Preparation method of battery negative electrode standard sample and battery negative electrode standard sample

Abstract

The invention provides a preparation method of a battery negative electrode standard sample and the battery negative electrode standard sample, and relates to the technical field of energy storage. The preparation method comprises the steps of preparation and circulation treatment of the soft package battery. The method comprises the following steps: carrying out die cutting, lamination, top side sealing, liquid injection and formation on a lithium iron phosphate graphite soft package battery to obtain a soft package battery, selecting a plurality of activated and screened batteries, standing the plurality of batteries at different design temperatures for a specific period of time, and carrying out continuous full-full charge-discharge cycle test in a constant-temperature environment. The preparation method is simple and convenient to operate, low in cost and high in repeatability, the prepared standard sample can be used for lithium dendrite growth mechanism research, battery safety performance evaluation and related material screening, and an important tool is provided for improving the safety of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and in particular to a method for preparing a battery negative electrode standard and the battery negative electrode standard. Background Technology

[0002] Lithium-ion battery energy storage systems account for as much as 97.3% of the energy storage industry, holding an absolute dominant position in the field of electrochemical energy storage. However, under extreme conditions such as low-temperature charging (e.g., <0℃), high-rate charging (fast charging), overcharging, or over-discharging, current lithium-ion battery systems struggle to embed themselves into the graphite anode interlayer structure in a timely and sufficient manner due to the sluggish lithium-ion diffusion kinetics and increased interfacial charge transfer impedance. This easily leads to irreversible lithium metal deposition (lithium plating) on ​​the anode surface, forming lithium dendrites. Lithium dendrites possess high mechanical strength, and their continuous growth can pierce the polyolefin-based separator, causing direct connection between the positive and negative electrodes and triggering internal micro-short circuits. When a large number of widely distributed micro-short circuit networks form inside the battery, the resulting localized Joule heating can induce a chain of exothermic reactions, ultimately triggering thermal runaway of the battery.

[0003] Battery thermal runaway is a violent, self-accelerating exothermic process that can cause the internal temperature of a battery to rise rapidly to over 500°C in a very short time. This process is accompanied by violent electrolyte decomposition (producing CO, CO2, H2, hydrocarbons, and HF, etc.), exothermic SEI film rebuilding, oxygen release from the decomposition of the positive electrode active material, and reaction between the negative electrode and the electrolyte. This leads to a sudden increase in internal battery pressure, the opening of safety valves, the ejection of gases and active materials, and battery casing rupture, ultimately causing serious safety accidents such as fires and explosions. It also releases toxic and flammable gases and fluorine / phosphorus compounds, posing a significant threat to personnel safety and equipment. Therefore, real-time monitoring and accurate assessment of the lithium plating state of the negative electrode in lithium-ion batteries are crucial for preventing thermal runaway and improving the inherent safety of batteries. Summary of the Invention

[0004] This invention provides a method for preparing a battery negative electrode standard and the battery negative electrode standard, so as to establish the structure-property relationship between lithium dendrite morphology and battery thermal safety performance.

[0005] The present invention provides a method for preparing a battery negative electrode standard sample, which uses lithium iron phosphate graphite pouch battery to prepare the standard sample. The preparation method includes the preparation and cycling of the pouch battery.

[0006] The preparation of the pouch cell includes the following steps:

[0007] Based on the markings established in the line drawing process, the positive and negative electrode tabs are produced by stamping.

[0008] The cells are automatically stacked according to a set number of layers and sealed with high-temperature resistant tape to produce battery cells.

[0009] The positive and negative electrode tabs of the battery cell are welded together, and the battery cell is automatically top-sealed and side-sealed using a pre-punched aluminum-plastic film.

[0010] Vacuum injection of liquid into the cell;

[0011] The soft-pack battery is obtained by applying constant pressure to perform a formation process.

[0012] The loop process includes the following steps:

[0013] Multiple batteries that have undergone activation screening are selected, and after each battery is left to stand at a specific time at a different design temperature, continuous full-charge-discharge cycle tests are conducted in a constant temperature environment.

[0014] In one embodiment of the present invention, during the top sealing process of the battery cell, a 1-2 cm exposed section is reserved in the rectangular adhesive area on the surface of the positive electrode tab and the negative electrode tab; during the side sealing process of the battery cell, the sealing range does not cover the pre-punched pit area of ​​the aluminum-plastic film.

[0015] In one embodiment of the present invention, when the battery cell is automatically top-sealed and side-sealed, the temperature of the upper and lower sealing stations of the sealing machine is 180°C.

[0016] In one embodiment of the present invention, when vacuum liquid injection is performed into the inside of the battery cell, the fixed height of the battery cell is repeatedly adjusted until the injection gun tip can be completely inserted into the bottom of the battery cell; after the liquid injection is completed, the injection gun tip and pipeline are cleaned with dimethyl carbonate.

[0017] In one embodiment of the present invention, after vacuum liquid injection into the interior of the battery cell, the preparation method further includes transferring the battery cell to a sealed and dry environment for storage.

[0018] In one embodiment of the present invention, the current multiplier during continuous full charge-discharge cycle testing is 0.05 to 3C.

[0019] In one embodiment of the present invention, the positive electrode tab is made of aluminum, and the negative electrode tab is made of nickel.

[0020] In one embodiment of the present invention, during continuous full charge and discharge cycle testing at a constant temperature of 25°C, the charging mode is constant current and constant voltage until the voltage reaches 3.65V, and the cutoff current is 0.05C. The discharging mode is constant current until the voltage reaches 2.5V.

[0021] In one embodiment of the present invention, before pre-punching the aluminum-plastic film, the preparation method further includes cleaning the worktable of the punching instrument and the surface of the aluminum-plastic film.

[0022] The present invention also provides a battery negative electrode standard sample, which is prepared using any of the preparation methods described above.

[0023] The beneficial effects of this invention are as follows: This invention proposes a method for preparing battery negative electrode standards. This method uses lithium iron phosphate / graphite pouch cells, which undergo die-cutting, stacking, top-side sealing, electrolyte injection, and formation. The cells are then cycled at different current rates until failure, producing standard samples coated with dense lithium dendrites of varying morphologies. By applying controllable extreme electrochemical stress (different current rates), the electrochemical environment at the graphite negative electrode / electrolyte interface can be actively controlled, allowing for a systematic study of the structure-property relationship between lithium dendrite morphology (such as dendrite density and length) and battery thermal safety performance (such as thermal runaway trigger temperature T1 and the highest temperature T2 achievable by the thermal runaway battery). Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0025] In the attached diagram:

[0026] Figure 1 This is a flowchart illustrating the fabrication process of a pouch cell provided in one embodiment of this application.

[0027] Figure 2 The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 1;

[0028] Figure 3 The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 2;

[0029] Figure 4 The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 3;

[0030] Figure 5 The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 4;

[0031] Figure 6 The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 5;

[0032] Figure 7 The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 6;

[0033] Figure 8The scanning electron microscope (SEM) morphology characterization results of the negative electrode standard prepared in Example 7;

[0034] Figure 9 The results show the scanning electron microscope (SEM) morphology characterization of the graphite electrode sheet that has not undergone cycling in Comparative Example 1. Detailed Implementation

[0035] The following specific examples illustrate the implementation 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 embodiments. 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. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0036] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0037] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0038] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0039] Please see Figure 1 The present invention provides a method for preparing a battery negative electrode standard, the method comprising the preparation and cycling of a pouch cell.

[0040] The fabrication of a pouch cell includes the following steps:

[0041] S1. Using the markings established in the line drawing process as a reference, the positive electrode tab and the negative electrode tab are produced by stamping forming process;

[0042] S2. The cells are automatically stacked according to the set number of layers and sealed with high-temperature resistant tape to obtain the battery cell;

[0043] S3. Weld the positive and negative tabs of the battery cell separately, and use pre-punched aluminum-plastic film to automatically seal the top and side of the battery cell.

[0044] S4. Vacuum injection of electrolyte into the cell;

[0045] S5. Apply constant pressure to perform formation treatment to obtain a pouch cell;

[0046] In step S11, the material of the positive electrode tab is aluminum, and the material of the negative electrode tab is nickel.

[0047] In step S13, during the top sealing process of the battery cell, a 1-2 cm exposed section is reserved on the rectangular adhesive area of ​​the positive and negative electrode tabs. During the side sealing process of the battery cell, the sealing range does not cover the pre-punched area of ​​the aluminum-plastic film. When automatically top-sealing and side-sealing the battery cell, the temperature of the upper and lower sealing stations of the sealing machine is 180℃. The sealing pressure and sealing time are adaptively adjusted according to the heat-sealing characteristics of the aluminum-plastic film, and the sealing pressure and sealing time are matched with the heat-sealing characteristics of the aluminum-plastic film. During the encapsulation process, it is necessary to ensure that the diaphragm surface is flat and wrinkle-free, and strictly control the positive and negative electrode plates to avoid direct contact to prevent short circuits in the battery cell. Before punching the aluminum-plastic film, the worktable of the punching instrument and the surface of the aluminum-plastic film must be wiped with anhydrous alcohol to avoid...

[0048] In step S14, during vacuum electrolyte injection, the fixed height of the cell is repeatedly adjusted until the injection gun tip can be fully inserted into the bottom of the cell. After injection, the injection gun tip and tubing are cleaned with dimethyl carbonate (DMC). The amount of electrolyte injected during vacuum injection is determined based on the electrolyte weight to battery capacity ratio (E / C ratio). After injection, the cell is transferred to a sealed, dry environment for storage, avoiding stacking or compression to prevent self-discharge.

[0049] In step S15, the formation process takes, for example, 10 hours.

[0050] The loop process includes the following steps:

[0051] Multiple activated and screened batteries were selected, and each battery was allowed to stand at different design temperatures for a specific duration before undergoing continuous full-charge-discharge cycle tests in a constant-temperature environment. The purpose of standing is to allow the electrolyte to fully saturate the batteries, and the temperature during standing can be adjusted according to actual needs. For example, the standing temperature is 25°C or 45°C, and the standing time is, for example, 24 hours. 25°C simulates electrical abuse behavior at actual room temperature, while the high temperature of 45°C damages the solid electrolyte interphase (SEI) film inside the battery, simulating electrical abuse behavior at high temperatures. In other embodiments, other temperatures can be selected to simulate electrical abuse behavior at high temperatures, such as 60°C. For example, during full charge-discharge cycle testing, charging is performed in constant current-constant voltage (CC-CV) mode to 3.65V, with a cutoff current of 0.05C. Discharging is performed in constant current (CC) mode to 2.5V. The current ratio during cycle testing ranges from 0.05 to 3C, such as any value within the range of 0.05C, 0.1C, 0.2C, 1C, and 3C. During cycle processing, when the discharge capacity of any battery decays to the point of battery failure, the cycle experiment is stopped, and the batteries are immediately disassembled to obtain positive and negative electrode samples with different aging histories and degrees of lithium plating for subsequent morphology, composition, and thermal stability analysis. The isothermal environment during cycle testing can be adjusted according to actual needs, such as 25℃ or -20℃, to study the effect of temperature on lithium plating on the negative electrode. A standard sample with a specific lithium dendrite morphology is prepared for each current ratio and different temperature conditions.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] (1) The preparation method provided by the present invention is simple to operate and has low raw material cost. Specifically, the lithium dendrite morphology can be adjusted by only different current ratios during the process. It has high repeatability, short preparation cycle, abundant raw material resources and low price. At the same time, the process does not involve special equipment and can be used for scientific research.

[0054] (2) This invention, by precisely applying a charge-discharge strategy from low rate (0.05C) to high rate (3C), can actively induce and distinguish lithium dendrite morphologies of different sizes, densities, and structures (e.g., lithium deposition at low rates forms dense bulk dendrites, while at high rates, graphite undergoes lithium deposition, forming sparse needle-like lithium dendrites and dead lithium). Existing technologies (such as electrolyte additives, interface modification, and structural design) mainly focus on "passively suppressing" the overall formation of lithium dendrites, making it difficult to precisely control their specific morphological characteristics. This invention's "programmable" control over dendrite morphology provides an active control method for in-depth research on dendrite growth mechanisms, evaluation of material / interface stability, and exploration of the potential applications of dendrites with specific morphologies, surpassing the limitations of existing passive protection technologies.

[0055] (3) This invention introduces cycling temperature as a key control parameter to achieve diversified and controllable preparation of lithium dendrite morphology. Compared with existing technologies that rely on special additives, complex surface coatings, or expensive three-dimensional framework structures, this invention does not require changes to the intrinsic composition of the electrode or electrolyte system, significantly reducing implementation complexity and cost, and possessing good compatibility with current mainstream graphite anode and electrolyte material systems. This characteristic makes this invention a highly versatile and efficient research tool and potential process control strategy that is easy to embed into existing battery R&D and production processes, especially suitable for large-scale material screening, process window evaluation, and standardized testing scenarios.

[0056] This invention also provides a battery negative electrode standard sample, prepared using the above-described method. The graphite negative electrode surface of the standard sample is coated with a distinguishable lithium dendrite structure: Standard samples prepared by low-rate cycling at 0.05C, 0.1C, or 0.2C maintain a relatively intact graphite negative electrode structure, with only a few surface microcracks and edge peeling; lithium deposition occurs in large areas of dense blocks or moss-like structures. Standard samples prepared by high-rate cycling at 1C or 3C exhibit severe graphite particle breakage and pulverization, with a thick and uneven surface covered by deposits. Abnormal deposits caused by graphite lithium deposition are directly observed, including needle-shaped lithium dendrites or lithium deposition conversion products. After standing at 45℃ for 24 hours, the negative electrode surface after cycling at different current rates (1C, 3C) in a constant temperature environment of -20℃ shows almost entirely highly branched, sharp dendritic lithium dendrites.

[0057] The technical solution of the present invention will be described in detail below through several specific embodiments. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0058] Example 1

[0059] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0060] (2) Select activated and screened batteries, let them stand at 25°C for 24 hours, and then conduct continuous full charge and discharge cycle tests at a current rate of 0.05C in a constant temperature environment of 25°C.

[0061] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0062] The morphological characterization results of the pristine graphite electrodes prepared in this embodiment under a scanning electron microscope are as follows: Figure 2 As shown. From Figure 2 As can be seen, after cycling at a current rate of 0.05C, some overlapping of the layered structure of the graphite electrode can be observed in the lithium iron phosphate (LFP)||graphite battery. However, at this time, the current rate is too small, and lithium ions can normally carry out the lithium insertion and extraction process between the graphite layers. Therefore, the overall structure of the graphite electrode does not change significantly.

[0063] Example 2

[0064] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0065] (2) Select activated and screened batteries, let them stand at 25°C for 24 hours, and then conduct continuous full charge and discharge cycle tests at a current rate of 0.1C in a constant temperature environment of 25°C.

[0066] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0067] The morphological characterization results of the pristine graphite electrodes prepared in this embodiment under a scanning electron microscope are as follows: Figure 3 As shown.

[0068] from Figure 3 As can be seen, after cycling at a current rate of 0.1C, the graphite electrodes of the lithium iron phosphate (LFP)||graphite battery exhibit more pronounced overlapping. At this point, the increase in current rate accelerates the lithium ion insertion and extraction process in the graphite interlayer, but the layered structure does not change significantly.

[0069] Example 3

[0070] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0071] (2) Select activated and screened batteries, let them stand at 25°C for 24 hours, and then conduct continuous full charge and discharge cycle tests at a current rate of 0.2C in a constant temperature environment of 25°C.

[0072] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0073] The morphological characterization results of the pristine graphite electrodes prepared in this embodiment under a scanning electron microscope are as follows: Figure 4 As shown. From Figure 4 As can be seen, after cycling at a current rate of 0.2C, the overall particle integrity of the lithium iron phosphate (LFP)||graphite battery is still good, but the surface begins to be slightly uneven. A small amount of disordered flocculent or moss-like deposits can be observed at the edges of the graphite, which is a typical characteristic of the initial lithium plating.

[0074] Example 4

[0075] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0076] (2) Select activated and screened batteries, let them stand at 25°C for 24 hours, and then conduct continuous full charge and discharge cycle tests at 1C current rate in a constant temperature environment of 25°C.

[0077] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0078] The morphological characterization results of the pristine graphite electrodes prepared in this embodiment under a scanning electron microscope are as follows: Figure 5 As shown. From Figure 5 As can be seen, when the current ratio reaches 1C, the morphology of graphite particles deteriorates significantly, lithium plating becomes more common and severe, the amount of deposits increases significantly, and local aggregation begins to form.

[0079] Example 5

[0080] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0081] (2) Select activated and screened batteries, and after standing at 25°C for 24 hours, conduct continuous full charge and discharge cycle tests at 3C current rate under constant temperature of 25°C.

[0082] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0083] The morphological characterization results of the pristine graphite electrodes prepared in this comparative example under a scanning electron microscope are as follows: Figure 6 As shown. From Figure 6As can be seen, after lithium iron phosphate (LFP)||graphite batteries undergo 3C high-rate cycling to failure, the graphite anode structure suffers catastrophic damage, the surface morphology of the anode is severely deteriorated, a large number of obvious dendritic deposits with sharp protrusions appear, the surface is covered with thick and uneven deposits (including SEI and possible lithium plating conversion products), and abnormal deposits caused by lithium plating are directly observed.

[0084] Example 6

[0085] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0086] (2) Select activated and screened batteries, and after standing at 45°C for 24 hours, conduct continuous full charge and discharge cycle tests at 1C current rate in a constant temperature environment of -20°C.

[0087] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0088] The morphological characterization results of the pristine graphite electrodes prepared in this comparative example under a scanning electron microscope are as follows: Figure 7 As shown. From Figure 7 As can be seen, after high-temperature storage and low-temperature 1C current rate cycling, the graphite anode structure of lithium iron phosphate (LFP)||graphite batteries suffers catastrophic damage, and tiny sharp fibrous structures resembling tree branches or needle tips made of metallic lithium are observed.

[0089] Example 7

[0090] (1) Using commercial-grade lithium iron phosphate cathode, graphite anode and separator, the electrode assembly is stacked, packaged, injected and formed to prepare a soft pack battery in its initial state.

[0091] (2) Select activated and screened batteries, and after standing at 45°C for 24 hours, conduct continuous full charge and discharge cycle tests at 3C current rate in a constant temperature environment of -20°C.

[0092] (3) When the battery's discharge capacity decays to the point of battery failure, stop the cycle experiment and immediately disassemble the prepared soft-pack battery, and take out the negative electrode to study the lithium plating situation.

[0093] The morphological characterization results of the pristine graphite electrodes prepared in this comparative example under a scanning electron microscope are as follows: Figure 8 As shown. From Figure 8As can be seen, after high-temperature storage and low-temperature 3C current rate cycling to failure, the fibrous lithium dendrite structure of the graphite negative electrode of lithium iron phosphate (LFP)||graphite batteries becomes more severe. Specifically, the increased current rate directly leads to the evolution of lithium dendrite morphology from fibrous to highly branched, sharp dendritic, which grows faster and is more fatal to the battery.

[0094] Comparative Example 1

[0095] This comparative example uses commercially available, uncirculated graphite electrodes, cut into 1*1cm pieces. 2 Size was determined, and morphology was characterized using scanning electron microscopy. The results are as follows: Figure 9 As shown. From Figure 9 As can be seen, obvious graphite layered structure features can be observed in graphite electrodes that have not undergone recycling.

[0096] The effect of different magnification ratios on the lithium dendrite morphology on the graphite surface mainly stems from the differences in lithium-ion deposition kinetics. Figures 2 to 9 As can be seen, after standing at 25℃ for 24 hours and cycling at current rates of 0.05C and 0.1C at room temperature, the surface of the negative electrode still maintains a relatively smooth and flat morphology, and clear graphite layered structure characteristics can be observed, with no obvious lithium metal deposition. Under the cycling condition at room temperature with a current rate of 0.2C, a small amount of irregular deposits in the flocculent or moss-like form begin to appear at the edge of the negative electrode, which is a typical manifestation of the initial deposition of lithium metal. When the current rate is increased to 1C, the lithium deposition on the negative electrode surface becomes more significant, the amount of deposits increases significantly, the distribution range expands, and a local aggregation trend is observed. Under the high-rate cycling condition of 3C, the negative electrode surface undergoes severe deterioration, forming a large number of typical dendritic structures with sharp protrusions; these lithium dendrites not only lead to irreversible loss of active lithium, but also significantly increase the safety risk of piercing the separator and causing internal short circuits in the battery. After standing at 45℃ for 24 hours, the negative electrode surface after cycling at different current rates (1C and 3C) in a constant temperature environment of -20℃ showed almost entirely sharp protruding lithium dendrite structures, indicating that extensive lithium metal deposition occurred on the electrode surface.

[0097] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

[0098] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a battery negative electrode standard sample, using a lithium iron phosphate || graphite soft package battery to prepare a standard sample, characterized in that, The preparation method comprises preparation of the soft package battery and cycle processing; The preparation of the soft package battery comprises the following steps: The positive and negative tabs are prepared by a stamping forming process based on the marks established in the marking process; The layers are automatically stacked according to the set number, and the high-temperature-resistant adhesive tape is used for packaging to obtain the battery cell; The positive and negative tabs of the battery cell are welded, and the battery cell is automatically top-sealed and side-sealed by using the pre-punched aluminum plastic film; Vacuum injection is performed on the inside of the battery cell; Constant pressure is applied for formation treatment to obtain the soft package battery; The cycle processing comprises the following steps: A plurality of batteries screened after activation are selected, and the batteries are respectively placed at different design temperatures for a specific time, and then continuously full-charge and full-discharge cycle tests are performed in a constant temperature environment.

2. The production method according to claim 1, characterized by, During the top-sealing process of the battery cell, 1-2 cm of bare section is reserved on the rectangular adhesive area on the surface of the positive and negative tabs; during the side-sealing process of the battery cell, the sealing range does not cover the pre-punched area of the aluminum plastic film.

3. The method of claim 2, wherein, During the automatic top-sealing and side-sealing of the battery cell, the temperature of the upper and lower sealing stations of the sealing machine is 180 DEG C.

4. The method of claim 1, wherein, During the vacuum injection into the inside of the battery cell, the fixed height of the inverted battery cell is repeatedly adjusted until the injection gun head can be completely inserted into the inside bottom of the battery cell; after the injection is completed, the injection gun head and pipeline are cleaned by using dimethyl carbonate.

5. The preparation method according to claim 1, characterized in that, After the vacuum injection into the inside of the battery cell, the preparation method further comprises transferring the battery cell to a sealed and dried environment for storage.

6. The method of claim 1, wherein, The current ratio during the continuous full-charge and full-discharge cycle test is 0.05-3C.

7. The preparation method according to claim 1, characterized in that, The material of the positive tab is aluminum, and the material of the negative tab is nickel.

8. The method of claim 1, wherein, During the continuous full-charge and full-discharge cycle test in a constant temperature environment of 25 DEG C, the charging adopts a constant current and constant voltage mode to 3.65V, and then the cutoff current is 0.05C, and the discharging adopts a constant current mode to 2.5V.

9. The method of claim 1, wherein, Before the pre-punching of the aluminum plastic film, the preparation method further comprises cleaning the workbench surface of the punching instrument and the surface of the aluminum plastic film.

10. The battery anode standard of claim 1, wherein, The preparation method is prepared by using any one of claims 1-9.

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