Formation method of battery and pre-lithiation battery

Abstract

This invention discloses a battery formation method and a pre-lithiated battery. The battery includes a pre-lithiated material, and the decomposition voltage of the pre-lithiated material includes a first decomposition voltage V. a Second decomposition voltage V b The formation method is characterized by sequentially performing the following operations on the battery: pre-charging; performing a first pulse charge-discharge to raise the voltage to V1, V1 <V a ; Charged using constant current and constant voltage to the first decomposition voltage V a Perform a second pulse charge / discharge to bring the voltage to V2, V a <V2<V b Charge to the second decomposition voltage V b Perform a third pulse charge / discharge to bring the voltage to V3, where V3 ≥ V b The formation method of this invention can reduce formation time, increase aging voltage, and achieve more complete decomposition of pre-lithiated materials. Simultaneously, by introducing positive voltage, the interface can be improved, which is beneficial for enhancing battery performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and to a battery formation method and a pre-lithiated battery. Background Technology

[0002] With the rapid development of energy storage technology, a large number of research topics on long-life lithium-ion batteries have been carried out. Among them, adding positive electrode lithium replenishment materials to the positive electrode can make up for the loss of lithium ions during the formation process, thereby improving the performance of the battery.

[0003] The lithium replenishment effect varies depending on the type of lithium replenishment material. Taking Li5FeO4 as an example, it has a high theoretical specific capacity and has received widespread attention as a positive electrode lithium replenisher. However, Li5FeO4 has two decomposition voltage plateaus during its formation process, requiring charging to 4.1V–4.2V. Therefore, for lithium replenishment materials with a decomposition plateau greater than one plateau, the formation time is generally longer and the polarization is greater, which reduces the electrochemical performance of the battery.

[0004] Therefore, it is necessary to provide a battery formation method that allows the lithium-replenishing materials in the battery to fully exert their lithium-replenishing effect while shortening the formation time and reducing polarization, thereby improving battery performance. Summary of the Invention

[0005] In view of the above-mentioned technical problems existing in the prior art, the purpose of this invention is to provide a battery formation method and a pre-lithiated battery.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for forming a battery, the battery comprising a pre-lithiation material, wherein the decomposition voltage of the pre-lithiation material includes a first decomposition voltage V. a Second decomposition voltage V b The formation method includes performing the following operations on the battery in sequence:

[0008] Precharge;

[0009] Perform the first pulse charge and discharge to raise the voltage to V1, V1 <V a ;

[0010] The device is charged to the first decomposition voltage V using constant current and constant voltage. a ;

[0011] Perform a second pulse charge and discharge to bring the voltage to V2, V a <V2<V b ;

[0012] Charge to the second decomposition voltage V b;

[0013] Perform a third pulse charge / discharge to bring the voltage to V3, where V3 ≥ V b .

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] Preferably, during the first pulsed charging and discharging process, the forward current is 0.5C to 1C and the reverse current is 0.2C to 0.4C.

[0016] Preferably, V a -V1 is 0.1V to 0.3V.

[0017] Preferably, after the voltage rises to V1, let it stand for 2 to 4 minutes.

[0018] As a preferred embodiment of the formation method of the present invention, during the second pulsed charge and discharge process, the forward current is 0.1C-0.4C and the reverse current is 0.1C-0.2C.

[0019] Preferably, V b -V2 is 0.1V to 0.3V.

[0020] Preferably, after the voltage reaches V2, let it stand for 4 to 6 minutes.

[0021] As a preferred embodiment of the formation method of the present invention, during the third pulsed charge-discharge process, the forward current is 0.05C to 0.2C and the reverse current is 0.03C to 0.05C.

[0022] Preferably, V3-V b The voltage range is 0 to 0.2V.

[0023] Preferably, after the voltage reaches V3, let it stand for 5 to 10 minutes.

[0024] As a preferred embodiment of the formation method of the present invention, after the third pulse charge-discharge, a fourth pulse charge-discharge is performed to make the voltage reach V4, where V4≥V b .

[0025] Preferably, during the fourth pulse charging and discharging process, the forward current is 0.05C to 0.2C, and the reverse current is 0.03C to 0.05C.

[0026] Preferably, V4-V b The voltage range is 0 to 0.2V.

[0027] Preferably, after the voltage reaches V4, let it stand for 5 to 10 minutes.

[0028] As a preferred embodiment of the formation method of the present invention, the pre-charging includes:

[0029] First, charge with a current of 0.05C to 0.1C for 10 to 30 minutes, then let stand for 2 to 4 minutes;

[0030] Then charge with a current of 0.2C to 0.3C for 50 to 70 minutes, and let stand for 2 to 4 minutes.

[0031] Preferably, the first pulse charge-discharge is performed when the battery is pre-charged to 20% SOC.

[0032] Preferably, the constant current and constant voltage charging process includes sequential constant current charging and constant voltage charging, with constant voltage charging reaching a preset cutoff current and then stopping charging.

[0033] Preferably, the constant current charging current is 0.2C to 0.3C.

[0034] Preferably, the preset cutoff current is 0.04C to 0.06C.

[0035] Preferably, the constant current and constant voltage charging is performed until the first decomposition voltage V is reached. a Then, let it stand for 4 to 6 minutes.

[0036] Preferably, the charge is performed using a constant current charging method until the second decomposition voltage V is reached. b .

[0037] Preferably, the constant current charging current is 0.04C to 0.06C.

[0038] Preferably, charging to the second decomposition voltage V b Then, let it stand for 5 to 10 minutes.

[0039] Preferably, the charging to the second decomposition voltage V b Then, before the third pulse charge / discharge, perform the following steps: charge to V5 using a current of 0.01C to 0.03C, where V5 ≥ V b .

[0040] Preferably, V5-V b The voltage range is 0 to 0.2V.

[0041] Preferably, after charging to V5, let it stand for 5 to 10 minutes.

[0042] As a preferred embodiment of the formation method of the present invention, the formation method shall satisfy at least one of the following conditions (1)-(4):

[0043] (1) Perform a second pulse charge and discharge to make the voltage reach V2, and then let it stand under positive pressure. Preferably, after standing, the gas is discharged by using negative pressure.

[0044] (2) Charge to the second decomposition voltage V b Then, let it stand under positive pressure, preferably let it stand and then use negative pressure to discharge the gas;

[0045] (3) Perform the third pulse charge and discharge to make the voltage reach V3, and then let it stand under positive pressure. Preferably, after standing, the gas is discharged by using negative pressure.

[0046] (4) Charge to V5 and let stand under positive pressure. Preferably, let stand and then use negative pressure to discharge the gas.

[0047] Preferably, the positive pressure in options (1)-(4) above is independently 40 kPa to 50 kPa.

[0048] Preferably, the duration of the positive pressure in options (1)-(4) above is 1 min to 3 min.

[0049] In a second aspect, the present invention provides a pre-lithiated battery, which is formed using the method described in the first aspect.

[0050] Compared with existing technologies, the present invention has the following beneficial effects:

[0051] (1) The method of the present invention, by introducing a three-step pulse charge-discharge process, can greatly reduce the formation process and reduce the formation time by more than 2 hours compared with the prior art, thereby reducing production costs. Moreover, it can reduce the polarization of the pre-lithiated battery and the decomposition of the lithium replenishment material is more complete, which is beneficial to improving the performance of the battery.

[0052] (2) The pre-lithiated battery prepared by the formation method of the present invention has good storage performance and cycle performance.

[0053] (3) This invention breaks through the previous negative pressure formation method and introduces positive pressure to more effectively remove gas and improve the interface, thereby improving the performance of the battery. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0055] In one embodiment, the present invention provides a method for forming a battery, the battery comprising a pre-lithiation material, wherein the decomposition voltage of the pre-lithiation material includes a first decomposition voltage V. aSecond decomposition voltage V b The formation method includes performing the following operations on the battery in sequence:

[0056] Precharge;

[0057] Perform the first pulse charge and discharge to raise the voltage to V1, V1 <V a ;

[0058] The device is charged to the first decomposition voltage V using constant current and constant voltage. a ;

[0059] Perform a second pulse charge and discharge to bring the voltage to V2, V a <V2<V b ;

[0060] Charge to the second decomposition voltage V b ;

[0061] Perform a third pulse charge / discharge to bring the voltage to V3, where V3 ≥ V b .

[0062] The current in the pulse charging and discharging process is a pulsed current, which is different from the conventional constant current charging. Pulse charging and discharging allows for high current charging and discharging, which can accelerate formation, reduce formation time, and reduce cell polarization, making the SEI film more stable.

[0063] In one embodiment of the present invention, pre-charging can activate the battery cell and initially form an SEI film; the first pulse charge-discharge first reaches a voltage V1, which can accelerate formation while reducing cell polarization and making the SEI film more stable; the constant current and constant voltage charging method is continued to raise the voltage to the first decomposition voltage V. a This method is more stable than pulse charging and discharging, which is beneficial for V a Under constant voltage, the pre-lithiation material decomposes fully; the second pulse charge-discharge cycle accelerates formation while reducing cell polarization, allowing the pre-lithiation material to decompose fully; charging continues until the second decomposition voltage V is reached. b This allows for a more complete secondary decomposition of the pre-lithiation material; the third pulse charge-discharge method reduces cell polarization and promotes the full decomposition of the pre-lithiation material. In summary, through the synergistic relationship of the above steps, the lithium replenishment material in the battery can fully exert its lithium replenishment effect while shortening the formation time and reducing polarization, thereby improving battery performance.

[0064] One embodiment of the present invention introduces a three-step pulse charge-discharge process, which significantly reduces the formation process, decreasing the formation time by more than two hours compared to existing methods, thereby lowering production costs. Furthermore, it reduces polarization in pre-lithiated batteries, resulting in more complete decomposition of the lithium replenishment material and improving battery performance.

[0065] The pre-lithiated battery obtained by the method of one embodiment of the present invention has good storage performance and cycle performance.

[0066] This invention does not specifically limit the type of pre-lithiation material; for example, it can be Li5FeO4, and the first decomposition voltage V of this material... a The second decomposition voltage is 3.7V. b It is 4.1V.

[0067] In one embodiment, the battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode to isolate the positive electrode from the negative electrode.

[0068] In one embodiment, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, wherein the positive active layer includes a positive active material, a first conductive agent, a first binder, and a lithium supplementation material.

[0069] In one embodiment, the positive current collector is aluminum foil.

[0070] In one embodiment, the first conductive agent comprises carbon nanotubes (CNTs) and Super P (SP).

[0071] In one embodiment, the first adhesive is polyvinylidene fluoride (PVDF).

[0072] In one embodiment, the mass ratio of the positive electrode active material, the first conductive agent, the first binder, and the lithium replenishing material is (90-96):(0.5-3):(0.5-3):(1-4), wherein the positive electrode active material is selected from the range of "90-96", for example, it can be 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, or 96, etc.; the first conductive agent is selected from the range of "0.5-3", for example, it can be 0.5, 1, 1.5, 2, 2.5, or 3, etc.; the first binder is selected from the range of "0.5-3", for example, it can be 0.5, 1, 1.5, 2, 2.5, or 3, etc.; and the lithium replenishing material is selected from the range of "1-4", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5, or 4, etc.

[0073] In one embodiment, the method for preparing the positive electrode includes the following steps: homogenizing the positive electrode active material, the first conductive agent, the first binder and the lithium supplement material in a solvent to obtain a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then drying and cold pressing to obtain the positive electrode.

[0074] In one embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material, a second conductive agent, and a second binder.

[0075] In one embodiment, the negative current collector is a copper foil.

[0076] In one embodiment, the second conductive agent comprises Super P.

[0077] In one embodiment, the second binder comprises styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC).

[0078] In one embodiment, the mass ratio of the negative electrode active material, the second conductive agent, and the second binder is (91-97):(0.5-3):(1-5), wherein the negative electrode active material is selected from the range of "91-97", for example, it can be 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, or 97, etc.; the second conductive agent is selected from the range of "0.5-3", for example, it can be 0.5, 1, 1.5, 2, 2.5, or 3, etc.; the second binder is selected from the range of "1-5", for example, it can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5, etc.

[0079] In one embodiment, the method for preparing the negative electrode includes the following steps: homogenizing the negative electrode active material, the second conductive agent, and the second binder in a solvent to obtain a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then drying and cold pressing to obtain the negative electrode.

[0080] In one embodiment, the diaphragm includes a base membrane and a ceramic layer disposed on at least one surface of the base membrane, the ceramic layer including an adhesive and a ceramic material.

[0081] In one embodiment, the base film includes a (polyethylene) PE film, a (polypropylene) PP film, or a composite film of PE and PP. In one embodiment, the battery assembly method is as follows: the positive electrode, the negative electrode, and the separator are wound into a bare cell, the bare cell is placed into a casing and welded, baked, and filled with electrolyte to obtain the battery.

[0082] In one embodiment, during the first pulsed charge-discharge process, the forward current is 0.5C to 1C, for example, 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, or 1C; the reverse current is 0.2C to 0.4C, for example, 0.2C, 0.3C, or 0.4C. After pre-charging, the SEI film continues to grow with buffering; therefore, constant current high-rate charging cannot be used, otherwise it will affect the film formation performance. The first pulsed charge-discharge process provided by one embodiment of the present invention uses a large current for charging and discharging, which can accelerate formation while reducing cell polarization, making the SEI film more stable.

[0083] In one implementation, V a -V1 is 0.1V to 0.3V, for example, it can be 0.1V, 0.15V, 0.2V, 0.25V or 0.3V, etc.

[0084] In one embodiment, after the voltage rises to V1, the cell is allowed to stand for 2 to 4 minutes, for example, 2.5 minutes, 3 minutes, 3.5 minutes, or 4 minutes. This standing period reduces cell polarization, allowing the cell to reach the first decomposition voltage V1. a Make preparations.

[0085] In one embodiment, during the second pulsed charging and discharging process, the forward current is 0.1C-0.4C, for example, 0.1C, 0.2C, 0.3C, or 0.4C; the reverse current is 0.1C-0.2C, for example, 0.1C, 0.15C, or 0.2C. During the second pulsed charging and discharging process, since the voltage has exceeded the first decomposition voltage V... a If the charge / discharge rate is too high, although the formation rate is fast, the lithium replenishment material will not be able to react fully; if the charge / discharge rate is too low, the formation rate will be slowed down and the time will be prolonged. Considering the above, under the above-mentioned limited charge / discharge rate conditions, the lithium replenishment material can react fully and has a high formation rate.

[0086] In one implementation, V b -V2 is 0.1V to 0.3V, for example, it can be 0.1V, 0.15V, 0.2V, 0.25V or 0.3V, etc.

[0087] In one embodiment, after the voltage reaches V2, the material is left to stand for 4 to 6 minutes, for example, 4 minutes, 5 minutes, or 6 minutes. This standing time facilitates the complete decomposition of the pre-lithiated material.

[0088] In one embodiment, during the third pulsed charge-discharge process, the forward current is 0.05C to 0.2C, for example, it can be 0.05C, 0.07C, 0.1C, 0.12C, 0.15C, 0.18C, or 0.2C; the reverse current is 0.03C to 0.05C, for example, it can be 0.03C, 0.04C, or 0.05C.

[0089] In one implementation, V3-V b The voltage range is 0 to 0.2V, for example, it can be 0, 0.01V, 0.03V, 0.05V, 0.08V, 0.1V, 0.13V, 0.16V, 0.18V, or 0.2V, etc. When the value is 0, it represents V3 and V... b equal.

[0090] In one embodiment, after the voltage reaches V3, the material is left to stand for 5 to 10 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes. This standing time facilitates the complete decomposition of the pre-lithiated material.

[0091] In one embodiment, after the third pulse charge-discharge, a fourth pulse charge-discharge is performed to bring the voltage to V4, where V4 ≥ V b Introducing this step facilitates the full decomposition of the lithium replenishing material at or slightly above the second decomposition voltage, resulting in a smaller subsequent voltage rebound. This allows the material to maintain a higher voltage state during the subsequent aging process, which is more conducive to the decomposition of the lithium replenishing material during aging.

[0092] In one embodiment, during the fourth pulse charging and discharging process, the forward current is 0.05C to 0.2C, for example, it can be 0.05C, 0.07C, 0.1C, 0.12C, 0.15C, 0.18C, or 0.2C; the reverse current is 0.03C to 0.05C, for example, it can be 0.03C, 0.04C, or 0.05C.

[0093] In one implementation, V4-V b The voltage range is 0 to 0.2V, for example, it can be 0, 0.01V, 0.03V, 0.05V, 0.08V, 0.1V, 0.13V, 0.16V, 0.18V, or 0.2V, etc. When the value is 0, it represents V4 and V... b equal.

[0094] In one embodiment, after the voltage reaches V4, the material is allowed to stand for 5 to 10 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes. This standing time facilitates the complete decomposition of the pre-lithiated material.

[0095] In one embodiment, the pre-charging includes:

[0096] S100: First, charge with a current of 0.05C to 0.1C (e.g., 0.05C, 0.07C, or 0.1C) for 10 to 30 minutes (e.g., 10 minutes, 15 minutes, 20 minutes, 25 minutes, or 30 minutes), then let stand for 2 to 4 minutes (e.g., 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, or 4 minutes).

[0097] S200, then charge with a current of 0.2C to 0.3C (e.g., 0.2C, 0.22C, 0.25C, 0.27C, or 0.3C) for 50-70 minutes (e.g., 50 minutes, 55 minutes, 60 minutes, 65 minutes, or 70 minutes), and let stand for 2-4 minutes (e.g., 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, or 4 minutes).

[0098] Step S100 uses a small current to activate the cell, allowing it to form a film slowly at the beginning of film formation. Step S200 appropriately increases the small current to accelerate film formation while ensuring the formation of a dense and stable SEI film. The settling steps in steps S100 and S200 contribute to the uniform formation and stabilization of the SEI film.

[0099] In one embodiment, the first pulse charge-discharge is performed when the battery is precharged to 20% SOC.

[0100] The first 20% of the battery's SOC is generally the SOC range for film formation, so precharging within this range is beneficial for film formation.

[0101] In one embodiment, the constant current and constant voltage charging process includes sequential constant current charging and constant voltage charging, with constant voltage charging reaching a preset cutoff current and then stopping charging.

[0102] In one embodiment, the constant current charging current is 0.2C to 0.3C, for example, it can be 0.2C, 0.22C, 0.25C, 0.27C, or 0.3C. Since the pre-lithiation material does not produce much gas during decomposition under the first decomposition voltage, the above-mentioned current can be used for constant current charging, resulting in a better formation effect.

[0103] In one embodiment, the preset cutoff current is 0.04C to 0.06C, for example, it can be 0.04C, 0.05C or 0.06C.

[0104] In one embodiment, the device is charged to the first decomposition voltage V using a constant current and constant voltage method.a After that, let it stand for 4 to 6 minutes, for example, 4 minutes, 4.5 minutes, 5 minutes, 5.5 minutes or 6 minutes.

[0105] In one embodiment, the battery is charged to the second decomposition voltage V using a constant current charging method. b .

[0106] In one embodiment, the constant current charging current is 0.04C to 0.06C, for example, it can be 0.04C, 0.05C or 0.06C.

[0107] Under low current conditions, constant current charging is performed until the second decomposition voltage V is reached. b This process allows the lithium-supplementing material to decompose fully.

[0108] In one embodiment, the battery is charged to the second decomposition voltage V. b After that, let it stand for 5 to 10 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes.

[0109] In one embodiment, the charging to the second decomposition voltage V b Then, before the third pulse charge / discharge, perform the following steps: charge to V5 using a current of 0.01C to 0.03C (0.01V, 0.02V, or 0.03V, etc.), where V5 ≥ V b Introducing this step allows for a more complete decomposition of the lithium-replenishing material.

[0110] In one implementation, V5-V b The voltage range is 0 to 0.2V, for example, it can be 0, 0.01V, 0.03V, 0.05V, 0.08V, 0.1V, 0.13V, 0.16V, 0.18V, or 0.2V, etc. When the value is 0, it represents V5 and V... b equal.

[0111] In one embodiment, after charging to V5, the battery is left to stand for 5 to 10 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes.

[0112] In one embodiment, the formation method satisfies at least one of the following conditions (1)-(4):

[0113] (1) Perform a second pulse charge and discharge to make the voltage reach V2, and then let it stand under positive pressure. Preferably, after standing, the gas is discharged by using negative pressure.

[0114] (2) Charge to the second decomposition voltage V bThen, let it stand under positive pressure, preferably let it stand and then use negative pressure to discharge the gas;

[0115] (3) Perform the third pulse charge and discharge to make the voltage reach V3, and then let it stand under positive pressure. Preferably, after standing, the gas is discharged by using negative pressure.

[0116] (4) Charge to V5 and let stand under positive pressure. Preferably, let stand and then use negative pressure to discharge the gas.

[0117] In this embodiment of the invention, as the lithium-supplementing material decomposes, gas (e.g., O2) is generated. However, since the bubbles are generated at the interface, it is difficult to remove the gas using conventional negative pressure formation methods.

[0118] One embodiment of the present invention can directly squeeze out small bubbles that are difficult to remove by introducing positive pressure and allowing them to stand in at least one of the conditions (1)-(4), or form large bubbles and then extract them by negative pressure.

[0119] One embodiment of the present invention breaks through the previous method of formation under negative pressure throughout the process and introduces a positive pressure method to more effectively remove generated gas, resulting in a better interface and thus improving battery performance.

[0120] In one embodiment, the positive pressure in options (1)-(4) above is independently 40 kPa to 50 kPa, for example, it can be 40 kPa, 41 kPa, 42 kPa, 43 kPa, 44 kPa, 45 kPa, 46 kPa, 47 kPa, 48 kPa, 49 kPa or 50 kPa, etc.

[0121] Preferably, the duration of the positive pressure in options (1)-(4) above is 1 min to 3 min, for example, it can be 1 min, 1.5 min, 2 min, 2.5 min or 3 min, etc.

[0122] In another embodiment of the present invention, a pre-lithiated battery is provided, which is formed using the method described above. In the pre-lithiated battery formed using the above method, the lithium-replenishing material undergoes sufficient decomposition and reaction, thereby achieving a good lithium-replenishment effect and improving the electrochemical performance of the pre-lithiated battery. The pre-lithiated battery formed by this method exhibits good storage performance and cycle performance.

[0123] Based on the above implementation methods, the following typical but non-limiting embodiments are provided:

[0124] In the following embodiments, the specific types and parameters of the batteries to be formed are as follows:

[0125] The positive electrode includes an aluminum foil (12 μm thick) and positive electrode active layers on both sides. The positive electrode active layers include positive electrode active material, CNT, SP, PVDF and lithium supplementation material. The positive electrode active material is lithium iron phosphate and the lithium supplementation material is Li5FeO4 (abbreviated as LFO). The ratio of positive electrode active material: CNT: PVDF: Li5FeO4: SP (mass ratio) is 95.5:0.4:1.5:2:0.6.

[0126] The negative electrode includes a copper foil (6 μm thick) and negative electrode active layers on both sides. The negative electrode active layers include negative electrode active material, SP, CMC and SBR. The negative electrode active material is a carbon material. The ratio of negative electrode active material to SP:CMC:SBR (mass ratio) is 96.5:0.6:1.1:1.8.

[0127] The membrane includes a PE base film (7 μm thick) and ceramic layers (3 μm thick on each side) disposed on both surfaces of the PE base film. The ceramic layers include PVDF and ceramic materials, with a PVDF:ceramic material (mass ratio) of 1:7.

[0128] Example 1

[0129] This embodiment provides a battery formation method, including the following steps:

[0130] Step 1: Secure the battery in the restraint tray and apply external pressure to the battery to prevent the cell from bulging and deforming during the formation process;

[0131] Step 2: Charge the battery with a small current of 0.05C for 30 minutes to activate the battery cell, then let it stand for 3 minutes.

[0132] Step 3: Charge with a small current of 0.2C for 60 minutes, then let stand for 3 minutes;

[0133] Step 4 involves the first pulse charge and discharge cycle, wherein the forward charge is performed by charging with a forward current of 0.6C for 60 seconds every 3 seconds, and the negative discharge is performed by discharging with a reverse current of 0.2C for 10 seconds every 2 seconds, until the voltage reaches 3.5V, and then resting for 3 minutes.

[0134] Step 5 involves constant current and constant voltage charging to 3.7V (the first decomposition voltage plateau of Li5FeO4), where the constant current charging current is 0.2C, the cutoff current is 0.05C, and the charge is left to stand for 5 minutes.

[0135] Step 6 involves the second pulse charge and discharge cycle, wherein the forward charge is performed at 0.2C for 60 seconds every 5 seconds; the negative discharge is performed at 0.1C for 10 seconds every 3 seconds; after charging to 3.9V, the device is left to stand for 5 minutes.

[0136] Step 7: Charge the product to 4.1V (the second decomposition voltage plateau of Li5FeO4) using a small current of 0.05C, and let it stand for 8 minutes.

[0137] Step 8: Charge to 4.1V using a small current of 0.01C, and let stand for 7 minutes;

[0138] Step 9 performs the third pulse charge and discharge, wherein the forward charge is performed at 0.05C for 60 seconds every 5 seconds; the negative discharge is performed at 0.03C for 10 seconds every 3 seconds, charging to 4.1V and then resting for 8 minutes.

[0139] Step 10 performs the fourth pulse charge and discharge, wherein the forward charge is performed at 0.05C for 60 seconds every 5 seconds; the negative discharge is performed at 0.03C for 10 seconds every 3 seconds, charging to 4.1V and then resting for 8 minutes.

[0140] In the above-mentioned lithium replenishment formation process, during the standing process in steps 6, 7, 8, and 9, the vacuum is broken for 1 minute, the positive pressure is 50 kPa for 2 minutes, and the negative pressure of -70 kPa continues after the positive pressure. The remaining process is under negative pressure of -70 kPa throughout.

[0141] The pre-lithiated battery obtained after formation in this embodiment is denoted as A1.

[0142] Example 2

[0143] This embodiment provides a battery formation method, including the following steps:

[0144] Step 1: Secure the battery in the restraint tray and apply external pressure to the battery to prevent the cell from bulging and deforming during the formation process;

[0145] Step 2: Charge the battery with a small current of 0.05C for 30 minutes to activate the battery cell, then let it stand for 3 minutes.

[0146] Step 3: Charge with a small current of 0.2C for 60 minutes, then let stand for 3 minutes;

[0147] Step 4 involves the first pulse charge and discharge cycle, wherein the forward charge is performed by charging with a forward current of 0.8C for 60 seconds every 3 seconds, and the negative discharge is performed by discharging with a reverse current of 0.3C for 10 seconds every 2 seconds, until the voltage reaches 3.5V, and then resting for 3 minutes.

[0148] Step 5 involves constant current and constant voltage charging to 3.7V (the first decomposition voltage plateau of Li5FeO4), where the constant current charging current is 0.2C, the cutoff current is 0.05C, and the charge is left to stand for 5 minutes.

[0149] Step 6 involves the second pulse charge and discharge cycle, wherein the forward charge is performed at 0.4C for 60 seconds every 5 seconds; the negative discharge is performed at 0.2C for 10 seconds every 3 seconds; the voltage is charged to 3.9V and then left to stand for 5 minutes.

[0150] Step 7: Charge the battery with a small current of 0.05C to 4.1V (the second decomposition voltage plateau of Li5FeO4), and let it stand for 10 minutes.

[0151] Step 8: Charge to 4.1V using a small current of 0.01C, and let stand for 5 minutes;

[0152] Step 9 performs the third pulse charge and discharge, wherein the forward charge is performed at 0.08C for 60 seconds every 5 seconds; the negative discharge is performed at 0.04C for 10 seconds every 3 seconds, charging to 4.1V and then resting for 8 minutes.

[0153] Step 10 performs the fourth pulse charge and discharge, wherein the forward charge is performed by charging at 0.05C for 60 seconds every 5 seconds; the negative discharge is performed by discharging at 0.03C for 10 seconds every 3 seconds, charging to 4.1V, and then resting for 10 minutes.

[0154] In the above-mentioned lithium replenishment formation process, during the standing process in steps 6, 7, 8, and 9, the vacuum is broken for 1 minute, the positive pressure is 40 kPa for 2 minutes, and the negative pressure of -70 kPa continues after the positive pressure. The remaining process is under negative pressure of -70 kPa throughout.

[0155] The pre-lithiated battery obtained after formation in this embodiment is denoted as A2.

[0156] Example 3

[0157] This embodiment provides a battery formation method, including the following steps:

[0158] Step 1: Secure the battery in the restraint tray and apply external pressure to prevent the battery cell from bulging and deforming during the formation process;

[0159] Step 2: Charge the battery with a small current of 0.08C for 20 minutes to activate the battery cell, then let it stand for 4 minutes.

[0160] Step 3: Charge with a small current of 0.25 for 50 minutes, then let stand for 3 minutes;

[0161] Step 4 involves the first pulse charge and discharge cycle, wherein the forward charge is performed by charging with a 1C forward current for 60 seconds every 3 seconds, and the negative discharge is performed by discharging with a 0.4C reverse current for 10 seconds every 2 seconds, until the voltage reaches 3.5V, and then resting for 3 minutes.

[0162] Step 5 involves constant current and constant voltage charging to 3.7V (the first decomposition voltage plateau of Li5FeO4), where the constant current charging current is 0.2C, the cutoff current is 0.05C, and the charge is left to stand for 5 minutes.

[0163] Step 6 performs the second pulse charge and discharge, wherein the forward charge is performed at 0.3C for 60 seconds every 5 seconds; the negative discharge is performed at 0.15C for 10 seconds every 3 seconds; charge to 3.9V and let stand for 5 minutes.

[0164] Step 7: Charge the product to 4.1V (the second decomposition voltage plateau of Li5FeO4) using a small current of 0.05C, and let it stand for 8 minutes.

[0165] Step 8: Charge to 4.1V using a small current of 0.01C, and let stand for 7 minutes;

[0166] Step 9 involves the third pulse charge and discharge cycle. Forward charging is performed at 0.15C for 60 seconds every 5 seconds; negative discharging is performed at 0.05C for 10 seconds every 3 seconds. The voltage is charged to 4.1V and then left to stand for 8 minutes.

[0167] Step 10 performs the fourth pulse charge and discharge, wherein the forward charge is performed by charging at 0.1C for 60 seconds every 5 seconds; the negative discharge is performed by discharging at 0.05C for 10 seconds every 3 seconds, charging to 4.1V, and then resting for 5 minutes.

[0168] In the above-mentioned lithium replenishment formation process, during the standing process in steps 6, 7, 8, and 9, the vacuum is broken for 1 minute, the positive pressure is 45 kPa for 1 minute, and the negative pressure is continued at -60 kPa after the positive pressure. The remaining process is under negative pressure at -60 kPa throughout.

[0169] The pre-lithiated battery obtained after formation in this embodiment is denoted as A3.

[0170] Example 4

[0171] This embodiment provides a battery formation method, which differs from Embodiment 1 in that step 10 is not performed.

[0172] The pre-lithiated battery obtained after formation in this embodiment is denoted as A4.

[0173] Comparative Example 1

[0174] This comparative example provides a battery formation method, which differs from Example 1 in that:

[0175] Step 4 is to charge the battery to 3.5V using a 0.4C charge and let it stand for 3 minutes.

[0176] Step 6 is: charge to 3.9V using 0.1C and let stand for 5 minutes.

[0177] Step 9 is to charge the battery to 4.1V using a small current of 0.01C and let it stand for 8 minutes.

[0178] Step 10 is: charge to 4.1V with a small current of 0.01C and let stand for 8 minutes.

[0179] The pre-lithiated battery obtained after formation in this comparative example is denoted as B1.

[0180] Comparative Example 2

[0181] This comparative example provides a battery formation method, which differs from Example 1 in that:

[0182] Step 4 is to charge the battery to 3.5V using a 0.4C charge and let it stand for 3 minutes.

[0183] The pre-lithiated battery obtained after formation in this comparative example is denoted as B2.

[0184] Comparative Example 3

[0185] This comparative example provides a battery formation method, which differs from Example 1 in that:

[0186] Step 6 is: charge to 3.9V using 0.1C and let stand for 5 minutes.

[0187] The pre-lithiated battery obtained after formation in this comparative example is denoted as B3.

[0188] Comparative Example 4

[0189] This comparative example provides a battery formation method, which differs from Example 1 in that:

[0190] Step 9 is to charge the battery to 4.1V using a small current of 0.01C and let it stand for 8 minutes.

[0191] Step 10 is: charge to 4.1V with a small current of 0.01C and let stand for 8 minutes.

[0192] The pre-lithiated battery obtained after formation in this comparative example is denoted as B4.

[0193] Comparative Example 5

[0194] This comparative example provides a battery formation method, which differs from Example 1 in that the lithium replenishment formation process is conducted under a negative pressure of -70 kPa throughout.

[0195] The pre-lithiated battery obtained after formation in this comparative example is denoted as B5.

[0196] The formation times of Examples 1-4 and Comparative Examples 1-5 are recorded in Table 1.

[0197] The pre-lithiated batteries obtained by the formation methods of Examples 1-4 and Comparative Examples 1-5 were subjected to the following tests:

[0198] (1) Interface test: Disassemble the pre-lithiated battery to check whether there are phenomena such as lithium plating, bubbles and black spots on the negative electrode interface.

[0199] (2) Gas production from the decomposition of pre-lithiated materials: The gas production of the pre-lithiated battery was collected and recorded by a gas flow meter.

[0200] (3) Aging voltage: The voltage is measured and the data is recorded before the cell ages.

[0201] (4) Storage performance: Store at 25℃ for 1 month and observe the swelling.

[0202] (5) Cycling performance: Under 0.5P charge and discharge conditions, the system is cycled 5000 times at a high temperature of 60℃. The discharge capacity of the first cycle and the discharge capacity of the 5000th cycle are recorded. The capacity retention rate is calculated as follows: Capacity retention rate = discharge capacity of the 5000th cycle / discharge capacity of the first cycle × 100%.

[0203] The results are shown in Table 1.

[0204] Table 1

[0205]

[0206]

[0207] As shown in Table 1, the formation method of the present invention can reduce the formation time, increase the aging voltage, and achieve more complete decomposition of the pre-lithiated material.

[0208] Meanwhile, a comparison between Example 1 and Comparative Example 5 shows that by introducing positive pressure, the previous method of creating a negative pressure vacuum can be broken through, which can more effectively remove gas and improve the black spots on the interface bubbles.

[0209] A comparison between Example 1 and Example 4 shows that the pulse charge and discharge in step 10 is beneficial for cell depolarization, promotes the decomposition of the lithium replenishment material LFO under the second decomposition voltage, and at the same time makes the aging voltage higher, promoting the decomposition of LFO during the aging process.

[0210] The comparison between Example 1 and Comparative Examples 1-4 shows that the formation process is greatly reduced by using three-stage pulse charge and discharge. This can effectively reduce the formation time, reduce pre-lithiation of the battery, avoid lithium plating at the cell interface, and make the lithium iron phosphate decomposition more complete. The voltage during aging is higher and closer to the lithium iron phosphate decomposition plateau, thereby improving the battery performance and improving the 60°C high-temperature cycling performance.

[0211] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0212] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for forming a battery, the battery comprising a pre-lithiation material, wherein the decomposition voltage of the pre-lithiation material includes a first decomposition voltage V. a Second decomposition voltage V b Its characteristics are, The formation method includes performing the following operations on the battery in sequence: Precharge; Perform the first pulse charge and discharge to raise the voltage to V1, V1 <V a ; The device is charged to the first decomposition voltage V using constant current and constant voltage. a ; Perform a second pulse charge and discharge to bring the voltage to V2, V a <V2<V b ; Charge to the second decomposition voltage V b ; Perform a third pulse charge / discharge to bring the voltage to V3, where V3 ≥ V b .

2. The battery formation method according to claim 1, characterized in that, During the first pulse charging and discharging process, the forward current is 0.5C-1C, and the reverse current is 0.2C-0.4C. Preferably, V a -V1 is 0.1V to 0.3V; Preferably, after the voltage rises to V1, let it stand for 2 to 4 minutes.

3. The battery formation method according to claim 1 or 2, characterized in that, During the second pulse charging and discharging process, the forward current is 0.1C-0.4C, and the reverse current is 0.1C-0.2C. Preferably, V b -V2 is 0.1V to 0.3V; Preferably, after the voltage reaches V2, let it stand for 4 to 6 minutes.

4. The battery formation method according to any one of claims 1-3, characterized in that, During the third pulsed charge-discharge process, the forward current is 0.05C to 0.2C, and the reverse current is 0.03C to 0.05C. Preferably, V3-V b The voltage range is 0 to 0.2V. Preferably, after the voltage reaches V3, let it stand for 5 to 10 minutes.

5. The battery formation method according to any one of claims 1-4, characterized in that, After the third pulse charge-discharge, a fourth pulse charge-discharge is performed to bring the voltage to V4, where V4 ≥ V. b ; Preferably, during the fourth pulse charging and discharging process, the forward current is 0.05C to 0.2C, and the reverse current is 0.03C to 0.05C. Preferably, V4-V b The voltage range is 0 to 0.2V. Preferably, after the voltage reaches V4, let it stand for 5 to 10 minutes.

6. The battery formation method according to any one of claims 1-5, characterized in that, The pre-charge includes: First, charge with a current of 0.05C to 0.1C for 10 to 30 minutes, then let stand for 2 to 4 minutes; Then charge with a current of 0.2C to 0.3C for 50 to 70 minutes, and let stand for 2 to 4 minutes; Preferably, the first pulse charge-discharge is performed when the battery is pre-charged to 20% SOC.

7. The battery formation method according to any one of claims 1-6, characterized in that, The constant current and constant voltage charging process includes sequential constant current charging and constant voltage charging, with constant voltage charging reaching a preset cutoff current and then stopping charging. Preferably, the constant current charging current is 0.2C to 0.3C; Preferably, the preset cutoff current is 0.04C to 0.06C; Preferably, the constant current and constant voltage charging is performed until the first decomposition voltage V is reached. a Then, let it stand for 4 to 6 minutes.

8. The battery formation method according to any one of claims 1-7, characterized in that, Charge to the second decomposition voltage V using constant current charging. b ; Preferably, the constant current charging current is 0.04C to 0.06C; Preferably, charging to the second decomposition voltage V b Then, let it stand for 5 to 10 minutes; Preferably, the charging to the second decomposition voltage V b Then, before the third pulse charge / discharge, perform the following steps: charge to V5 using a current of 0.01C to 0.03C, where V5 ≥ V b ; Preferably, V5-V b The voltage range is 0 to 0.2V. Preferably, after charging to V5, let it stand for 5 to 10 minutes.

9. The battery formation method according to any one of claims 1-8, characterized in that, The formation method shall satisfy at least one of the following conditions (1)-(4): (1) Perform a second pulse charge and discharge to make the voltage reach V2, and then let it stand under positive pressure. Preferably, after standing, the gas is discharged by using negative pressure. (2) Charge to the second decomposition voltage V b Then, let it stand under positive pressure, preferably let it stand and then use negative pressure to discharge the gas; (3) Perform the third pulse charge and discharge to make the voltage reach V3, and then let it stand under positive pressure. Preferably, after standing, the gas is discharged by using negative pressure. (4) Charge to V5 and let stand under positive pressure. Preferably, after standing, use negative pressure to discharge the gas. Preferably, the positive pressure in options (1)-(4) above is independently 40 kPa to 50 kPa; Preferably, the duration of the positive pressure in options (1)-(4) above is 1 min to 3 min.

10. A pre-lithiated battery, formed using the methods of claims 1-9.

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