Preparation method of lithium metal cylindrical battery with built-in buffer structure

Abstract

The invention discloses a preparation method of a lithium metal cylindrical battery with a built-in buffer structure. The preparation method comprises the following steps: winding a positive plate, a lithium metal negative plate and a diaphragm into a battery cell; a buffer structure is arranged on the outer side of the battery cell, the buffer structure is located between the battery cell and the battery shell, and the buffer structure is a membrane material with a porous structure and resilience; injecting an electrolyte and completing packaging; standing pretreatment is carried out under set conditions, so that the buffer structure absorbs part of the electrolyte and forms a stable elastic buffer structure; and performing battery formation to obtain the lithium metal cylindrical battery. An acrylate rubber film is introduced between a battery cell and a cylindrical battery shell as a buffer structure, so that the stress generated by volume change of lithium metal in the charge-discharge cycle process is effectively absorbed, and the metal fatigue and fracture risk caused by repeated expansion and compression of a steel shell is remarkably reduced; and the structural stability, the safety and the reliability of the battery in medium and long-term circulation are enhanced.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a method for preparing a lithium metal cylindrical battery with a built-in buffer structure. Background Technology

[0002] Existing lithium metal batteries, due to their high theoretical specific capacity and low potential, have become a key research focus for next-generation high-energy-density batteries. In current applications, common lithium metal battery structures include prismatic, pouch, and cylindrical cells.

[0003] Among them, the soft-pack structure has a certain degree of flexibility, but its aluminum-plastic film has low mechanical strength and cannot withstand the expansion force of lithium metal on its own. It needs to rely on external clamping and pressure, resulting in low integration and high cost, which limits its large-scale application. The square shell structure has strong compressive strength, but the angular design is prone to stress concentration points, and it is also difficult to withstand the cyclic expansion of lithium metal for a long time. The cylindrical steel shell is considered to be a more suitable structural solution for lithium metal anodes because its geometric structure has a good ability to distribute stress evenly.

[0004] However, even with a cylindrical steel shell structure, the battery inevitably faces cyclic stress impacts from the internal expansion of lithium metal during long-term cycling. Without an effective buffering mechanism, the steel shell is highly susceptible to cracking under stress fatigue, affecting safety and lifespan. Therefore, there is an urgent need for a built-in buffer structure that can effectively absorb the volume changes and stress fluctuations caused by lithium metal charging and discharging within the battery, ensuring the stability and safety of the battery structure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a lithium metal cylindrical battery with a built-in buffer structure. By introducing a buffer structure between the cell and the cylindrical battery casing, the stress generated by the volume change of lithium metal during charge and discharge cycles is effectively absorbed, significantly reducing the risk of metal fatigue and cracking caused by repeated expansion and compression of the steel casing, and enhancing the structural stability and safety reliability of the battery in medium and long-term cycles.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for preparing a lithium metal cylindrical battery with a built-in buffer structure includes the following steps:

[0008] S1. The positive electrode, lithium metal negative electrode and separator are wound into a battery cell;

[0009] S2. A buffer structure is provided on the outside of the battery cell, and then the battery cell with the buffer structure is installed into the battery casing; or a buffer structure is fixed on the inside of the battery casing, and then the battery cell is installed into the battery casing with the buffer structure; the buffer structure is located between the battery cell and the battery casing, and the buffer structure is a membrane material with a porous structure and resilience.

[0010] S3. Inject electrolyte and complete encapsulation;

[0011] S4. Under set conditions, allow the buffer structure to absorb part of the electrolyte and form a stable elastic buffer structure.

[0012] S5. Perform battery formation to obtain a lithium metal cylindrical battery.

[0013] Preferably, the buffer structure is one or more composite structures selected from acrylate rubber membrane, carbon fiber membrane, styrene-butadiene rubber membrane, chloroprene rubber membrane, and polypropylene membrane.

[0014] Preferably, the buffer structure has any one or more of the following structural combinations: a cylindrical integral covering structure, a longitudinal arc-shaped strip structure, or a ring-shaped strip structure with multiple axially arranged rings.

[0015] Preferably, the thickness of the membrane material in the buffer structure is 30 μm to 100 μm.

[0016] Preferably, the buffer structure is disposed on the outer surface of the cell or the inner wall of the battery casing and is fixed by means of pasting, hot pressing, nesting or molding.

[0017] Preferably, the temperature for static pretreatment in step S4 is 40℃~60℃, and the time is 12 hours to 48 hours.

[0018] Preferably, the buffer structure absorbs the electrolyte to form a gel-like buffer layer, which can buffer the expansion pressure of lithium metal and stably release the electrolyte during the cycle.

[0019] Preferably, the electrolyte is a carbonate electrolyte containing LiPF6, or a composite electrolyte system further comprising additives FEC, LiNO3 and DME.

[0020] Preferably, the battery casing is made of steel or aluminum.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] 1. By assembling lithium metal batteries using a cylindrical battery structure, the stability and safety of the batteries are improved. Compared with lithium metal pouch batteries, there is no need for clamping plates to apply pressure, which expands the application scenarios.

[0023] 2. By introducing a membrane material such as an acrylic rubber film between the cell and the cylindrical battery casing as a buffer structure, the stress generated by the volume change of lithium metal during the charge and discharge cycle is effectively absorbed, significantly reducing the risk of metal fatigue and cracking caused by repeated expansion and compression of the steel casing, and enhancing the structural stability and safety reliability of the battery in medium and long-term cycles.

[0024] 3. Our research has found that membrane materials such as acrylic rubber membranes have good electrolyte absorption and slow release capabilities. During static pretreatment, they absorb electrolyte to form a flexible swelling layer, which increases the electrolyte retention of the battery. They also absorb part of the electrolyte and help reduce electrolyte migration and extrusion during long-term cycling, promoting uniform distribution of electrolyte during battery cycling, reducing drying and interface failure problems, and extending battery cycle life. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the battery cell structure in this invention;

[0027] Figure 2 This is a schematic diagram of the cylindrical battery structure in this invention.

[0028] In the diagram: 1. Battery cell; 11. Positive electrode; 12. Separator; 13. Negative electrode; 2. Battery casing; 3. Buffer structure. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0030] Example 1

[0031] A method for preparing a lithium metal cylindrical battery with a built-in buffer structure includes the following steps:

[0032] S1. Preparing the cell structure: The positive electrode sheet, separator, and lithium metal negative electrode sheet are wound into a cell.

[0033] Positive electrode material: NCM811 ternary positive electrode material is selected to prepare coated positive electrode sheets, and aluminum foil is used as the current collector;

[0034] Anode material: 50μm thick lithium metal foil, current collector is copper foil;

[0035] Membrane material: Polypropylene / Polyethylene (PP / PE) composite membrane.

[0036] S2. Cut the acrylic rubber film, which serves as a buffer structure, into a cylindrical film with a thickness of 60μm. Wrap the entire film around the outside of the wound battery cell, ensuring it adheres tightly to the surface of the battery cell. Then, insert the battery cell with the acrylic rubber film on it into a battery casing with a matching diameter, so that the acrylic rubber film is used as a buffer structure between the battery cell and the battery casing.

[0037] S3. Inject electrolyte No. 1, with the amount of electrolyte matched to the volume of conventional cells. Then, complete the encapsulation under sealed conditions. The battery capacity is 6Ah.

[0038] Electrolyte: Use 1M LiPF6 dissolved in a mixed solvent of FEC and EMC (volume ratio 1:1), denoted as Electrolyte No. 1.

[0039] S4. Place the battery in a constant temperature environment, set the static temperature to 45℃, and the static time to 24h, so that the acrylic rubber film can fully absorb the electrolyte and form a stable elastic buffer structure.

[0040] S5. After the battery has been left to stand, it is subjected to a conventional formation process to obtain a lithium metal cylindrical battery. After multiple charge-discharge cycles, the acrylate rubber film was observed to have not peeled or suffered structural damage, and the battery casing showed no signs of bulging or cracking.

[0041] That is, the prepared lithium metal cylindrical battery, such as Figure 1 and 2 As shown, the battery includes a cylindrical battery casing 2, a battery cell 1, and a buffer structure 3 disposed between the battery casing 2 and the battery cell 1. The battery cell 1 includes a positive electrode 11, a negative electrode 13, and a separator 12 with a winding structure. The negative electrode 13 is made of lithium metal material.

[0042] Example 2

[0043] The difference between this embodiment and Embodiment 1 is that the acrylic rubber film is cut into a cylindrical sheet with a thickness of 60 μm, and the entire sheet is inserted into the battery casing and tightly adhered to the inner wall of the battery casing. To integrate the acrylic rubber film with the battery casing, multiple adhesive application points are provided on the inner wall of the battery casing for bonding with the acrylic rubber film.

[0044] Example 3

[0045] The difference between this embodiment and Embodiment 1 is that NCM622 ternary cathode material is selected, and the electrolyte is a lithium nitrate electrolyte containing ether, consisting of 1M LiPF6 + 0.1M LiNO3 / FEC-EMC-DME (1:1:1 volume ratio), and this electrolyte is designated as electrolyte No. 2.

[0046] Example 4

[0047] The difference between this embodiment and Embodiment 3 is that the thickness of the acrylate rubber film is 30 μm.

[0048] Example 5

[0049] The difference between this embodiment and Embodiment 3 is that the thickness of the acrylate rubber film is 100 μm.

[0050] Example 6

[0051] The difference between this embodiment and Embodiment 3 is that the standing temperature is 45°C and the standing time is 6 hours.

[0052] Example 7

[0053] The difference between this embodiment and Embodiment 3 is that the standing temperature is 45°C and the standing time is 12 hours.

[0054] Example 8

[0055] The difference between this embodiment and Embodiment 3 is that the standing temperature is 45°C and the standing time is 36 hours.

[0056] Example 9

[0057] The difference between this embodiment and Embodiment 3 is that the standing temperature is 25°C and the standing time is 24 hours.

[0058] Example 10

[0059] The difference between this embodiment and Embodiment 3 is that the standing temperature is 60°C and the standing time is 24 hours.

[0060] Example 11

[0061] The difference between this embodiment and Embodiment 3 is that the acrylic rubber film is cut into three annular strips with an axial length of 1 cm and a thickness of 60 μm, and these strips are spaced apart and fitted onto the outside of the wound battery cell to ensure close contact with the battery cell surface. Then, the battery cell with the acrylic rubber film is installed into a battery casing with a matching diameter, so that the acrylic rubber film is used as a buffer structure between the battery cell and the battery casing.

[0062] Example 12

[0063] The difference between this embodiment and Embodiment 1 is that a carbon fiber membrane is used as the buffer structure.

[0064] Comparative Example 1

[0065] The lithium metal battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode material is a nickel-cobalt-manganese ternary material, specifically NCM811. The negative electrode material is lithium metal with a thickness of 50 μm. The electrolyte is 1M LiPF6 / FEC-EMC, designated as electrolyte No. 1. The battery capacity is 6 Ah.

[0066] Comparative Example 2

[0067] The lithium metal battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode material is a nickel-cobalt-manganese ternary material, specifically NCM622. The negative electrode material is lithium metal with a thickness of 50 μm. The electrolyte is a lithium nitrate-containing electrolyte containing ether, consisting of 1M LiPF6 + 0.1M LiNO3 / FEC-EMC-DME (1:1:1 volume ratio). This electrolyte is designated as electrolyte No. 2. The battery capacity is 6 Ah.

[0068] All embodiments 1-10 and comparative examples 1-2 of this invention use the same battery system, and the capacity of each individual cell is within the range of 6 ± 0.3 Ah. All batteries were tested at 25°C, with voltage tests ranging from 3.0V to 4.35V, a charge rate of 0.5C, and a discharge rate of 1C. When the battery's discharge capacity retention rate falls below 80.0%, the battery is considered to have reached its service life, and the number of cycles is recorded. See Table 1.

[0069] Electrolyte type Buffer structure thickness Settling time (h) Standing temperature (°C) Number of cycles Example 1 1 60 24 45 521 Example 2 1 60 24 45 496 Example 3 2 60 24 45 591 Example 4 2 30 24 45 357 Example 5 2 100 24 45 364 Example 6 2 60 6 45 388 Example 7 2 60 12 45 500 Example 8 2 60 36 45 404 Example 9 2 60 24 25 472 Example 10 2 60 24 60 376 Example 11 2 Ring-shaped 24 45 362 Example 12 1 60 24 45 516 Comparative Example 1 1 / 24 45 51 Comparative Example 2 2 / 24 45 39

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a lithium metal cylindrical battery with a built-in buffer structure, characterized in that, Includes the following steps: S1. The positive electrode, lithium metal negative electrode and separator are wound into a battery cell; S2. A buffer structure is provided on the outside of the battery cell, and then the battery cell with the buffer structure is installed into the battery casing; or a buffer structure is fixed on the inside of the battery casing, and then the battery cell is installed into the battery casing with the buffer structure; the buffer structure is located between the battery cell and the battery casing, and the buffer structure is a membrane material with a porous structure and resilience. S3. Inject electrolyte and complete encapsulation; S4. Under set conditions, allow the buffer structure to absorb part of the electrolyte and form a stable elastic buffer structure. S5. Perform battery formation to obtain a lithium metal cylindrical battery.

2. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, The buffer structure is one or more composite structures selected from acrylate rubber membrane, carbon fiber membrane, styrene-butadiene rubber membrane, chloroprene rubber membrane, and polypropylene membrane.

3. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 2, characterized in that, The buffer structure has any one or more of the following structural combinations: a cylindrical integral covering structure, a longitudinal arc-shaped strip structure, or a ring-shaped strip structure with multiple axially arranged rings.

4. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, The thickness of the membrane material in the buffer structure is 30μm to 100μm.

5. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, The buffer structure is set on the outer surface of the cell or the inner wall of the battery casing and is fixed by means of pasting, hot pressing, nesting or molding.

6. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, In step S4, the temperature for static pretreatment is 40℃~60℃, and the time is 12 hours to 48 hours.

7. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, The buffer structure absorbs the electrolyte and forms a gel-like buffer layer, which can buffer the expansion pressure of lithium metal and stably release the electrolyte during the cycle.

8. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, The electrolyte is a carbonate electrolyte containing LiPF6, or a composite electrolyte system further including additives FEC, LiNO3 and DME.

9. The method for preparing a lithium metal cylindrical battery with a built-in buffer structure according to claim 1, characterized in that, The battery casing is made of steel or aluminum.

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