Preparation method of silicon-carbon lithium ion battery and lithium compound liquid lithium battery

Abstract

The invention provides a preparation method of a silicon-carbon lithium ion battery and lithium compound liquid lithium battery, and belongs to the technical field of lithium ion battery preparation. Aiming at the problems that a conventional lithium ion battery is short in cycle life, insufficient in single charging endurance and long in charging time, and a silicon material is high in specific capacity but poor in cycle performance, large in volume expansion and weak in conductivity and lithium ion conductivity, 1%-80% of silicon powder is added into a negative electrode to improve the energy density of the negative electrode; 0.1%-800% of a lithium compound is sprayed on the surface of a negative pole piece to supplement lithium lost by circulation of a silicon-carbon negative pole, and the lithium battery with high energy density and long cycle performance is prepared by matching positive pole preparation and battery assembly. The battery can replace a conventional lithium ion battery and is suitable for the new energy fields of power batteries, energy storage and the like.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, specifically to a method for preparing silicon-carbon lithium-ion batteries and lithium compound liquid lithium batteries. Background Technology

[0002] In the current domestic lithium battery field, the market demand for new energy lithium batteries such as power batteries and energy storage batteries is constantly growing. However, conventional lithium-ion batteries still have technical pain points that are difficult to overcome: on the one hand, the cycle life of the battery is relatively short, the range after a single charge is insufficient, and the charging time is relatively long, which cannot meet the actual needs of new energy vehicles and energy storage systems for long range and fast charging; on the other hand, the energy density of conventional lithium-ion batteries is relatively low, and the cycle life performance is generally average, making it difficult to adapt to the high performance requirements of batteries in fields such as photovoltaic new energy.

[0003] Meanwhile, research has revealed that silicon possesses extremely high specific capacity, making it a promising electrode material. However, silicon exhibits significant drawbacks in practical applications: during the lithium insertion / extraction process of battery cycling, silicon undergoes substantial volume expansion. This expansion triggers significant mechanical stress, disrupting the spatial stability of the battery matrix material, leading to electrode structure collapse and pulverization, ultimately resulting in reversible capacity loss. Furthermore, the volume effect of silicon can cause poor contact between silicon and the current collector, resulting in the silicon surface being exposed to the electrolyte and forming a solid electrolyte interphase (SEI) film, reducing the battery's initial charge / discharge efficiency. Additionally, silicon's inherently weak lithium-ion conductivity and electrical conductivity affect the battery's cycle performance under high-current charge / discharge scenarios. These issues limit the large-scale application of silicon in lithium-ion batteries. Based on these limitations, a lithium-ion battery technology that balances fast charging / discharging, long cycle life, and extended battery life is urgently needed to replace existing conventional lithium-ion batteries. Summary of the Invention

[0004] The present invention aims to solve the problems mentioned in the background art by providing a method for preparing silicon-carbon lithium-ion batteries and lithium compound liquid lithium batteries.

[0005] The specific technical solution is as follows:

[0006] A method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery includes the following steps:

[0007] (1) Preparation of negative electrode sheet: Graphite and silicon powder are mixed, wherein the proportion of silicon powder in the total mass of graphite and silicon powder is 1%-80%, solvent is added to the mixture to make negative electrode slurry, the negative electrode slurry is coated on the surface of the current collector, and the negative electrode sheet is obtained after drying and rolling.

[0008] (2) Spraying lithium compound: Spraying lithium compound onto the surface of the negative electrode obtained in step (1), wherein the amount of lithium compound sprayed is 0.1%-800% of the mass of the negative electrode, and drying after spraying to obtain a negative electrode containing lithium compound.

[0009] (3) Preparation of positive electrode sheet: Mix positive active material, conductive agent and binder, add solvent to make positive electrode slurry, coat the positive electrode slurry on the surface of current collector, and obtain positive electrode sheet after drying and rolling.

[0010] (4) Assemble the battery: Stack the negative electrode sheet containing lithium compound obtained in step (2), the separator, and the positive electrode sheet obtained in step (3) in sequence to form a battery cell. Put the battery cell into the battery shell, inject liquid electrolyte, and seal it to obtain a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery.

[0011] The specific capacity of the negative electrode prepared in step (1) is 380-3700 mAh / g.

[0012] This preparation method introduces silicon powder into the negative electrode, utilizing the high specific capacity of silicon to improve the energy density of the negative electrode, thereby increasing the overall energy density of the battery. Simultaneously, spraying lithium compounds onto the surface of the negative electrode can compensate for the irreversible capacity loss generated by the silicon-carbon negative electrode during cycling, improving the battery's cycle performance. Combined with the complete steps of positive electrode preparation and battery assembly, the battery can be properly formed and function, ultimately achieving a combination of high energy density and long cycle performance, solving the problems of low energy density and mediocre cycle performance in conventional lithium-ion batteries.

[0013] In the above-mentioned method for preparing silicon-carbon lithium-ion batteries and lithium compound liquid lithium batteries, the particle size of the silicon powder in step (1) is 10 nm-5 μm. By limiting the specific particle size range of the silicon powder, it is possible to make the silicon powder more easily and uniformly dispersed when mixed with graphite, avoiding the occurrence of silicon powder agglomeration, thereby ensuring the stability of the internal structure of the negative electrode; this uniformly dispersed state can reduce the local mechanical stress caused by the volume expansion of the silicon powder during the lithium insertion and extraction cycle, reduce the risk of negative electrode structure collapse and pulverization, further help maintain the stability of the negative electrode energy density, and improve the cycle performance of the battery.

[0014] The above-mentioned method for preparing a silicon-carbon lithium-ion battery with added lithium compound liquid lithium battery, wherein the lithium compound in step (2) is selected from at least one of lithium oxide, lithium carbonate, and lithium hydroxide. Selecting at least one of lithium oxide, lithium carbonate, and lithium hydroxide as the lithium compound ensures that such compounds can stably provide a lithium source and effectively compensate for lithium loss caused by volume effects and other factors during battery cycling, maintaining capacity stability during battery cycling. Simultaneously, the selected lithium compound has chemical properties suitable for the negative electrode environment, can combine well with the negative electrode, and will not adversely affect the conductivity, structural stability, etc., of the negative electrode, ensuring the normal performance of the overall negative electrode.

[0015] The above-mentioned method for preparing silicon-carbon lithium-ion batteries with added lithium compound liquid lithium batteries, wherein the spraying in step (2) is carried out by electrostatic spraying or pneumatic spraying, and the drying temperature after spraying is 50-120℃, and the drying time is 1-4h. Using electrostatic spraying or pneumatic spraying allows the lithium compound to form a uniform coating on the surface of the negative electrode, avoiding localized accumulation or insufficient coverage of the lithium compound, ensuring that all areas of the electrode receive lithium replenishment; the set drying temperature and time allow the lithium compound to stably adhere to the surface of the negative electrode, preventing the lithium compound from falling off during subsequent battery processing or use, ensuring that the lithium compound continues to play a role in replenishing lithium loss throughout the entire battery life cycle, and guaranteeing the stability of the battery's cycle performance.

[0016] The above-mentioned method for preparing silicon-carbon lithium-ion batteries and lithium compound liquid lithium batteries includes a negative electrode slurry in step (1) that further includes a binder and a conductive agent. The binder is polyvinylidene fluoride (PVDF), and the conductive agent is carbon black. Based on the total mass of the negative electrode slurry, the mass percentage of the binder is 2%-5%, and the mass percentage of the conductive agent is 1%-3%. Adding PVDF as a binder to the negative electrode slurry can firmly bond the negative electrode components such as silicon powder and graphite together and tightly adhere them to the surface of the current collector, reducing the phenomenon of negative electrode sheet pulverization and detachment during battery cycling and maintaining the integrity of the negative electrode structure. Adding carbon black as a conductive agent can improve the conductivity of the negative electrode, improve the transmission efficiency of lithium ions and electrons inside the negative electrode, avoid the problem of limited charge and discharge performance due to insufficient conductivity of the negative electrode, and thus improve the cycle stability and charge and discharge efficiency of the battery.

[0017] The above-mentioned method for preparing silicon-carbon lithium-ion batteries with added lithium compounds in liquid lithium batteries includes a liquid electrolyte in step (4) comprising a lithium salt and an organic solvent. The lithium salt is lithium hexafluorophosphate, and the organic solvent is a mixture of ethylene carbonate and dimethyl carbonate, wherein the mass ratio of ethylene carbonate to dimethyl carbonate is 1:1-3:1; based on the total mass of the liquid electrolyte, the mass percentage of lithium salt is 8%-15%. In the liquid electrolyte, lithium hexafluorophosphate, as a lithium salt, can provide sufficient lithium ions for the battery to meet the migration requirements of lithium ions during the charging and discharging process; the mixture of ethylene carbonate and dimethyl carbonate can fully dissolve the lithium salt, forming a stable electrolyte system, reducing the transport resistance of lithium ions in the electrolyte, promoting the smooth migration of lithium ions between the positive and negative electrodes, reducing energy loss during ion transport, and helping to improve the charging and discharging performance and cycle stability of the battery.

[0018] In the above-mentioned method for preparing silicon-carbon lithium-ion batteries with lithium compound liquid lithium batteries, the positive electrode active material in step (3) is selected from ternary positive electrode materials or lithium iron phosphate, wherein the ternary positive electrode material is lithium nickel cobalt manganese oxide. Selecting ternary positive electrode materials or lithium iron phosphate as positive electrode active materials ensures that these materials possess good energy density and cycle performance, enabling performance matching with the high energy density and long cycle characteristics of the silicon-carbon lithium compound negative electrode in this invention. This avoids limiting the overall battery performance due to insufficient positive electrode performance, ensuring that the positive electrode and negative electrode can work synergistically to fully leverage the overall performance advantages of the battery's high energy density and long cycle life.

[0019] The above-described method for preparing silicon-carbon lithium-ion batteries plus lithium compound liquid lithium batteries includes a silicon-carbon lithium-ion battery plus lithium compound liquid lithium battery obtained in step (4) which is used as a power battery or energy storage battery. Applying the prepared battery to the fields of power batteries or energy storage batteries, due to its high energy density and long cycle performance, it can meet the requirements of power batteries for range and lifespan, reducing the need for frequent charging during power battery use; at the same time, it can also meet the requirements of energy storage batteries for long-term stable energy storage and multiple charge-discharge cycles, adapting to the core performance requirements of these two application scenarios and expanding the battery's applicability.

[0020] The above-described method for preparing a silicon-carbon lithium-ion battery with added lithium compound liquid lithium battery, wherein the silicon-carbon lithium-ion battery with added lithium compound liquid lithium battery obtained in step (4) has a capacity increase of 25-70% and a cycle life increase of 2-10 times compared to conventional lithium-ion batteries. Compared to conventional lithium-ion batteries, the battery prepared by this method has an increased energy density due to the introduction of silicon powder in the negative electrode, resulting in an increased battery capacity; and the lithium compound compensates for the irreversible capacity loss of the silicon-carbon negative electrode, improving cycle performance and extending the battery cycle life; ultimately achieving a dual improvement in battery capacity and cycle life, extending the overall battery lifespan, and reducing the battery replacement frequency.

[0021] The above-mentioned method for preparing silicon-carbon lithium-ion batteries and lithium compound liquid lithium batteries includes a step (1) in which the silicon powder undergoes surface pretreatment before mixing with graphite. This pretreatment involves coating the silicon powder surface with a carbon layer, the thickness of which is 5-20 nm. This carbon layer pretreatment before mixing the silicon powder and graphite buffers the volume expansion of the silicon powder during lithium insertion / extraction cycling, reducing the degree of silicon powder structural collapse and pulverization. Simultaneously, the carbon layer improves the conductivity and lithium-ion conductivity of the silicon powder, addressing the shortcomings of silicon material's inherent conductivity and ion transport performance. Furthermore, it reduces irreversible capacity loss during battery cycling, stabilizes the negative electrode structure and performance, and helps improve the battery's energy density and cycle stability.

[0022] The present invention has the following beneficial effects:

[0023] 1. Improve battery energy density: By adding 1%-80% silicon powder to the negative electrode, the high specific capacity of silicon material significantly improves the lithium storage capacity of the negative electrode, thereby improving the overall energy density of the battery. This solves the problem of low energy density in conventional lithium-ion batteries and effectively extends the battery's range after a single charge, meeting the demand for long range in new energy vehicles and energy storage systems.

[0024] 2. Improved battery cycle performance: By spraying lithium compounds onto the surface of the negative electrode, the lithium compounds can replenish the irreversible lithium loss caused by the volume expansion and structural pulverization of the silicon-carbon negative electrode during battery cycling, alleviating the defect of poor cycle performance of silicon materials. At the same time, it reduces the damage to the negative electrode structure caused by silicon volume expansion, thereby improving the cycle life of the battery. This solves the problem of the generally limited cycle life of conventional lithium-ion batteries and reduces the frequency of battery replacement due to cycle degradation.

[0025] 3. Adapting to fast charging and discharging requirements: This solution improves the weak conductivity of silicon materials by optimizing the conductivity of silicon-carbon anodes (e.g., by adding conductive agents) and lithium-ion conductivity. At the same time, the liquid electrolyte ensures the rapid migration of lithium ions, enabling the battery to adapt to high-current charging and discharging scenarios and achieve fast charging and discharging, thus solving the pain point of long charging time of conventional lithium-ion batteries.

[0026] 4. Practical application feasibility: The addition of silicon powder to the negative electrode can be achieved through simple stirring, and the lithium compound spraying process does not require complex or special equipment. The overall preparation process is highly compatible with conventional lithium-ion battery processes and is easy to scale up for production. The batteries made can directly replace existing conventional lithium-ion batteries and are suitable for the application needs of new energy fields such as power batteries and energy storage, and have strong practical application value. Attached Figure Description

[0027] Figure 1 A flowchart illustrating the preparation method of a silicon-carbon lithium-ion battery and a lithium compound liquid lithium battery provided in this embodiment of the invention. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0030] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0031] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] Reference Figure 1 The following three embodiments are provided in this specific implementation.

[0033] Example 1

[0034] I. Technical Solution

[0035] 1. Preparation of negative electrode sheet: Weigh 70 parts of graphite, 30 parts of silicon powder (silicon powder particle size 1μm), 3 parts of polyvinylidene fluoride (binder), and 2 parts of carbon black (conductive agent) according to the mass ratio. Add the above materials to N-methylpyrrolidone (solvent) and stir for 4 hours at a stirring rate of 500r / min to prepare a uniform negative electrode slurry. Coat the negative electrode slurry onto the surface of a copper foil (current collector) with a thickness of 12μm using a doctor blade coating method. Control the coating thickness to 100μm. Then place it in an 80℃ forced-air drying oven to dry for 2 hours. After drying, roll it through a roller press (pressure 10MPa) to obtain the negative electrode sheet.

[0036] 2. Lithium compound spraying: Lithium carbonate is selected as the lithium compound. The lithium carbonate is sprayed onto the surface of the above negative electrode sheet using a pneumatic spraying method. The amount of spraying is 5% of the mass of the negative electrode sheet. After the spraying is completed, the negative electrode sheet is placed in a vacuum drying oven at 60°C and dried for 3 hours to obtain a negative electrode sheet containing lithium compound.

[0037] 3. Preparation of positive electrode sheet: Weigh 85 parts of lithium iron phosphate (positive electrode active material), 5 parts of carbon black (conductive agent), and 10 parts of polyvinylidene fluoride (binder) according to the mass ratio, add them to N-methylpyrrolidone, and stir for 3 hours to prepare positive electrode slurry; coat the positive electrode slurry onto the surface of an aluminum foil (current collector) with a thickness of 15 μm, the coating thickness is 80 μm, dry at 75℃ for 2.5 hours, and obtain the positive electrode sheet after being rolled under a pressure of 12 MPa.

[0038] 4. Battery Assembly: A lithium compound-containing negative electrode, a 20μm thick polypropylene separator, and a positive electrode are sequentially stacked to form a stacked cell. The cell is then placed in an aluminum-plastic film soft-pack casing, vacuum-sealed (vacuum degree -0.095MPa), and injected with liquid electrolyte. After standing for 24 hours, formation is performed (0.1C charging to 3.65V, standing for 1 hour, and 0.2C discharging to 2.5V), ultimately yielding a silicon-carbon lithium-ion battery with added lithium compound liquid lithium batteries. The liquid electrolyte consists of 12% lithium hexafluorophosphate (lithium salt) and 88% a mixed organic solvent (ethylene carbonate: dimethyl carbonate = 2:1).

[0039] II. Working Principle

[0040] During charging, lithium ions are released from the lithium iron phosphate at the positive electrode and migrate to the negative electrode through the mixed organic solvent in the liquid electrolyte. Silicon powder in the negative electrode undergoes an alloying reaction with the lithium ions (forming a Li-Si alloy), while graphite undergoes an intercalation reaction to store lithium ions. The high specific capacity of silicon directly enhances the lithium storage capacity of the negative electrode, thereby increasing the overall energy density of the battery. During discharging, the Li-Si alloy decomposes and releases lithium ions, which return to the positive electrode, completing one charge-discharge cycle.

[0041] During multiple cycles, silicon powder undergoes volume expansion due to alloying / dealloying, which can easily lead to localized pulverization of the negative electrode structure and lithium-ion loss. Meanwhile, lithium carbonate on the surface of the negative electrode slowly releases lithium ions during battery cycling, replenishing the irreversible lithium loss caused by the volume effect in the silicon-carbon negative electrode and reducing capacity decay. Simultaneously, polyvinylidene fluoride binder firmly bonds graphite, silicon powder, and carbon black to the copper foil surface, preventing the negative electrode components from detaching during cycling. Carbon black constructs a conductive network, improving the electron conduction efficiency of the negative electrode. Lithium hexafluorophosphate in the liquid electrolyte provides sufficient lithium ions, and the mixed organic solvent ensures smooth lithium ion migration, all working together to maintain stable battery operation.

[0042] III. Experimental Data

[0043] The performance of the battery prepared in this embodiment was compared with that of a conventional lithium-ion battery (without silicon powder or lithium compound coating on the negative electrode). The test conditions were 1C charge-discharge (charged to 3.65V and discharged to 2.5V) at room temperature.

[0044] Cycle performance: Conventional lithium-ion batteries retain 60% of their capacity after 300 cycles, while the battery in this embodiment retains 85% of its capacity after 500 cycles.

[0045] Initial charge / discharge efficiency: The initial charge / discharge efficiency of the battery in this embodiment is 88%, while that of a conventional lithium-ion battery is 80%.

[0046] Capacity performance: The 1C discharge capacity of the battery in this embodiment is 35% higher than that of conventional lithium-ion batteries.

[0047] IV. Technical Effects

[0048] By introducing 30 parts of silicon powder into the negative electrode, the high lithium storage capacity of silicon material significantly improves the energy density of the battery, meeting the high capacity requirements. Spraying lithium carbonate onto the surface of the negative electrode effectively compensates for irreversible lithium loss during the cycling process of the silicon-carbon negative electrode, greatly improving the battery's cycle performance and extending its service life. The combination of polyvinylidene fluoride binder and carbon black conductive agent ensures the structural integrity and conductivity of the negative electrode, preventing performance degradation due to structural collapse or insufficient conductivity. The lithium iron phosphate positive electrode and a suitable liquid electrolyte form a synergistic effect with the silicon-carbon lithium compound negative electrode, ensuring that the battery as a whole can stably and efficiently achieve charging and discharging functions, comprehensively solving the problems of low energy density and mediocre cycle performance in conventional lithium-ion batteries.

[0049] Example 2

[0050] I. Technical Solution

[0051] 1. Silicon powder pretreatment: Silicon powder (particle size 500nm) is coated with a carbon layer by chemical vapor deposition. Acetylene is used as the carbon source and the reaction is carried out at 800℃ for 2 hours to form a uniform carbon layer with a thickness of 10nm, thus obtaining silicon powder with a carbon layer.

[0052] 2. Preparation of negative electrode sheet: Weigh 50 parts of graphite, 50 parts of silicon powder coated with carbon layer, 3 parts of polyvinylidene fluoride and 2 parts of carbon black according to the mass ratio, add them to N-methylpyrrolidone, stir at 800 r / min for 5 h to prepare negative electrode slurry; coat the slurry on the surface of 10 μm copper foil (coating thickness 120 μm), dry at 75℃ for 2.5 h, and roll press at 15 MPa to obtain negative electrode sheet.

[0053] 3. Lithium compound spraying: Lithium hydroxide was selected as the lithium compound and was sprayed onto the surface of the negative electrode sheet using electrostatic spraying (voltage 50kV). The amount of spraying was 10% of the mass of the negative electrode sheet. After spraying, the negative electrode sheet was dried in a vacuum drying oven at 70℃ for 2.5h to obtain a negative electrode sheet containing lithium compound.

[0054] 4. Preparation of positive electrode sheet: Same as in Example 1 (85 parts lithium iron phosphate, 5 parts carbon black, 10 parts polyvinylidene fluoride, coated with aluminum foil and then dried and rolled).

[0055] 5. Battery assembly: The negative electrode sheet containing lithium compound, the polyethylene separator (18μm thick), and the positive electrode sheet are stacked to form a battery cell, which is then packed into a soft-pack casing and injected with the same liquid electrolyte as in Example 1 (12% lithium hexafluorophosphate, ethylene carbonate: dimethyl carbonate = 2:1). After encapsulation, the battery is formed (charged to 3.65V at 0.1C, left to stand for 1.5h, and discharged to 2.5V at 0.2C) to obtain the target battery.

[0056] II. Working Principle

[0057] During charging, lithium ions are extracted from the positive electrode (lithium iron phosphate) and migrate to the negative electrode via the electrolyte. Some lithium ions form a Li-Si alloy with silicon powder coated with a carbon layer (the carbon layer can reduce the direct contact between silicon and the electrolyte, reducing the excessive growth of the SEI film), while other lithium ions are embedded in graphite. During discharging, the Li-Si alloy decomposes, the graphite de-intercalates and inserts lithium ions, and the lithium ions return to the positive electrode.

[0058] The carbon layer on the surface of silicon powder has a certain degree of elasticity, which can buffer the volume expansion of silicon during alloying / dealloying, reducing the degree of silicon powder pulverization and negative electrode structure collapse. At the same time, the carbon layer itself has good conductivity, which can improve the electronic conduction efficiency of silicon powder and improve the problem of the weak conductivity of silicon material itself. The electrostatic spraying method forms a uniform coating of lithium hydroxide on the surface of the negative electrode sheet, ensuring that lithium ions can be stably released in all areas during battery cycling, continuously replenishing irreversible lithium loss; the other components (binder, conductive agent, electrolyte) play the same role as in Example 1, jointly ensuring battery performance.

[0059] III. Experimental Data

[0060] The battery of this embodiment and the "silicon-carbon anode battery without carbon coating" (other parameters are the same as in this embodiment, only the silicon powder is not coated with a carbon layer) were subjected to 1C charge-discharge tests (room temperature, 3.65V-2.5V):

[0061] Cyclic performance: In this embodiment, the battery retains 82% of its capacity after 600 cycles, while the battery without a carbon coating retains only 70% of its capacity after 500 cycles.

[0062] Initial charge / discharge efficiency: The initial charge / discharge efficiency of the battery in this embodiment is 90%, while that of the battery without a carbon coating is 83%.

[0063] High current performance: Under 2C charge and discharge conditions, the battery capacity retention rate in this embodiment is 78%, while that of the battery without carbon coating is 65%.

[0064] IV. Technical Effects

[0065] By pretreating silicon powder with a carbon layer, the elastic buffering effect of the carbon layer alleviates the volume expansion problem during silicon powder cycling, reducing the risk of negative electrode structure pulverization and collapse. On the other hand, the conductivity of the carbon layer improves the electronic conduction efficiency of silicon powder, overcoming the defect of weak conductivity in silicon materials. Electrostatic spraying of lithium hydroxide, compared with pneumatic spraying, results in a more uniform lithium compound coating, ensuring stable lithium replenishment in all areas of the battery and further reducing irreversible capacity loss. Combined with suitable positive and negative electrodes and electrolytes, the battery not only maintains high energy density but also significantly improves cycle stability and high-current charge-discharge performance, making it particularly suitable for scenarios with certain requirements for charge-discharge rates.

[0066] Example 3

[0067] I. Technical Solution

[0068] 1. Preparation of negative electrode sheet: Weigh 90 parts of graphite, 10 parts of silicon powder (particle size 2μm), 4 parts of polyvinylidene fluoride, and 3 parts of carbon black according to the mass ratio, add them to N-methylpyrrolidone, stir at 600 r / min for 3.5 h to prepare negative electrode slurry; coat the slurry on the surface of 15 μm copper foil (coating thickness 90 μm), dry at 85℃ for 1.5 h, and roll press at 13 MPa to obtain negative electrode sheet.

[0069] 3. Lithium compound spraying: Lithium oxide is selected as the lithium compound. The lithium oxide is sprayed onto the surface of the negative electrode sheet using a pneumatic spraying method. The amount of spraying is 3% of the mass of the negative electrode sheet. After spraying, it is placed in a vacuum drying oven at 80℃ and dried for 2 hours to obtain a negative electrode sheet containing lithium compound.

[0070] 4. Preparation of positive electrode sheet: Weigh 88 parts of lithium nickel cobalt manganese oxide (NCM622, ternary positive electrode material), 4 parts of carbon black, and 8 parts of polyvinylidene fluoride according to the mass ratio, add them to N-methylpyrrolidone, stir for 4 hours to prepare positive electrode slurry; coat the slurry on the surface of 12μm aluminum foil (coating thickness 70μm), dry at 80℃ for 2 hours, and roll press at 14MPa to obtain positive electrode sheet.

[0071] 5. Battery Assembly: A cylindrical cell (model 18650) is formed by winding a lithium compound-containing negative electrode, a polypropylene / polyethylene composite separator (22μm thick), and a positive electrode. The cell is then placed in a cylindrical steel shell and injected with liquid electrolyte (10% lithium hexafluorophosphate, ethylene carbonate: dimethyl carbonate = 1:1). After sealing, formation is performed (charged to 3.0V at 0.05C, left to stand for 2 hours, charged to 4.2V at 0.1C, left to stand for 1 hour, and discharged to 3.0V at 0.2C) to obtain the target battery suitable for power batteries.

[0072] II. Working Principle

[0073] During charging, nickel, cobalt, and manganese ions in the positive electrode NCM622 undergo oxidation, and lithium ions are released and migrate to the negative electrode via the electrolyte (a 1:1 mixture of ethylene carbonate and dimethyl carbonate is more suitable for ion migration under high current). A small amount of silicon powder in the negative electrode forms a Li-Si alloy with lithium ions (low silicon content can reduce volume expansion and meet the needs of frequent charging and discharging of power batteries), and graphite intercalation stores lithium. During discharging, the Li-Si alloy decomposes, the graphite deintercalates and inserts / extracts lithium ions, and the lithium ions return to the positive electrode, completing the energy release.

[0074] During cycling, lithium oxide slowly releases lithium ions to compensate for the irreversible lithium loss of the silicon-carbon anode; the high proportion of carbon black (3 parts) in the anode improves the electron conduction efficiency, which is suitable for the conductivity requirements of high-current charging and discharging of power batteries; the NCM622 cathode itself has a high energy density, which forms a performance match with the low silicon content silicon-carbon anode, avoiding the limitation of the overall battery performance due to the imbalance of positive and negative electrode performance; the cylindrical assembly method improves the mechanical strength of the battery and meets the environmental requirements of power battery use.

[0075] III. Experimental Data

[0076] Performance tests were conducted on the power battery of this embodiment and a conventional power battery (without silicon powder or lithium compound coating on the negative electrode, and NCM622 on the positive electrode). The test conditions were 1C charge-discharge (charged to 4.2V and discharged to 3.0V) at room temperature, which meets the power battery industry testing standards.

[0077] Cycle performance: Conventional power batteries retain 65% of their capacity after 500 cycles, while the battery in this embodiment retains 80% of its capacity after 800 cycles.

[0078] High-current charge / discharge time: During 2C charging, the battery in this embodiment takes 20% less time to fully charge (3.0V to 4.2V) than conventional power batteries;

[0079] Life test: According to the standard of full charge cycle of power battery (charge to 4.2V and discharge to 3.0V each cycle), the life of the battery in this embodiment is 3 times longer than that of conventional power battery.

[0080] IV. Technical Effects

[0081] By using a low proportion (10 parts) of silicon powder, the energy density of the battery is improved while the volume expansion effect of the silicon powder is effectively controlled, making it suitable for the frequent high-current charging and discharging scenarios of power batteries. The spraying of lithium oxide replenishes irreversible lithium loss, and combined with a high proportion of carbon black conductive agent, it ensures the performance stability of the battery after multiple high-current cycles and extends the service life of the power battery. The selection of NCM622 ternary cathode material, whose high energy density characteristics synergize with the silicon-carbon anode, further improves the overall energy density of the battery and meets the power battery's requirements for range. The cylindrical structure design improves the mechanical reliability of the battery and is suitable for complex usage environments such as vehicles. Ultimately, the battery meets the core requirements of power batteries in terms of energy density, cycle life, and high-current performance.

[0082] In summary, the working principle of the lithium battery prepared by the method for preparing silicon-carbon lithium-ion batteries and lithium compound liquid lithium batteries provided in this embodiment revolves around the synergistic effect of "silicon-carbon anode + lithium compound supplementation", and the specific process is as follows:

[0083] 1. Energy Density Improvement Principle: The battery negative electrode uses a mixture of graphite and silicon powder. During charging, after lithium ions are released from the positive electrode, some lithium ions undergo an alloying reaction with the silicon powder (forming a lithium-silicon alloy), while the other part of the lithium ions are embedded between the graphite layers. Due to the high specific capacity of silicon materials, compared with a simple graphite negative electrode, the silicon-carbon hybrid negative electrode can store more lithium ions, directly improving the energy density of the negative electrode, thereby driving the improvement of the overall battery energy density and providing a foundation for long battery life.

[0084] 2. Cycle Performance Guarantee Principle: During discharge, the lithium-silicon alloy decomposes and releases lithium ions. These lithium ions return to the positive electrode along the electrolyte, completing one charge-discharge cycle. After multiple cycles, silicon powder undergoes volume expansion due to repeated alloying and dealloying, which can easily lead to pulverization of the negative electrode structure and lithium ion loss, causing irreversible capacity loss in the battery. The lithium compound pre-coated on the surface of the negative electrode sheet slowly releases lithium ions during battery cycling, replenishing the aforementioned irreversibly lost lithium, maintaining stable battery capacity, mitigating the damage to the negative electrode structure caused by silicon volume expansion, and improving the poor cycle performance of silicon materials.

[0085] 3. Principle of stable basic performance: In the silicon-carbon hybrid system, the presence of graphite can buffer the volume expansion of silicon to a certain extent, reducing the risk of negative electrode structure collapse; at the same time, the entire battery system provides a stable source of lithium ions through positive electrode active materials, and the liquid electrolyte ensures the smooth migration of lithium ions between the positive and negative electrodes, jointly maintaining the stability of the battery charging and discharging process, and ensuring that the battery can achieve fast charging and fast discharging functions.

[0086] How to use

[0087] The application of lithium batteries prepared by this method needs to be discussed from two aspects: "preparation process" and "application scenarios," as detailed below:

[0088] Battery manufacturing steps:

[0089] Step 1: Preparation of silicon-carbon negative electrode sheet. Graphite is mixed with 1%-80% silicon powder in a certain proportion, and a solvent (such as a conventional lithium battery negative electrode slurry solvent) is added. At the same time, binders and conductive agents can be added to improve the structural stability and conductivity of the electrode sheet to make a negative electrode slurry. The slurry is coated on the surface of a current collector (such as copper foil), and after drying and rolling, a silicon-carbon negative electrode sheet is obtained.

[0090] Step 2: Spraying lithium compound. Spray 0.1%-800% (relative to the mass of the negative electrode sheet) of lithium compound (such as lithium oxide, lithium carbonate, etc.) onto the surface of the prepared silicon-carbon negative electrode sheet. After spraying, perform drying treatment to ensure that the lithium compound is stably attached to the surface of the negative electrode sheet, thus obtaining a negative electrode sheet containing lithium compound.

[0091] Step 3: Preparation of the positive electrode sheet. Following the conventional lithium-ion battery positive electrode preparation process, the positive electrode active material (such as ternary materials, lithium iron phosphate) is mixed with a conductive agent and a binder, and a solvent is added to form a positive electrode slurry. This slurry is then coated onto the surface of a current collector (such as aluminum foil), and after drying and rolling, the positive electrode sheet is obtained.

[0092] Step 4: Assemble the battery. Stack (or wind) the negative electrode, separator, and positive electrode containing lithium compounds in sequence to form a cell. Insert the cell into the battery casing, inject liquid electrolyte, and finally seal it to produce a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery.

[0093] Practical application: This battery can directly replace existing conventional lithium-ion batteries and be used in fields such as power batteries (e.g., new energy vehicles) and energy storage batteries (e.g., photovoltaic energy storage systems). When using it, it should be assembled according to the battery installation specifications of the corresponding equipment and follow the conventional lithium battery charging and discharging operation procedures. No additional special operations are required, and it can adapt to the existing equipment's requirements for lithium battery use.

[0094] Overall technical effect

[0095] This technical solution addresses the core issues of conventional lithium-ion batteries and silicon material applications through a combination of "silicon-carbon anode design + lithium compound coating." The specific technical effects are derived as follows:

[0096] 1. Improve battery energy density: By adding 1%-80% silicon powder to the negative electrode, the high specific capacity of silicon material significantly improves the lithium storage capacity of the negative electrode, thereby improving the overall energy density of the battery. This solves the problem of low energy density in conventional lithium-ion batteries and effectively extends the battery's range after a single charge, meeting the demand for long range in new energy vehicles and energy storage systems.

[0097] 2. Improved battery cycle performance: By spraying lithium compounds onto the surface of the negative electrode, the lithium compounds can replenish the irreversible lithium loss caused by the volume expansion and structural pulverization of the silicon-carbon negative electrode during battery cycling, alleviating the defect of poor cycle performance of silicon materials. At the same time, it reduces the damage to the negative electrode structure caused by silicon volume expansion, thereby improving the cycle life of the battery. This solves the problem of the generally limited cycle life of conventional lithium-ion batteries and reduces the frequency of battery replacement due to cycle degradation.

[0098] 3. Adapting to fast charging and discharging requirements: This solution improves the weak conductivity of silicon materials by optimizing the conductivity of silicon-carbon anodes (e.g., by adding conductive agents) and lithium-ion conductivity. At the same time, the liquid electrolyte ensures the rapid migration of lithium ions, enabling the battery to adapt to high-current charging and discharging scenarios and achieve fast charging and discharging, thus solving the pain point of long charging time of conventional lithium-ion batteries.

[0099] 4. Practical application feasibility: The addition of silicon powder to the negative electrode can be achieved through simple stirring, and the lithium compound spraying process does not require complex or special equipment. The overall preparation process is highly compatible with conventional lithium-ion battery processes and is easy to scale up for production. The batteries made can directly replace existing conventional lithium-ion batteries and are suitable for the application needs of new energy fields such as power batteries and energy storage, and have strong practical application value.

[0100] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery, characterized in that, Includes the following steps: (1) Preparation of negative electrode sheet: Graphite and silicon powder are mixed, wherein the proportion of silicon powder in the total mass of graphite and silicon powder is 1%-80%, solvent is added to the mixture to make negative electrode slurry, the negative electrode slurry is coated on the surface of the current collector, and the negative electrode sheet is obtained after drying and rolling. (2) Spraying lithium compound: Spraying lithium compound onto the surface of the negative electrode obtained in step (1), wherein the amount of lithium compound sprayed is 0.1%-800% of the mass of the negative electrode, and drying after spraying to obtain a negative electrode containing lithium compound. (3) Preparation of positive electrode sheet: Mix positive active material, conductive agent and binder, add solvent to make positive electrode slurry, coat the positive electrode slurry on the surface of current collector, and obtain positive electrode sheet after drying and rolling. (4) Assemble the battery: Stack the negative electrode sheet containing lithium compound obtained in step (2), the separator, and the positive electrode sheet obtained in step (3) in sequence to form a battery cell. Put the battery cell into the battery shell, inject liquid electrolyte, and seal it to obtain a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery. The specific capacity of the negative electrode prepared in step (1) is 380-3700 mAh / g.

2. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The particle size of the silicon powder mentioned in step (1) is 10nm-5μm.

3. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1 or 2, characterized in that, The lithium compound mentioned in step (2) is selected from at least one of lithium oxide, lithium carbonate, and lithium hydroxide.

4. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The spraying in step (2) is carried out by electrostatic spraying or pneumatic spraying. The drying temperature after spraying is 50-120℃ and the drying time is 1-4h.

5. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The negative electrode slurry in step (1) also includes a binder and a conductive agent. The binder is polyvinylidene fluoride and the conductive agent is carbon black. Based on the total mass of the negative electrode slurry, the mass ratio of the binder is 2%-5% and the mass ratio of the conductive agent is 1%-3%.

6. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The liquid electrolyte in step (4) includes lithium salt and organic solvent. The lithium salt is lithium hexafluorophosphate, and the organic solvent is a mixed solvent of ethylene carbonate and dimethyl carbonate, wherein the mass ratio of ethylene carbonate to dimethyl carbonate is 1:1-3:

1. Based on the total mass of the liquid electrolyte, the mass percentage of lithium salt is 8%-15%.

7. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The positive electrode active material mentioned in step (3) is selected from ternary positive electrode materials or lithium iron phosphate, wherein the ternary positive electrode material is lithium nickel cobalt manganese oxide.

8. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The silicon-carbon lithium-ion battery and lithium compound liquid lithium battery obtained in step (4) can be used as power batteries or energy storage batteries.

9. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1, characterized in that, The silicon-carbon lithium-ion battery plus lithium compound liquid lithium battery obtained in step (4) has a capacity increase of 25-70% and a cycle life increase of 2-10 times compared with conventional lithium-ion batteries.

10. The method for preparing a silicon-carbon lithium-ion battery plus a lithium compound liquid lithium battery according to claim 1 or 2, characterized in that, The silicon powder in step (1) undergoes surface pretreatment before being mixed with graphite. The pretreatment involves coating the silicon powder surface with a carbon layer, the thickness of which is 5-20 nm.

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