Long-circulation lithium battery and preparation method thereof

Abstract

The invention discloses a long-circulation lithium battery and a preparation method thereof, and relates to the technical field of lithium battery preparation, the long-circulation lithium battery comprises a gradient doped ternary material-spinel composite structure positive electrode material, a designed porous carbon skeleton confined silicon nanoparticle (Si-C) negative electrode material, and a lithium bis (fluorosulfonyl) imide (LiFSI)-based high-concentration electrolyte, the surface of the polyimide (PI)-based composite diaphragm is coated with a boron nitride nanosheet (BNNS) and polydopamine (PDA), and a three-dimensional porous current collector and a gradient porosity electrode are introduced into the battery structure; through gradient doping and composite coating of a positive electrode material, negative electrode porous carbon confinement silicon and pre-lithiation, collaborative optimization of a high-concentration electrolyte, a high-heat-resistance self-repairing diaphragm and design of a three-dimensional porous current collector and a gradient porosity electrode, remarkable improvement of the battery in the aspects of high energy density, ultra-long cycle life, high safety and rapid charge and discharge performance is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery preparation, and more specifically, to a long-cycle lithium battery and a preparation method thereof. Background Art

[0002] With the rapid development of modern technology, lithium batteries, as an efficient and clean energy storage device, have been widely used in many fields such as electric vehicles, portable electronic devices, and large-scale energy storage systems. However, current lithium battery technology still faces many challenges in practical applications and urgently needs further optimization and improvement, as follows: 1. Positive electrode materials Traditional ternary materials (such as LiNi x Co y Mn n O2, etc.) as positive electrode materials for lithium batteries, although they have high energy density, they have some inherent defects. On the one hand, during the charge and discharge cycle, especially in high nickel systems, lattice distortion is prone to occur. This is because the radius of nickel ions is similar to that of lithium ions. During the lithium ion deintercalation process, nickel ions easily migrate to the lithium layer, thereby destroying the layered structure integrity of the positive electrode material, resulting in a decrease in the cycle stability of the material and accelerated capacity decay. For example, the common LiNi 0.8 Co 0.1 Mn 0.1 After multiple charge and discharge cycles, the capacity retention rate of O2 materials is often difficult to meet the application requirements of long cycle life. Usually, after about 1,000 cycles at a 1C rate, the capacity retention rate can only reach about 70%.

[0003] On the other hand, during high-voltage charge and discharge, the surface structure of traditional ternary materials is prone to changes, triggering side reactions such as electrolyte decomposition and transition metal dissolution, which not only further reduces the battery capacity but also affects the battery's safety and overall performance. Although some simple doping or coating methods have been used to improve their performance, the results are still not ideal and cannot simultaneously meet the performance requirements of high energy density, high voltage stability, and long cycle life.

[0004] 2. Negative electrode materials Currently, graphite is the most widely used anode material, but its relatively low theoretical specific capacity (372 mAh / g) limits further increases in the overall energy density of lithium batteries. Silicon-based materials, due to their ultra-high theoretical specific capacity (approximately 4200 mAh / g), have become a highly promising alternative. However, silicon undergoes a significant volume expansion during the charge and discharge process (up to 300% or more). This volume change can cause the electrode material to pulverize and detach, further damaging the electrode structure and dramatically reducing the battery's cycling performance. Furthermore, silicon materials experience significant irreversible capacity loss during the initial charge and discharge process, which also affects the battery's actual performance.

[0005] Although silicon-based negative electrodes have been modified through some nano-sizing and composite methods, such as the preparation of silicon-carbon composite materials, the ideal effect has not been achieved in alleviating volume expansion and improving the initial coulombic efficiency, and it is difficult to meet the comprehensive requirements of high-performance lithium batteries for long cycle life and high energy density of negative electrode materials.

[0006] 3. Electrolyte Conventional electrolyte systems have also exposed numerous issues during the long-term use of lithium batteries. For example, commonly used lithium salts (such as LiPF6) easily decompose under conditions of high temperature and high voltage, producing corrosive substances such as HF. This not only corrodes the electrode materials but also damages the solid electrolyte interface (SEI) film formed within the battery, leading to a decrease in battery performance. Furthermore, the ionic conductivity of traditional electrolytes is insufficient to meet the requirements for rapid lithium ion transport during high-rate charge and discharge, limiting the battery's fast-charging performance.

[0007] Although the performance of the electrolyte can be improved to a certain extent by adding some additives, there is a lack of effective synergy between the various components, making it difficult to comprehensively improve the adaptability of the electrolyte in terms of high energy density, long cycle life, and fast charging and discharging.

[0008] 4. Diaphragm Existing separator materials, such as polyolefin separators (e.g., polyethylene (PE) and polypropylene (PP) separators), while possessing certain mechanical properties and chemical stability, suffer from poor heat resistance. In high-temperature environments, they are prone to thermal shrinkage and even thermal runaway, seriously compromising battery safety. Furthermore, over long-term use, conventional separators, influenced by factors such as internal battery stress and temperature fluctuations, may develop microcracks and other damage that are unable to repair themselves, thus affecting battery performance and lifespan.

[0009] 5. Battery structure Traditional two-dimensional planar current collector structures and uniform porosity electrode designs have limitations in ion transport efficiency. Lithium ions travel a long distance within the electrode, which can lead to ion transport congestion, especially during high-rate charge and discharge. This increases battery polarization and reduces charge and discharge efficiency, limiting the battery's rapid charge and discharge capabilities and overall performance improvements.

[0010] In summary, existing lithium batteries have deficiencies in several key components and structural designs, making it difficult to simultaneously meet the requirements for high energy density, ultra-long cycle life, high safety, and rapid charge and discharge performance. Therefore, there is an urgent need to develop a new lithium battery design and preparation method that can coordinately optimize multiple dimensions, including positive electrode materials, negative electrode materials, electrolytes, separators, and battery structures, to overcome the limitations of existing technologies and meet the growing demand for high-performance lithium battery applications.

[0011] Based on the above background, the present invention proposes a long-cycle lithium battery and a preparation method thereof, aiming to solve the problems existing in the above-mentioned prior art and achieve an all-round improvement in the performance of the lithium battery. Summary of the Invention

[0012] In view of the shortcomings of the prior art, the present invention aims to provide a long-cycle lithium battery and a preparation method thereof.

[0013] To achieve the above object, the present invention provides the following technical solutions: A long-cycle lithium battery includes a positive electrode material of a gradient-doped ternary material@spinel composite structure, a negative electrode material of silicon nanoparticles (Si@C) confined by a porous carbon skeleton, a high-concentration electrolyte based on lithium bis(fluorosulfonyl)imide (LiFSI), a polyimide (PI)-based composite separator, and a surface of the polyimide (PI)-based composite separator coated with boron nitride nanosheets (BNNS) and polydopamine (PDA), and the battery structure introduces a three-dimensional porous current collector and a gradient porosity electrode.

[0014] Furthermore, the cathode material is co-doped with magnesium (Mg) and titanium (Ti) to suppress lattice distortion and composite spinel phase LiNi 0. 5Mn1.5O4 (LNMO).

[0015] Furthermore, the negative electrode material is combined with a pre-lithiation process to compensate for the first irreversible capacity loss.

[0016] Furthermore, boron-containing ionic liquid (IL-B) and cyclic vinyl sulfate (DTD) were added to the high-concentration electrolyte to synergistically optimize the SEI / CEI membrane.

[0017] Furthermore, a method for preparing a long-cycle lithium battery comprises the following steps: Step 1: The precursor is mixed with Mg(NO3)2 and Ti(OC4H9)4 and ball-milled. In an oxygen atmosphere, it is sintered in two stages: the first stage is kept at 850℃ for 12 hours, and the second stage is annealed at 750℃ for 5 hours to form NCM-MgTi. The NCM-MgTi particles are mixed with LiOH and Mn(NO3)2 at a ratio of Li:Mn=1:1.5, and a LNMO layer is formed on the surface by spray drying to finally obtain the NCM-MgTi@LNMO composite positive electrode. Step 2: Mix silicon nanoparticles with phenolic resin, carbonize to obtain porous carbon-coated silicon, activate with KOH to create pores, and immerse the porous carbon-coated silicon negative electrode in a solution containing Li + In the organic solution (Li2S6 / DOL-DME), the pre-lithiation amount accounts for 10% of the total capacity; Step 3: Mixing the base solvent, lithium salt, and additives to prepare a high-concentration electrolyte; Step 4: Select the base film, disperse BNNS (5 wt%) and PDA (2 wt%) in NMP, coat them on both sides of the PI film, and form a BNNS-PDA / PI composite membrane after drying; Step 5: The positive electrode uses a three-dimensional aluminum foam current collector, and the negative electrode uses a copper mesh current collector. The electrode porosity gradually decreases from the current collector to the surface; Step 6: After the positive electrode, separator and negative electrode are wound, the electrolyte is injected and packaged into a long-cycle lithium battery.

[0018] Furthermore, in step 1, the doping amount of Mg(NO3)2 is 1%, the doping amount of Ti(OC4H9)4 is 0.5%, the mixed ball milling time is 6h, the thickness of the LNMO layer is 50-100 nm, and the molar ratio of the precursor, Mg(NO3)2, and Ti(OC4H9)4 is 8:1:1=Ni:Co:Mn.

[0019] Furthermore, in step 2, the mass ratio of silicon nanoparticles to phenolic resin is 1:3, the porosity of pore formation by KOH activation is controlled at 60%-70%, and the particle size of the silicon nanoparticles is 50 nm.

[0020] Furthermore, in step three, the base solvent is: EC:EMC = 3:7 (volume ratio), the lithium salt is: LiFSI concentration is 1.8 mol / L, and the additives are: IL-B (1wt%), DTD (2wt%), and LiPO2F2 (0.5wt%).

[0021] Furthermore, the base film is a polyimide (PI) film with a thickness of 20 μm.

[0022] Compared with the prior art, the present invention has the following beneficial effects: The long-cycle lithium battery and its preparation method provided by the present invention achieve significant improvements in the battery's high energy density, ultra-long cycle life, high safety and fast charge and discharge performance through gradient doping and composite coating of positive electrode materials, porous carbon-confined silicon and pre-lithiation of the negative electrode, synergistic optimization of high-concentration electrolyte, high heat-resistant self-healing diaphragm and three-dimensional porous current collector + gradient porosity electrode design. DETAILED DESCRIPTION

[0023] A long-cycle lithium battery includes a positive electrode material of a gradient-doped ternary material@spinel composite structure, a negative electrode material of silicon nanoparticles (Si@C) confined by a porous carbon skeleton, a high-concentration electrolyte based on lithium bis(fluorosulfonyl)imide (LiFSI), a polyimide (PI)-based composite separator, and a surface of the polyimide (PI)-based composite separator coated with boron nitride nanosheets (BNNS) and polydopamine (PDA), which has both high heat resistance and self-healing functions. The battery structure introduces a three-dimensional porous current collector and a gradient porosity electrode to improve ion transmission efficiency.

[0024] The positive electrode material suppresses lattice distortion by co-doping with magnesium (Mg) and titanium (Ti), and improves high voltage stability by compounding the spinel phase LiNi0.5Mn1.5O4 (LNMO).

[0025] The negative electrode material is combined with the pre-lithiation process to compensate for the first irreversible capacity loss.

[0026] Boron-containing ionic liquid (IL-B) and cyclic vinyl sulfate (DTD) were added to the high-concentration electrolyte to synergistically optimize the SEI / CEI membrane.

[0027] A long cycle lithium battery and a preparation method thereof, comprising the following steps: Step 1: The precursor was mixed with Mg(NO3)2 (doping amount 1%) and Ti(OC4H9)4 (doping amount 0.5%) and ball milled for 6 hours. In an oxygen atmosphere, it was sintered in two stages: the first stage was kept at 850℃ for 12 hours, and the second stage was annealed at 750℃ for 5 hours to form LiNi0.8Co0.1Mn0.1Mg0.01Ti0.005O2 (abbreviated as NCM-MgTi). The NCM-MgTi particles were mixed with LiOH and Mn(NO3)2 at a ratio of Li:Mn=1:1.5, and a LNMO layer (thickness 50-100 nm) was formed on the surface by spray drying. Finally, the NCM-MgTi@LNMO composite cathode was obtained. The molar ratio of the precursor, Mg(NO3)2, and Ti(OC4H9)4 is 8:1:1=Ni:Co:Mn.

[0028] Step 2: Mix silicon nanoparticles with phenolic resin (mass ratio 1:3), carbonize to obtain porous carbon-coated silicon (Si@C), activate with KOH to create pores, control the porosity at 60%-70%, and immerse the Si@C negative electrode in a solution containing Li + In the organic solution (Li2S6 / DOL-DME), the pre-lithiation amount accounts for 10% of the total capacity; The particle size of the silicon nanoparticles is 50 nm.

[0029] Step 3: Mixing the base solvent, lithium salt, and additives to prepare a high-concentration electrolyte; Basic solvent: EC:EMC = 3:7 (volume ratio); Lithium salt: LiFSI concentration 1.8 mol / L; Additives: IL-B (1wt%), DTD (2wt%), LiPO2F2 (0.5wt%).

[0030] Step 4: Select the base film, disperse BNNS (5 wt%) and PDA (2 wt%) in NMP, coat them on both sides of the PI film, and form a BNNS-PDA / PI composite membrane after drying; The base film was a polyimide (PI) film (thickness 20 μm).

[0031] Step 5: The positive electrode uses a three-dimensional foam aluminum current collector, and the negative electrode uses a copper mesh current collector. The electrode porosity gradually decreases from the current collector to the surface (80%→50%).

[0032] Step 6: After the positive electrode, separator and negative electrode are wound, the electrolyte is injected and packaged into a long-cycle lithium battery.

[0033] Example 1: Positive electrode material performance test XRD analysis: The half-width of the (003) peak of NCM-MgTi@LNMO is reduced by 30% compared with the undoped sample, indicating that the lattice integrity is improved.

[0034] Cycling test: At 2.8-4.5 V and 1C rate, the capacity retention rate after 1000 cycles increased from 72% of conventional NCM811 to 92%.

[0035] Example 2: Negative electrode volume expansion suppression effect SEM observation: The volume expansion rate of the Si@C anode after 100 cycles is 18% (conventional silicon-carbon material is 45%). First Coulombic efficiency: increased from 75% to 89% after pre-lithiation.

[0036] Example 3: High temperature stability of electrolyte 45°C storage test: The capacity of the battery using this electrolyte decayed by only 3% after 7 days (the traditional electrolyte decayed by 12%). EIS analysis: interface impedance decreased by 50%.

[0037] Example 4: Thermal safety of diaphragm Thermal shrinkage: The shrinkage of BNNS-PDA / PI membrane is less than 5% at 200°C for 30 minutes (the shrinkage of ordinary PE membrane is greater than 60%). Needle penetration test: The battery did not experience thermal runaway.

[0038]

[0039] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

[0040] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A long cycle lithium battery, characterized in that: The long-cycle lithium battery includes a positive electrode material of a gradient-doped ternary material@spinel composite structure, a negative electrode material of silicon nanoparticles (Si@C) confined by a porous carbon skeleton, a high-concentration electrolyte based on lithium bis(fluorosulfonyl)imide (LiFSI), a polyimide (PI)-based composite separator, and a polyimide (PI)-based composite separator coated with boron nitride nanosheets (BNNS) and polydopamine (PDA). The battery structure introduces a three-dimensional porous current collector and a gradient porosity electrode.

2. A long cycle lithium battery according to claim 1, characterized in that: The cathode material suppresses lattice distortion by co-doping magnesium (Mg) and titanium (Ti) and composites spinel phase LiNi 0. 5Mn1.5O4 (LNMO).

3. A long cycle lithium battery according to claim 1, characterized in that: The negative electrode material is combined with the pre-lithiation process to compensate for the first irreversible capacity loss.

4. A long cycle lithium battery according to claim 1, characterized in that: Boron-containing ionic liquid (IL-B) and cyclic vinyl sulfate (DTD) were added to the high-concentration electrolyte to synergistically optimize the SEI / CEI membrane.

5. A method for preparing a long-cycle lithium battery, applied to a long-cycle lithium battery according to any one of claims 1 to 4, characterized in that: Here are the steps: Step 1: The precursor is mixed with Mg(NO3)2 and Ti(OC4H9)4 and ball-milled. In an oxygen atmosphere, it is sintered in two stages: the first stage is kept at 850℃ for 12 hours, and the second stage is annealed at 750℃ for 5 hours to form NCM-MgTi. The NCM-MgTi particles are mixed with LiOH and Mn(NO3)2 at a ratio of Li:Mn=1:1.5, and a LNMO layer is formed on the surface by spray drying to finally obtain the NCM-MgTi@LNMO composite positive electrode. Step 2: Mix silicon nanoparticles with phenolic resin, carbonize to obtain porous carbon-coated silicon, activate with KOH to create pores, and immerse the porous carbon-coated silicon negative electrode in a solution containing Li + In the organic solution (Li2S6 / DOL-DME), the pre-lithiation amount accounts for 10% of the total capacity; Step 3: Mixing the base solvent, lithium salt, and additives to prepare a high-concentration electrolyte; Step 4: Select the base film, disperse BNNS (5 wt%) and PDA (2 wt%) in NMP, coat them on both sides of the PI film, and form a BNNS-PDA / PI composite membrane after drying; Step 5: The positive electrode uses a three-dimensional foam aluminum current collector, and the negative electrode uses a copper mesh current collector. The electrode porosity gradually decreases from the current collector to the surface; Step 6: After the positive electrode, separator and negative electrode are wound, the electrolyte is injected and packaged into a long-cycle lithium battery.

6. The method for preparing a long-cycle lithium battery according to claim 5, characterized in that: In step 1, the doping amount of Mg(NO3)2 is 1%, the doping amount of Ti(OC4H9)4 is 0.5%, the mixed ball milling time is 6h, the thickness of the LNMO layer is 50-100 nm, and the molar ratio of the precursor, Mg(NO3)2, and Ti(OC4H9)4 is 8:1:1=Ni:Co:Mn.

7. The method for preparing a long-cycle lithium battery according to claim 5, characterized in that: In step 2, the mass ratio of silicon nanoparticles to phenolic resin is 1:3, the porosity of KOH-activated pores is controlled at 60%-70%, and the particle size of the silicon nanoparticles is 50 nm.

8. The method for preparing a long-cycle lithium battery according to claim 5, characterized in that: In step 3, the base solvent is EC:EMC = 3:7 (volume ratio), the lithium salt is LiFSI with a concentration of 1.8 mol / L, and the additives are IL-B (1 wt%), DTD (2 wt%), and LiPO2F2 (0.5 wt%).

9. The method for preparing a long-cycle lithium battery according to claim 5, characterized in that: The base film is a polyimide (PI) film with a thickness of 20 μm.

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