Gradient coating and conductive bridging synergistic composite lithium supplement agent and preparation method thereof

Abstract

The invention relates to the technical field of high-capacity lithium supplement of lithium ion batteries, in particular to a gradient coating and conductive bridging synergistic composite lithium supplement agent and a preparation method thereof. Aiming at the problem that the improvement thought of the existing lithium supplement agent is difficult to consider structural stability, efficient transmission and interface compatibility, the invention provides the following technical scheme: the lithium supplement agent comprises an inner core, a middle layer, a buffer layer and a chemical bridging conductive network which are sequentially arranged from inside to outside; the inner core is a metal oxide with high lithium content, and the middle layer is of a gradient structure; the buffer layer is made of flexible lithiated polymer gel; and the chemical bridging conductive network is formed by chemically bonding an aminated carbon material and the buffer layer through an amidation reaction. Through collaborative design of gradient coating, the doped transition layer and the chemical bridging conductive network, inner core volume expansion is adapted, ion and electron transmission is enhanced, interface impedance is reduced, interface optimization from the structure to transmission is achieved, and the first effect and the cycling stability of the battery are improved.

Description

Composite lithium supplementer with synergistic gradient coating and conductive bridging and its preparation method Technical Field

[0001] This invention relates to the field of high-capacity lithium replenishment technology for lithium-ion batteries, and particularly to a composite lithium replenishment agent with gradient coating and conductive bridging synergy, and its preparation method. Background Technology

[0002] With the increasing demand for high-energy-density lithium-ion batteries in new energy vehicles, energy storage equipment, and other fields, pre-lithiation technology has become a core means to compensate for active lithium loss and improve the battery's initial coulombic efficiency. Among these technologies, lithium-rich cathode additives (lithium replenishers) have become the preferred direction for industrial applications due to their good process compatibility and high safety. The performance of lithium replenishers directly determines the battery's energy density, cycle stability, and high-current output capability. However, their technological development still faces some challenges. Traditional oxide lithium replenishers experience severe volume expansion during delithiation, leading to particle breakage and coating peeling. This, in turn, triggers interfacial side reactions where the electrolyte erodes the core, resulting in the continuous accumulation of irreversible capacity loss. Coating technologies often employ homogeneous coatings of a single density, which can only passively block the electrolyte and cannot adapt to changes in the core's volume, making it difficult to fundamentally solve the structural collapse problem. Furthermore, the conductive network of existing lithium replenishers largely relies on the physical mixing of conductive agents and lithium replenisher particles, resulting in loose interfacial contact that is prone to detachment.

[0003] Although existing technologies have introduced improvements such as chemically bonded conductive networks and composite intermediate layers, the former fails to address the synergistic issue of ion transport and volume expansion, while the latter lacks a gradient transport channel design, thus failing to achieve a unified optimization of structural stability, efficient transport, and interface compatibility. Therefore, this invention proposes a composite lithium supplement with a stable structure that adapts to volume changes, a continuous and efficient transport channel, and a gradient coating and conductive bridging mechanism at a low-impedance interface, along with its preparation method. Summary of the Invention

[0004] The purpose of this invention is to address the problems in the prior art, such as the severe volume expansion during delithiation of existing lithium replenishing agents, structural collapse caused by incompatible coating layers, and loose interfacial contact due to physical mixing of conductive networks. The improvement approach struggles to balance structural stability, efficient transmission, and interfacial compatibility. This invention proposes a composite lithium replenishing agent with synergistic gradient coating and conductive bridging, and its preparation method.

[0005] The technical solution of the present invention: a composite lithium replenishing agent with gradient coating and conductive bridging synergy, comprising a core, an intermediate layer, a buffer layer and a chemically bridging conductive network arranged sequentially from the inside to the outside;

[0006] The core is a high-lithium-content metal oxide with a particle size D50 of 50-200 nm.

[0007] The intermediate layer has a gradient structure, including an inner shell and an outer shell; the inner shell is an ion conductor material with a thickness of 1-5 nm; the outer shell is a hybrid electron and ion conductor material with a thickness of 3-10 nm.

[0008] A doped transition layer is provided between the inner shell layer and the outer shell layer. The doped transition layer is a composite phase of ionic conductor material and electronic and ionic mixed conductor material, with a doping molar ratio of 1:0.3-0.7 and a thickness of 1-3 nm.

[0009] The buffer layer is a flexible lithium-ion polymer gel with a thickness of 2-8 nm and an elastic modulus of 0.05-2 GPa.

[0010] The chemically bridged conductive network is formed by the chemical bonding of aminated carbon material to the buffer layer through an amidation reaction. The carbon material accounts for 0.5%-5% of the total mass of the lithium supplement and has a conductivity ≥102-104 S / cm.

[0011] Optionally, the core is Li5FeO4, Li6CoO4, or Li5Fe1- x Co x At least one of the O4 solid solutions.

[0012] Optionally, the inner shell layer is at least one of Li3PO4, Li3BO3, and Li4SiO4;

[0013] The outer shell layer is at least one of Li2TiS3, Li2MoS3, and Li3NbS4;

[0014] The composite phase of the doped transition layer is formed by stepwise doping through atomic layer deposition and sol-gel method to form a continuous gradient transport channel and reduce the Li+ diffusion barrier to ≤0.8eV.

[0015] Optionally, the buffer layer is at least one of lithium-ion polyacrylic acid, lithium-ion polyacrylonitrile, and lithium-ion polyacrylamide.

[0016] Optionally, the buffer layer is doped with 0.1%-1% nano-Li2CO3 particles with a particle size of 5-20nm to synergistically suppress interfacial side reactions between the electrolyte and the core, thereby reducing irreversible capacity loss during the first cycle.

[0017] Optionally, the aminated carbon material is at least one of CNT-NH2 and graphene-NH2, and a Ti-SC / NCO covalent bond is formed at the chemical bridging interface, with an XPS binding energy range of 398.2-398.8 eV.

[0018] This invention also proposes a method for preparing a composite lithium supplement agent with synergistic gradient coating and conductive bridging, comprising the following steps:

[0019] Step 1: Core preparation: High-lithium-content metal oxide cores are synthesized via the sol-gel method;

[0020] Step 2, Gradient Coating of Intermediate Layer: An ionic conductor inner shell layer is deposited on the core surface using ALD deposition for 10-50 cycles. Then, a doped transition layer is formed on the surface of the inner shell layer by stepwise doping using ALD deposition and sol-gel method. Finally, an electronic and ionic mixed conductor outer shell layer is coated using sol-gel method.

[0021] Step 3: Coating the buffer layer: Mix the lithium polymer gel solution with nano Li2CO3 particles evenly, immerse the product obtained in Step 2 into the mixed solution, coat the buffer layer by the impregnation method and dry;

[0022] Step 4: Constructing a chemically bridged conductive network: Aminated carbon material and thioacetamide crosslinking agent are added to NMP solvent and mixed with the product obtained in Step 3. Chemical bonding is achieved through amidation reaction. After drying, a composite lithium supplement precursor is obtained.

[0023] Step 5, in-situ activation: The precursor and electrode material are mixed to prepare an electrode sheet. After rolling, a pulse current of 1-10 A / cm² is applied in an inert atmosphere to induce the formation of a transition layer at the interface, thus obtaining the finished composite lithium supplement.

[0024] Optionally, the molar ratio of Li3PO4 to Li2TiS3 in the doped transition layer is 1-1.05:0.5-0.6, and the thickness is 1.8-2.2 nm.

[0025] Optionally, the pulse width of the pulse current in step five is 5-200 ms, and the inert atmosphere is Ar or N2.

[0026] In summary, this application includes at least one of the following beneficial technical effects:

[0027] This invention employs a gradient coating design consisting of an ionic conductor inner shell, a doped transition layer, and an electronic and ionic mixed conductor outer shell, combined with a flexible lithium-based polymer gel buffer layer. This design can adapt to the volume expansion during core delithiation, preventing particle breakage and coating layer peeling. The nano-Li2CO3 particles doped in the buffer layer can further suppress interfacial side reactions between the electrolyte and the core, significantly reducing irreversible capacity loss and greatly improving the cycling stability of the lithium replenishment agent.

[0028] In this invention, the doped transition layer between the inner shell and the outer shell forms a continuous gradient transport interface, effectively eliminating the transport bottleneck between the two layers. At the same time, the three-dimensional conductive network formed by the aminated carbon material through the amidation reaction and chemical bonding with the buffer layer replaces the traditional physical mixing mode, greatly improving the interface contact stability, ensuring the synchronous and efficient transport of ions and electrons, shortening the activation time of the lithium replenishment agent, and adapting to the high current charging and discharging requirements of the battery.

[0029] The synergistic effect of chemically bridged conductive networks and in-situ activation processes enables the formation of low-resistance covalent bonds and transition layers at the lithium replenishment interface. The synergistic design of gradient coating structure, chemically bridged network and buffer layer modification solves the three core problems of structural stability, efficient transport and interface compatibility, significantly improving the initial coulombic efficiency and long-term cycle stability of lithium-ion batteries.

[0030] The preparation method of this invention adopts mature processes such as sol-gel method, ALD deposition method, and impregnation method. The steps are clear and easy to scale up. The lithium replenishing agent is compatible with the existing lithium-ion battery electrode preparation process. No additional adjustment of production equipment is required. It can be directly applied to the industrial production of high energy density batteries and has broad industrialization prospects.

[0031] In summary, this invention, through the synergistic design of gradient coating, doped transition layer and chemically bridged conductive network, adapts to core volume expansion, enhances ion and electron transport, and reduces interface impedance, thereby achieving interface optimization from structure to transport and improving battery first efficiency and cycle stability. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0033] A Li5FeO4-based gradient core-shell lithium supplementer was prepared by combining gradient coating and conductive bridging synergistic composite lithium supplementer and its preparation method.

[0034] Example 1

[0035] The method for preparing the composite lithium supplement agent with gradient coating and conductive bridging synergy proposed in this invention includes the following steps:

[0036] Step 1: Preparation of the core: Fe(NO3)3・9H2O and LiOH・H2O were mixed at a molar ratio of Li:Fe=2:1 and hydrothermally reacted at 160℃ for 18h. After washing the product, it was vacuum dried at 80℃ to obtain a Li5FeO4 core with D50=100nm.

[0037] Step 2, Gradient Coating of Intermediate Layer: Using LiHMDS and TMPO as precursors, ALD deposition was performed at 150℃ for 30 cycles to form a 2nm thick Li3PO4 inner shell layer; the particles were dispersed in a solution containing Ti(OiPr)4 and Li2S and reacted at 60℃ for 3h to form a 5nm thick Li2TiS3 outer shell layer; at the same time, a 2nm thick Li3PO4-Li2TiS3 transition layer was formed between the inner shell layer and the outer shell layer through stepwise doping.

[0038] Step 3: Coating the buffer layer: Immerse the coated particles in a 2wt% LiPAA solution and dry at 60℃ to form a 3nm thick flexible gel layer. The gel layer is doped with 0.5wt% nano-Li2CO3 with a particle size of 10nm.

[0039] Step 4: Constructing a chemically bridged conductive network: Add 2wt% CNT-NH2 to NMP solvent containing 0.5wt% TAA, ultrasonically disperse for 2 hours, and then anneal at 80℃ for 1 hour to form a Ti-SC covalent interface;

[0040] LiNi containing a gradient core-shell lithium supplement was prepared by combining the lithium supplement preparation methods in steps one through four above. 0.8 Co 0.1 Mn 0.1 The O2 positive electrode plate specifically includes the following steps:

[0041] 1. Slurry formulation: Take LiNi 0.8 Co 0.1 Mn 0.1 90 parts of O2, 5 parts of lithium supplement, 2 parts of carbon black, and 3 parts of PVDF were mixed and then NMP was added to prepare a slurry with a solid content of 45%.

[0042] 2. Coating and activation: The slurry is coated onto carbon-coated aluminum foil with a wet film thickness of 200 μm. It is pre-dried at 80℃ for 15 min and finally dried at 120℃ for 20 min. It is then rolled to an electrode thickness of 60 μm. Activation is completed by applying a pulsed current of 3 A / cm² in an Ar atmosphere.

[0043] Example 2

[0044] Based on the lithium supplement preparation method in Example 1, a LiFePO4 positive electrode sheet with a high lithium supplement addition amount was prepared, specifically including the following steps:

[0045] 1. Slurry formulation: Take 85 parts of LiFePO4, 2 parts of lithium supplement, 0.5 parts of graphene, and 1 part of PVDF, mix them, and add NMP to prepare a slurry with a solid content of 40%.

[0046] 2. Coating and activation: The slurry is coated onto carbon-coated aluminum foil with a wet film thickness of 180 μm. It is pre-dried at 80℃ for 20 min and finally dried at 110℃ for 25 min. The film is then rolled to a thickness of 60 μm. Activation is completed by applying a pulsed current of 5 A / cm² in an Ar atmosphere.

[0047] Example 3

[0048] Based on the lithium supplement preparation method of Example 1, a LiNi0.8Co0.1Mn0.1O2 positive electrode sheet with high lithium supplement addition was prepared, specifically including the following steps:

[0049] 1. Slurry formulation: Take 95 parts of LiNi0.8Co0.1Mn0.1O2, 8 parts of lithium supplement, 5 parts of graphene, and 4 parts of PVDF, mix them, and add NMP to prepare a slurry with a solid content of 48%.

[0050] 2. Coating and activation: The slurry is coated onto carbon-coated aluminum foil with a wet film thickness of 220 μm. It is pre-dried at 90℃ for 15 min and finally dried at 130℃ for 15 min. The film is then rolled to an electrode thickness of 65 μm. Activation is completed by applying a pulsed current of 8 A / cm² in an Ar atmosphere.

[0051] control group

[0052] A conventional positive electrode sheet without the addition of the gradient core-shell lithium supplementation agent of the present invention was used as a control group. Its preparation method was the same as that of the positive electrode active material in the corresponding Example 1, but it did not contain the lithium supplementation agent and pulse current activation was not performed in the process.

[0053] The experimental data comparing the performance of the lithium-added positive electrode cells of Examples 1-3 and the control group are shown in the table below. The test conditions were "2032 type coin cell, positive electrode corresponding to the example electrode / control group electrode, negative electrode metallic lithium", 25±3℃, 0.1C charge and discharge".

[0054] Table 1. Comparative Experimental Data of Lithium-Added Positive Electrode Battery Performance

[0055] Performance Indicators Example 1 Example 2 Example 3 Control Group Initial Discharge Capacity 165mAh / g 152-158mAh / g 170-175mAh / g 156mAh / g Coulombic Efficiency (First Week) 97.2% 95-96.5% 97.5-98.0% 89.30% 200-Cycle Retention Rate 97.5% >96% >97.5% 91.5% Interface Impedance (Rint) 3.8Ω·cm² <4.2Ω·cm² <4.0Ω·cm² 18.7Ω·cm² High Temperature Expansion Rate 1.8% <2.2% 1.9% 7.5% surface

[0056] Based on the data table above, it can be seen that the gradient coating and conductive bridging synergistic composite lithium supplement agent prepared by this invention can significantly improve the battery performance of different cathode systems (LiNi0.8Co0.1Mn0.1O2, LiFePO4):

[0057] Capacity and efficiency improvements: The initial discharge capacity and first-week coulombic efficiency of Examples 1-3 were superior to the control group. Among them, Example 3 with high lithium replenishment achieved an initial capacity of 170-175 mAh / g and a first-week efficiency of over 97.5%.

[0058] Enhanced cyclic stability: The retention rate after 200 cycles was >96%, significantly higher than the 91.5% of the control group;

[0059] Interface and structure optimization: The interface impedance is reduced to below 4.5Ω・cm², and the high-temperature expansion rate is <2.2%, which solves the problems of structural collapse and interfacial side reactions in traditional lithium supplementation agents.

[0060] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A composite lithium supplement agent with synergistic gradient coating and conductive bridging, characterized in that, The system comprises, from the inside out, a core, an intermediate layer, a buffer layer, and a chemically bridging conductive network. The core is a high-lithium-content metal oxide with a particle size D50 of 50-200 nm. The intermediate layer has a gradient structure, including an inner shell and an outer shell. The inner shell is an ionic conductor material with a thickness of 1-5 nm; the outer shell is a hybrid electron-ion conductor material with a thickness of 3-10 nm. A doped transition layer is provided between the inner and outer shell layers. This transition layer is a composite phase of the ionic conductor material and the hybrid electron-ion conductor material, with a doping molar ratio of 1:0.3-0.7 and a thickness of 1-3 nm. The buffer layer is a flexible lithium-ionized polymer gel with a thickness of 2-8 nm and an elastic modulus of 0.05-2 GPa. The chemically bridging conductive network is formed by the chemical bonding of aminated carbon material to the buffer layer via an amidation reaction. The carbon material accounts for 0.5%-5% of the total mass of the lithium supplement and has a conductivity ≥10. 2 -10 4 S / cm.

2. The composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 1, characterized in that, The core is Li5FeO4, Li6CoO4, or Li5Fe1- x Co x At least one of the O4 solid solutions.

3. The composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 1, characterized in that, The inner shell is at least one of Li3PO4, Li3BO3, and Li4SiO4; the outer shell is at least one of Li2TiS3, Li2MoS3, and Li3NbS4; the composite phase of the doped transition layer is formed by stepwise doping via atomic layer deposition and sol-gel method, used to form continuous gradient transport channels and reduce Li + The diffusion barrier is ≤0.8eV.

4. The composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 1, characterized in that, The buffer layer is at least one of lithium-ion polyacrylic acid, lithium-ion polyacrylonitrile, and lithium-ion polyacrylamide.

5. The composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 4, characterized in that, The buffer layer is doped with 0.1%-1% nano-Li2CO3 particles with a particle size of 5-20nm, which is used to synergistically suppress the interfacial side reactions between the electrolyte and the core, and reduce irreversible capacity loss in the first cycle.

6. The composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 1, characterized in that, The aminated carbon material is at least one of CNT-NH2 and graphene-NH2, and a Ti-SC / NCO covalent bond is formed at the chemical bridging interface, with an XPS binding energy range of 398.2-398.8 eV.

7. A method for preparing a composite lithium supplement agent with gradient coating and conductive bridging synergy according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Core Preparation: A high-lithium-content metal oxide core is synthesized via a sol-gel method. Step 2: Gradient Coating of the Intermediate Layer: An ionic conductor inner shell is deposited on the core surface using ALD deposition for 10-50 cycles. Then, stepwise doping is performed using ALD deposition and a sol-gel method to form a doped transition layer on the inner shell surface. Finally, a mixed electron-ion conductor outer shell is coated using a sol-gel method. Step 3: Buffer Layer Coating: A lithium-based polymer gel solution is uniformly mixed with nano-Li₂CO₃ particles. The product obtained in Step 2 is immersed in the mixed solution, and a buffer layer is coated using an impregnation method and then dried. Step 4: Construction of a Chemically Bridging Conductive Network: Aminated carbon material and thioacetamide crosslinking agent are added to NMP solvent and mixed with the product obtained in Step 3. Chemical bonding is achieved through an amidation reaction. After drying, a composite lithium supplement precursor is obtained. Step 5: In-situ Activation: The precursor is mixed with electrode materials to prepare an electrode sheet. After rolling, a pulsed current of 1-10 A / cm² is applied in an inert atmosphere to induce the formation of a transition layer at the interface, resulting in the finished composite lithium supplement.

8. The method for preparing the composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 7, characterized in that, The molar ratio of Li3PO4 to Li2TiS3 in the doped transition layer is 1-1.05:0.5-0.6, and the thickness is 1.8-2.2 nm.

9. The method for preparing the composite lithium supplement agent with gradient coating and conductive bridging synergy according to claim 7, characterized in that, The pulse width of the pulsed current in step five is 5-200 ms, and the inert atmosphere is Ar or N. 2。