A non-destructive analysis method for the degradation of layered cathode material structure in lithium-ion batteries

Abstract

This invention discloses a non-destructive analysis method for the degradation of layered cathode material structure in lithium-ion batteries, comprising the following steps: Step S1: Obtaining key electrochemical parameters of fresh batteries and batteries experiencing capacity degradation; Step S2: Extracting key electrochemical parameters from fresh batteries and batteries experiencing capacity degradation; Step S3: Calculating the degradation coefficient and discrimination coefficient for batteries experiencing capacity degradation; Step S4: Dynamically evaluating the degradation mode of the battery's internal structure based on the degradation coefficient and discrimination coefficient. This invention discloses a non-destructive analysis method for the degradation of layered cathode material structure in lithium-ion batteries. It does not require battery disassembly and mainly analyzes the degradation mode of the battery electrode material structure based on the correlation mapping and inversion between the crystal structure characteristics and electrochemical performance of the layered electrode material, providing a basis and direction for the health status assessment of lithium-ion batteries based on layered cathode materials.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a non-destructive analysis method for the degradation of layered cathode material structures in lithium-ion batteries. Background Technology

[0002] Layered cathode materials have attracted widespread attention due to their high energy density and low cost. Currently, lithium-ion batteries based on layered cathode materials are widely used in the field of electric vehicle power supplies. However, as an intercalation material, layered cathode materials undergo complex phase transitions and severe lattice contraction during lithium-ion insertion / extraction. The resulting structural degradation not only causes rapid capacity decay but also increases the battery's internal resistance. Typically, the main modes of structural degradation in high-nickel layered materials include mechanical bending deformation and irreversible phase transitions. Mechanical bending deformation is mainly attributed to lattice strain caused by interlayer lithium-ion diffusion. Under stress, bending deformation bands, surface twisting bands, and bulk twisting bands are generated. This type of structural degradation maintains certain characteristics of the layered structure and has little impact on the electrochemical performance of the electrode material, without causing severe capacity and voltage decay. However, in a highly delithiated state, the migration barrier of nickel atoms from the transition metal layer to the lithium layer decreases, making it easier for an irreversible phase transition to occur from layered phase to spinel phase to rock salt phase. The occurrence of such irreversible phase transitions not only causes rapid capacity decay, but also increases electrode polarization, resulting in severe voltage decay, while generating more ohmic heat, leading to battery overheating and thermal runaway.

[0003] For lithium-ion batteries in service, the structural degradation state of the layered cathode material not only reflects the degree of electrochemical performance decline but also serves as an important parameter for battery health. For lithium-ion batteries that need to be recycled after retirement, the structural degradation state of the high-nickel cathode material can be used as a criterion for graded recycling, thereby achieving efficient short-range recycling of cathode materials.

[0004] For a long time, electrode material failure analysis has been based on destructive analysis, which can only perform physicochemical characterization on electrode materials obtained after disassembling batteries under different service conditions. This type of detection technology is costly and slow, and is not suitable for large-scale testing and analysis of battery products. Therefore, developing a non-destructive and efficient structural degradation identification technology to monitor the structural evolution of layered materials in real time during service is of great significance for battery health assessment and recycling. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing analytical techniques by providing a non-destructive analysis method for the failure of layered cathode materials in lithium-ion batteries.

[0006] In view of this, the present invention provides a non-destructive analysis method for the structural degradation of layered cathode materials in lithium-ion batteries. Based on the mapping relationship between the crystal structure characteristics and electrochemical performance of different electrode materials, the present invention achieves rapid and accurate assessment of the structural degradation state of layered cathode materials during service by combining charge-discharge tests at specific rates with simple data analysis and processing, without damaging the battery structure.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a non-destructive analysis method for the degradation of layered cathode material structures in lithium-ion batteries, the method comprising the following steps:

[0009] Step S1: Obtain key electrochemical parameters for both fresh and capacity-degraded batteries: Record the functional relationship curve between the discharge specific capacity Q0 and the dynamic potential V0 during the complete discharge process of the fresh battery at a low rate current, denoted as the Q0-V0 curve. This preset operation is used to indicate the changes in electrode material structure parameters of the fresh battery. Perform a discharge test at the same rate current on the cycled battery that has experienced capacity degradation, denoted as Q... d -V d curve;

[0010] Among them, fresh batteries are those that have not experienced capacity decay and are of the same formula ratio, batch, and model as batteries that have experienced capacity decay;

[0011] Step S2: Extract key electrochemical parameters from fresh and capacity-degraded batteries: extract the discharge specific capacities Q0 and Q2 from the fresh and capacity-degraded batteries recorded in S1. d With the dynamic potential V0, V during the process d Perform second-order differential operations to obtain d. 2 Q0 / dV0 2 d 2 Q d / dV d 2 The value of the derivative is used to mark the zeros of the derivative in ascending order along the X-axis as V. 01 V 02 V 03 ...V 0n V d1 V d2 V d3 ...V dn With V 02 and V 04 Using this as the dividing line, the discharge curve of the fresh battery is divided into three intervals, corresponding to the three phase transition stages H1-M, M-H2, and H2-H3, respectively. The discharge specific capacity of the three phase transition stages is denoted as C. 01 C02 C 03 Similarly, with V d2 and V d4 Using this as a dividing line, batteries exhibiting capacity decay were subjected to the same data processing to obtain the discharge specific capacity C for the three phase transition stages. d1 C d2 C d3 ;

[0012] Step S3: Calculate the degradation coefficient and discrimination coefficient for batteries experiencing capacity decay: Calculate the ratio of the discharge capacity of the battery experiencing capacity decay during the three phase transition stages (H1-M, M-H2, H2-H3) to the discharge capacity of the fresh battery during the three phase transition stages, denoted as r1, r2, and r3. That is, r1 = C d1 / C 01 r2 = C d2 / C 02 r3 = C d3 / C 03 Calculate the discriminant coefficient R (R = r1 / r3);

[0013] Step S4: Based on the attenuation coefficient and the discrimination coefficient, dynamically evaluate the degradation mode of the battery's internal structure: when r1, r2, and r3 are all greater than 0.9, there is no obvious structural degradation; when r1, r2, and r3 are not all greater than 0.9 and R is less than R0, the material structure degradation is mainly mechanical bending; when r1, r2, and r3 are not all greater than 0.9 and R is greater than or equal to R0, the material structure degradation is mainly irreversible phase transition.

[0014] R0 depends on the composition of the layered material. This value is an empirical parameter that can be obtained through extensive experimental statistics, using LiNi as an example. 0.8 Co 0.1 Mn 0.1 Taking O2 (NCM811) as an example, its R0 is 1.2.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) This invention is a non-destructive testing technology that can qualitatively analyze the degradation of the internal structure of electrode materials without destroying the battery structure.

[0017] (2) The present invention is compatible with existing battery monitoring systems and has strong feasibility.

[0018] (3) The present invention has high identification accuracy and can be used as an important basis for assessing the health status of lithium-ion batteries. Attached Figure Description

[0019] Figure 1This is a process flow diagram of the method for non-destructive identification of the degradation of layered cathode material structure provided in the specific embodiments of the present invention.

[0020] Figure 2 In a specific embodiment of the present invention, the discharge capacity C corresponding to the three phase transition stages H1-M, M-H2, and H2-H3 is obtained from the discharge curve. d1 C d2 C d3 A schematic diagram;

[0021] Figure 3 The discharge curves and differential capacity curves of the lithium-ion battery in Example 1 of this invention before and after aging are shown.

[0022] Figure 4 This is a transmission electron microscopy image of the NCM811 cathode material in Example 1 of the present invention before aging;

[0023] Figure 5 This is a transmission electron microscopy image of the NCM811 cathode material in Example 1 of the present invention after aging.

[0024] Figure 6 The discharge curves and differential capacity curves of the lithium-ion battery in Example 2 of this invention before and after aging are shown.

[0025] Figure 7 This is a transmission electron microscopy image of the NCM811 cathode material in Example 2 of the present invention after aging.

[0026] Figure 8 The discharge curves and differential capacity curves of the lithium-ion battery in Example 3 of this invention before and after aging are shown.

[0027] Figure 9 This is a transmission electron microscopy image of the NCM811 cathode material in Example 3 of the present invention after aging.

[0028] Figure 10 The discharge curves and differential capacity curves of the lithium-ion battery in Example 4 of this invention before and after aging are shown.

[0029] Figure 11 This is a transmission electron microscopy image of the NCM811 cathode material in Example 4 of the present invention after aging.

[0030] Figure 12 The discharge curves and differential capacity curves of the lithium-ion battery in Example 5 of this invention before and after aging are shown.

[0031] Figure 13 This is a transmission electron microscopy image of the NCM811 cathode material in Example 5 of the present invention after aging.

[0032] Figure 14 The discharge curves and differential capacity curves of the lithium-ion battery in Example 6 of this invention before and after aging are shown.

[0033] Figure 15 This is a transmission electron microscopy image of the NCM811 cathode material in Example 6 of the present invention after aging. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0035] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0036] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0037] In the following embodiments:

[0038] (1) Cyclic performance test: The instrument used was a Neware CT-4008T, and the test parameters were: current density 0.25 mA / cm². -2 .

[0039] (3) Transmission electron microscopy test: The instrument model of the transmission electron microscope (TEM) is JEM-2100-f / TEM.

[0040] (4) Button battery assembly:

[0041] The button cell battery is assembled from a 2025 stainless steel casing, consisting of a negative electrode casing, a lithium metal negative electrode sheet, a polypropylene separator, an electrolyte, a high-nickel positive electrode, and a positive electrode casing. The lithium metal negative electrode sheet has a diameter of 16mm.

[0042] Preparation of the positive electrode: First, high-nickel positive electrode material, polyvinylidene fluoride (PVDF), and conductive carbon black were weighed in a mass ratio of 8:1:1 and placed in a mortar for grinding and mixing. Then, an appropriate amount of N-methylpyrrolidone (NMP) solution was added dropwise, and the mixture was ground thoroughly into a uniform, fluid slurry. The slurry was then uniformly coated onto aluminum foil and dried in a vacuum drying oven at 80°C for 12 hours. The foil was then sliced ​​into 11mm diameter discs using a slicer to obtain the pre-fabricated positive electrode. The average mass of the positive electrode disc was approximately 3.0 mg / cm³. -2 .

[0043] Assembly of button batteries: Lithium-ion batteries are assembled in an argon atmosphere with water and oxygen content <0.01ppm. The positive electrode, the separator, and the lithium metal negative electrode are placed in the positive electrode shell in sequence, 80μL of electrolyte is added, the negative electrode shell is added, and the battery is pressed together with a sealing machine to obtain a button battery.

[0044] Example 1

[0045] NCM811 button cell assembly: Assemble CR2025 stainless steel button cells using NCM811 materials according to the method described above.

[0046] NCM811 button cell activation: Activate the assembled button cell with an activation voltage range of 2.7-4.3V and a current of 0.1C (1C = 200mAh / g).

[0047] NCM811 button cell aging: The activated cells undergo electrochemical aging, with an aging cycle of 200 cycles, an aging voltage range of 2.7-4.3V, and a current of 1 / 3C.

[0048] NCM811 button cell battery diagnostics: Obtain the complete discharge curve after battery aging, with a test voltage range of 2.7-4.3V and a current of 0.1C. The corresponding discharge curve and DQ / DV curve are as follows: Figure 3 As shown.

[0049] NCM811 button cell structural degradation type identification: Based on steps (2) and (3), the values ​​of r1, r2, r3 and R are calculated to be 0.98, 0.68, 0.60 and 1.64 respectively. It is determined that the structural degradation of NCM811 material in this embodiment is mainly due to irreversible phase transition.

[0050] Transmission electron microscopy (TEM) results: TEM results of NCM811 material in its initial state at room temperature are as follows... Figure 4 As shown in the figure, the initial state of NCM811 material maintains a good layered structure. The transmission electron microscopy results of the positive electrode after the battery of this embodiment was disassembled and fully discharged at room temperature are as follows: Figure 5 As shown, the structural degradation of the electrode material is mainly due to irreversible phase transitions, which is consistent with the results obtained by the method proposed in this invention.

[0051] Example 2

[0052] NCM811 button cell assembly: Assemble CR2025 stainless steel button cells using NCM811 materials according to the method described above.

[0053] NCM811 button cell activation: Activate the assembled button cell with an activation voltage range of 2.7-4.3V and a current of 0.1C (1C = 200mAh / g).

[0054] NCM811 button cell aging: The activated cells undergo electrochemical aging, with an aging cycle of 200 cycles, an aging voltage range of 2.7-4.3V, and a current of 1C.

[0055] NCM811 button cell battery diagnostics: Obtain the complete discharge curve after battery aging, with a test voltage range of 2.7-4.3V and a current of 0.1C. The corresponding discharge curve and DQ / DV curve are as follows: Figure 6 As shown.

[0056] NCM811 button cell structural degradation type identification: Based on steps (2) and (3), the values ​​of r1, r2, r3 and R are calculated to be 0.98, 0.81, 0.81 and 1.22 respectively. It is determined that the structural degradation of NCM811 material in this embodiment is mainly due to irreversible phase transition.

[0057] Transmission electron microscopy (TEM) testing: The battery in this embodiment was disassembled after aging. The TEM results of the positive electrode after complete discharge at room temperature are as follows: Figure 7 As shown, the structural degradation of the electrode material is mainly due to irreversible phase transitions, which is consistent with the results obtained by the method proposed in this invention.

[0058] Example 3

[0059] NCM811 button cell assembly: Assemble CR2025 stainless steel button cells using NCM811 materials according to the method described above.

[0060] NCM811 button cell activation: Activate the assembled button cell with an activation voltage range of 2.7-4.3V and a current of 0.1C (1C = 200mAh / g).

[0061] NCM811 button cell aging: The activated cells undergo electrochemical aging, with an aging cycle of 200 cycles, an aging voltage range of 2.7-4.3V, and a current of 5C.

[0062] NCM811 button cell battery diagnostics: Obtain the complete discharge curve after battery aging, with a test voltage range of 2.7-4.3V and a current of 0.1C. The corresponding discharge curve and DQ / DV curve are as follows: Figure 8 As shown.

[0063] NCM811 button cell structural degradation type identification: Based on steps (2) and (3), the values ​​of r1, r2, r3 and R are calculated to be 0.91, 0.85, 0.82 and 1.12 respectively. It is determined that the structural degradation of NCM811 material in this embodiment is mainly mechanical bending deformation.

[0064] Transmission electron microscopy (TEM) testing: The battery in this embodiment was disassembled after aging. The TEM results of the positive electrode after complete discharge at room temperature are as follows: Figure 9 As shown, the structural degradation of the electrode material is mainly due to mechanical bending deformation, which is consistent with the results obtained by the method proposed in this invention.

[0065] Example 4

[0066] NCM811 button cell assembly: Assemble CR2025 stainless steel button cells using NCM811 materials according to the method described above.

[0067] NCM811 button cell activation: Activate the assembled button cell with an activation voltage range of 2.7-4.3V and a current of 0.1C (1C = 200mAh / g).

[0068] NCM811 button cell aging: The activated cells undergo electrochemical aging, with an aging cycle of 200 cycles, an aging voltage range of 2.7-4.3V, and a current of 10C.

[0069] NCM811 button cell battery diagnostics: Obtain the complete discharge curve after battery aging, with a test voltage range of 2.7-4.3V and a current of 0.1C. The corresponding discharge curve and DQ / DV curve are as follows: Figure 10 As shown.

[0070] NCM811 button cell structural degradation type identification: Based on steps (2) and (3), the values ​​of r1, r2, r3 and R are calculated to be 0.91, 0.97, 0.83 and 1.09 respectively. It is determined that the structural degradation of NCM811 material in this embodiment is mainly mechanical bending deformation.

[0071] Transmission electron microscopy (TEM) testing: The battery in this embodiment was disassembled after aging. The TEM results of the positive electrode after complete discharge at room temperature are as follows: Figure 11 As shown, the structural degradation of the electrode material is mainly due to mechanical bending deformation, which is consistent with the results obtained by the method proposed in this invention.

[0072] Example 5

[0073] NCM811 button cell assembly: Assemble CR2025 stainless steel button cells using NCM811 materials according to the method described above.

[0074] NCM811 button cell activation: Activate the assembled button cell with an activation voltage range of 2.7-4.3V and a current of 0.1C (1C = 200mAh / g).

[0075] NCM811 button cell aging: The activated cells undergo electrochemical aging, with an aging cycle of 200 cycles, an aging voltage range of 2.7-4.7V, and a current of 1C.

[0076] NCM811 button cell battery diagnostics: Obtain the complete discharge curve after battery aging, with a test voltage range of 2.7-4.3V and a current of 0.1C. The corresponding discharge curve and DQ / DV curve are as follows: Figure 12 As shown.

[0077] NCM811 button cell structural degradation type identification: Based on steps (2) and (3), the values ​​of r1, r2, r3 and R are calculated to be 0.98, 0.68, 0.60 and 1.64 respectively. It is determined that the structural degradation of NCM811 material in this embodiment is mainly due to irreversible phase transition.

[0078] Transmission electron microscopy (TEM) testing: The battery in this embodiment was disassembled after aging. The TEM results of the positive electrode after complete discharge at room temperature are as follows: Figure 13 As shown, the structural degradation of the electrode material is mainly due to irreversible phase transitions, which is consistent with the results obtained by the method proposed in this invention.

[0079] Example 6

[0080] NCM811 button cell assembly: Assemble CR2025 stainless steel button cells using NCM811 materials according to the method described above.

[0081] NCM811 button cell activation: Activate the assembled button cell with an activation voltage range of 2.7-4.3V and a current of 0.1C (1C = 200mAh / g).

[0082] NCM811 button cell aging: The activated cell undergoes electrochemical aging, with an aging cycle of 200 cycles, an aging voltage range of 3.65-4.07V, and a current of 1C.

[0083] NCM811 button cell battery diagnostics: Obtain the complete discharge curve after battery aging, with a test voltage range of 2.7-4.3V and a current of 0.1C. The corresponding discharge curve and DQ / DV curve are as follows: Figure 14 As shown.

[0084] NCM811 button cell structural degradation type identification: Based on steps (2) and (3), the values ​​of r1, r2, r3 and R are calculated to be 0.99, 0.98, 0.98 and 1.01 respectively, indicating that the NCM811 material in this embodiment has no obvious structural degradation.

[0085] Transmission electron microscopy (TEM) testing: The battery in this embodiment was disassembled after aging. The TEM results of the positive electrode after complete discharge at room temperature are as follows: Figure 15 As shown, the structure of the electrode material remains largely unchanged, consistent with the results obtained using the method proposed in this invention.

[0086] The applicant declares that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above detailed methods, that is, it does not mean that the present invention must rely on the above detailed methods to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary raw materials, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A non-destructive analysis method for the degradation of layered cathode material structure in lithium-ion batteries, characterized in that, The method includes the following steps: Step S1: Obtain key electrochemical parameters for both fresh and capacity-degraded batteries: Record the functional relationship curve between the discharge specific capacity Q0 and the dynamic potential V0 during the complete discharge process of the fresh battery at a low rate current, denoted as the Q0-V0 curve. This preset operation is used to indicate the changes in the electrode material structure parameters of the fresh battery; Perform a discharge test at the same rate current on the cycled battery that has experienced capacity degradation, denoted as Q... d -V d curve; Among them, fresh batteries are those that have not experienced capacity decay and are of the same formula ratio, batch, and model as batteries that have experienced capacity decay; Step S2: Extract key electrochemical parameters from fresh and capacity-degraded batteries: extract the discharge specific capacities Q0 and Q2 from the fresh and capacity-degraded batteries recorded in S1. d With the dynamic potential V0, V during the process d Perform second-order differential operations to obtain d. 2 Q0 / dV0 2 d 2 Q d / dV d 2 The value of the derivative is used to mark the zeros of the derivative in ascending order along the X-axis as V. 01 V 02 V 03 ...V 0n V d1 V d2 V d3 ...V dn； With V 02 and V 04 Using this as the dividing line, the discharge curve of the fresh battery is divided into three intervals, corresponding to the three phase transition stages H1-M, M-H2, and H2-H3, respectively. The discharge specific capacity of the three phase transition stages is denoted as C. 01 C 02 C 03 Similarly, with V d2 and V d4 Using this as a dividing line, batteries exhibiting capacity decay were subjected to the same data processing to obtain the discharge specific capacity C for the three phase transition stages. d1 C d2 C d3 ; Step S3: Calculate the degradation coefficient and discrimination coefficient for batteries experiencing capacity decay: Calculate the ratio of the discharge capacity of the battery experiencing capacity decay during the three phase transition stages H1-M, M-H2, and H2-H3 to the discharge capacity of the fresh battery during the three phase transition stages, denoted as r1, r2, and r3. 3， That is, r1 = C d1 / C 01 r2 = C d2 / C 02 r3 = C d3 / C 03， Calculate the discriminant coefficient R (R = r1 / r3); Step S4: Based on the attenuation coefficient and the discrimination coefficient, dynamically evaluate the degradation mode of the battery's internal structure: when r1, r2, and r3 are all greater than 0.9, there is no obvious structural degradation; when r1, r2, and r3 are not all greater than 0.9 and R is less than R0, the material structure degradation is mainly mechanical bending; when r1, r2, and r3 are not all greater than 0.9 and R is greater than or equal to R0, the material structure degradation is mainly irreversible phase transition. R0 depends on the composition of the layered material. This value is an empirical parameter that can be obtained through a large number of experimental statistics, using LiNi as an example. 0.8 Co 0.1 Mn 0.1 For example, O2 (NCM811) has an R0 of 1.

2.

2. The method according to claim 1, characterized in that, The layered cathode material mentioned in step S1 is LiNiO2, LiCoO2, LiMnO2, ternary layered materials and their derivatives, or lithium-rich manganese-based layered materials.

3. The method according to claim 1, characterized in that, The lithium-ion battery system in step S1 can be any one of button cell, cylindrical, pouch cell, or prismatic cell.

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