Lithium-rich manganese-based battery low-voltage formation method and application thereof

Abstract

The invention discloses a lithium-rich manganese-based battery low-voltage formation method and application thereof, and relates to the technical field of lithium batteries. The formation step is carried out after the standing step, in the low-voltage formation process, a constant-current charging mode is adopted to regulate and control the voltage to carry out formation on the battery so as to activate different lithium-rich manganese-based phases, and the activation degree of the Li2MnO3 phase in the positive electrode material is effectively controlled in the circulation process, so that the trend that the initial capacity is increased is shown, and the circulation is stable; the effect of improving the cycling stability is achieved. According to the low-voltage formation method, the gas production rate in the formation and circulation process is reduced, the capacity retention rate in the circulation process is improved, the formation time can be saved, the energy consumption of battery production is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a low-voltage formation method for a lithium-rich manganese-based battery and an application thereof. Background Art

[0002] With the continuous development of mobile communication equipment, light electric vehicles and new energy storage fields, higher requirements are placed on the low cost, long life and high safety of lithium-ion batteries. Among them, the lithium-ion battery system with medium and low voltage lithium-rich manganese-based positive electrode materials as the new generation of positive electrode materials is recognized by the industry as the next generation of superior positive electrode materials. In the production process of lithium-ion secondary batteries, the formation process is an extremely important process. The quality of the formation is directly related to the capacity, cycle and safety of the battery.

[0003] Due to the presence of the xLi2MnO3·(1-x)LiTMO2 dual-domain structure, the requirements for the formation voltage of lithium-rich manganese-based positive electrode materials are higher than those of other single-phase positive electrode materials. The activation voltages of Li2MnO3 and LiTMO2 in lithium-rich materials are different. The Li2MnO3 phase can only be activated when the voltage is higher than 4.4V. As the voltage increases, the activation degree of the Li2MnO3 phase is different. Therefore, the battery performance of different lithium-rich manganese-based lithium-ion batteries at different formation voltages varies greatly. Traditional lithium-rich manganese-based batteries generally use a higher voltage for formation to fully utilize the capacity of the LiTMO2 phase and the Li2MnO3 phase. During the cycle, a lower voltage is used to achieve an excellent cycle retention rate. How to partially activate the Li2MnO3 phase at a low voltage and exert its capacity, improve the battery's first cycle coulomb efficiency, reduce the gas production during the formation and cycle process, and improve the capacity retention rate during the cycle while saving formation time is one of the technical problems that need to be solved in this field.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a low-voltage formation method for a lithium-rich manganese-based battery and its application to solve the above-mentioned technical problems.

[0006] The present invention is achieved in that:

[0007] In a first aspect, an embodiment of the present invention provides a low-voltage formation method for a lithium-rich manganese-based battery, the low-voltage formation method comprising a standing step and a formation step, wherein the formation step is performed after the standing step;

[0008] Among them, the formation step includes: using a current density of I1 to charge the lithium-rich manganese-based battery at a constant current to a voltage of V1, standing for t1 minutes, and then using a current density of I2 to discharge the lithium-rich manganese-based battery at a constant current to a voltage of V2, and the number of formation cycles is n cycles; wherein I1 is 0.01C-0.5C, V1 is 3.8V-4.4V, t1 is 3min-100min, I2 is 0.05C-1C, V2 is 1.5V-3V, and n is 1-5.

[0009] In a second aspect, an embodiment of the present invention provides an application of the low-voltage formation method as described above, and the low-voltage formation method is applied to at least one of the following devices:

[0010] (1) Lithium battery made of lithium-rich manganese-based materials; (2) Lithium ion battery made of lithium-rich manganese-based materials; (3) Lithium ion capacitor made of lithium-rich manganese-based materials.

[0011] The present invention has the following beneficial effects:

[0012] The low-voltage formation method of the lithium-rich manganese-based battery provided by the embodiment of the present invention is conducive to the electrolyte fully infiltrating the battery core, forming a uniform interface film at the electrode interface, and the negative electrode SEI film is more stable, which is conducive to forming a uniform interface film and improving the first cycle coulomb efficiency of the battery. In addition, during the formation process, the voltage is regulated by constant current charging to form the battery to activate different lithium-rich manganese-based phases. By effectively controlling the activation degree of the Li2MnO3 phase in the positive electrode material during the cycle, the initial capacity shows a trend of increasing, thereby stabilizing the cycle and achieving the effect of improving the cycle stability. The low-voltage formation method of the present invention reduces the gas production during the formation and cycle process, improves the capacity retention rate during the cycle process, and can save formation time, save energy consumption in battery production, and improve production efficiency.

[0013] The low-voltage formation method for lithium-rich manganese-based batteries provided in the embodiment of the present invention is applicable to lithium-rich manganese-based lithium batteries, lithium-rich manganese-based lithium ion batteries and lithium-rich manganese-based lithium ion capacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 The capacity retention rate curve of the lithium-rich manganese-based battery after 500 cycles in Experimental Examples 1-5 and Comparative Examples 1-4;

[0016] Figure 2The capacity retention rate curve of the lithium-rich manganese-based battery in the first 50 cycles in Experimental Example 1-5 and Comparative Example 1-4;

[0017] Figure 3 The charging capacity and charging voltage curves of the first formation process of the lithium-rich manganese-based battery in Comparative Example 3;

[0018] Figure 4 The charging capacity and charging voltage curves of the first formation process of the lithium-rich manganese-based battery in Comparative Example 4. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0020] In the production process of lithium-ion secondary batteries, the formation process is an extremely important process. The formation process is essentially the process of battery initialization. The quality of the formation is directly related to the battery's capacity, cycle and safety. Formation refers to the process of the battery's first few charge and discharge after injection. Its important purpose is to form the CEI film of the positive electrode and the SEI film of the negative electrode through the electrochemical reaction during the charge and discharge process. These films can help protect the stability of the material in subsequent cycles.

[0021] Conventional lithium-rich manganese-based battery materials have a dual-domain structure, which is different from general positive electrode materials. The formation of lithium-rich manganese-based materials generally has a critical voltage of about 4.4V. Voltages less than 4.4V will only activate the LiTMO2 phase to exert capacity, and cannot fully activate the Li2MnO3 phase. Therefore, traditional lithium-rich manganese-based batteries generally use a higher voltage formation to give full play to the capacity of the LiTMO2 phase and the Li2MnO3 phase, and then use a lower voltage during the cycle to achieve an excellent cycle retention rate. The present invention adopts a low-voltage formation method, that is, the degree of activation of the Li2MnO3 phase is not required under high voltage, so that the Li2MnO3 phase is partially activated to exert a certain capacity, and the other part that is not activated can slowly release capacity in subsequent cycles, thereby improving the cycle stability of the battery.

[0022] In a first aspect, an embodiment of the present invention provides a low-voltage formation method for a lithium-rich manganese-based battery. The low-voltage formation method includes a standing step and a formation step, and the formation step is performed after the standing step.

[0023] Among them, the formation step includes: using a current density of I1 to charge the lithium-rich manganese-based battery at a constant current to a voltage of V1, standing for t1 minutes, and then using a current density of I2 to discharge the lithium-rich manganese-based battery at a constant current to a voltage of V2, and the number of formation cycles is n cycles; wherein I1 is 0.01C-0.5C, V1 is 3.8V-4.4V, t1 is 3min-100min, I2 is 0.05C-1C, V2 is 1.5V-3V, and n is 1-5.

[0024] It should be noted that battery formation, also known as battery aging, is an important process in the production of lithium-ion batteries. Its principle is to activate the internal positive and negative electrode materials through a specific charging and discharging method to improve the battery's charging and discharging performance and improve the battery's comprehensive performance in its initial manufacturing stage, such as self-discharge and storage. The main factors affecting the quality of formation are formation current, formation voltage, formation temperature and external pressure.

[0025] If the formation voltage is higher than the set value, "white spots" will appear on the negative electrode of the battery at a higher voltage. The "white spots" are metallic lithium or lithium compounds deposited on the surface of the negative electrode. The production of this compound on the negative electrode material is an irreversible reaction, which leads to excessive lithium or lithium compounds being embedded on the surface of the negative electrode. At the same time, this also leads to low initial efficiency and large internal resistance of the electrode during battery formation, which in turn affects the battery cycle performance. At a higher voltage, the final charge and discharge efficiency of the battery will be lower, the internal resistance of the electrode will be larger, and the cycle performance will be lower.

[0026] Reasonable setting of formation temperature can improve the cycle performance and storage performance of the battery. This is because the SEI film layer can fully react at a slightly higher temperature, enhance the liquid absorption of the diaphragm and reduce the gas expansion of the battery; but high temperature will also aggravate the dissolution of the SEI film and the co-embedding of solvent molecules, which will bring some other problems, such as reducing the stability of the SEI film, the SEI film cannot protect the electrode well, and will further lead to poor battery cycle performance. Therefore, a slightly higher formation temperature can not only ensure the structure and composition of the SEI film, but also take into account the efficiency and speed of SEI production.

[0027] Applying appropriate pressure during the charging process can significantly eliminate the gas generated by the battery during the formation process (organic matter decomposes under high pressure to produce gas). The presence of gas will eventually lead to a decrease in the battery charging capacity. Applying external pressure to eliminate gas can not only increase the battery formation capacity, but also significantly improve the battery rate and cycle performance. At the same time, applying appropriate pressure can also help eliminate lithium precipitation on the negative electrode.

[0028] Reasonable control of the formation current density makes it easier to obtain a uniform and dense SEI film. Studies have found that low current density formation can effectively increase the content of inorganic components in the inner layer of the SEI film, thereby improving the electrochemical performance of lithium-ion batteries. After formation with a smaller current, the inorganic components of the SEI film formed on the surface of the negative electrode account for a larger proportion, and the inner layer is thicker and more uniform and dense than the outer layer, which can not only better cover and wrap the negative electrode material, but also significantly improve the stability of the SEI film. However, long-term low-current charging will increase the impedance of the SEI film, thereby affecting the battery's rate and cycle performance, and simple low-current formation will significantly increase the time required for formation, reducing workshop production efficiency. Studies have found that the use of a step-by-step current formation method in the constant current charging stage can not only reduce the polarization level of the battery and increase the charging capacity, but also effectively reduce the charging time and improve the formation efficiency.

[0029] The number of formation cycles n has a certain influence on the formation and stability of the SEI film. An appropriate number of formation cycles helps to form a denser and more stable SEI film, thereby improving the battery's cycle performance, rate performance, and internal resistance.

[0030] In an optional embodiment of the present invention, the standing step includes: standing the lithium-rich manganese-based battery cell after injection at a vacuum degree of P0 for a time of t2 to exhaust, releasing the vacuum, and then standing at a vacuum degree of P1 for a time of t3 to exhaust; then sealing at a temperature of T1 to make a battery; after the prepared battery is stood at a temperature of T2 for a time of t4, a pressure of P2 is applied to the battery to enhance the contact between the electrodes, and the battery is stood at a temperature of T3 for t5 hours.

[0031] Among them, P0 is -0.3MPa-0 MPa, t2 is 5min-60min, P1 is -0.3MPa-0 MPa, t3 is 5min-60min, T1 is 160℃-230℃, T2 is 25℃-60℃, t4 is 6h-48h, P2 is 50N / m 2 -200 N / m 2 , T3 is 20℃-60℃, and t5 is 1h-10h.

[0032] It should be noted that the reason for standing treatment at vacuum degree P0 and vacuum degree P1 and decompression treatment in the middle is to reduce bubbles in the diaphragm and positive and negative electrodes so that the electrolyte can fully penetrate into the battery cell. If the pressure is not released and the battery is directly placed at vacuum degree P0 for twice the time, it may lead to insufficient electrolyte infiltration, bubbles between the diaphragm and the electrode, which may easily cause low battery discharge capacity and poor electrochemical performance of the battery.

[0033] Further, in the standing step, P0 is -0.2MPa to -0.1MPa, t2 is 5min-20min, P1 is -0.2MPa to -0.1MPa, t3 is 5min-20min, T1 is 170℃-200℃, T2 is 30℃-45℃, t4 is 10h-15h, P2 is 60N / m 2 -100N / m 2 , T3 is 25℃-35℃, and t5 is 1h-1.5h.

[0034] It should be noted that if lithium-rich manganese-based batteries are not left to stand before formation, the electrolyte inside the battery will be uneven, the battery polarization will increase, the battery voltage will not be able to reach the set voltage during charging, and there will be certain safety hazards. On the premise of ensuring that the electrolyte fully infiltrates the battery cell, the battery's standing temperature and time can be slightly changed.

[0035] In an optional embodiment of the present invention, the lithium-rich manganese-based battery cell after injection is processed in the static step; before testing in the formation step, the lithium-rich manganese-based battery cell needs to be clamped and placed on the charging and discharging equipment.

[0036] In an optional embodiment of the present invention, in the formation step, I1 is 0.05C-0.15C, V1 is 4.0V-4.4V, t1 is 30min-60min, I2 is 0.05C-0.15C, and V2 is 2.0V-2.5V.

[0037] It should be noted that after the formation, the lithium-rich manganese-based battery is subjected to capacity separation and cycle testing. The highest voltage of the lithium-rich manganese-based battery during the cycle is V3, V3 is 4.2V-4.7V, and V1 <V3。

[0038] If V1>V3 of lithium-rich manganese-based batteries during the cycle test, the Li2MnO3 phase in the lithium-rich manganese-based material will be activated in the first cycle of formation, and oxygen will participate in the reaction, resulting in a low initial efficiency of the battery and more gas generation. The size of the formation current will affect the formation process and characteristics of the SEI film. When the formation voltage is large, the SEI film structure will be loose and not firmly attached to the negative electrode surface; at low current density, the SEI film structure will be denser. Choosing a suitable formation current has a great influence on the internal resistance, capacity and cycle performance of the battery.

[0039] It should be noted that the voltage during the formation process is lower than the voltage during the cycle process mainly due to the chemical reactions and physical changes inside the battery. During the formation process of the battery, the formation of the SEI film is an irreversible process, which consumes the lithium ions in the battery, resulting in a voltage drop; the formation of the SEI film also increases the resistance of the electrode / electrolyte interface, further resulting in voltage hysteresis. In addition, the internal resistance of the battery after formation is usually reduced because the formation of the SEI film reduces unnecessary energy loss and resistance, making the electrochemical reaction inside the battery more stable and efficient. Therefore, the voltage during the formation process is usually lower than the voltage during the cycle process.

[0040] The battery formation and capacity separation process is a key step in the entire battery production process, which helps to improve battery performance and capacity and make lithium-ion batteries popular in more application areas.

[0041] Capacity division is a process carried out after formation, which involves charging and discharging the battery and measuring various battery parameters, and then assembling the battery according to the measured parameters.

[0042] The significance of using the capacity division process is that due to manufacturing reasons, differences between cells are unavoidable. When the electrical device requires greater energy and power, multiple cells need to be connected in series and parallel to meet the application requirements. The consistency of the cells varies (cell consistency mainly refers to the consistency of open circuit voltage, charge and discharge capacity, self-discharge rate, average internal resistance and other indicators), which will directly affect the performance and service life of the battery system.

[0043] In an optional embodiment of the present invention, the lithium-rich manganese-based battery further comprises: preparing a positive electrode sheet of the battery and preparing a negative electrode sheet of the battery before low-voltage formation.

[0044] The preparation of the positive electrode sheet of the battery includes: mixing lithium-rich manganese-based positive electrode materials, conductive carbon black, carbon nanotubes and polyvinylidene fluoride with N-methylpyrrolidone in a mass ratio of (90-97): (1-3): (0.1-0.3): (1.5-2.0) to prepare a positive electrode slurry; the positive electrode slurry is coated, baked, the electrode moisture test (less than 200ppm), rolled and cut to obtain a battery positive electrode sheet.

[0045] The preparation of the battery negative electrode sheet includes: mixing graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of (90-100): (0.1-1.2): (1.8-2.5): (0.8-1.2) with water to prepare a negative electrode slurry; the negative electrode slurry is coated, baked, tested for electrode moisture (less than 200ppm), rolled and cut to obtain a battery negative electrode sheet.

[0046] In an optional embodiment of the present invention, the ratio of the above raw materials can be reasonably selected according to actual needs. Among them, the mass ratio of lithium-rich manganese-based positive electrode material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride in the battery positive electrode sheet is selected from any one of 91:2:0.2:1.8, 95:2:0.2:2.0, 96:2:0.2:1.8 and 97:2:0.25:2.0, or other values ​​in the range of (90-97):(1-3):(0.1-0.3):(1.5-2.0).

[0047] Furthermore, the mass ratio of the lithium-rich manganese-based positive electrode material, the conductive carbon black, the carbon nanotubes and the polyvinylidene fluoride is 96:2:0.2:1.8.

[0048] The mass ratio of graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in the battery negative electrode sheet is selected from any one of 93:0.5:2:0.9, 95:1:2:1, 96:1:2:1 and 98:1.2:2.3:1.2, or other values ​​within the range of (90-100):(0.1-1.2):(1.8-2.5):(0.8-1.2).

[0049] Furthermore, the mass ratio of graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) is 96:1:2:1.

[0050] It should be noted that the setting of the raw material ratio during the preparation of the positive electrode slurry or the negative electrode slurry has a great impact on the performance and quality of the battery. Too high viscosity will lead to flow difficulties and affect the uniformity of coating; too low viscosity will cause the slurry to be too fluid, which is prone to turbidity, foaming and other problems. In addition, the mixed materials are continuously stirred during the slurry preparation process to avoid particle aggregation and ensure that the microstructure of the slurry is uniform, thereby improving the performance and quality of the battery.

[0051] In order to ensure the stability and safety of battery materials during the baking process and avoid material damage or performance degradation due to excessive temperature or prolonged time, the baking temperature of the battery positive electrode is 100℃-115℃, and the baking temperature of the battery negative electrode is 118℃-125℃.

[0052] In an optional embodiment of the present invention, a battery positive electrode sheet, a battery negative electrode sheet and a separator are made into a dry battery cell, which is encapsulated with an aluminum-plastic film and then injected with a lithium salt electrolyte with a molar concentration of 0.9 mol / L-1.3 mol / L; the lithium salt electrolyte includes a lithium salt and an organic solvent; wherein the molar concentration of the lithium salt is preferably 1 mol / L, and the lithium salt is selected from any one of lithium carbonate (Li2CO3), lithium tetrafluoroborate (LiBF4) and lithium hexafluorophosphate (LiPF6), preferably lithium hexafluorophosphate (LiPF6).

[0053] The diaphragm in the battery plays the role of isolating the positive and negative electrode materials, and prevents the electrons in the battery from passing freely, allowing the ions in the electrolyte to pass freely between the positive and negative electrodes to prevent the battery from short-circuiting. The performance of the diaphragm directly affects the safety performance and capacity of the battery. High-quality diaphragms can provide good ion transmission performance, mechanical strength and chemical stability, ensuring the efficient operation and safety of the battery.

[0054] The type of the separator used in the embodiment of the present invention is selected from any one of a single-layer polyethylene (PE) film, a single-layer polypropylene (PP) film, a three-layer PP film, a three-layer PE film or a three-layer PP / PE composite film.

[0055] In an optional embodiment of the present invention, the organic solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and propylene carbonate (PC).

[0056] It should be noted that the lithium salt in the electrolyte plays the role of conducting ions and is a key component of the electrolyte; the organic solvent, which occupies a large proportion, is the main component of the electrolyte; the type of organic solvent can be reasonably adjusted according to actual conditions. The organic solvent in the present invention is a composite reagent, which can be selected from dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) / propylene carbonate (PC), ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) / ethylene carbonate (EC), ethylene carbonate (EC) / dimethyl carbonate (DMC) / diethyl carbonate (DEC) or other reasonable combinations.

[0057] Furthermore, the lithium salt is lithium hexafluorophosphate (LiPF6), and the electrolyte includes EMC, DEC and EC in a volume ratio of (1.8-2.2): (4.5-5.2): (2.5-3.3). The volume ratio of the organic solvent in the electrolyte is reasonably set according to the actual raw material components, and can be selected from any one of 1.8:4.8:3, 2:4.8:3.2, 2:5:3 and 2.2:5.2:3, or other values ​​within the range of (1.8-2.2): (4.5-5.2): (2.5-3.3).

[0058] Aluminum-plastic film is a key material for soft-pack lithium batteries. It has a wide range of applications due to its light weight, low mold cost, and high safety. Aluminum-plastic film can effectively isolate moisture and oxygen, maintain the internal environment of the battery cell, and prevent organic solvents inside the battery cell from reacting with moisture and oxygen to affect the electrochemical performance of the battery. In addition, packaging can protect the battery from the influence of the external environment and prevent leakage of internal battery substances, thereby reducing the probability of problems during battery use.

[0059] In an optional embodiment of the present invention, the positive electrode material of the lithium-rich manganese-based battery is xLi2MnO3·(1-x)LiTMO2, wherein TM is selected from at least one of Ni, Co, and Mn, and 0<x<1.

[0060] It should be noted that the positive electrode material of lithium-rich manganese-based batteries uses lithium-rich metal oxides. The use of lithium-rich manganese-based positive electrode materials has the following advantages: (1) Compared with iron-lithium positive electrode materials, lithium-rich positive electrode materials have higher gram capacity, and the lithium-ion batteries they form have higher energy density; (2) Lithium-rich manganese-based materials have good thermal stability, so they can improve the safety performance of lithium-ion batteries; (3) Compared with ternary materials, lithium-rich manganese-based materials mainly use manganese elements and are cheaper. At present, the cost of positive electrode materials in batteries accounts for more than 30%. Using lithium-rich manganese-based materials as positive electrodes is conducive to reducing the cost of battery materials.

[0061] Furthermore, the positive electrode material of the lithium-rich manganese-based battery is selected from Li 1.1 Mn 0.37 Ni 0.45 Co 0.18 O 2.1 and Li 1.1 Ni 0.45 Co 0.18 Mn 0.46 O 0.21 Any one of .

[0062] In a second aspect, an embodiment of the present invention provides an application of the low-voltage formation method as described above, and the low-voltage formation method is applied to at least one of the following devices:

[0063] (1) Lithium-rich manganese-based lithium batteries;

[0064] (2) Lithium-ion batteries made of lithium-rich manganese-based materials;

[0065] (3) Lithium-ion capacitors made of lithium-rich manganese-based materials.

[0066] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0067] Example 1

[0068] This embodiment provides a lithium-rich manganese-based battery cell, the preparation of which includes the following steps:

[0069] (1) Preparation of battery positive electrode

[0070] The lithium-rich manganese-based positive electrode material (Li 1.1 Mn 0.37 Ni 0.45 Co 0.18 O 2.1), conductive carbon black, carbon nanotubes and polyvinylidene fluoride, mixed with N-methylpyrrolidone, and the positive electrode slurry was stirred evenly to make positive electrode slurry. Then, the positive electrode sheet of the battery was obtained by coating, baking at 110°C, testing the moisture content of the electrode sheet (less than 200ppm), rolling and slitting.

[0071] (2) Preparation of battery negative electrode

[0072] Graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 96:1:2:1 are mixed with water, and the negative electrode slurry is stirred evenly to form the negative electrode slurry. Then, the negative electrode slurry is coated, baked at 120°C, tested for the moisture content of the electrode (less than 200ppm), rolled, and cut to obtain the negative electrode sheet of the battery.

[0073] (3) The prepared positive electrode sheet, negative electrode sheet and separator are prepared into a dry battery cell by stacking, encapsulating with an aluminum-plastic film, and injecting 1 mol / L LiPF6 EMC / DEC / EC=2:5:3 electrolyte to obtain a lithium-rich manganese-based battery cell.

[0074] Example 2

[0075] This embodiment provides a lithium-rich manganese-based battery cell, the preparation of which differs from that of embodiment 1 only in that:

[0076] (1) Preparation of battery positive electrode

[0077] Li-rich manganese-based cathode material is Li 1.1 Ni 0.45 Co 0.18 Mn 0.46 O 0.21 .

[0078] Experimental Example 1

[0079] This experimental example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 1. The specific process is as follows:

[0080] 1) Place the lithium-rich manganese-based battery cell under a vacuum of -0.15 MPa for 10 minutes and then release the vacuum.

[0081] 2) Continue to evacuate the chamber, leave it at a vacuum degree of -0.15 MPa for 10 min, and then release the vacuum.

[0082] 3) After evacuating for 3 seconds, the battery was sealed at 180°C to produce a lithium-rich manganese-based battery.

[0083] 4) Let stand at 30°C for 12 hours.

[0084] 5) Apply 80N / m to lithium-rich manganese-based batteries 2The external temperature is 25℃ and the formation duration is 1h.

[0085] The specific procedure for forming the lithium-rich manganese-based battery in this embodiment is: charging at a rate of 0.1C to 4.2V, standing for 1 hour, and then discharging at a rate of 0.1C to 2.5V to obtain a lithium-rich manganese-based battery with low voltage formation treatment.

[0086] Experimental Example 2

[0087] This experimental example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 1. The specific process is different from that of Experimental Example 1 in that:

[0088] 5) The formation procedure is: charge at a rate of 0.1C to 4.3V.

[0089] Experimental Example 3

[0090] This experimental example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 1. The specific process is different from that of Experimental Example 1 in that:

[0091] 5) The formation procedure is: charge at a rate of 0.1C to 4.1V.

[0092] Experimental Example 4

[0093] This experimental example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 2. The specific process is different from that of Experimental Example 1 in that:

[0094] 5) The formation procedure is: charge at a rate of 0.1C to 4.3V.

[0095] Experimental Example 5

[0096] This experimental example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 2. The specific process is different from that of Experimental Example 1 in that:

[0097] 5) The formation procedure is: charge at a rate of 0.1C to 4.1V.

[0098] Comparative Example 1

[0099] This comparative example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 1. The specific process is different from that of Experimental Example 1 in that:

[0100] 5) The formation procedure is: charge at a rate of 0.1C to 4.5V.

[0101] Comparative Example 2

[0102] This comparative example uses a low voltage formation method to treat the lithium-rich manganese-based battery cell prepared in Example 2. The specific process is different from that of Experimental Example 1 in that:

[0103] 5) The formation procedure is: charge at a rate of 0.1C to 4.5V.

[0104] Comparative Example 3

[0105] This comparative example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 1. The specific process is different from that of Experimental Example 1 in that:

[0106] 4) After the lithium-rich manganese-based battery is made, step 4 is missing.

[0107] Comparative Example 4

[0108] This comparative example uses a low voltage formation method to process the lithium-rich manganese-based battery cell prepared in Example 1. The specific process is different from that of Experimental Example 1 in that:

[0109] 4) After the lithium-rich manganese-based battery is made, it is allowed to stand at 30° C. for 3 hours.

[0110] Test Example 1

[0111] In this test example, the lithium-rich manganese-based batteries obtained by low-voltage formation treatment in Experimental Examples 1-5 and Comparative Examples 1-4 were tested for cycle capacity retention rate. The test instrument was Xinwei Battery Test System, model CT-ZWJ-4'S-T-1U. The specific test method was: the battery was cycled at 2.5V-4.4V under the condition of 1C rate. The relevant results are shown in Figure 1 Among them, the relevant results of the capacity retention rate details of the first 50 cycles can be found in Figure 2 For comparative examples 3-4, the relevant results of the formation charge-discharge voltage-capacity curves are shown in Figure 3-4 .

[0112] Test Example 2

[0113] This test example tests the battery performance of the lithium-rich manganese-based batteries obtained by low-voltage formation treatment in Experimental Examples 1-5 and Comparative Examples 1-4, that is, after battery production and formation, the relevant results of the lithium-rich manganese-based battery cycle performance test are specifically shown in Table 1.

[0114] Table 1 Battery performance test results

[0115]

[0116] Combining the data in Table 1 and Figure 1 , Figure 2 , Figure 3 , Figure 4It can be seen that the technical solutions in Experimental Examples 1-5 of the present invention with the formation voltage set within the range are compared with the technical solutions in Comparative Examples 1-4 outside the range. After cycling, the battery formation time is shorter, the first coulomb efficiency of the battery is higher, the capacity retention rate is better, and the battery does not produce gas during the cycle; the capacity retention rate of Experimental Example 1 is increased by more than 10% compared with that of Comparative Examples 1-2, and the overall performance of the battery is also better. Comparative Examples 3-4 had problems in the first cycle of formation, and Comparative Example 4 had a rapid capacity retention rate decay in the first 20 cycles during the later cycle. The present invention is conducive to the formation of a uniform interface film, thereby reducing the decomposition of the electrolyte during the cycle and improving the battery capacity retention rate.

[0117] In summary, the low-voltage formation method for lithium-rich manganese-based batteries provided by the embodiment of the present invention is short in time, saves power consumption during the formation process, optimizes the process system, and the obtained lithium-rich manganese-based battery has high capacity and low internal resistance, and the battery is not easy to produce gas during the cycle process, and has good cycle performance. The low-voltage formation method does not use the degree of activation of the Li2MnO3 phase under high voltage, so that the Li2MnO3 phase is partially activated to exert a certain capacity, and the other part that is not activated can slowly release the capacity in subsequent cycles, thereby improving the cycle stability of the battery.

[0118] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low voltage formation method for lithium-rich manganese-based batteries, characterized in that: The low voltage formation method comprises a standing step and a formation step, wherein the formation step is performed after the standing step; The formation step includes: using a current density of I1 to charge the lithium-rich manganese-based battery to a voltage of V1 at a constant current, standing for t1 minutes, and then using a current density of I2 to discharge the lithium-rich manganese-based battery to a voltage of V2 at a constant current, and the number of formation cycles is n; wherein I1 is 0.01C-0.5C, V1 is 3.8V-4.4V, t1 is 3min-100min, I2 is 0.05C-1C, V2 is 1.5V-3V, and n is 1-5.

2. The low voltage formation method according to claim 1, characterized in that: The standing step comprises: standing the injected lithium-rich manganese-based battery cell for t2 hours at a vacuum degree of P0 to exhaust, releasing the vacuum, and then standing for t3 hours at a vacuum degree of P1 to exhaust; then sealing the battery at a temperature of T1 to make a battery; standing the prepared battery at a temperature of T2 for t4 hours, applying a pressure of P2 on the battery to enhance the contact between the electrodes, and standing at a temperature of T3 for t5 hours; Among them, P0 is -0.3MPa-0 MPa, t2 is 5min-60min, P1 is -0.3MPa-0 MPa, t3 is 5min-60min, T1 is 160℃-230℃, T2 is 25℃-60℃, t4 is 6h-48h, P2 is 50N / m 2 -200 N / m 2 , T3 is 20℃-60℃, and t5 is 1h-10h.

3. The low voltage formation method according to claim 2, characterized in that: In the standing step, P0 is -0.2MPa to -0.1MPa, t2 is 5min-20min, P1 is -0.2MPa to -0.1MPa, t3 is 5min-20min, T1 is 170℃-200℃, T2 is 30℃-45℃, t4 is 10h-15h, P2 is 60N / m 2 -100 N / m 2 , T3 is 25℃-35℃, and t5 is 1h-1.5h.

4. The low voltage formation method according to claim 1, characterized in that: In the formation step, I1 is 0.05C-0.15C, V1 is 4.0V-4.4V, t1 is 30min-60min, I2 is 0.05C-0.15C, and V2 is 2.0V-2.5V.

5. The low voltage formation method according to claim 1, characterized in that: Before the low voltage formation, the lithium-rich manganese-based battery also includes: preparation of the positive electrode sheet of the battery and preparation of the negative electrode sheet of the battery; The preparation of the positive electrode sheet of the battery comprises: mixing a lithium-rich manganese-based positive electrode material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride with N-methylpyrrolidone in a mass ratio of (90-97): (1-3): (0.1-0.3): (1.5-2.0) to prepare a positive electrode slurry; the positive electrode slurry is coated, baked, the electrode sheet moisture test is performed, rolled and cut to obtain the positive electrode sheet of the battery; The preparation of a negative electrode sheet of a battery comprises: mixing graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of (90-100): (0.1-1.2): (1.8-2.5): (0.8-1.2) with water to prepare a negative electrode slurry; and preparing the negative electrode sheet of the battery by coating, baking, testing the moisture content of the electrode sheet, rolling and slitting the negative electrode slurry.

6. The low voltage formation method according to claim 5, characterized in that: The battery positive electrode sheet, the battery negative electrode sheet and the separator are made into a dry battery cell, and after encapsulating with an aluminum-plastic film, a lithium salt electrolyte with a molar concentration of 0.9 mol / L-1.3 mol / L is injected, wherein the lithium salt electrolyte comprises a lithium salt and an organic solvent; The molar concentration of the lithium salt is preferably 1 mol / L, and the lithium salt is selected from any one of lithium carbonate, lithium tetrafluoroborate and lithium hexafluorophosphate, preferably lithium hexafluorophosphate.

7. The low voltage formation method according to claim 6, characterized in that: The organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and propylene carbonate.

8. The low voltage formation method according to claim 7, characterized in that: The organic solvent is a composite reagent, which includes ethyl methyl carbonate, diethyl carbonate and ethylene carbonate in a volume ratio of (1.8-2.2):(4.5-5.2):(2.5-3.3).

9. The low voltage formation method according to claim 1, characterized in that: The positive electrode material of the lithium-rich manganese-based battery is xLi2MnO3·(1-x)LiTMO2, where TM is selected from at least one of Ni, Co, and Mn, and 0<x<1; Preferably, the positive electrode material of the lithium-rich manganese-based battery is selected from Li 1.1 Mn 0.37 Ni 0.45 Co 0.18 O 2.1 and Li 1.1 Ni 0.45 Co 0.18 Mn 0.46 O 0.21 Any one of .

10. An application of the low voltage formation method according to any one of claims 1 to 9, characterized in that: The low voltage formation method is applied to at least one of the following devices: (1) Lithium-rich manganese-based lithium batteries; (2) Lithium-ion batteries made of lithium-rich manganese-based materials; (3) Lithium-ion capacitors made of lithium-rich manganese-based materials.

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