Patent Application
20230411598
This application claims all benefits under 35 U.S.C. § 119 from the Chinese Patent Application No. 202210690849.0, filed on Jun. 17, 2022, in the China National Intellectual Property Administration, the disclosure of which is incorporated herein by reference.
The present application relates to a silicon-carbon pre-lithium composite anode material and a method for making the silicon-carbon pre-lithium composite anode material.
Currently, pre-lithium processing of lithium-ion batteries is an important method to improve energy density and cycle life of the batteries. The pre-lithium processing is divided into making cathode electrode pre-lithium and anode electrode pre-lithium. The cathode electrode pre-lithium is made by adding lithium-rich oxides to the cathode electrode to supplement the lithium source loss during a first activation process. The anode electrode pre-lithium is made by inserting lithium ions into the anode electrode active material by pressing a lithium source such as a lithium metal thin film on the surface of the anode electrode active material layer. Although such processing can improve the lifetime by reducing the initial irreversibility of the silicon-based anode electrode active material, the above described process also generates a number of by-products during the pre-lithiation of the lithium source to the silicon-based anode electrode active material. However, lithium oxide with low conductivity is produced mostly on the surface of silicon-based anode active materials, so this method has a limit to reduce the irreversibility.
The pre-lithium method in the prior art can only realize one-time replenishment of the anode electrode in the first activation to improve the loss of active lithium caused by the first charge. However, after the one-time replenishment pre-lithium processing, most of the pre-lithium materials exists in the battery in the form of an inert substance, which reduces the overall energy density and power density. Therefore, the one-time replenishment pre-lithium method cannot effectively replenish the lithium loss caused by the charge-discharge cycles during the continuous use of the lithium-ion battery, and cannot achieve the effect of continuous replenishment during the cycles. The current solutions are mainly to pre-store a part of the lithium source on the anode electrode, but the solutions may have a great risk of thermal runaway during the first charging process. At the same time, due to the volume expansion of the silicon-based anode electrode active material during the charge and discharge process, solid electrolyte interfaces are repeatedly formed, and the amount of lithium in the battery system will also be consumed.
Therefore, there is room for improvement in the art.
In order to illustrate the technical solutions of the embodiments of the present application more clearly, the accompanying drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be seen as the limiting the scope. For one of ordinary skill in the art, other related drawings can also be obtained from these drawings without any creative work.
Implementations of the present technology will now be described, by way of embodiments, with reference to the attached figures, wherein:
It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein.
The term “outside” refers to a region that is beyond the outermost confines of a physical object. The term “inside” indicates that at least a portion of a region is partially contained within a boundary formed by the object. The term “substantially” is defined to essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.
A first embodiment of a method of making a silicon-carbon pre-lithium composite anode material comprises:
The numbering of the steps S1-S4 is only for the convenience of the following description, and the order of the steps is not limited. In addition, between each step, other steps may also be included as required.
In step S1, the silicon material can be a semiconductor-grade silicon material, and the size of the silicon material can be selected from a micron level, such as greater than or equal to 10 microns. The realization of nanonization process can include mechanical processing, mechanical ball milling, etc. Mechanical ball milling can be dry milling or wet milling.
The nanonization process is carried out in a protective environment. The protective environment may be a vacuum environment, or the protective environment may be obtained by passing an inert gas or adding a solvent. The inert gas includes at least one of argon (Ar), nitrogen (N2) or helium (He). The inert gas can provide an oxygen-free environment to prevent the nano-silicon particles from being oxidized, so that the silicon-carbon pre-lithium composite anode electrode material prepared subsequently is basically free of SiOx, which is beneficial to improve the electrochemical performance of the silicon-carbon pre-lithium composite anode electrode material and reduce the volume effect. The solvent can be diethylene glycol (DEG), polyethylene glycol (PEG), propylene glycol (PG), dimethylsulfoxide (DMSO) or a combination thereof. The solvent can prevent nano-silicon from being oxidized, so that the silicon-carbon pre-lithium composite anode electrode material is basically free of SiOx, which is beneficial to improve the electrochemical performance of the silicon-carbon pre-lithium composite anode electrode material and reduce the volume effect. The size of the nano-silicon particles is 10 nanometers to 50 nanometers. The nano-silicon particles is conducive to the homogenization treatment of carbon materials to obtain the silicon-carbon pre-lithium composite anode electrode materials with suitable particle sizes.
The polymer is an amphoteric polymer and has a hydrophobic group and a hydrophilic group. The polymer can be N-allyl-(2-ethylxanthate) propionamide (NAPA), dimethylformamide (DMF) or a combination thereof. The polymer is a medium containing, for example, amino groups, hydroxyl groups, etc. The polymer has a hydrophilic group at one end and a hydrophobic group at the other end, which can improve the difference in hydrophilicity and hydrophobicity between nano-silicon and carbon materials. In one embodiment, one end of the polymer having a hydrophilic group is bonded to the nano-silicon, and the other end having a hydrophobic group is bonded to the carbon materials, so that the nano-silicon is firmly coated on the carbon materials and is not easy to agglomerate with other nano-silicon.
The carbon materials can be pitch, graphite, graphene, carbon black, carbon nanotubes, nanofibers and the like. During the homogenization treatment of the carbon materials, the particles escape phenomenon triggers exothermic reaction. The carbon materials can perform thermal diffusion, avoid agglomeration, and prevent nano-silicon from being oxidized due to exothermic phenomena.
The homogenization treatment can be mechanical processing, electrical discharge machining, or mechanical ball milling. The mechanical ball milling can be dry milling or wet milling. The homogenization treatment enables nano-silicon, polymer and carbon materials to complete orderly stack self-assembly coating, and obtain a layered silicon-carbon composite.
In step S2, the pre-lithium nanomaterial (LiyM) can be Li5B4, Li22Si5, Li22Sn5, Li22Ge5, Li3N, Li2O, LiF, LiCl, LiI, Li2S, Li3PO4, LiAlO2, Li2TiO3, etc. In one embodiment, the pre-lithium nanomaterial is Li3N. Furthermore, the pre-lithium nanomaterial can be synthesized by mixing lithium raw materials and active substances. The lithium raw materials can be at least one of lithium oxide (Li2O), lithium powder, lithium hydroxide (LiOH), lithium nitrate (LiNO3), lithium carbonate (LiCO3), etc. The active substances can be at least one of B, Si, Ge, Sn, N, O, F, Cl, I, S, P, AlO2, TiO2. The pre-lithium nanomaterials can be obtained according to the type of the active materials.
The synthesis reaction of the lithium raw material and the active substance needs to be carried out in a sealed environment. Furthermore, nitrogen or argon can also be passed into the sealed environment for internal circulation for heat dissipation. In one embodiment, the synthesis reaction is achieved by grinding the lithium raw material and the active substance in a sealed environment. The particle size of the pre-lithium nanomaterial obtained through grinding is a nanoscale particle size. The particle size of the pre-lithium nanomaterial is smaller than the particle size of the silicon-carbon composite, so that the pre-lithium nanomaterial can be easily coated on the silicon-carbon composite during the granulation process. Furthermore, a solvent can be added during the grinding process for heat dissipation. The solvent can be an alkane solvent such as hexane, heptane, octane or the like. The solvent can be removed by vacuum drying after the grinding process.
In step S3, the silicon-carbon composite and pre-lithium nanomaterials are uniformly mixed and granulated to prepare solid spheres to prepare solid spheres that can be used for subsequent pulping. In one embodiment, the mass ratio of the pre-lithium nanomaterial to the silicon-carbon composite is 1%-5%.
The granulation process includes but not limited to two-fluid granulation, four-fluid granulation, cyclone granulation, spray granulation, dry granulation or wet granulation. Referring to
After the granulation process, the particle size of the silicon-carbon pre-lithium composite precursor is 5 microns to 15 microns, which is suitable for the pulping process of lithium secondary batteries, and can also avoid agglomeration in the subsequent sintering process.
In step S4, the sintering process can be carried out under a protective atmosphere or a low vacuum environment to increase the compactness and integrity of the pre-lithium nanomaterial as a cladding layer. The protective atmosphere can be a nitrogen-hydrogen mixed atmosphere. The sintering temperature is 500 Celsius degrees˜1200 Celsius degrees.
A second embodiment of a silicon-carbon pre-lithium composite anode material is provided. Referring to
A third embodiment of a battery is provided. The battery includes a positive pole piece, a negative pole piece and a separator, and the negative pole piece comprises the silicon-carbon pre-lithium composite anode electrode material. The battery can be a secondary battery, such as a lithium-ion secondary battery, a sodium-ion battery, etc., but the battery is not limited thereto.
The method of making the silicon-carbon pre-lithium composite anode electrode material provided by the application is to obtain a composite structure formed by the pre-lithium nanomaterial coated on the silicon-carbon composite. And the composite structure is obtained by adopting the steps of mixing the silicon-carbon composite and the pre-lithium nanomaterials homogeneously and by granulation and sintering. The pre-lithium nanomaterials can form a stable SEI film and provide a buffer space for the volume expansion of silicon materials. At the same time, the pre-lithium nanomaterials can also be used as a lithium-rich phase for lithium source replenishment, so that the cycle performance of the silicon-carbon pre-lithium composite anode electrode material can be greatly improved. The silicon-carbon pre-lithium composite anode electrode material provided in this application has a high specific capacity (>1600 mAh g-1), and the Faraday efficiency of the half-cell formed by the silicon-carbon pre-lithium composite anode electrode material can reach more than 90%, and the half-cell can have high cycle stability.
The present application can be further described below in conjunction with specific embodiments.
S1, putting semiconductor grade silicon material (≥10 μm), diethylene glycol and polymer N-allyl-(2-ethylxanthyl) propionamide into a grinder for mechanical processing, wherein the rotating speed of a grinder is 2400˜3000 rpm, the silicon material is processed into nano-silicon, and the grain size of the nano-silicon is 15-50 nanometers. Then a carbon material containing 10 wt % flake natural graphite was added, and nano-silicon is composited on the surface of the carbon material through an ordered stacking self-assembly process to obtain a silicon-carbon composite.
S2, putting Li2O and B powders in the atomic ratio of LiyB in an argon-sealed environment for grinding and taking out after grinding for 24 hours to carry out vacuum drying to obtain the pre-lithium nanomaterials; wherein an octane can be added as heat-dissipating solvent during grinding, and the speed of grinding is 2400˜3000 rpm.
S3, mixing and homogenizing the silicon-carbon composite and one percent pre-lithium nanomaterials, and then co-granulating to obtain the silicon-carbon pre-lithium composite precursors.
S4, putting the silicon-carbon pre-lithium composite precursor into a sintering furnace containing nitrogen-hydrogen mixed gas to obtain a silicon-carbon pre-lithium composite anode electrode material, wherein the gas flow rate is 2 L/min, and the temperature is 550 Celsius degrees for heat treatment for 8 hours.
Referring to
The silicon-carbon pre-lithium composite anode electrode material with the pre-lithium nanomaterials of LiyB is marked as sample 1. A silicon-carbon pre-lithium composite anode electrode material with the pre-lithium nanomaterials of LiySi is marked as sample 2. A silicon-carbon pre-lithium composite anode electrode material with the pre-lithium nanomaterials of LiyN is marked as sample 3. A silicon-carbon anode electrode material without a pre-lithium nanomaterial is marked as sample 4. Each sample, conductive agent and binder are dissolved in water at a mass ratio of 88:1:11 to obtain a mixture, and the mixture is a slurry with a solid content of 50%. The slurry is coated on a copper foil current collector and dried in vacuum to obtain a negative electrode sheet. A ternary positive pole piece, lithium salt electrolyte, and Celgard 2400 diaphragm by conventional production process for pouch battery stacking. The lithium salt electrolyte is the combination of LiPF6/EC, DMC, EMC. The battery assembled from sample 1 is marked as battery 1, the battery assembled from sample 2 is marked as battery 2, the battery assembled from sample 3 is marked as battery 3, and the battery assembled from sample 4 is marked as battery 4. Battery 1, battery 2, battery 3 and battery 4 are subjected to the following performance tests respectively.
A test of the negative electrode lithium ion extraction capacity is provided. The current density is 0.1 C, the voltage drops to 2.0V. The extraction capacity is obtained by converting the negative electrode gram capacity according to a following formula.
The above performance test results are shown in table 1.
As can be seen from Table 1, the battery assembled by the silicon-carbon pre-lithium composite anode electrode material of the present application has significantly higher extraction capacity and extraction capacity retention than the battery without pre-lithium nanomaterial. It shows that the silicon-carbon pre-lithium composite anode electrode material containing pre-lithium nanomaterial of the present application improves the conductivity and cycle stability of the battery.
Since the pre-lithium nanomaterial LiyM can form a stable SEI film on the surface of the silicon-carbon composite, and the pre-lithium nanomaterial LiyM can replenish the lithium source during the battery cycle and can also provide the buffer space for the volume expansion of silicon materials, the cycle performance of the silicon-carbon pre-lithium composite anode material is greatly improved. At the same time, M can be used as a reserved vacancy for lithium intercalation, and it can be used as a buffer when the volume of the silicon-carbon pre-lithium composite anode electrode changes. The method of making the silicon-carbon pre-lithium composite anode electrode material of the present application is simple in process. And the method is easy to control the process, and suitable for industrial production.
The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims.
Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. The description and the claims drawn to a method may comprise some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion for ordering the steps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210690849.0 | Jun 2022 | CN | national |
