coulomb efficiency of each lithium-ion battery to be tested corresponding to its cycle number was obtained using an ultra-high precision coulomb tester. Figure 2 Coulomb efficiency curve.

[0059] For this embodiment, the test conditions are based on the recommendations of this system. If a different battery system is used, the recommended test conditions specified by the manufacturer shall be followed. Under the condition that the test environment temperature is stable at 23°C ± 2°C, charge with a current of 1C to a charging cut-off voltage of 4.2V, switch to constant voltage charging to a cut-off current of 0.05C, let stand for 0.5h, and then discharge with a current of 1C to a cut-off voltage of 2.5V, and let stand for 0.5h. The reference sample and the comparison sample are fully charged and discharged respectively, and the battery discharge capacity at this time is recorded as the initial discharge capacity (C0). According to the set charge and discharge conditions, the reference sample and the comparison sample are repeatedly charged and discharged. One cycle includes one charge and one discharge. After each cycle is completed, the battery discharge capacity (C n ), until the SOH reaches 80%, we get Figure 3 Capacity retention rate cycle curve.

[0060] Will Figure 2 The Coulomb efficiency curve and Figure 3 The capacity retention rate cycle curves of Figure 2 It can be seen that the Coulomb efficiency of the comparison sample is better than that of the reference sample; Figure 3 It can be seen that the cycling performance of the benchmark sample is first better than that of the comparison sample. A "crossover" appears in the curve at the 18th cycle period, and then the cycling performance of the comparison sample is better than that of the benchmark sample. The final result of the cycling performance is consistent with the coulomb efficiency, and it can be judged as a qualified product.

[0061] From the above case results, it can be seen that when the initial cycle attenuation curve of the battery deviates from the Coulomb efficiency curve, the cycle attenuation curve will "cross" in the later stage. The cycle life of the battery to be tested can be predicted based on the curve after the intersection point in the capacity retention rate cycle curve.

[0062] It can be seen that the qualified judgment method for solid-state batteries using Example 1 has a shorter cycle number, and only more than 10 cycles are needed to achieve judgment, thereby achieving rapid and accurate prediction of the battery's cycle life and reducing testing costs.

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for judging the quality of a solid-state battery, characterized in that: The steps include: Perform cycle performance test on the battery to be tested after capacity division to obtain coulomb efficiency curve and capacity retention rate cycle curve; Comparing the coulombic efficiency curve and the capacity retention rate cycle curve of the battery to be tested with the coulombic efficiency curve and the capacity retention rate cycle curve of the standard battery respectively; If the coulombic efficiency curve and capacity retention rate cycle curve of the battery to be tested are better than those of the standard battery, it is a qualified product; If the coulombic efficiency curve and the cycle curve of the battery to be tested are both lower than those of the standard battery, it is a defective product; If the cycle curve of the battery to be tested is better than that of the standard battery, but the coulomb efficiency curve of the battery to be tested is lower than that of the standard battery, then the battery to be tested is a defective product; If the cycle curve of the battery to be tested is lower than that of the standard battery, but the coulomb efficiency curve of the battery to be tested is better than that of the standard battery, then if the capacity retention rate of the battery to be tested is not less than 85% after 100 cycles, it can be regarded as a qualified product, otherwise it is an unqualified product.

2. The method for judging the quality of a solid-state battery according to claim 1, characterized in that: If the coulombic efficiency curve of the battery to be tested is better than that of the standard battery, at this time, if the cycle curve of the battery to be tested within n cycles is lower than that of the standard battery, and the cycle curve of the battery to be tested after n cycles is higher than that of the standard battery, where n≤100, it can be regarded as a qualified product.

3. The method for judging the quality of a solid-state battery according to claim 1, characterized in that: The cycle performance test of the battery to be tested after capacity division is carried out to obtain the coulombic efficiency curve and the capacity retention rate cycle curve. The operation is as follows: the cycle performance test of the battery to be tested after capacity division is carried out under low rate charge and discharge conditions to obtain the coulombic efficiency curve; the cycle performance test of the battery to be tested after capacity division is carried out under normal rate charge and discharge conditions to obtain the capacity retention rate cycle curve.

4. The method for judging the quality of a solid-state battery according to claim 3, characterized in that: The charge and discharge rate under the low-rate charge and discharge conditions does not exceed 0.1C, and the charge and discharge rate under the conventional-rate charge and discharge conditions is 1C to 2C.

5. The method for judging the quality of a solid-state battery according to claim 3 or 4, characterized in that: The capacity-divided battery to be tested is subjected to a cycle performance test under low-rate charge and discharge conditions. When the coulomb efficiency curve test is completed, the number of cycles of the cycle performance test is 15 to 20 cycles.

6. The method for judging the quality of a solid-state battery according to claim 3 or 4, characterized in that: The capacity-divided battery to be tested is subjected to a cycle performance test under conventional rate charge and discharge conditions until it cycles to 80% SOH, thereby obtaining a capacity retention rate cycle curve.

7. The method for judging the quality of a solid-state battery according to claim 1, characterized in that: The solid-state battery is a solid-state lithium-ion battery.

8. The method for judging the quality of a solid-state battery according to claim 7, characterized in that: The solid-state lithium-ion battery comprises a positive electrode, a solid electrolyte and a negative electrode; and / or The positive electrode comprises a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a conductive agent and a binder; The solid electrolyte includes one of a halide, a sulfide and an oxide; The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder.

9. The method for judging the quality of a solid-state battery according to claim 7, characterized in that: The solid-state lithium-ion battery comprises a positive electrode, a solid electrolyte and a negative electrode current collector. The solid-state lithium-ion battery relies on lithium ions to deposit on the negative electrode current collector to achieve a negative electrode reaction.

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