Silicon-based negative electrode controllable lithium pre-supplementing method based on sandwich structure and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode controllable lithium pre-supplementing method based on a sandwich structure and a lithium ion battery. The invention discloses a controllable lithium pre-supplementing method for a silicon-based negative electrode based on a sandwich structure, and the method comprises the following steps: placing a negative electrode piece in an electrolyte containing a lithium salt, and carrying out infiltration treatment to obtain a humidified electrode; the humidifying electrode, the isolating membrane and the lithium foil form a sandwich structure, then a resistor and a voltmeter are added, and a closed loop is formed through a wire; carrying out lithium pre-supplementing treatment on the lithium foil and the electrode to obtain a lithium pre-supplemented electrode; and assembling the electrode for pre-supplementing lithium into the lithium ion battery. According to the controllable lithium pre-supplementing method disclosed by the invention, the problems of poor safety (such as dust explosion risk), high cost, non-uniform lithium supplementing, lithium precipitation and the like in a traditional lithium pre-supplementing technology are solved, and meanwhile, low first coulombic efficiency and irreversible capacity loss caused by formation of an SEI film are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for controllable pre-replenishment of lithium in a silicon-based negative electrode based on a sandwich structure and a lithium-ion battery. Background Art

[0002] As the global demand for clean energy and efficient energy storage systems continues to grow, the performance improvement of lithium-ion batteries, as core components of electric vehicles, portable electronic devices and other application fields, is particularly important. In recent years, high energy density has become an inevitable trend in the development of power batteries. Silicon-based negative electrode materials have become an important choice for the development of lithium batteries because of their theoretical specific capacity far higher than traditional graphite materials and excellent fast charging performance.

[0003] However, in practical applications, silicon-based negative electrode materials face many challenges. The most significant problem is that the solid electrolyte interface (SEI) film formed during the first charge and discharge process consumes a large amount of electrolyte components, resulting in low initial coulombic efficiency and accompanied by irreversible capacity loss. In addition, the volume expansion and contraction of silicon during the charge and discharge process can also cause damage to the electrode structure, further affecting battery life and safety performance.

[0004] In order to solve these problems, pre-lithium replenishment technology has been proposed and widely studied. Pre-lithium replenishment technology aims to improve the overall electrochemical performance of the battery by replenishing lithium sources to the silicon-based negative electrode in advance to compensate for the lithium ions lost due to the formation of the SEI film. At present, several major pre-lithium replenishment methods at home and abroad include:

[0005] Mixed pulping method: Lithium metal powder is mixed with active materials, adhesives, etc. and then coated on copper foil to form an electrode. This method has the risk of dust explosion and is difficult to achieve uniform distribution.

[0006] Direct battery assembly method: Use electrochemical methods to assemble lithium foil, negative electrode, and positive electrode into a battery to directly pre-replenish lithium. This method may introduce additional safety risks and has low control accuracy.

[0007] Vapor deposition: Lithium metal vapor is deposited onto the surface of the electrode. This method is expensive and not practical for large-scale production.

[0008] Precursor mixing method: lithium powder or lithium salt is added to the precursor during the preparation stage and then ball-milled to mix as electrode material. Although it is simple and easy to implement, it can easily cause uneven distribution of lithium, affecting the final effect.

[0009] Therefore, these existing pre-lithium replenishment methods generally have problems such as poor safety, high cost, insufficient lithium replenishment uniformity and lithium precipitation, which limit their large-scale industrial application. Therefore, a more safe, reliable, economical and efficient controllable pre-lithium replenishment method and lithium-ion battery that can be easily scaled up are urgently needed to meet market demand. Summary of the invention

[0010] The present application provides a method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure and a lithium-ion battery. In the method for controllable pre-lithium replenishment, a sandwich structure consisting of a silicon-based negative electrode impregnated with a lithium salt electrolyte, an isolation membrane and a lithium foil is constructed, and a closed loop is formed under external pressure, temperature and electric field strength to replenish lithium. Through an external resistor and a voltmeter, a potential difference is used under specific conditions to induce lithium transfer from the lithium foil to the surface of the silicon-based negative electrode, thereby achieving a uniform and controllable pre-lithium replenishment process, thereby solving the problems of poor safety (such as dust explosion risk), high cost, uneven lithium replenishment and lithium precipitation in traditional pre-lithium replenishment technologies, and at the same time avoiding the low initial coulombic efficiency and irreversible capacity loss caused by the formation of an SEI film.

[0011] The technical solution adopted by this application to solve its technical problem is:

[0012] In a first aspect, the present application provides a method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure, comprising the following steps:

[0013] (1) Electrode surface pretreatment

[0014] Placing the negative electrode sheet in an electrolyte containing lithium salt for infiltration treatment to obtain a wetted electrode;

[0015] (2) Forming a sandwich structure and a closed loop

[0016] The humidified electrode, isolation membrane, and lithium foil are formed into a sandwich structure, and then a resistor and a voltmeter are added to form a closed loop through a wire;

[0017] (3) Pre-replenishment of lithium

[0018] The lithium foil and the electrode are subjected to a pre-lithium replenishment treatment to obtain a pre-lithium replenished electrode;

[0019] (4) Assemble into battery

[0020] The electrodes pre-supplemented with lithium are assembled into lithium-ion batteries.

[0021] In one or more technical solutions, in step (1), the negative electrode plate is made of silicon-oxygen material and / or silicon-carbon material.

[0022] In one or more technical solutions, the silicon-oxygen material is silicon monoxide, and the silicon-carbon material is a material obtained by physically compounding silicon and graphite.

[0023] In one or more technical solutions, in step (1), the electrolyte containing lithium salt is an electrolyte containing LiPF6 components, and the immersion time of the immersion treatment is 10 minutes.

[0024] In one or more technical solutions, in step (2), the resistance is 2-5Ω.

[0025] In one or more technical solutions, in step (3), the pre-lithium replenishment treatment is performed at a pressure of 10-15KPa, a temperature of 45°C, and an electric field strength of 400V / m for 5-8min.

[0026] In one or more technical solutions, in step (4), the pre-lithium-supplemented electrode is cleaned, dried, and rolled, and then assembled with the positive electrode sheet into a lithium-ion battery;

[0027] The cleaning was performed using a dimethyl carbonate cleaning solution.

[0028] In one or more technical solutions, the drying temperature is 120°C.

[0029] In a second aspect, the present application provides a lithium-ion battery, including a battery obtained by the method described in the first aspect.

[0030] In one or more technical solutions, the initial coulombic efficiency of the lithium-ion battery is 83.80%, and the capacity retention rate of the battery after 315 cycles is 93.15%.

[0031] The beneficial effects of this application are:

[0032] The method for controllable pre-lithium replenishment described in the present application solves the problems of low initial coulombic efficiency and poor cycle stability of the silicon-based negative electrode by forming a sandwich structure with a silicon-based negative electrode plate, a lithium foil and an isolation membrane, and performing pre-lithium replenishment treatment under certain pressure, temperature and electric field strength, thereby improving the technical effect of improving the initial coulombic efficiency and cycle stability of the battery, while avoiding the safety problems caused by the introduction of lithium sources such as lithium metal, achieving precise control of the amount of pre-lithium replenishment, simplifying the process flow, reducing costs, and having good feasibility of scale-up.

[0033] The lithium-ion battery described in the present application significantly improves the initial coulombic efficiency and cycle stability through a controllable lithium pre-supplementation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0035] Figure 1 This is a process flow chart of the method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure described in this application;

[0036] Figure 2 This is a diagram showing the voltage variation process of the electrode pre-replenishment of lithium under the condition of external connection of 2Ω to the sandwich structure of Example 1 described in this application;

[0037] Figure 3 This is a graph showing the 1C / 1C cycle performance results of the battery of Comparative Example 1 (before pre-replenishment of lithium) and the battery of Example 1 (after pre-replenishment of lithium) described in the present application. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0040] In the present application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0041] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0042] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0043] The weight of the relevant components mentioned in the embodiment description of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the embodiment description of the present application, it is within the scope disclosed in the embodiment description of the present application. Specifically, the mass described in the embodiment description of the present application can be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0044] The terms "first" and "second" are used only for descriptive purposes to distinguish objects such as substances from each other, and should not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0045] Terminology explanation:

[0046] SEI film: Solid Electrolyte Interphase film, is a layer of film formed on the surface of the negative electrode of the battery, which plays a role in protecting the electrode and improving battery performance.

[0047] LiPF6: Lithium hexafluorophosphate, a lithium salt commonly used in the electrolyte of lithium-ion batteries, with the chemical formula LiPF6.

[0048] EC: Ethylene carbonate, with the chemical formula C3H4O3, is an organic solvent with excellent performance and is used as the electrolyte solvent in this application.

[0049] DMC: Dimethyl carbonate, with the chemical formula C3H6O3, is an organic compound commonly used as a solvent.

[0050] DEC: diethyl carbonate, chemical formula is C5H 10 O3, commonly used as a solvent, is used as an electrolyte solvent in this application.

[0051] NCM811: refers to a high-nickel ternary positive electrode material, in which "811" means that the ratio of nickel, cobalt and manganese is 8:1:1.

[0052] like Figure 1 A method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure is shown, comprising the following steps:

[0053] (1) Electrode surface pretreatment

[0054] Placing the negative electrode sheet in an electrolyte containing lithium salt for infiltration treatment to obtain a wetted electrode;

[0055] (2) Forming a sandwich structure and a closed loop

[0056] The humidified electrode, isolation membrane, and lithium foil are formed into a sandwich structure, and then a resistor and a voltmeter are added to form a closed loop through a wire;

[0057] (3) Pre-replenishment of lithium

[0058] The lithium foil and the electrode are subjected to a pre-lithium replenishment treatment to obtain a pre-lithium replenished electrode;

[0059] (4) Assemble into battery

[0060] The electrodes pre-supplemented with lithium are assembled into lithium-ion batteries.

[0061] In one or more technical solutions, in step (1), the negative electrode plate is a silicon-oxygen material and / or a silicon-carbon material. The silicon-oxygen material is silicon monoxide, and the silicon-carbon material is a material obtained by physically compounding silicon and graphite. The electrolyte containing lithium salt is an electrolyte containing LiPF6, and the immersion time of the immersion treatment is 10 minutes.

[0062] Specifically, in step (1), the negative electrode plate is a silicon-oxygen material and / or a silicon-carbon material, and the high theoretical specific capacity characteristics of these materials are used to increase the energy density of the lithium-ion battery and improve the fast charging performance of the battery; silicon-oxygen materials (such as silicon monoxide SiO) and silicon-carbon materials (such as materials obtained by physical composite of silicon and graphite) as silicon-based negative electrode materials can provide higher energy density than traditional graphite negative electrodes, because the theoretical specific capacity of silicon is much higher than that of graphite.

[0063] In step (1), an electrolyte containing LiPF6 is used. LiPF6 is a common lithium salt widely used in lithium-ion battery electrolytes. It has good electrochemical stability and conductivity. Moreover, LiPF6 can decompose on the surface of the negative electrode to form a stable solid electrolyte interface (SEI) film. This film can effectively prevent further reaction between the electrolyte and the active material while allowing lithium ions to pass through, thereby protecting the electrode and improving the safety and cycle life of the battery. In addition, LiPF6 has good compatibility with silicon-based negative electrode materials, which helps to ensure the effective transfer of lithium ions during the pre-lithium replenishment process.

[0064] More specifically, the concentration of LiPF6 in the lithium salt-containing electrolyte is 1-3 mol / L, and the preparation process is: after EC, DMC, and EMC are fully mixed in a mass ratio of 1:1:1, LiPF6 is added to prepare an electrolyte containing lithium salt with a LiPF6 concentration of 1-3 mol / L.

[0065] Therefore, in step (1), the negative electrode plate is pretreated by immersion for 10 minutes to allow the lithium salt in the electrolyte to completely penetrate into the pores of the negative electrode material, ensuring that each active site can contact the lithium ions, thereby achieving a uniform pre-lithium replenishment effect.

[0066] In one or more technical solutions, in step (2), the resistance is 2-5Ω.

[0067] Specifically, in step (2), the resistance is 2-5Ω, which can limit the current passing through the electrode and avoid problems such as local overheating and lithium precipitation caused by excessive current; and the resistance is 2-5Ω, which helps to maintain a stable and controllable current density and achieve controllable lithium ion transfer. From the perspective of safety, by setting a suitable resistance value, short circuits or other electrical failures can be prevented during the pre-lithium replenishment process, reducing potential safety risks;

[0068] In addition, the resistance is 2-5Ω, so that the actual amount of lithium replenishment can be calculated by monitoring the voltage change, thereby achieving precise control of the pre-lithium replenishment level; according to Ohm's law (V=IR), the current flowing can be determined by the known resistance and the measured voltage, thereby estimating the amount of lithium replenishment. At the same time, keeping the resistance at 2-5Ω and maintaining a consistent resistance value throughout the battery manufacturing process can ensure that batteries produced in different batches have similar pre-lithium replenishment effects, improving product consistency and reliability.

[0069] In the present application, if the resistance exceeds 2-5Ω, the higher resistance will cause the current to further decrease, slowing down the speed of pre-lithium replenishment, and it may take longer to reach the desired level of lithium replenishment; due to the reduction in current, the number of lithium ions transferred to the negative electrode per unit time will also decrease, reducing the efficiency of pre-lithium replenishment, which will cause the time to be extended and the pre-lithium replenishment to be incomplete, which may result in low initial coulombic efficiency and affected cycle performance.

[0070] If the resistance is lower than 2-5Ω, the lower resistance will increase the current and accelerate the pre-lithium replenishment process, but this may cause the local current density to be too high, causing safety problems such as local overheating or metal lithium deposition (lithium plating), which will not only affect the battery performance but also pose a safety hazard; and the large current may cause the lithium ions to be unevenly distributed on the negative electrode surface, resulting in excessive lithium replenishment in some areas and insufficient lithium replenishment in other places, affecting the overall performance and life of the battery; at the same time, the large current fluctuation makes it difficult to accurately measure the amount of lithium replenishment, and it is impossible to ensure that each battery has the same pre-lithium replenishment level.

[0071] In one or more technical solutions, in step (3), the pre-lithium replenishment treatment is performed at a pressure of 10-15KPa, a temperature of 45°C, and an electric field strength of 400V / m for 5-8min.

[0072] Therefore, through the above-mentioned technical solution, the safety, uniformity and efficiency of the pre-lithium replenishment process are ensured, while the first coulombic efficiency and cycle performance of the battery are optimized.

[0073] Specifically, in step (3), the pressure is designed to be 10-15Kpa to ensure close contact between the lithium foil and the negative electrode material and promote the effective transfer of lithium ions; however, excessive pressure may damage the electrode structure, and insufficient pressure may not achieve good contact, affecting the lithium replenishment effect. The temperature is 45°C, which can ensure that the lithium ions have a certain diffusion rate, improve the lithium replenishment efficiency, and facilitate the formation of a stable SEI film. The electric field strength is set to 400V / m, which can promote the directional movement of lithium ions from the lithium foil to the negative electrode, ensuring the controllability and uniformity of the lithium replenishment process; excessive electric field strength may cause excessive local current density, triggering lithium precipitation or other side reactions, thereby affecting battery performance and even safety. When the electric field strength is lower than 400V / m, the migration speed of lithium ions slows down, the lithium replenishment efficiency decreases, and it also takes longer to complete the pre-lithium replenishment.

[0074] In one or more technical solutions, in step (4), the pre-lithium-supplemented electrode is cleaned, dried, and rolled, and then assembled with the positive electrode sheet into a lithium-ion battery; the cleaning is performed using a dimethyl carbonate cleaning solution. The drying temperature is 120°C.

[0075] Specifically, by using dimethyl carbonate cleaning solution, the electrolyte or other impurities that may remain on the electrode surface during the pre-lithium replenishment process can be effectively removed to ensure the cleanliness of the electrode surface. The drying temperature of 120°C can ensure that the electrode is completely dry after cleaning without affecting the electrode material, avoiding residual moisture affecting battery performance.

[0076] At the same time, the present application provides a lithium-ion battery, including a battery obtained by the above method.

[0077] Preparation Example 1

[0078] Preparation of silicon-oxygen negative electrode:

[0079] Using silicon oxide material, the capacity is 450mAh g -1 ;

[0080] The mass ratio of active material: conductive agent (SP): binder (CMC+SBR) is 94 (SP): 2 (CMC): 4 (SBR);

[0081] The silicon-oxygen negative electrode sheet was prepared by slurry preparation and electrode coating, with a surface density of 6.99 mg cm -2 , negative electrode size 92×102mm.

[0082] Preparation of high nickel ternary positive electrode:

[0083] Using high nickel ternary material (NCM811);

[0084] The mass ratio of active material: conductive agent (CNT+SP): binder (PVDF) is 95 (CNT): 3 (SP): 2 (PVDF);

[0085] Slurry preparation and electrode coating were performed to prepare NCM811 ternary positive electrode sheets, the surface density of which was 40 mg / cm 2 The compaction density of the positive electrode is 3.4g / cm 3 , size: 90×100mm.

[0086] Example 1

[0087] A method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure comprises the following steps:

[0088] (1) Electrode pretreatment:

[0089] The silicon oxide negative electrode sheet of Preparation Example 1 was wetted in LiPF6 lithium salt electrolyte for 10 min. After the wetting was completed, a wetted silicon oxide electrode was obtained. The concentration of LiPF6 in the LiPF6 lithium salt electrolyte was 1 mol / L.

[0090] (2) The wetted silicon oxide electrode, the isolation membrane, and the lithium foil (thickness 5 μm) are formed into a sandwich structure, and an external resistor and a voltmeter are connected to form a closed loop with a wire, and the resistance is 2Ω.

[0091] (3) The sandwich structure was subjected to a pressure of 10 KPa and pre-replenished with lithium at an electric field of 400 V / m and a temperature of 45° C. for 5 minutes.

[0092] (4) The sandwich structure was taken out, the lithium salt electrolyte was cleaned off with a dimethyl carbonate cleaning solution, and then dried in a nitrogen atmosphere at a drying temperature of 120°C.

[0093] (5) Take out the dried sandwich structure and roll it through a roller press to make its compaction density reach 1.4g / cm 3 , obtaining a pre-supplemented lithium silicon oxide electrode;

[0094] (6) The pre-filled lithium silicon oxide electrode is assembled with the NCM811 positive electrode (preparation example 1) into a 2Ah laminated soft-package battery.

[0095] Example 2

[0096] A method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure comprises the following steps:

[0097] (1) Electrode pretreatment:

[0098] The silicon oxide negative electrode sheet of Preparation Example 1 was wetted in LiPF6 lithium salt electrolyte for 10 min. After the wetting was completed, a wetted silicon oxide electrode was obtained. The concentration of LiPF6 in the LiPF6 lithium salt electrolyte was 3 mol / L.

[0099] (2) The wetted silicon oxide electrode, the isolation membrane, and the lithium foil (thickness 5 μm) are formed into a sandwich structure, and an external resistor and a voltmeter are connected to form a closed loop with a wire, and the resistance is 5Ω.

[0100] (3) The sandwich structure was subjected to a pressure of 15 KPa and pre-replenished with lithium at an electric field of 400 V / m and a temperature of 45° C. for 8 minutes.

[0101] (4) The sandwich structure was taken out, the lithium salt electrolyte was cleaned off with a dimethyl carbonate cleaning solution, and then dried in a nitrogen atmosphere at a drying temperature of 120°C.

[0102] (5) Take out the dried sandwich structure and roll it through a roller press to make its compaction density reach 1.6g / cm 3 , obtaining a pre-supplemented lithium silicon oxide electrode;

[0103] (6) The pre-filled lithium silicon oxide electrode is assembled with the NCM811 positive electrode (preparation example 1) into a 2Ah laminated soft-package battery.

[0104] Example 3

[0105] A method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure comprises the following steps:

[0106] (1) Electrode pretreatment:

[0107] The silicon oxide negative electrode sheet of Preparation Example 1 was wetted in LiPF6 lithium salt electrolyte for 10 min. After the wetting was completed, a wetted silicon oxide electrode was obtained. The concentration of LiPF6 in the LiPF6 lithium salt electrolyte was 2 mol / L.

[0108] (2) The wetted silicon oxide electrode, the isolation membrane, and the lithium foil (thickness 5 μm) are formed into a sandwich structure, and an external resistor and a voltmeter are connected to form a closed loop with a wire, and the resistance is 3Ω.

[0109] (3) The sandwich structure was subjected to a pressure of 14 KPa and pre-replenished with lithium at an electric field of 400 V / m and a temperature of 45° C. for 7 minutes.

[0110] (4) The sandwich structure was taken out, the lithium salt electrolyte was cleaned off with a dimethyl carbonate cleaning solution, and then dried in a nitrogen atmosphere at a drying temperature of 120°C.

[0111] (5) Take out the dried sandwich structure and roll it through a roller press to make its compaction density reach 1.5g / cm 3 , obtaining a pre-supplemented lithium silicon oxide electrode;

[0112] (6) The pre-filled lithium silicon oxide electrode is assembled with the NCM811 positive electrode (preparation example 1) into a 2Ah laminated soft-package battery.

[0113] Comparative Example 1

[0114] The non-pre-charged lithium silicon oxide electrode is combined with the NCM811 positive electrode to assemble a 2Ah stacked soft-package battery.

[0115] The specific process includes the following steps:

[0116] (1) Electrode pretreatment:

[0117] The silicon oxide negative electrode sheet of Preparation Example 1 was wetted in LiPF6 lithium salt electrolyte for 10 min. After the wetting was completed, a wetted silicon oxide electrode was obtained. The concentration of LiPF6 in the LiPF6 lithium salt electrolyte was 1 mol / L.

[0118] (2) Take out the wet silicon oxide electrode, clean the lithium salt electrolyte with dimethyl carbonate cleaning solution, and then dry it in a nitrogen atmosphere at a drying temperature of 120°C.

[0119] (3) Take out the dried silicon oxide electrode and roll it through a roller press to make its compaction density reach 1.4g / cm 3 , obtaining a pre-supplemented lithium silicon oxide electrode;

[0120] (4) The pre-filled lithium silicon oxide electrode is assembled with the NCM811 positive electrode (preparation example 1) into a 2Ah laminated soft-package battery.

[0121] For Examples 1-3 and Comparative Example 1, after battery formation, a 1C / 1C cycle performance test was performed at 25°C; the theoretical discharge capacity of 5 min was obtained by integrating the ratio of the pre-lithiation voltage to the corresponding resistance over the pre-lithiation time; the first charge capacity, first discharge capacity, and first coulombic efficiency are summarized in Table 1.

[0122] Table 1

[0123] Battery First charge capacity (mAh) First discharge capacity (mAh) First coulombic efficiency (%) Comparative Example 1 3155 2486 78.80 Example 1 3144 2635 83.81 Example 2 3186 2683 84.21 Example 3 3175 2693 84.82

[0124] It can be seen from Table 1 that after the pre-replenishment of lithium, the first coulombic efficiency of the battery in Example 1 is increased from 78.81% to at least 83.80%, which is a significant increase.

[0125] from Figure 2It can be seen that the voltage of the sandwich structure closed loop of the present invention changes with the electrode pre-lithium replenishment time under a resistance of 2Ω. As the pre-lithium replenishment proceeds, the voltage of the closed loop continues to decrease, that is, the potential difference continues to decrease. After 5 minutes of pre-lithium replenishment, the voltage drops to 0.25V.

[0126] Figure 3 The cycling performance comparison of NCM811 / silicon oxide soft-package batteries with and without lithium pre-supplement is shown. When the nominal capacity of the battery is 2Ah, it can be seen that after 315 cycles, the capacity retention rate of the soft-package battery without lithium pre-supplement is 90.10%, and the capacity retention rate of the soft-package battery with lithium pre-supplement reaches 93.15%, and the cycling performance is significantly improved.

[0127] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for controllable pre-lithium replenishment of a silicon-based negative electrode based on a sandwich structure, characterized in that: The following steps are involved: (1) Electrode surface pretreatment Placing the negative electrode sheet in an electrolyte containing lithium salt for infiltration treatment to obtain a wetted electrode; (2) Forming a sandwich structure and a closed loop The humidified electrode, isolation membrane, and lithium foil are formed into a sandwich structure, and then a resistor and a voltmeter are added to form a closed loop through a wire; (3) Pre-replenishment of lithium The lithium foil and the electrode are subjected to a pre-lithium replenishment treatment to obtain a pre-lithium replenished electrode; (4) Assemble into battery The electrodes pre-supplemented with lithium are assembled into lithium-ion batteries.

2. The method according to claim 1, characterized in that In step (1), the negative electrode plate is made of silicon-oxygen material and / or silicon-carbon material.

3. The method according to claim 2, characterized in that The silicon-oxygen material is silicon monoxide, and the silicon-carbon material is a material obtained by physically compounding silicon and graphite.

4. The method according to claim 1, characterized in that: In step (1), the electrolyte containing lithium salt is an electrolyte containing LiPF6 components, and the immersion time of the immersion treatment is 10 minutes.

5. The method according to claim 1, characterized in that: In step (2), the resistance is 2-5Ω.

6. The method according to claim 1, characterized in that In step (3), the pre-lithium replenishment treatment is performed at a pressure of 10-15 KPa, a temperature of 45° C., and an electric field strength of 400 V / m for 5-8 minutes.

7. The method according to claim 1, characterized in that In step (4), the pre-lithium-supplemented electrode is cleaned, dried, and rolled, and then assembled with the positive electrode sheet into a lithium-ion battery; The cleaning was performed using a dimethyl carbonate cleaning solution.

8. The method according to claim 7, characterized in that The drying temperature is 120°C.

9. A lithium-ion battery, characterized in that A battery obtained by the method according to any one of claims 1 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The initial coulombic efficiency of the lithium ion battery is 83.80%, and the capacity retention rate of the battery after 315 cycles is 93.15%.

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