Laminated battery cell as well as preparation method and application thereof

Abstract

The invention discloses a laminated battery cell as well as a preparation method and application thereof. The laminated battery cell provided by the invention comprises a negative pole piece, the negative pole piece consists of a pole piece A and a pole piece B; the pole piece A is a graphite pole piece and is positioned in the battery cell; the B pole pieces are lithium-plated graphite pole pieces and are positioned on the upper surface and the lower surface of the battery cell, and the outer side surfaces of the B pole pieces are subjected to lithium plating treatment. According to the invention, lithium is embedded into graphite crystal lattices (LixC6) in an atomic state, so that the purpose of increasing battery circulation by supplementing lithium can be achieved, and potential safety hazards caused by built-in lithium metal can also be avoided.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a stacked battery cell, its preparation method, and its application. Background Technology

[0002] Electrochemical pre-lithiation involves embedding lithium ions into the negative electrode surface through an electrochemical reaction to compensate for the lithium consumed by the SEI film formed during subsequent charging and discharging, thereby improving the battery's coulombic efficiency in the first cycle. However, placing pure lithium inside the cell not only increases the battery thickness and results in higher activity, but also leads to poor safety performance and a higher risk of thermal runaway. Furthermore, lithium ions will continue to migrate to the negative electrode during battery resting, easily causing localized lithium plating on the electrode.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a stacked battery cell and a slow-release pre-lithium battery prepared therefrom, by embedding lithium in an atomic state into a graphite lattice (Li... x C6 can both replenish lithium to increase battery cycle life and avoid the safety hazards caused by built-in lithium metal.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a stacked battery cell, including a negative electrode sheet; The negative electrode plate is composed of an A electrode plate and a B electrode plate; The A electrode is a graphite electrode and is located inside the battery cell; The B electrode is a lithium-plated graphite electrode located on the upper and lower surfaces of the battery cell, and the outer surface of the B electrode is treated with lithium plating.

[0006] This invention, based on existing automatic pre-lithiation technology, optimizes and utilizes the redundant upper and lower negative electrode plates on conventional battery cells, changing the source of supplementary lithium ions so that lithium ions are generated in the form of Li. x The lithium ions are stored in the form of C6 in the graphite lattice, which effectively avoids the safety hazards caused by the built-in metallic lithium. As the battery cell is discharged and charged, the lithium ions on the lithium-plated electrode gradually migrate from the side of the battery cell to the positive and negative electrodes and participate in the battery cell cycle, which improves the battery performance and increases the safety of the pre-lithium battery.

[0007] The number of A electrodes is N, where N≥1; the number of B electrodes is 2.

[0008] The surface density of the two sides of the A electrode is the same, with a surface density of 80-100 g / m³. 2 The thickness is 100-130μm.

[0009] The areal density of the inner surface of the B electrode is the same as that of the A electrode, which is 80-100 g / m². 2 .

[0010] The surface density of the outer surface of the B electrode is greater than or equal to the surface density of the A electrode, and the surface density is 100-130 g / m³. 2 .

[0011] The thickness of the B electrode is 117-300 μm, of which the thickness of the lithium-plated outer surface is 70-200 μm.

[0012] In one specific embodiment of the present invention, the areal density of the A electrode is 90 g / m². 2 The surface density of the outer surface of the B electrode is 120 g / m². 2 .

[0013] Li is formed in the graphite lattice on the outer surface of the B electrode. x C6, 0≤x≤1.

[0014] The tabs of the B electrode located on the upper and lower surfaces of the battery cell are mirror-shaped.

[0015] The battery cell also includes a positive electrode and a separator; the positive electrode and the A electrode are stacked alternately; the separator is separated in a Z-stack configuration.

[0016] Secondly, the present invention provides a method for preparing the above-mentioned stacked battery cell, comprising the following steps: S1. Coating of A-electrode and B-electrode, then roll forming into rolls; S2. Perform electrochemical lithium plating on the B electrode sheet obtained in step S1. S3. The lithium-plated B electrode obtained in step S2 is stacked and assembled with the A electrode and separator obtained in step S1 to obtain the battery cell.

[0017] The lithium plating process is carried out as follows: the B electrode and the lithium source are placed in an electrolytic cell and the discharge is controlled. The lithium source is placed on the outer side of the electrode, and lithium is intercalated on the outer side of the electrode through an electrochemical reaction.

[0018] As a specific embodiment of the present invention, the lithium plating process is performed according to the following operations: (1) A lithium source is pre-placed in the electrolytic cell. The width of the lithium source is the same as the width of the electrode plate of the B electrode. The lithium source is connected to the negative electrode site of the battery tester through a wire. (2) Inject electrolyte into the electrolytic cell, with the liquid level 0.2-10 mm higher than the lithium source; (3) Slowly unwind the B electrode after it has been rolled up, with the outer side facing the lithium source, and pass through the liquid surface above the electrolytic cell so that the electrode is as close as possible to the lithium source but does not directly contact the lithium source. After being dried by air at the end of the electrolytic cell, it is wound up. During the process, the current collector of the electrode roll is connected to the positive electrode point of the battery tester through a wire. (4) During the process of the electrode passing through the electrolytic cell, the electrode is controlled by the battery tester to discharge the lithium source. The discharge current is 0.1-4C of the design capacity of a single electrode. (5) Cut the lithium-plated electrode sheets into pieces for later use.

[0019] In step S1, the graphite raw material used in the slurry for coating the A and B electrodes is a secondary particulate carbonized product.

[0020] Thirdly, the present invention provides a lithium-ion battery comprising the above-mentioned stacked cells.

[0021] In the lithium-ion battery, the hot-pressing temperature of the cell is ≤55℃.

[0022] During the battery cycle, the battery can be discharged at a small current to accelerate the release of lithium ions in the thick electrode; the discharge current can be controlled between 0.02C and 0.1C.

[0023] The dew point of the lithium-ion battery preparation, operation, and storage environment is below -40°C.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention improves the performance of stacked battery cells and enhances the safety of pre-lithiated batteries through a special design of the electrode sheets. At the same time, the pre-lithiation method provided by this invention requires minimal modification to current conventional battery production line processes, resulting in lower modification costs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the stacked battery cell provided by the present invention.

[0026] Figure 2 This is a schematic diagram of the lithium-plated electrode preparation process provided by the present invention.

[0027] Figure 3 The working principle diagram of lithium-ion battery lithium replenishment provided by the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0030] Unless otherwise specified, all reagents, materials, instruments, etc. used in the following examples are commercially available.

[0031] Example 1: Preparation of Lithium-plated Stacked Cells and Lithium-ion Batteries Taking the lithium iron phosphate / carbon (LFP / C) battery cell system as an example, the specific preparation steps are as follows: (1) Slurry mixing: The graphite raw material is a secondary particulate carbonized product, and the slurry mixing is carried out in accordance with the conventional battery slurry mixing process.

[0032] (2) Coating of A and B electrodes: Conventional coating process is adopted. The process is the same on both sides of the A electrode, and the surface density on one side is 90 g / m². 2 The B electrode has different areal densities on its two sides, with one side having an areal density of 90 g / m². 2 The surface density of the other side is 120 g / m³. 2 Thicker electrodes can provide more lithium storage sites.

[0033] (3) Roll forming: The conventional roll forming process is adopted, with a roll forming speed of 10-30m / min and a roll forming pressure of (60±20)T.

[0034] (4) Lithium plating on B electrode: Lithium is inserted (lithium plating) on ​​the thickened electrode surface of the obtained B electrode through an electrolytic cell. The electrolyte in the electrolytic cell is consistent with the electrolyte in the cell system. The tabs of the two electrodes of a single cell are mirror images. The dew point of the lithium plating environment is ≤-40℃.

[0035] like Figure 2 As shown, the specific preparation process of the lithium-plated electrode sheet is carried out as follows: A lithium source is pre-placed in the electrolytic cell, with the width of the lithium source consistent with the width of the battery electrode sheet. The lithium source is connected to the negative electrode site of the battery tester via a wire. Electrolyte is injected into the electrolytic cell, and then the rolled electrode sheet is slowly unwound, with the thick side (i.e., the outer side) of the B electrode sheet corresponding to the lithium source, passing through the liquid surface above the electrolytic cell, so that the electrode sheet is as close to the lithium source as possible but does not directly contact the lithium source. After air drying at the end of the electrolytic cell, it is wound up. During the process, the current collector of the electrode roll is connected to the positive electrode site of the battery tester via a wire. As the electrode sheet passes through the electrolytic cell, the battery tester controls the electrode sheet to discharge to the lithium source. At this time, under the action of the electric field, lithium ions are detached from the lithium source and embedded in the graphite lattice to form a relatively stable Li. x C6 is used to fabricate lithium-plated B-electrode sheets through air showering and slitting.

[0036] (5) Stacking: Two electrode hoppers are added to the stacking machine for placing lithium-plated B electrodes (distinguished by the tab direction). During stacking, the B electrodes are placed on the upper and lower sides of the stack core with the lithium-plated side facing outwards. The positive and A electrodes are stacked alternately in the middle. The separator adopts a Z-stacking scheme to separate the electrodes, thus producing the battery cell. The total number of stacked negative electrodes is 30, including 28 A electrodes and 2 B electrodes. Figure 1 As shown.

[0037] (6) The battery cells obtained above are used to manufacture batteries using conventional assembly, liquid injection, formation and capacity testing processes; The working principle diagram of the lithium-ion battery described in this invention is as follows: Figure 3 As shown, during battery discharge, lithium ions detach from the lithium-plated electrode and slowly enter the positive electrode through the side of the cell. During battery charging, the lithium ions replenished to the positive electrode migrate to the negative electrode to participate in the cell cycle, thereby compensating for the lithium ion consumption caused by various side reactions during the cell cycle and achieving the goal of improving battery cycle performance.

[0038] Example 2 This embodiment provides a method for preparing a lithium-plated laminated battery cell, which differs from Embodiment 1 in that: in step (2), the areal density of both A and B electrodes is 90 g / m². 2 .

[0039] Example 3 This embodiment provides a method for preparing a lithium-plated laminated battery cell, which differs from Embodiment 1 in that: in step (2), the B electrode is designed with different areal densities on both sides, with one side having an areal density of 90 g / m². 2 The surface density of the other side is 140 g / m³. 2 .

[0040] Comparative Example 1 This comparative example provides a method for preparing a lithium-ion battery with an integrated lithium band. Taking a lithium iron phosphate / carbon (LFP / C) cell system as an example, the specific preparation steps are as follows: (1) Slurry mixing: The graphite raw material is a secondary particulate carbonized product, and the slurry mixing is carried out in accordance with the conventional battery slurry mixing process.

[0041] (2) Electrode coating: Conventional coating process is adopted, with consistent surface density on both sides and a surface density of 90 g / m² on one side. 2 .

[0042] (3) Roll forming: The conventional roll forming process is adopted, with a roll forming speed of 10-30m / min and a roll forming pressure of (60±20)T.

[0043] (4) Stacking: The stacking machine adds two lithium copper composite sheet material bins for placing lithium copper composite sheets (distinguished by the tab direction). The lithium plating amount on the lithium copper composite sheet is 0.2g. When stacking, the lithium copper composite sheet material is placed on the upper and lower sides of the stack core with the lithium plating side facing outward. The positive electrode sheet and A electrode sheet are stacked alternately in the middle. The separator adopts the Z stacking scheme for separation. The tabs on the lithium copper composite sheet correspond to the negative electrode tabs of the battery cell and are welded to the negative electrode post together with the negative electrode tabs of the battery cell to obtain the battery cell. The total number of stacked negative electrode sheets is 32 pieces and lithium copper composite sheets are 2 pieces.

[0044] (5) The battery cells obtained above are used to manufacture batteries using conventional assembly, liquid injection, formation and capacity testing processes.

[0045] Comparative Example 2 This comparative example provides a method for preparing a lithium-ion battery with a built-in lithium band. The difference from Example 4 is that the amount of lithium plating on the lithium-copper composite sheet in step (4) is 0.5g.

[0046] Comparative Example 3 This comparative example provides a method for preparing a lithium-ion battery with a built-in lithium band. The difference from Example 4 is that the amount of lithium plating on the lithium-copper composite sheet in step (4) is 1g.

[0047] Comparative Example 4 This embodiment provides a method for preparing a lithium-ion battery, which differs from Embodiment 4 in that no lithium-copper composite sheet is placed on the top or bottom of the stacked core.

[0048] Test Analysis Record the pre-formation voltage, capacity grading, and cycle data of the batteries obtained in the above embodiments and comparative examples; conduct thermal runaway tests on the batteries after capacity grading; disassemble the batteries at 500cls and record the interface conditions. The results are as follows.

[0049] Table 1. Test results of lithium-ion batteries obtained in the examples and comparative examples.

[0050] From the above results, we can conclude that: (1) Compared with the lithium battery without pre-lithiation scheme in Comparative Example 4, the lithium-ion batteries prepared in Examples 1-3 have significant advantages in battery capacity and capacity retention after pre-lithiation, and are also highly safe.

[0051] (2) As can be seen from the test results of Examples 1-3, within a certain range, the higher the surface density of the lithium-plated electrode (i.e., the more lithium insertion sites), the better the capacity and cycle life. However, if the surface density of the lithium-plated electrode is too high, the outer electrode will lose material slightly.

[0052] (3) Comparative Examples 1-3 use a built-in lithium strip scheme for pre-lithiation, which can improve the cell capacity cycle, but there will always be non-consumable lithium metal element inside the cell, which has poor safety, is difficult to pass the safety test, and is prone to side lithium plating, increasing safety hazards.

[0053] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A laminated battery cell, characterized in that, Including the negative electrode sheet; The negative electrode plate is composed of an A electrode plate and a B electrode plate; The A electrode is a graphite electrode and is located inside the battery cell; The B electrode is a lithium-plated graphite electrode located on the upper and lower surfaces of the battery cell, and the outer surface of the B electrode is treated with lithium plating.

2. The laminated battery cell according to claim 1, characterized in that, The number of A electrodes is N, where N≥1; the number of B electrodes is 2. The surface density of the two sides of the A electrode is the same, with a surface density of 80-100 g / m³. 2 The thickness is 100-130μm; The areal density of the inner surface of the B electrode is the same as that of the A electrode, which is 80-100 g / m². 2 ; The surface density of the outer surface of the B electrode is greater than or equal to the surface density of the A electrode, and the surface density is 100-130 g / m³. 2 ; The thickness of the B electrode is 117-300 μm, of which the thickness of the lithium-plated outer surface is 70-200 μm.

3. The laminated battery cell according to claim 1 or 2, characterized in that, Li is formed in the graphite lattice on the outer surface of the B electrode. x C6, 0≤x≤1.

4. The laminated battery cell according to claim 1, characterized in that, The tabs of the B electrode located on the upper and lower surfaces of the battery cell are mirror-shaped.

5. The laminated cell according to any one of claims 1-4, characterized in that, The battery cell also includes a positive electrode plate and a separator; The positive electrode and the A electrode are stacked alternately; The diaphragm is separated in a Z-stack configuration.

6. The method for preparing a laminated battery cell according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Coating of A-electrode and B-electrode, then roll forming into rolls; S2. Perform electrochemical lithium plating on the B electrode sheet obtained in step S1. S3. The lithium-plated B electrode obtained in step S2 is stacked and assembled with the A electrode and separator obtained in step S1 to obtain the battery cell.

7. The preparation method according to claim 6, characterized in that, In step S2, the lithium plating process is carried out as follows: the B electrode and the lithium source are placed in an electrolytic cell and the discharge is controlled. The lithium source is placed on the outer side of the electrode, and lithium is intercalated on the outer side of the electrode through an electrochemical reaction.

8. The preparation method according to claim 6 or 7, characterized in that, In step S1, the graphite raw material used in the slurry for coating the A and B electrodes is a secondary particulate carbonized product.

9. A lithium-ion battery comprising a stacked cell as described in any one of claims 1-5.

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