CN114039038A - Preparation method of coated modified silicon monoxide long-cycle negative electrode - Google Patents

Abstract

The invention discloses a preparation method of a coated modified silicon monoxide long-cycle negative electrode, and relates to the technical field of lithium ion batteries. The preparation method of the coated modified silicon monoxide long-cycle negative electrode comprises the following steps: s1, mixing: adding CNT slurry and a carbon source into a solvent for uniform dispersion to obtain a solution A, adding micron-sized silicon monoxide and the solution A into a mixing device, and then mixing, wherein the solvent is one or more of heavy oil, ethanol, isopropanol, methanol, water, coal tar and kerosene. According to the preparation method of the coated modified silicon monoxide long-cycle cathode, the carbon coating layer is embedded with CNT, so that the toughness of the carbon coating layer is greatly improved, and the mechanical property of the coating layer for resisting the expansion of the silicon monoxide is improved, thereby improving the cycle performance of the material.

Description

Preparation method of coated modified silicon monoxide long-cycle negative electrode

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a coated modified silicon monoxide long-circulating negative electrode.

Background

In recent years, with the wide application of lithium ion batteries, the energy density of lithium ion batteries is increasingly required by markets such as power, digital and electric tools, and in the aspect of negative electrode materials, the energy density of traditional graphite negative electrodes is close to that of ceilings, so that the requirement of high-energy-density batteries is difficult to meet. The silicon-based material is concerned about the theoretical specific capacity as high as 4200mAh/g, but the volume expansion is as high as 300 percent in the charging and discharging processes, so that the reversible capacity is low, the cycle performance is poor, and no good method is provided for solving the problems at present.

The silicon oxide negative electrode material is concerned by high specific capacity and low volume expansion (150-. The presence of silica in the silica somewhat relieves the silicon from volumetric expansion during lithium intercalation, but the volumetric expansion of the silica approaching 200% also results in poorer cycle performance compared to that of graphite at around 12%.

Although partial cycle performance can be improved by coating, the cycle performance is still far from ideal because the soft carbon coating formed by the traditional solid/gas phase coating has insufficient hardness, weak toughness and easy cracking under the higher volume expansion of the silicon oxide.

The patent CN 113363479A adopts a mode of firstly carrying out solid phase/liquid phase and then carrying out gas phase to coat the silicon oxide, the process is complex, and the cycle promotion is limited. Patent CN 110828786A firstly carries out pyrolysis coating, then grows CNT by catalytic CVD, and has complex process, influences the first effect of a finished product and has insignificant cyclic improvement effect.

Disclosure of Invention

Technical problem to be solved

Aiming at the defects of the prior art, the invention provides a preparation method of a coated modified silicon monoxide long-circulating negative electrode, which solves the problems that a soft carbon coating layer formed by the traditional solid phase/gas phase coating has insufficient hardness and low toughness and is easy to crack under the higher volume expansion of the silicon monoxide, so that the circulating performance is still far from ideal.

(II) technical scheme

In order to achieve the purpose, the invention is realized by the following technical scheme: a preparation method of a coated modified silicon monoxide long-cycle negative electrode comprises the following steps:

s1, mixing: adding CNT slurry and a carbon source into a solvent for uniform dispersion to obtain a solution A, adding micron-sized silica and the solution A into a mixing device, and then mixing, wherein the solvent is one or more of heavy oil, ethanol, isopropanol, methanol, water, coal tar and kerosene, the particle size D50 of the silica is 1-10 mu m, the carbon source is one or more of coal-series asphalt, petroleum-series asphalt, phenolic resin and furfural resin, the mixing device is a fusion machine or a VC machine, the adding amount of the CNT slurry is 0.2-2 wt%, the adding amount of pure CNT is calculated by dividing the adding amount of the silica, and similarly, the adding amount of the carbon source is 1-10 wt%, and the adding amount of the solvent is 10-200 wt%;

s2, heating and hardening: heating the mixed materials in a heating device in an inert gas atmosphere to volatilize the solvent and harden the carbon source, wherein the heating device is a roller kiln, a rotary kiln, a pushed slab kiln, a hot-pack kettle, a fusion or VC machine with a heating device, the heating temperature is 200-500 ℃, the heating time is 0.5-8 hours, and the inert gas is one or more of nitrogen, argon and helium;

s3, depolymerization: depolymerizing the hardened material again, wherein the depolymerizing device is a mechanical pulverizer, a shaping machine, a jet mill, a VC machine and a fusion machine; the particle size of the depolymerized material is 2-15 μm;

s4, carbonization: and heating and carbonizing the depolymerized material again in an inert gas atmosphere to obtain a finished product, wherein the heating device is a roller kiln, a rotary kiln, a pushed slab kiln, a hot-pack kettle, a fusion or VC machine with a heating device, the heating temperature is 500-1100 ℃, the heating time is 0.5-8 hours, and the inert gas is one or more of nitrogen, argon and helium.

(III) advantageous effects

The invention provides a preparation method of a coated modified silicon monoxide long-cycle negative electrode. The method has the following beneficial effects:

according to the preparation method of the coated modified silicon monoxide long-cycle cathode, the carbon coating layer is embedded with CNT, so that the toughness of the carbon coating layer is greatly improved, and the mechanical property of the coating layer for resisting the expansion of the silicon monoxide is improved, thereby improving the cycle performance of the material. The CNT is a linear structure with small diameter but long length, has excellent mechanical property, and can play a role similar to that between 'steel bar' and 'cement' when uniformly embedded in a soft carbon coating layer in a liquid phase coating mode. The negative effects of SEI film cracking repair, active lithium loss, active substance pulverization and shedding and the like caused by the expansion and shrinkage of the silicon oxide can be obviously reduced, the cycle performance of the material is further improved, the CNT is added in the liquid phase coating process through a simple method, the coated modified silicon oxide long-cycle negative electrode material is prepared, and the improvement cost is relatively low.

Drawings

FIG. 1 is an SEM image of the present invention;

fig. 2 is a plot of the charging cycle for example 1, example 2, and comparative example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, the present invention provides a technical solution: a preparation method of a coated modified silicon monoxide long-cycle negative electrode comprises the following steps:

s1, mixing: adding CNT slurry and a carbon source into a solvent for uniform dispersion to obtain a solution A, adding micron-sized silica and the solution A into a mixing device, and then mixing, wherein the solvent is one or more of heavy oil, ethanol, isopropanol, methanol, water, coal tar and kerosene, the particle size D50 of the silica is 1-10 mu m, the carbon source is one or more of coal-series asphalt, petroleum-series asphalt, phenolic resin and furfural resin, the mixing device is a fusion machine or a VC machine, the adding amount of the CNT slurry is 0.2-2 wt%, the adding amount of pure CNT is calculated by dividing the adding amount of the silica, and similarly, the adding amount of the carbon source is 1-10 wt%, and the adding amount of the solvent is 10-200 wt%;

s2, heating and hardening: heating the mixed materials in a heating device in an inert gas atmosphere to volatilize the solvent and harden the carbon source, wherein the heating device is a roller kiln, a rotary kiln, a pushed slab kiln, a hot-pack kettle, a fusion or VC machine with a heating device, the heating temperature is 200-500 ℃, the heating time is 0.5-8 hours, and the inert gas is one or more of nitrogen, argon and helium;

s3, depolymerization: depolymerizing the hardened material again, wherein the depolymerizing device is a mechanical pulverizer, a shaping machine, a jet mill, a VC machine and a fusion machine; the particle size of the depolymerized material is 2-15 μm;

s4, carbonization: and heating and carbonizing the depolymerized material again in an inert gas atmosphere to obtain a finished product, wherein the heating device is a roller kiln, a rotary kiln, a pushed slab kiln, a hot-pack kettle, a fusion or VC machine with a heating device, the heating temperature is 500-1100 ℃, the heating time is 0.5-8 hours, and the inert gas is one or more of nitrogen, argon and helium.

Example 1

(1) Mixing: the CNT paste (solid content 4.6%), petroleum pitch, and heavy oil were uniformly dispersed at a weight ratio of 23:5.3:71.7, and solution a and silica having a particle size of 6.1 μm in D50 were added to a fusion machine at a weight ratio of 40:60, followed by mixing at 300rpm for 30 minutes.

(2) And (3) heating and hardening: after mixing, the fusion machine was purged with nitrogen and then warmed and held according to the following program: heating to 400 ℃ at the speed of 3 ℃/min, and stirring at the rotating speed of 300 rpm; keeping the temperature at 400 ℃ for 2 hours, and stirring at the rotating speed of 400 rpm.

(3) Depolymerization: after the heating and hardening are finished, the rotating speed of the fusion machine is increased to 500rpm and is kept for 30 minutes, and the materials are depolymerized. The depolymerized material D50 was 7.3 μm

(4) Carbonizing: and (3) feeding the depolymerized material into a roller kiln in a nitrogen atmosphere, wherein the calcining temperature and the calcining time are 900 ℃ and 4 hours respectively, and calcining to obtain a finished product.

The capacity of the finally obtained lithium ion negative electrode material is 1624mAh/g, the first effect is 75.94%, and the capacity retention rate of the electricity-retaining battery in 0.5C1C cycle 90 weeks is 90.98%.

Example 2

(1) Mixing: the CNT slurry (solid content: 4.6%), coal-based asphalt and heavy oil were uniformly dispersed in a weight ratio of 20:7:73, and solution A and 4.2 μm silica D50 were added to a VC machine in a weight ratio of 50:50, followed by mixing at 200rpm for 40 minutes.

(2) And (3) heating and hardening: adding the mixed materials into a hot ladle kettle, introducing nitrogen, and then heating and preserving heat according to the following procedures: heating to 450 ℃ at the speed of 2 ℃/min, and stirring at the rotating speed of 20 Hz; keeping the temperature at 450 ℃ for 4 hours, and stirring at the rotating speed of 25 Hz.

(3) Depolymerization: and (3) putting the heated material in the hot ladle kettle into mechanical crushing for depolymerization treatment, wherein the mechanical crushing main machine is 20Hz, and the feeding is 10 Hz. The depolymerized material D50 was 4.7 μm

(4) Carbonizing: and (3) feeding the depolymerized material into a rotary furnace in a nitrogen atmosphere, and calcining at 800 ℃ for 3 hours to obtain a finished product.

The capacity of the finally obtained lithium ion negative electrode material is 1653mAh/g, the first effect is 76.04%, and the capacity retention ratio of the electricity-saving battery 0.5C1C in 85 cycles is 89.35%

Comparative example 1

(1) Mixing: petroleum pitch and silica, D50 ═ 6 μm, were added to a VC machine in a weight ratio of 7:93, and then mixed at 300rpm for 40 minutes.

(2) Carbonizing: and (3) feeding the depolymerized material into a rotary furnace in a nitrogen atmosphere, wherein the calcining temperature and the calcining time are respectively 800 ℃ and 3 hours.

(3) Depolymerization: and putting the carbonized material into mechanical crushing for depolymerization treatment, wherein the mechanical crushing main machine is 20Hz, and the feeding is 10 Hz. The depolymerized material D50 was 6.5 μm, which was the final product.

The capacity of the finally obtained lithium ion negative electrode material is 1592mAh/g, the first effect is 76.15%, and the capacity retention rate of the electricity-saving battery 0.5C1C after 90 cycles is 55.11%.

In conclusion, the preparation method of the coated modified silicon monoxide long-cycle cathode adopts the method that the CNT is embedded in the carbon coating layer, so that the toughness of the carbon coating layer is greatly improved, and the mechanical property of the coating layer for resisting the expansion of the silicon monoxide is improved, thereby improving the cycle performance of the material. The CNT is a linear structure with small diameter but long length, has excellent mechanical property, and can play a role similar to that between 'steel bar' and 'cement' when uniformly embedded in a soft carbon coating layer in a liquid phase coating mode. The negative effects of SEI film cracking repair, active lithium loss, active substance pulverization and shedding and the like caused by the expansion and shrinkage of the silicon oxide can be obviously reduced, the cycle performance of the material is further improved, the CNT is added in the liquid phase coating process through a simple method, the coated modified silicon oxide long-cycle negative electrode material is prepared, and the improvement cost is relatively low.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (1)

1. A preparation method of a coated modified silicon monoxide long-cycle negative electrode is characterized by comprising the following steps: the method comprises the following steps:

s1, mixing: adding CNT slurry and a carbon source into a solvent for uniform dispersion to obtain a solution A, adding micron-sized silica and the solution A into a mixing device, and then mixing, wherein the solvent is one or more of heavy oil, ethanol, isopropanol, methanol, water, coal tar and kerosene, the particle size D50 of the silica is 1-10 mu m, the carbon source is one or more of coal-series asphalt, petroleum-series asphalt, phenolic resin and furfural resin, the mixing device is a fusion machine or a VC machine, the adding amount of the CNT slurry is 0.2-2 wt%, the adding amount of pure CNT is calculated by dividing the adding amount of the silica, and similarly, the adding amount of the carbon source is 1-10 wt%, and the adding amount of the solvent is 10-200 wt%;

s2, heating and hardening: heating the mixed materials in a heating device in an inert gas atmosphere to volatilize the solvent and harden the carbon source, wherein the heating device is a roller kiln, a rotary kiln, a pushed slab kiln, a hot-pack kettle, a fusion or VC machine with a heating device, the heating temperature is 200-500 ℃, the heating time is 0.5-8 hours, and the inert gas is one or more of nitrogen, argon and helium;

s3, depolymerization: depolymerizing the hardened material again, wherein the depolymerizing device is a mechanical pulverizer, a shaping machine, a jet mill, a VC machine and a fusion machine; the particle size of the depolymerized material is 2-15 μm;

s4, carbonization: and heating and carbonizing the depolymerized material again in an inert gas atmosphere to obtain a finished product, wherein the heating device is a roller kiln, a rotary kiln, a pushed slab kiln, a hot-pack kettle, a fusion or VC machine with a heating device, the heating temperature is 500-1100 ℃, the heating time is 0.5-8 hours, and the inert gas is one or more of nitrogen, argon and helium.

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