A method for preparing a high energy density lithium ion battery

Abstract

The present invention relates to the field of lithium-ion batteries, in particular to a method for preparing a high-energy-density lithium-ion battery, which is used to solve the technical problem in the prior art that the inherent physical and chemical properties of NCM622 limit the capacity of the lithium-ion battery. The method comprises the following steps: step 1: negative electrode sheet pre-lithiation pretreatment process: preparing a pre-lithiation reagent and spraying it onto the surface of a graphite electrode sheet, and rolling the electrode sheet at a low speed; step 2: negative electrode pre-lithiation process; step 3: positive electrode over-lithiation process: discharging the battery at a constant current of 0.01C to 0.5V; step 4: battery formation; step 5: sequentially performing high-temperature aging and secondary liquid injection operations on the battery; and step 6: capacity separation. Compared with the prior art, the present invention effectively increases the storage capacity of reversible lithium ions in the NCM622 material by finely controlling the pre-lithiation process and the degree of positive electrode over-lithiation, thereby opening up a new path for the development of high-energy-density batteries.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, in particular to a method for preparing a high energy density lithium ion battery. Background Art

[0002] Layered transition metal oxide cathode materials, a leading core component of lithium-ion batteries, have paved a new path for building high-capacity, high-energy-density lithium-ion batteries thanks to their unique intercalation chemistry. Among these materials, NCM622 (lithium nickel cobalt manganese oxide with a nickel-cobalt-manganese ratio of 6:2:2) holds a significant position in the commercial lithium-ion battery market thanks to its exceptional reversible capacity, excellent chemical stability, and cost-effectiveness. However, despite its numerous advantages, NCM622's inherent physical and chemical properties present obstacles to further development: its band structure limits its upper voltage limit, while its fragile crystal structure makes it difficult to withstand the stress changes caused by deep lithium-ion insertion and extraction. These factors collectively restrict further increases in its practical usable capacity, creating a key bottleneck in achieving breakthroughs in high-energy-density lithium-ion battery technology.

[0003] In order to significantly improve the energy density of NCM622 ternary materials, the method currently widely adopted in the industry is to increase the nickel (Ni) content in the positive electrode material or increase its charge cutoff voltage. However, this strategy has significant drawbacks: excessively increasing the Ni content will weaken the structural stability of the material, accelerate its transformation from ordered layered to disordered spinel and even rock salt structure, and thus lead to a surge in interfacial impedance and a sharp drop in reversible capacity. In addition, excessively high Ni content or increasing the charge cutoff voltage may also induce lattice collapse, a surge in internal mechanical stress, frequent particle breakage, and intensified side reactions, ultimately significantly accelerating the decline of battery capacity. Summary of the Invention

[0004] The present invention provides a method for preparing a high-energy-density lithium-ion battery, and creatively proposes a solution combining negative electrode pre-lithiation with positive electrode over-lithiation.

[0005] A method for preparing a high energy density lithium ion battery comprises the following steps:

[0006] Step 1: Pre-lithiation treatment of the negative electrode: Stable lithium metal powder, styrene-butadiene rubber, and toluene are mixed and dispersed uniformly in proportion to prepare a pre-lithiation reagent. The pre-lithiation reagent is evenly sprayed onto the surface of the graphite electrode sheet. After the toluene solvent on the surface of the electrode sheet has evaporated, the electrode sheet is rolled at a low speed to complete the pre-lithiation treatment of the graphite electrode sheet.

[0007] Step 2: Negative electrode pre-lithiation process: Assemble the treated graphite electrode sheet and NCM622 electrode sheet into a cylindrical battery, and complete the liquid injection, high-temperature immersion and static standing in sequence to complete the negative electrode pre-lithiation;

[0008] Step 3: Positive electrode overlithiation process: discharge the battery at a constant current density of 0.01C to 0.5V;

[0009] Step 4: Battery formation: 1) Charge the battery at a constant current of 0.05C to 4.2V; 2) Allow to stand for 30 minutes; 3) Charge the battery at a constant current of 0.1C to 4.2V; 4) Allow to stand for 15 minutes; 5) Charge the battery at a constant current of 0.2C to 4.2V; 6) Allow to stand for 10 minutes;

[0010] Step 5: Perform high temperature aging and secondary liquid filling operations on the battery in sequence;

[0011] Step 6: Capacity division: 1) Charge the battery at a constant current of 0.5C to 4.2V; 2) Charge at a constant voltage of 4.2V until the current drops to 0.05C; 3) Let it stand for 30 minutes; 4) Discharge the battery at a constant current of 0.5C to 3.0V; 5) Charge the battery at a constant current of 0.2C to 3.0V; 6) Charge the battery at a constant current of 0.1C to 3.0V; 7) Let it stand for 30 minutes; 8) Charge the battery at a constant current of 0.5C for 30 minutes; 9) Let it stand for 30 minutes.

[0012] Preferably, the pre-lithiation reagent in step 1 is 3 g of stable lithium metal powder dissolved in 1 L of toluene-styrene-butadiene rubber mixed solution, and the ratio of toluene to styrene-butadiene rubber in the toluene-styrene-butadiene rubber mixed solution is 9:1.

[0013] Preferably, the speed of the low-speed rolling in step 1 is 0.1 m / min.

[0014] Preferably, the pressure of the low-speed rolling in step 1 is 10 MPa.

[0015] Preferably, the temperature of the high-temperature soaking and standing in step 2 is 45° C. and the time is 24 hours.

[0016] Preferably, the temperature of high temperature aging in step 5 is 45°C.

[0017] Compared to existing technologies, this invention focuses on the overlithiation technology of NCM622 ternary materials. By carefully controlling the pre-lithiation process and the degree of overlithiation of the positive electrode, it effectively increases the reversible lithium ion storage capacity of the NCM622 material, opening up a new path for the development of high-energy-density batteries. More importantly, this technological innovation achieves a significant increase in the reversible lithium ion content of the NCM622 material without changing the existing production process framework for cylindrical batteries, thereby directly enhancing the energy density of cylindrical batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of step 1.

[0019] Figure 2 This is a schematic diagram of step 4.

[0020] Figure 3 This is a schematic diagram of step 6.

[0021] Figure 4 This is the voltage-time curve of the NCM622 over-lithiation process.

[0022] Figure 5 Comparison of XRD patterns of original and over-lithiated NCM622.

[0023] Figure numerals: 1. pre-lithiation reagent tank; 2. graphite coating; 3. copper foil; 4. pre-lithiation reagent layer; 5. oven; 6. roller press. DETAILED DESCRIPTION

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of such features.

[0025] In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0026] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0027] like Figure 1-3 A method for preparing a high energy density lithium ion battery is shown, comprising the following steps:

[0028] 1. Negative electrode pre-lithiation pretreatment: Stable lithium metal powder, styrene-butadiene rubber (SBR), and toluene are mixed and dispersed uniformly to prepare a pre-lithiation reagent. Dissolve 3g of stable lithium metal powder in 1L of a toluene-SBR mixed solution, where the ratio of toluene to SBR is 9:1. Spray the pre-lithiation reagent evenly onto the surface of the graphite electrode. After the toluene solvent evaporates from the electrode surface, roll the electrode at a low speed (0.1m / min) and a pressure of 10 MPa to complete the graphite electrode pre-lithiation treatment.

[0029] The electrode sheet is mainly composed of a current collector and a graphite coating. Copper foil is the current collector. Graphite is coated on the copper foil and dried to form a graphite coating. Then, a pre-lithiation reagent is sprayed on the surface of the graphite coating. After the solvent evaporates, the production process of the graphite electrode sheet is completed. The subsequent operations are winding the battery cell, injecting liquid, etc.

[0030] 2. Negative electrode pre-lithiation process: Assemble the treated graphite electrode sheet and NCM622 electrode sheet into a cylindrical battery, and complete the liquid injection, high temperature (45°C) immersion and static for 24 hours to complete the negative electrode pre-lithiation. Negative electrode pre-lithiation process: During the high temperature static process, the electrons in the lithium metal powder migrate into the graphite due to the potential difference, and the generated lithium ions dissolve in the electrolyte on the negative electrode surface. To maintain electrical neutrality, lithium ions will spontaneously migrate into the graphite and combine with electrons, thereby achieving the pre-lithiation effect;

[0031] 3. Positive electrode over-lithiation process: The battery is discharged to 0.5V at a constant current density of 0.01C to activate the high energy density characteristics of NCM622 material;

[0032] 4. Battery formation: 1) Charge the battery at a constant current density of 0.05C to 4.2V; 2) Let it stand for 30 minutes; 3) Charge the battery at a constant current density of 0.1C to 4.2V; 4) Let it stand for 15 minutes; 5) Charge the battery at a constant current density of 0.2C to 4.2V; 6) Let it stand for 10 minutes.

[0033] 5. Perform high temperature (45°C) aging and secondary refilling of the battery in sequence;

[0034] 6. Capacity adjustment: 1) Charge the battery at a constant current of 0.5C to 4.2V; 2) Charge at a constant voltage of 4.2V until the current drops to 0.05C; 3) Allow to stand for 30 minutes; 4) Discharge the battery at a constant current of 0.5C to 3.0V; 5) Charge the battery at a constant current of 0.2C to 3.0V; 6) Charge the battery at a constant current of 0.1C to 3.0V; 7) Allow to stand for 30 minutes; 8) Charge the battery at a constant current of 0.5C for 30 minutes; 8) Allow to stand for 30 minutes.

[0035] In the prior art, after the battery is manufactured, the formation operation should be performed, that is, charging should be performed first, and the voltage should increase over time. However, the positive electrode over-lithiation strategy in the present invention is to discharge the battery first, that is, the voltage gradually decreases over time (this process is to embed more / excessive lithium ions into the material). After this process, the structure of the NCM622 material will change, that is, the NCM622 material can accommodate more lithium ions for reversible embedding and extraction in the subsequent cycle process. Figure 4 As shown, the voltage platform near 1.7V corresponds to the first stage of excessive lithium ion embedding in NCM622 material. The embedded lithium ions in this stage are irreversible and the crystal structure of NCM622 material is still 1T phase. Then in the range of 1.7V-0.8V, with the further embedding of more lithium ions, the structure of NCM622 material begins to change from 1T phase to O3 phase (this process is a solid solution reaction, that is, the crystal structure of the material begins to change from 1T phase to O3 phase. The 1T phase represents that the excessive embedded lithium ions cannot be reversibly embedded and deintercalated, and the O3 phase represents that the embedded lithium ions can be reversibly embedded and deintercalated. Then, in the range of 0.8V-0.5V, accompanied by the embedding of excess lithium ions and the occurrence of material phase change (1T phase further converted to O3 phase), more excess lithium ions can be embedded in this stage, and the structure is further transformed into O3 phase. That is, after completing this stage, the NCM622 material not only stores lithium ions far exceeding the original stoichiometric ratio, but also the change in the material structure allows this part of the excess lithium ions to become active lithium ions that can be reversibly embedded and deintercalated. Therefore, even in the subsequent long cycle, the NCM622 material can still store more lithium ions for reversible deintercalation, ultimately greatly increasing the energy density of the lithium-ion battery.

[0036] Under normal temperature conditions, two groups of cylindrical batteries were used for a systematic comparative experiment. The other group was manufactured according to the method used in the present invention, and steps 1-3 were not used in the production process of one group of batteries. Figure 5As shown in the figure, the (003) crystal plane strength of the NCM622 material after over-lithiation is about twice that of the original NCM622, which means that the number of active lithium ions stored in the NCM622 material has increased, which ultimately greatly increases the energy density of the lithium-ion battery.

[0037] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for preparing a high energy density lithium ion battery, characterized in that: The following steps are involved: Step 1: Pre-lithiation treatment of the negative electrode sheet: Stable lithium metal powder, styrene-butadiene rubber, and toluene are mixed and dispersed uniformly in proportion to prepare a pre-lithiation reagent, which is evenly sprayed onto the surface of the graphite electrode sheet. After the toluene solvent on the surface of the electrode sheet is completely evaporated, the electrode sheet is rolled at a low speed to complete the pre-lithiation treatment of the graphite electrode sheet; Step 2: Negative electrode pre-lithiation process: Assemble the treated graphite electrode sheet and NCM622 electrode sheet into a cylindrical battery, and complete the liquid injection, high-temperature immersion and static standing in sequence to complete the negative electrode pre-lithiation; Step 3: Positive electrode overlithiation process: discharge the battery at a constant current density of 0.01C to 0.5V; Step 4: Battery formation: 1) Charge the battery at a constant current of 0.05C to 4.2V; 2) Allow to stand for 30 minutes; 3) Charge the battery at a constant current of 0.1C to 4.2V; 4) Allow to stand for 15 minutes; 5) Charge the battery at a constant current of 0.2C to 4.2V; 6) Allow to stand for 10 minutes; Step 5: Perform high temperature aging and secondary liquid filling operations on the battery in sequence; Step 6: Capacity division: 1) Charge the battery at a constant current of 0.5C to 4.2V; 2) Charge at a constant voltage of 4.2V until the current drops to 0.05C; 3) Let it stand for 30 minutes; 4) Discharge the battery at a constant current of 0.5C to 3.0V; 5) Charge the battery at a constant current of 0.2C to 3.0V; 6) Charge the battery at a constant current of 0.1C to 3.0V; 7) Let it stand for 30 minutes; 8) Charge the battery at a constant current of 0.5C for 30 minutes; 9) Let it stand for 30 minutes.

2. The method for preparing a high energy density lithium ion battery according to claim 1, wherein: In step 1, the pre-lithiation reagent is 3 g of stable lithium metal powder dissolved in 1 L of toluene-styrene butadiene rubber mixed solution, wherein the ratio of toluene to styrene butadiene rubber in the toluene-styrene butadiene rubber mixed solution is 9:

1.

3. The method for preparing a high energy density lithium ion battery according to claim 1, wherein: The speed of the low-speed rolling in step 1 is 0.1 m / min.

4. The method for preparing a high energy density lithium ion battery according to claim 1, wherein: The pressure of the low-speed roller pressing in step 1 is 10 MPa.

5. The method for preparing a high energy density lithium ion battery according to claim 1, wherein: In step 2, the temperature of the high-temperature soaking and standing is 45°C and the time is 24 hours.

6. The method for preparing a high energy density lithium ion battery according to claim 1, wherein: The temperature of high temperature aging in step 5 is 45°C.

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