Si / C negative electrode plate volume expansion inhibition method of silicon-carbon negative electrode lithium ion battery and application of Si / C negative electrode plate volume expansion inhibition method

Abstract

The invention discloses a volume expansion inhibition method and application of a Si / C negative plate of a silicon-carbon negative electrode lithium ion battery, the negative electrode of the silicon-carbon negative electrode lithium ion battery is set as a Si / C negative plate, and the positive electrode of the silicon-carbon negative electrode lithium ion battery is set as a pre-embedded lithium supplement positive plate; the pre-lithiation lithium-supplementing positive plate is composed of the following components in parts by solid mass: 1-10 parts of a lithium-supplementing agent, 5-10 parts of a binder, 5-10 parts of a conductive agent and the balance of a positive active material, and the pre-lithiation lithium-supplementing positive plate effectively compensates the lithium loss of the silicon-carbon negative lithium ion battery in the cycle process, and enhances the stability of a solid electrolyte interface and a catholyte interface layer of the silicon-carbon negative lithium ion battery; the pre-lithiation lithium supplement positive plate inhibits the volume expansion of the Si / C negative plate of the silicon-carbon negative electrode lithium ion battery and inhibits the generation of hydrogen in the charging and discharging process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon-carbon negative electrode lithium ion batteries, in particular to a Si / C negative electrode sheet volume expansion inhibition method for silicon-carbon negative electrode lithium ion batteries and application. BACKGROUND

[0002] LFO is a lithium supplement additive in the positive electrode material of lithium ion batteries, and its full name is lithium-rich lithium iron oxide (Li5FeO4). As a positive electrode lithium supplement, LFO can reduce the irreversible capacity loss of the first charge and discharge, and improve the cycle life and energy density of lithium batteries. Among various lithium supplement materials, Li5FeO4 (LFO) is a promising candidate for commercial applications due to its low cost, easy processing, and high compatibility with existing manufacturing infrastructure.

[0003] For silicon-carbon negative electrode lithium ion batteries, after adding the lithium supplement LFO, due to incomplete decomposition of LFO, residual LFO will release oxygen under high pressure, and LFO will release oxygen during cell formation, react with EC to form transition state oxides deposited on the negative electrode, and release hydrogen under low potential conditions to form hydrogen gas, which will worsen high-temperature storage and hot box. Excessive delithiation of lithium cobaltate under high operating voltage will cause the layered structure of the positive electrode material to be unstable, resulting in phase structure changes, accompanied by phase changes and volume changes, which will change the unit cell parameters, grain boundary dislocations, stress changes, and particle cracking, leading to rapid capacity decay. Moreover, the volume of the negative silicon-based electrode of the silicon-carbon negative electrode lithium ion battery will expand significantly, with an expansion ratio of the silicon-based electrode >300%, which will cause the silicon-based electrode material to crack and pulverize, resulting in a loss of contact between the active material and the current collector, which will further cause the solid electrolyte interface (SEI) layer to be unstable, leading to irreversible capacity loss and cycle performance deterioration. SUMMARY

[0004] In view of the deficiencies of existing lithium ion batteries with silicon-carbon systems, the purpose of the present application is to provide a Si / C negative electrode sheet volume expansion inhibition method for silicon-carbon negative electrode lithium ion batteries, which inhibits the reaction of free oxygen with EC to produce transition state oxides in the negative electrode, reduces irreversible capacity loss, and improves the expansion of LCO positive electrode particles and Si / C composite anodes, inhibits the production of hydrogen gas, reduces battery gas production, and improves battery safety performance.

[0005] To achieve the above purpose, the technical solution adopted by the present application is as follows: a Si / C negative electrode sheet volume expansion inhibition method for silicon-carbon negative electrode lithium ion batteries,

[0006] The negative electrode of the silicon-carbon negative electrode lithium ion battery is set as a Si / C negative electrode sheet, which is composed of irregular sheet-shaped silicon-carbon particle organizations;

[0007] The positive electrode of a silicon-carbon negative electrode lithium ion battery is provided as a pre-embedded lithium supplement positive electrode sheet, and the pre-embedded lithium supplement positive electrode sheet is prepared by using the following positive electrode sheet preparation method,

[0008] In a low-humidity environment with a humidity of <3.5%, the lithium supplement agent, the binder, the conductive agent, the positive electrode active material, and NMP are mixed and stirred, and after uniform stirring, a slurry is obtained. The slurry is coated on the surface of an aluminum foil, and then placed in a hot box for heating for 1-3 h at a temperature of 100-120°C. After heating, the NMP evaporates and disappears, and after solidification, a pre-lithiated lithium supplement positive electrode sheet is obtained,

[0009] The pre-lithiated lithium supplement positive electrode sheet is composed of 1-10 parts of a lithium supplement agent, 5-10 parts of a binder, 5-10 parts of a conductive agent, and the balance of a positive electrode active material, in terms of solid mass fraction.

[0010] The positive electrode active material includes LiCoO2 and / or NCM,

[0011] The lithium supplement agent includes Li5FeO4 and / or Li2NiO2;

[0012] The pre-lithiated lithium supplement positive electrode sheet has lithium supplement agent particles uniformly distributed around the positive electrode active material particles, and the positive electrode active material particles exhibit irregular block morphology, with a particle size distribution following a logarithmic normal mode, an average particle size of 1-2 μm, and a particle size of the lithium supplement agent ≤1 μm.

[0013] The pre-lithiated lithium supplement positive electrode sheet effectively compensates for the loss of lithium in the silicon-carbon negative electrode lithium ion battery during the cycling process, and enhances the stability of the solid electrolyte interface and the cathode electrolyte interface layer,

[0014] The pre-lithiated lithium supplement positive electrode sheet inhibits the volume expansion of the Si / C negative electrode sheet of the silicon-carbon negative electrode lithium ion battery and inhibits the generation of hydrogen gas during the charging and discharging process.

[0015] In a further technical solution, in the SEM image of the pre-lithiated lithium supplement positive electrode sheet,

[0016] The lattice stripe corresponding to the LiCoO2 organizational plane is 0.5±0.05 nm,

[0017] The lattice stripe corresponding to the NCM organizational plane is 0.5±0.05 nm,

[0018] The lattice stripe corresponding to the Li5FeO4 organizational plane is 0.2±0.05 nm,

[0019] The lattice stripe corresponding to the Li2NiO2 organizational plane is 0.2±0.05 nm.

[0020] In a further technical solution, the silicon-carbon negative electrode lithium-ion battery is provided with an electrolyte solution, which is composed of ethylene carbonate EC, methyl ethyl carbonate EMC and LiPF6, and uses a composite base membrane as a separator.

[0021] In a further technical solution, the thickness of the Si / C negative electrode sheet is 43±1μm, the growth rate of the thickness of the silicon-carbon electrode sheet is less than 4.5% with the increase of the number of cycles, and the gap between the silicon-carbon particles stabilizes at 45±0.5μm after 100 cycles.

[0022] The lithium supplement includes Li5FeO4 and Li2NiO2, with an average particle size of 0.5-2μm and a moisture content of 20-23ppm;

[0023] The positive electrode active materials include LiCoO2, LiFePO4, and NCM, with an average particle size of 1-3.5 μm and a specific surface area of ​​0.1-0.25 m². 2 / g, tap density is 2.5-3.5g / cm³ 3 .

[0024] In a further technical solution, the lithium replenishing agent comprises Li5FeO4 and Li2NiO2, wherein the weight ratio of Li5FeO4 to Li2NiO2 is 1~4:1.

[0025] In a further technical solution, the lithium replenishing agent includes Li5FeO4 and Li2NiO2, and the weight ratio of Li5FeO4 to Li2NiO2 is 1:1, 2:1, 3:1, 4:1, 1:2, 1:3 or 1:4.

[0026] In a further technical solution, the positive electrode active material includes lithium cobalt oxide, and the amount of lithium supplementer added is 1.5~5.5% or 2.5~3.5% of the lithium cobalt oxide by weight percentage;

[0027] The method for preparing the positive electrode sheet involves first weighing the lithium replenishing agent, binder, conductive agent, and positive electrode active material according to the solid mass fractions, and then separately weighing 1-10 parts by mass of NMP. The lithium replenishing agent, binder, conductive agent, positive electrode active material, and NMP are then mixed into a paste-like slurry.

[0028] In a further technical solution, the positive electrode active material includes LiCoO2, LiFePO4 and NCM, and the weight ratio of LiCoO2, LiFePO4 and NCM is 1~3:1:1.

[0029] In a further technical solution, the conductive agent includes at least one of conductive carbon black, graphene, and acetylene black, and the binder is selected from polyvinylidene fluoride;

[0030] The conductive agent comprises graphite and silicon, with a mass ratio of graphite to silicon of 2 to 4:1.

[0031] A silicon-carbon negative electrode lithium-ion battery for suppressing the volume expansion of Si / C negative electrode sheet, the silicon-carbon negative electrode lithium-ion battery includes a Si / C negative electrode sheet and a pre-embedded lithium-filled positive electrode sheet prepared by the method for suppressing the volume expansion of Si / C negative electrode sheet of the silicon-carbon negative electrode lithium-ion battery described in the present invention. The negative electrode of the silicon-carbon negative electrode lithium-ion battery is a Si / C negative electrode sheet composed of irregular sheet-like silicon-carbon particles.

[0032] The positive electrode of a silicon-carbon anode lithium-ion battery is a pre-embedded lithium-replenishing positive electrode sheet.

[0033] The pre-lithiated lithium-supplemented cathode sheet, by solid mass percentage, consists of 1-10 parts lithium-supplementing agent, 5-10 parts binder, 5-10 parts conductive agent, and the remainder being cathode active material.

[0034] Positive electrode active materials include LiCoO2 and / or NCM.

[0035] Lithium supplements include Li5FeO4 and / or Li2NiO2;

[0036] The positive active material particles of the pre-lithiated lithium-supplemented positive electrode sheet are uniformly distributed with lithium-supplementing particles around them. The positive active material particles exhibit an irregular blocky morphology, and the particle size distribution follows a log-normal pattern with an average particle size of 1-2 μm. The particle size of the lithium-supplementing particles is ≤1 μm.

[0037] The advantages of this invention compared to existing technologies are as follows: The lithium replenishing agent of this invention incorporates Li5FeO4 and Li2NiO2. Li2NiO2, as another important lithium replenishing agent, exhibits superior high-temperature stability compared to Li5FeO4. Its strong Ni³⁺ coordination ability stabilizes lattice oxygen, and its high oxygen vacancy formation energy allows it to function as an oxygen inhibitor, forming a mechanically robust and more uniform SEI film, effectively alleviating the gas generation problem of LFO during high-temperature storage. Therefore, in the lithium cobalt oxide silicon-carbon system, LFO is combined with LNO for lithium replenishment, reducing battery gas generation and bulging.

[0038] Pairing LFO with LCO cathode materials improves battery cycle performance, reduces observed irreversible capacity loss, and improves the expansion of LCO cathode particles and Si / C composite anodes. In the lithium cobalt oxide silicon-carbon system, LFO is combined with LNO for lithium replenishment, which reduces battery gas production and improves battery safety performance.

[0039] Silicon-carbon anode lithium-ion batteries are low-cost, and the maintenance of Si / C anode sheets is extremely simple and inexpensive. On the other hand, Si / C anode sheets only develop a series of problems due to cracking after a relatively long period of use, which are generally solved by replacement. Therefore, for commercially available products, the volume expansion defect of Si / C anode sheets in silicon-carbon lithium-ion batteries is relatively acceptable. Furthermore, solving the volume expansion problem of Si / C anode sheets in silicon-carbon lithium-ion batteries could lead to a cost increase exceeding market expectations, thereby reducing market competitiveness. Considering all these factors, manufacturers have neither wanted nor thought of fundamentally solving the problem of Si / C anode sheet volume expansion. This invention is a technical improvement based on this background, fundamentally suppressing the volume expansion of Si / C anode sheets at an extremely low cost. While solving this technical problem, it unexpectedly achieves a significant reduction in battery gas production at the same time.

[0040] Gas bulging has been a persistent technical problem in silicon-carbon anode lithium-ion batteries. However, due to factors such as battery characteristics, overall cost, and market competition, there is currently no good solution for gas bulging in silicon-carbon anode lithium-ion batteries. This invention significantly reduces battery gas production while suppressing the volume expansion of the Si / C anode sheet. This greatly extends the overall lifespan of silicon-carbon anode lithium-ion batteries, which is of great significance to them and represents a major improvement that can significantly enhance their market competitiveness. Attached Figure Description

[0041] Figure 1 Optical images of the LCO / LFO cathode prepared according to the present invention.

[0042] Figure 2 The cycle lifetime diagram shows the LCO / LFO‖Si / C full cell prepared according to the present invention.

[0043] Figure 3 This is a SEM image of the positive electrode cross-section of the LCO / LFO‖Si / C full cell prepared in this invention.

[0044] Figure 4 shows the XRD and TEM images of the positive electrode of the LCO / LFO‖Si / C full cell prepared in this invention.

[0045] Figure 5 This is a SEM image of the negative electrode cross-section of the LCO / LFO‖Si / C full cell prepared in this invention.

[0046] Figure 6 Optical images of the LCO / LFO-LNO cathode prepared according to the present invention.

[0047] Figure 7The image shows the cycle lifetime of the LCO / LFO-LNO‖Si / C full cell prepared according to this invention.

[0048] Figure 8 This is a graph showing the volume change of the LCO / LFO-LNO‖Si / C full cell prepared in this invention after high-temperature storage.

[0049] Figure 9. SEM and EDS images of the cross-sections of the LCO / LFO cathode and the hybrid cathode prepared in this invention.

[0050] Figure 10. Surface XPS spectrum and AFM image of Si / C anode after 100 cycles. Detailed Implementation

[0051] Example 1

[0052] In a low-humidity environment (<3.5%), lithium cobalt oxide (positive electrode active material, LiCoO2) and Li5FeO4 (lithium replenishment agent) were added to a glass bottle. The total mass percentage of lithium cobalt oxide and Li5FeO4 was 85%, and the weight of Li5FeO4 was 1.5%-5.5% of the weight of lithium cobalt oxide. Then, 5% conductive agent, 5% binder, and 5% solvent were added sequentially according to the total mass percentage. After stirring evenly, a slurry was obtained. The slurry was coated on the surface of aluminum foil (positive electrode current collector), and then heated in a 105℃ oven for 2 hours. Samples for multiple pre-lithiated lithium replenishment positive electrode sheets were obtained according to different mass ratios of lithium cobalt oxide and Li5FeO4. Figure 1 As shown, six samples were prepared. From left to right, the weights of Li5FeO4 were 0% (0LFO), 1.5% (1.5LFO), 2.5% (2.5LFO), 3.5% (3.5LFO), 4.5% (4.5LFO), and 5.5% (5.5LFO) of lithium cobalt oxide and lithium cobalt oxide, respectively.

[0053] LiCoO2 and Li5FeO4 were purchased, and conductive carbon black (Super P (SP)) was used as a conductive additive. The Si / C composite material was prepared by mixing graphite and silicon in a disperser and then continuously stirring to ensure uniform dispersion. A polyvinylidene fluoride (PVDF, Solvay 5310) solution with a mass concentration of 8% was prepared by dissolving PVDF (polyvinylidene fluoride) in NMP (N-methyl-2-pyrrolidone).

[0054] Figure 9(a) and (b) show SEM images of the cross-sections of the LCO and LCO / LFO electrodes, respectively. Figure 9(a) and (b) show that the LFO particles are randomly distributed within the cathode matrix, reflecting their different morphologies. Figure 9(c) shows the corresponding EDS spectrum of the region shown in Figure 9(b), highlighting the elemental distribution of LCO (Co Kα, OH Kα), LFO (Fe Kα), and carbon-based materials (c Kα, including conductive carbon and binder). The energy-dispersive X-ray spectroscopy (EDS) in Figure 9(c) confirms the uniform distribution of the iron signal within the LCO / LFO hybrid electrode, indicating that LFO was successfully incorporated into the LCO matrix. Figures 9(d) and (e) show TEM images of LFO and LCO, providing further structural insights. The transmission electron microscopy (TEM) images in Figures 9(d) and (e) show that the lattice fringes corresponding to the LFO (214) plane are 0.200 nm and the lattice fringes corresponding to the LCO (003) plane are 0.474 nm, confirming the structural integration of LFO in LCO.

[0055] To investigate the effect of lithium fluoride oxide (LFO) on the structural integrity of lithium cobalt oxide (LCO) particles, SEM analysis was performed on 0-LFO and 3.5-LFO cathodes before and after cycling.

[0056] Figure 3 (a) Cross-sectional SEM image of the cathode before cycling without pre-lithiation. Figure 3 (b) Cross-sectional SEM image of the pre-lithiated cathode before cycling. Figure 3 (c) SEM image of the cross-section of the cathode without pre-lithiation after 100 cycles. Figure 3 (d) Cross-sectional SEM of the pre-lithiated cathode after 100 cycles, Fig. 4(a) XRD pattern of the cathode without pre-lithiated cathode after cycling, Fig. 4(b) XRD pattern of the pre-lithiated cathode after cycling, Fig. 4(c and d) HRTEM images of LCO particles on the surface of the cathode with and without pre-lithiated cathode after 100 cycles.

[0057] Figure 3 The diagram shows the morphological evolution of the 0-LFO and 3.5-LFO cathodes before and after 100 full cell cycles. Before cycling, both electrodes exhibited smooth, intact surfaces in their cross-sections. Figure 3 ab). However, after 100 cycles, the 0-LFO cathode showed significant cracking and fissures (ab). Figure 3 c), while the 3.5-LFO cathode showed only slight cracks, mainly limited to secondary particles ( Figure 3 d). These observations indicate that the addition of LFO enhances the structural stability of LCO particles, reduces microstructure degradation, and improves cycling performance.

[0058] XRD analysis further supports these findings. Figure 4a -b). Pre-cycle XRD patterns of the 0-LFO and 3.5-LFO cathodes correspond to the layered structure of LCO (PDF#75-0532). After cycling, the shift of the 18.94° peak in the 0-LFO cathode to a lower angle indicates lattice expansion, likely caused by stress-induced lattice distortion, which may compromise the structural integrity of the LCO structure. In contrast, the 3.5-LFO cathode showed minimal change in peak position or width after cycling, indicating that the LFO effectively maintained the structural integrity of the LCO during long-term cycling. The near-surface structure of the LCO particles was further analyzed using high-resolution transmission electron microscopy (HR-TEM). Figure 4c As shown, after 100 cycles in the LCO||Si / C whole cell, a rock-salt layer with an average thickness of approximately 18.1 nm was observed on the surface of the LCO particles. In contrast, after adding LFO, the average thickness of the rock-salt layer on the LCO surface decreased to 15.5 nm. Figure 4d As shown in the figure. This result is consistent with SEM and XRD data, further confirming that the incorporation of LFO helps maintain the structural stability and electrochemical performance of LCO during cycling.

[0059] The electrodes were comprehensively morphologically characterized to investigate the effect of LFO on the anodic expansion behavior of Si / C. Figure 5 Comparative analysis of 0-LFO and 3.5-LFO before and after full-cell negative electrode cycling. Figure 5 The diagram shows the morphological changes observed in the 0-LFO and 3.5-LFO full-cell anodes before and after cycling. Prior to cycling, both electrodes exhibited relatively smooth surfaces. However, after 100 cycles, significant morphological differences became apparent. For the 0-LFO anode, numerous small voids formed after cycling, with the electrode thickness increasing from 25.6 μm to 44.5 μm, equivalent to a volume expansion of 73.8%. In contrast, the 3.5-LFO anode maintained a smoother surface after pre-lithiation, with the thickness increasing only slightly from 43.2 μm to 45.14 μm, resulting in a minimum volume expansion of 4.5%.

[0060] To better elucidate the mechanism by which our cathode pre-lithiation strategy improves electrochemical performance, we used surface-sensitive and chemically specific XPS to investigate the composition of the anode solid electrolyte interface before and after pre-lithiation.

[0061] Figure 10 shows the surface XPS spectra of the Si / C anode after 100 complete battery cycles, comparing the states before and after pre-lithiation. Figure 10(a) C1s, Figure 10(b) F1s, Figure 10(c) O1s spectra. AFM images of the Young's modulus distribution of the cyclic Si / C electrode (d) and (e) pre-lithiated Si / C electrode.

[0062] To further elucidate the mechanism by which the cathode pre-lithiation strategy improves the electrochemical performance of Si / C-based electrodes, we conducted a comprehensive analysis of the cycling electrodes. Surface-sensitive and chemically resolved X-ray photoelectron spectroscopy (XPS) was used to characterize the solid-electrolyte interface (SEI) phase composition on the negative electrode surface after 100 charge-discharge cycles. C1s spectra ( Figure 10a The results showed that C=O (287.19 eV and 288.71 eV

[25] ), CO (286.71 eV

[25] ), CC (284.8 eV) and C-li (282.98 eV and 282.92 eV) peaks existed both before and after pre-lithiation. It is worth noting that the intensity of the C-Li peak was relatively weaker than that of the CC peak after pre-lithiation, indicating that although Li+ was added, the LiCx content was still low, indicating that Li+ was effectively utilized. F1s spectrum ( Figure 10b The O1s spectrum highlights the significant enhancement of the PF (LixPOyFz, 685.25 eV) peak, a key feature associated with stable SEI formation. Figure 10c The presence of LiySiOz in the SEI layer

[37] (530.0 eV) indicates the presence of LiySiOz in the SEI layer. Furthermore, the ROLi peak significantly decreased after pre-lithiation, indicating substantial suppression of electrolyte decomposition. Additionally, AFM images showed that the Young's modulus distribution of the cyclic Si / C electrode was smaller and more non-uniform, ranging from -348.4 MPa to 1.7 GPa, with an average of 531 MPa. In contrast, the Young's modulus distribution of the pre-lithiation Si / C electrode was higher and more uniform, ranging from -198 MPa to 2 GPa, with an average Young's modulus of 867 MPa (530.0 eV). Figure 10d (and e). These XPS and AFM results together confirm that the incorporation of LFO helps form a mechanically robust and more uniform SEI film, thereby mitigating the volume expansion of the silicon-based anode during cycling. This observation is consistent with measurements of changes in the Si / C anode thickness before and after cycling.

[0063] Example 2

[0064] Six samples obtained in Example 1 were cut and assembled to obtain different LCO / LFO-Si / C button cells, which were then tested in the Blue Electric System.

[0065] The test procedure is as follows: Under a voltage of 2V-4.58V, first perform an initial charge-discharge cycle at 0.066C, then cycle at 1C for 100 times. The cycle test results are as follows. Figure 2As shown, after 100 cycles, the capacity of the LCO-Si / C battery was only 47.2% of its initial capacity, while adding 3.5% LFO significantly improved the battery capacity, with a capacity retention rate of 75.9%. Furthermore, the reversible capacity of the LCO-Si / C battery with 3.5% LFO increased from 66.2 mAh / g to 117.3 mAh / g. Figure 2 As shown.

[0066] The button cells prepared in Example 2 were disassembled and compared with those before and after cycling using SEM. Before cycling, the cross-sectional surfaces of both electrodes were smooth and intact. However, after 100 cycles, the 0-LFO cathode showed obvious cracks, while the 3.5-LFO cathode showed only slight cracks, mainly confined to secondary particles. Figure 3 As shown.

[0067] The button cell full cell prepared in Example 2 was disassembled before and after cycling, and XRD analysis was performed on the lithium supplementation suppression sheet. After cycling, the 18.94° peak of the 0-LFO cathode shifted to a lower angle, indicating lattice expansion, which is due to Li + The removal of ions reduces their shielding effect, and the increased repulsion between oxygen layers drives lattice expansion along the c-axis, which may compromise the integrity of the LCO structure. In contrast, the 3.5-LFO cathode shows little change in the position and width of the peaks after cycling, indicating that LFO effectively maintains the structural integrity of the LCO during long-term cycling, as shown in Figure 4.

[0068] The button cell full cell fabricated in Example 2 was disassembled before and after cycling, and SEM analysis was performed on the negative electrode. Before cycling, both electrodes exhibited relatively smooth surfaces. However, after 100 cycles, significant morphological differences emerged. For the 0-LFO anode, numerous small voids formed after cycling, and the electrode thickness increased from 25.6 μm to 44.5 μm, resulting in a volume expansion of 73.8%. In contrast, the 3.5-LFO anode maintained a smooth surface after pre-lithiation, with its thickness increasing only from 43.2 μm to 45.14 μm, and a volume expansion of 4.5%. Figure 5 As shown.

[0069] Example 3

[0070] In a low-humidity environment (<3.5%), lithium cobalt oxide (positive electrode active material) and lithium supplementer were added to a glass bottle. The total mass percentage of lithium cobalt oxide (positive electrode active material) and lithium supplementer was 85%. The lithium supplementer consisted of Li5FeO4 and Li2NiO2 in different mass ratios. LFO:LNO=0:0 indicates that the lithium supplementer did not contain Li5FeO4 and Li2NiO2, and LFO:LNO=3:1 indicates that the mass ratio of Li5FeO4 and Li2NiO2 in the lithium supplementer was 3:1. Then, 5% conductive agent, 5% binder, and 5% solvent were added sequentially according to the total mass percentage. After stirring evenly, a slurry was obtained. The slurry was coated on the surface of aluminum foil, and then heated in a 105℃ oven for 2 hours to obtain samples for two types of electrodes. Figure 6 As shown.

[0071] Two types of electrode samples were cut and assembled into LCO||Si / C pouch cells with different LFO:LNO composite ratios, and then tested in a blue-chip system. The test procedure was as follows: under a voltage of 3V-4.53V, an initial charge-discharge cycle of 0.066C was performed, followed by 100 cycles at 1C. The cycle test results are shown in the figure. After 100 cycles, the specific capacity of the pure LCO-Si / C pouch cell decreased from 121 mAh / g to 103.5 mAh / g, with a cycle retention rate of 85%. In comparison, the specific capacity of the pouch cell with an LFO:LNO ratio of 3:1 decreased from 139.4 mAh / g to 138.9 mAh / g after 100 cycles, a decrease of only 0.5 mAh / g, with a cycle retention rate of 99.4%. Figure 7 As shown.

[0072] The pouch cells were fully charged at 0.5C and stored in an 85°C hot box for 5 hours. The volume change before and after storage was measured. After LFO lithium replenishment, the cells produced gas after storage at 85°C, and the volume change increased from 7% to 13.9%. After LFO-LNO composite lithium replenishment, the high-temperature storage performance was improved, and the volume change decreased to 7.5%, consistent with the benchmark cell. Figure 8 As shown.

Claims

1. A method for suppressing volume expansion of Si / C anode sheets in silicon-carbon lithium-ion batteries, characterized in that: The negative electrode of the silicon-carbon negative electrode lithium-ion battery is set as a Si / C negative electrode sheet, which is composed of irregular sheet-like silicon-carbon particles. The positive electrode of the silicon-carbon anode lithium-ion battery is set as a pre-embedded lithium-compensated positive electrode sheet, which is prepared using the following positive electrode sheet preparation method. In a low-humidity environment (<3.5%), lithium supplementing agent, binder, conductive agent, positive electrode active material, and NMP are mixed and stirred to obtain a slurry. The slurry is then coated onto the surface of aluminum foil and heated in a hot oven at 100-120℃ for 1-3 hours. The NMP evaporates and disappears after heating, and the resulting solidified material is a pre-lithiated lithium supplementing positive electrode sheet. The pre-lithiated lithium-supplemented cathode sheet, by solid mass percentage, consists of 1-10 parts lithium-supplementing agent, 5-10 parts binder, 5-10 parts conductive agent, and the remainder being cathode active material. Positive electrode active materials include LiCoO2 and / or NCM. Lithium supplements include Li5FeO4 and / or Li2NiO2; The positive active material particles of the pre-lithiated lithium-supplemented positive electrode sheet are uniformly distributed with lithium-supplementing particles around them. The positive active material particles exhibit an irregular blocky morphology, and the particle size distribution follows a log-normal pattern with an average particle size of 1-2 μm. The particle size of the lithium-supplementing particles is ≤1 μm. Pre-lithiated cathode plates effectively compensate for lithium loss during cycling in silicon-carbon anode lithium-ion batteries, enhancing the stability of the solid electrolyte interface and cathode electrolyte interface layer. The volume expansion of the Si / C anode in silicon-carbon lithium-ion batteries is suppressed by pre-lithiating and lithium-replenishing cathodes, and the generation of hydrogen gas during charging and discharging is also suppressed.

2. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 1, characterized in that: The SEM image of the pre-lithiated lithium-added cathode sheet. The lattice fringes corresponding to the LiCoO2 tissue plane are 0.5 ± 0.05 nm. The lattice stripes corresponding to the NCM tissue plane are 0.5 ± 0.05 nm. The lattice fringes corresponding to the Li5FeO4 microstructure plane are 0.2 ± 0.05 nm. The lattice fringes corresponding to the Li2NiO2 microstructure plane are 0.2±0.05 nm.

3. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 1, characterized in that: The silicon-carbon negative electrode lithium-ion battery is equipped with an electrolyte solution, which is composed of ethylene carbonate EC, methyl ethyl carbonate EMC and LiPF6, and uses a composite base membrane as a separator.

4. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 1, characterized in that: The thickness of the Si / C negative electrode is 43±1μm. The thickness growth rate of the silicon-carbon electrode is less than 4.5% with the increase of the number of cycles, and the gap between the silicon-carbon particles stabilizes at 45±0.5μm after 100 cycles. The lithium supplement includes Li5FeO4 and Li2NiO2, with an average particle size of 0.5-2μm and a moisture content of 20-23ppm; The positive electrode active materials include LiCoO2, LiFePO4, and NCM, with an average particle size of 1-3.5 μm and a specific surface area of ​​0.1-0.25 m². 2 / g, tap density is 2.5-3.5g / cm³ 3 .

5. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 1, characterized in that: The lithium supplement includes Li5FeO4 and Li2NiO2, with a weight ratio of 1 to 4:

1.

6. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 1, characterized in that: The lithium replenishing agent includes Li5FeO4 and Li2NiO2, and the weight ratio of Li5FeO4 to Li2NiO2 is 1:1, 2:1, 3:1, 4:1, 1:2, 1:3 or 1:

4.

7. A method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to any one of claims 1 to 6, characterized in that: The positive electrode active material includes lithium cobalt oxide, and the amount of lithium supplementer added is 1.5~5.5% or 2.5~3.5% of the lithium cobalt oxide by weight percentage; The method for preparing the positive electrode sheet involves first weighing the lithium replenishing agent, binder, conductive agent, and positive electrode active material according to the solid mass fractions, and then separately weighing 1-10 parts by mass of NMP. The lithium replenishing agent, binder, conductive agent, positive electrode active material, and NMP are then mixed into a paste-like slurry.

8. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 7, characterized in that: The positive electrode active material includes LiCoO2, LiFePO4 and NCM, and the weight ratio of LiCoO2, LiFePO4 and NCM is 1~3:1:

1.

9. The method for suppressing volume expansion of Si / C negative electrode sheet in a silicon-carbon negative electrode lithium-ion battery according to claim 1, characterized in that: The conductive agent includes at least one of conductive carbon black, graphene, and acetylene black, and the binder is selected from polyvinylidene fluoride. The conductive agent comprises graphite and silicon, with a mass ratio of graphite to silicon of 2 to 4:

1.

10. A silicon-carbon negative electrode lithium-ion battery for suppressing volume expansion of Si / C negative electrode sheet, the silicon-carbon negative electrode lithium-ion battery comprising a Si / C negative electrode sheet prepared using the method for suppressing volume expansion of Si / C negative electrode sheet of a silicon-carbon negative electrode lithium-ion battery according to any one of claims 1 to 9 and a pre-embedded lithium-filled positive electrode sheet, characterized in that: The negative electrode of a silicon-carbon lithium-ion battery is a Si / C negative electrode sheet composed of irregularly shaped sheet-like silicon-carbon particles. The positive electrode of a silicon-carbon anode lithium-ion battery is a pre-embedded lithium-replenishing positive electrode sheet. The pre-lithiated lithium-supplemented cathode sheet, by solid mass percentage, consists of 1-10 parts lithium-supplementing agent, 5-10 parts binder, 5-10 parts conductive agent, and the remainder being cathode active material. Positive electrode active materials include LiCoO2 and / or NCM. Lithium supplements include Li5FeO4 and / or Li2NiO2; The positive active material particles of the pre-lithiated lithium-supplemented positive electrode sheet are uniformly distributed with lithium-supplementing particles around them. The positive active material particles exhibit an irregular blocky morphology, and the particle size distribution follows a log-normal pattern with an average particle size of 1-2 μm. The particle size of the lithium-supplementing particles is ≤1 μm.

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