CN116014145B - Pre-lithiated silica composite material, preparation method and application thereof, pole piece containing pre-lithiated silica composite material and battery - Google Patents
Pre-lithiated silica composite material, preparation method and application thereof, pole piece containing pre-lithiated silica composite material and battery Download PDFInfo
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Abstract
The invention discloses a pre-lithiated silica composite material, a preparation method and application thereof, a pole piece and a battery containing the same, wherein the pre-lithiated silica composite material is in a core-shell structure, and the core-shell structure comprises a core and a shell; the inner core is made of a pre-lithiated silica material; the shell is LiBO 2 /B 2 O 3 Or Li (lithium) 3 PO 4 /P 2 O 5 A coating layer; the average film thickness of the outer shell is 22-50nm. The composite material comprises LiBO 2 /B 2 O 3 Coating or Li 3 PO 4 /P 2 O 5 The coating layer and the pre-lithiated silica material can isolate air or water, and can greatly solve the problem of slurry gas production; the electrolyte and the pre-lithiated silica material can be isolated, and the side reaction of the pre-lithiated silica material in the charge and discharge process can be reduced; in addition, liBO in the coating layer 2 Or Li (lithium) 3 PO 4 Is a fast ion conductor, is favorable for Li + Is inserted into and removed from the housing.
Description
Technical Field
The invention relates to a pre-lithiated silica composite material, a preparation method and application thereof, a pole piece containing the same and a battery.
Background
With the development of society and the advancement of technology, the energy consumption is increased, the environmental pollution is also increased, and the future survival of human beings is threatened seriously, so that the development of clean and environment-friendly renewable energy is urgently needed. Among them, lithium Ion Batteries (LIBs) have been rapidly developed due to their advantages of high energy density, long cycle life, environmental friendliness, etc., and have been widely used in the fields of electronic products and electric automobiles. The carbon-based graphite anode material is most commonly used as the anode material of the lithium ion battery, has the advantages of rich sources and low price, but has lower specific capacity（372mAh g -1 ) The irreversible capacity loss is large, so that the lithium ion battery is difficult to meet the requirement of service performance, and the development space is difficult to break through. Silicon monoxide (SiOx, x≡1) has been recognized as one of the most promising alternatives to high energy density LIBs carbon-based negative electrode materials due to its high specific capacity and appropriate operating potential. However, the use of SiOx anodes in practical LIBs systems is often hampered by the large volume variation, poor electron conductivity, and low Initial Coulombic Efficiency (ICE). The silicon oxide has irreversible lithium silicate and lithium oxide generation in the first lithium intercalation process, so that the silicon oxide has low first efficiency. In order to improve the first efficiency of silicon oxide, a lithium pre-supplementing technology of various materials is developed in the industry, and irreversible capacity loss in the charge and discharge process is reduced by pre-supplementing part of lithium in a silicon-based material. However, the slurry is highly alkaline in water system due to the existence of residual lithium on the surface after the pre-lithiation, and the O component of Si-O in the silicon oxide is more converted into Li during the pre-lithiation 2 O、Li 2 SiO 3 、Li 2 Si 2 O 5 The components are equal, the rest Si in Si-O is easy to gather and even grow up, on one hand, the growth of silicon grains leads to large absolute volume change in the lithium intercalation process, which is not beneficial to the stability of the pole piece structure, and further leads to poor cycle performance; on the other hand, si microcrystals are generated to easily react under an alkaline aqueous solution system to generate H 2 Poor water resistance is unfavorable for slurry stabilization, affects processability such as coating uniformity, and further causes a problem of unsatisfactory final battery performance.
How to reduce the alkalinity of the pre-lithium product and effectively solve the problem of gas production of the pre-lithium product in water-based slurry is the key point of the current research. Most of the currently studied coatings are carbon layers which inhibit the gas production but still produce gas during subsequent storage or compounding. In the patent 'a negative electrode material, a preparation method, equipment and a lithium ion battery (CN 202110938869.0)', carbon-coated silicon oxide powder and atomized lithium source are uniformly mixed in an inert atmosphere, and the mixing temperature is 190-350 ℃. Atomizing the lithium source into liquid drops, and mixing with the carbon-coated silicon oxide powderUniform addition, can effectively avoid Li caused by local excessive lithiation reaction 4 SiO 4 、Li 2 SiO 3 、Li x The generation of lithium-rich products such as Si effectively improves the first efficiency of the silicon-oxygen anode material, effectively suppresses the occurrence of gas production phenomenon of water-based slurry, remarkably improves the stability of the slurry of the silicon-oxygen anode material applied to the battery preparation process, improves the applicability and also improves the material capacity. In another example, in the patent "a pre-lithiated silica composite material, a preparation method and an application (CN 202210085959.4)", silica is uniformly mixed with a metal salt before the pre-lithiation reaction, and then uniformly mixed with a pre-lithiation reagent to perform the pre-lithiation reaction; by adding the metal salt, all or part of the surfaces of the pre-lithiation reagent particles and the silicon oxide particles are wrapped, the problem that silicon grains are rapidly precipitated and grown due to non-uniform pre-lithiation is solved, and excellent cycle performance is further ensured. Therefore, the carbon coating does effectively solve the problem of gas production of the aqueous slurry in application, greatly improves the water resistance, but the defect that gas is generated in the subsequent storage or mixing process is still to be solved. The prior art has solved the problem of gas generation during storage or mixing by constructing an air or water protective layer, such as LiOH and Li generated in air/water surface by nickel-rich anode 2 CO 3 And the like, and reduces the electrochemical performance of the catalyst. For this purpose, an air/water protective layer is required to improve its stability, as in document "Enhanced Electrochemical Performance of Ni-Rich Cathode Materials with an In Situ-Formed LiBO 2 /B 2 O 3 Hybrid Coating Layer [J]ACS Applied Energy Materials, 2022, 5 (2): 2231-2241, "LiBO was prepared by wet coating method 2 /B 2 O 3 Coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 And (3) particles. A quantity of boric acid powder was added to 50ml of absolute ethanol and stirred at room temperature for 30 minutes to dissolve completely. Then the prepared LiNi 0.8 Co 0.1 Mn 0.1 O 2 The powder was slowly poured into a dilute boric acid solution and stirred at 70 ℃ until the absolute ethanol was completely evaporated. Finally, the obtained sample was subjected to an atmosphere of 500℃in ambient airCalcining for 5 hours to generate LiBO 2 /B 2 O 3 Coated LiNi 0.8 Co 0.1 Mn 0.1 O 2 And (3) a sample.
Disclosure of Invention
The invention aims to overcome the defect that the electrochemical performance is poor finally because gas is generated in the subsequent storage or mixing process when the gas is generated by adopting the carbon coating to solve the water-based slurry in the prior art, and provides a pre-lithiated silica composite material, a preparation method and application thereof, a pole piece containing the pre-lithiated silica composite material and a battery. The composite material comprises LiBO 2 /B 2 O 3 Coating or Li 3 PO 4 /P 2 O 5 The coating layer and the pre-lithiated silica material can isolate air or water, and can greatly solve the problem of slurry gas production; the electrolyte and the pre-lithiated silica material can be isolated, and the side reaction of the pre-lithiated silica material in the charge and discharge process can be reduced; in addition, liBO in this coating layer 2 Or Li (lithium) 3 PO 4 Is a fast ion conductor, is favorable for Li + Is inserted into and removed from the housing.
During the development process, the inventor finds that the silicon in the raw material precursor of the pre-lithiated silicon oxide material can react during the homogenization: si+2OH - +H 2 O=SiO 3 2- +2H 2 So that gas production may result. The present invention has been made to solve the above problems, and an object of the present invention is to suppress gas production by a method of simultaneously reducing residual alkali and isolating water. In particular, a liquid phase coating method is adopted, and boride (LiBO) 2 /B 2 O 3 ) Or phosphide (Li) 3 PO 4 /P 2 O 5 ) Coating the pre-lithiated silica material. LiBO is adopted 2 /B 2 O 3 Or Li (lithium) 3 PO 4 /P 2 O 5 The composite material obtained by the coated pre-lithiated silica material can greatly solve the problem of gas production of the pre-lithiated silica material in slurry, and improves the circulation stability of the pre-lithiated silica material. On the one hand, the content of residual alkali in the pre-lithiated silica material can be greatly reduced by reacting boric acid or phosphoric acid with residual lithium compounds on the surface of the pre-lithiated sample. LiBO on the other hand 2 Or Li (lithium) 3 PO 4 Presents electrochemical inertia in organic electrolyte, can well isolate the direct contact between electrolyte and pre-lithiated silicon oxide material, and LiBO 2 Or Li (lithium) 3 PO 4 Is a fast ion conductor, is favorable for Li + And provides a new idea for solving the gas production problem of the pre-lithiated silica material. Second LiBO 2 And B 2 O 3 、Li 3 PO 4 And P 2 O 5 All are high-viscosity substances, can be mutually adsorbed, and are firmly adsorbed on the surface of the pre-lithiated silica material.
In order to achieve the above object, the technical scheme provided by the invention is as follows:
the invention provides a pre-lithiated silica composite material which is of a core-shell structure, wherein the core-shell structure comprises an inner core and an outer shell;
the inner core is made of a pre-lithiated silica material;
the shell is LiBO 2 /B 2 O 3 Coating or Li 3 PO 4 /P 2 O 5 A coating layer;
the average film thickness of the shell is 22-53nm.
In the present invention, the residual alkali content of the pre-lithiated silicone material is preferably 3% or less, more preferably 2% or less.
In the present invention, the thinnest film thickness of the shell may be 5 to 16nm, preferably 8.5 to 14nm, for example 9nm, 9.5nm, 10nm, 12nm or 13nm. When the thinnest film thickness of the shell is large (for example, 19 nm), the intercalation and deintercalation of lithium ions are hindered, so that the migration speed of the lithium ions is low, and the electrochemical performance of the battery is poor. When the thinnest film thickness of the shell is small (e.g., 5 nm), the coating layer is uneven, so that the pre-lithiated silicone material precursor reacts with the electrolyte, consuming the electrolyte, and making the electrochemical performance of the battery poor.
In the present invention, the average film thickness of the outer shell is preferably 32 to 45nm, for example 35nm, 36nm, 38nm, 41nm or 44nm.
The invention provides a preparation method of a pre-lithiated silica composite material, which comprises the following steps:
mixing a pre-lithiated silica material raw material precursor with an acid solution, and performing heat treatment to obtain the pre-lithiated silica composite material;
wherein the acid solution is boric acid solution or phosphoric acid solution;
wherein the mass ratio of the acid in the acid solution to the raw material precursor of the pre-lithiated silica material is (0.1-0.2): 1, a step of;
wherein, the residual alkali content in the precursor of the raw material of the pre-lithiated silica material is 3-6%.
In the invention, the residual alkali content in the pre-lithiated silica material raw material precursor refers to the mass ratio of the mass of the alkali generated by the reaction of the lithium remained after the pre-lithiation of the silica material and water to the mass of the pre-lithiated silica material raw material precursor.
In the present invention, the acid solution may include an acid and a solvent.
Wherein the solvent may be a solvent which is conventional in the art to dissolve an acid, such as ethanol, ethyl acetate or toluene.
Wherein the solvent capable of dissolving the acid preferably satisfies the following conditions: (1) non-reactive with acid; (2) The water content is preferably 1% or less, more preferably 0.1% or less; (3) boiling point between 30 and 120 ℃, such as 78.3 ℃ or 110.6 ℃; (4) low toxicity.
Wherein the acid and the solvent may be mixed to produce the acid solution. After said mixing, a dispersing step is preferably also included. The dispersion is preferably an ultrasonic dispersion.
In the present invention, the mass ratio of the acid in the acid solution to the raw material precursor of the pre-lithiated silicone material is preferably (0.12-0.2): 1, for example 0.13:1, 0.15:1 or 0.2:1.
In the invention, when the mass ratio of the acid in the acid solution to the raw material precursor of the pre-lithiated silica material is relatively large (0.25:1), more B is generated 2 O 3 Or P 2 O 5 The impedance of the pre-lithiated silica composite material is larger, and the electrochemical performance of the battery is seriously reduced.When the mass ratio of the acid in the acid solution to the pre-lithiated silica material raw material precursor is large (0.05:1), the residual alkali in the pre-lithiated silica precursor cannot be completely consumed, and gas production may occur.
In the present invention, the residual alkali content of the raw material precursor of the pre-lithiated silicone material is preferably 4% to 5.8%, for example, 5.5%.
In the present invention, the particle size of the raw material precursor of the pre-lithiated silicone material is preferably 300 mesh or less.
In the present invention, the preparation method of the pre-lithiated silica material raw material precursor may be conventional in the art, for example, including the following steps: (1) carbon coating; (2) etching; (3) lithium absorption; (4) heat treatment.
In step (1), the step of carbon coating is preferably: and (3) carrying out heat treatment on the silicon oxide, and introducing a carbon source to carry out carbon coating, so as to obtain the carbon-coated silica material.
The carbon source is preferably acetylene.
The temperature of the heat treatment may be 700-900 ℃, for example 800 ℃.
The heat treatment is preferably carried out under an inert atmosphere. The inert atmosphere is preferably an argon atmosphere.
The carbon coating is preferably carried out under an inert atmosphere; the inert atmosphere is preferably an argon atmosphere. The volume ratio of the carbon source to the inert atmosphere is preferably (8-10): 1, e.g., 9:1.
The carbon coating time may be 0.5 to 2 hours, for example 1 hour.
The carbon-coated silicone material may be sio@c.
In step (2), the etching step is preferably: and mixing the carbon-coated silica material with a hydrogen fluoride solution, and carrying out etching reaction to obtain the carbon-coated silica material with a porous structure.
The concentration of hydrogen fluoride is preferably 0.1 to 0.3M, for example 0.2M.
The mixing is preferably followed by stirring, filtration and washing steps conventional in the art. The stirring time is preferably 1 to 3 hours, for example 2 hours. The washing may be conventional in the art, for example, washing with deionized water. The number of washes is preferably 3-5, for example 4.
In the art, the structure of the carbon-coated silica material having a porous structure may be a hollow structure of core-void-shell.
Wherein in the step (3), the lithium source for absorbing lithium may be an organic solution containing lithium.
The mass ratio of the silicon oxide material after the carbon coating and the etching to the lithium-containing organic solution is preferably 1: (3-4).
The lithium-containing organic solution may include a lithium-containing organic material and a solvent. The mass fraction of the lithium-containing organic matter in the lithium-containing organic solution may be 30% -50%.
The lithium-containing organic matter may be conventional in the art, such as phenyl lithium.
The solvent may be conventional in the art, preferably aromatic dimethyl ether or diethyl ether.
The lithium-containing organic solution may be prepared under an inert atmosphere, for example under an argon atmosphere.
In step (3), the mixing is followed by a further step of stirring as is conventional in the art. The stirring time is preferably 3 to 5 hours, for example 4 hours.
Preferably, the method further comprises an alcohol washing step after the lithium absorption and before the heat treatment. The alcohol wash may be a wash with ethanol.
In step (4), the heat treatment is preferably performed in a tube furnace.
The heat treatment is preferably carried out under an inert atmosphere. The inert atmosphere is preferably an argon atmosphere.
The temperature of the heat treatment is preferably 400-600 ℃, for example 500 ℃.
The time of the heat treatment is preferably 0.5 to 2 hours, for example 1 hour.
The heat treatment is preferably followed by a step of reducing the temperature. The temperature of the cooling is preferably room temperature, for example 20-30 ℃.
In the present invention, the heat treatment is preferably preceded by a step of removing the solvent after the mixing.
Wherein the evaporation rate of the solvent when the solvent is removed can be 1mL/min-12mL/min, preferably 3mL/min-10mL/min.
The solvent is removed by any means known in the art, preferably by rotary evaporation or evaporation.
Wherein the solvent is preferably removed while stirring is also performed. The stirring speed can be 500-2000r/min.
In the present invention, the heat treatment may be conventional in the art, and preferably the reactants are placed in a crucible and heat-treated in a molybdenum wire furnace.
In the present invention, the atmosphere of the heat treatment may be an inert atmosphere such as an argon atmosphere.
In the present invention, the temperature of the heat treatment may be a temperature conventionally used in the art to allow the reaction of boric acid or phosphoric acid with the residual alkali contained in the pre-lithiated silicone material raw material precursor, preferably 500 to 600 ℃, more preferably 530 to 580 ℃, for example 550 ℃. When the temperature of the heat treatment is higher than 600 ℃, silicon grains can grow up, and the performance of the pre-lithiated silica composite material can be inferior to that of the pre-lithiated silica composite material obtained at 500-600 ℃. When the temperature of the heat treatment is too low, the removal of crystal water in the reaction process is not facilitated, and the performance of the pre-lithiated silica composite material is also inferior to that of the pre-lithiated silica composite material obtained at 500-600 ℃.
In the present invention, the rate of temperature rise at the time of the heat treatment may be 1 to 20℃per minute, preferably 4 to 6℃per minute, for example 5℃per minute.
In the present invention, the time of the heat treatment may be 1 to 10 hours, preferably 4 to 6 hours, for example 5 hours.
The invention also provides a pre-lithiated silica composite material which is prepared by the preparation method.
The invention also provides application of the pre-lithiated silica composite material in an electrode material.
The invention also provides a negative electrode plate which is prepared from the pre-lithiated silica composite material.
In the present invention, the preparation method of the negative electrode sheet may be conventional in the art, and for example, includes the following steps: and (3) homogenizing the mixture of the pre-lithiated silica composite material, the binder and the conductive agent, coating the homogenized mixture on a copper foil, and carrying out vacuum drying and rolling to obtain the negative electrode plate.
Wherein, the mass ratio of the pre-lithiated silica composite material, the binder and the conductive agent can be 70:20:10.
Wherein the conductive agent is preferably Super P. The binder is preferably LA132 (10 wt%). The dispersant is preferably deionized water.
The invention also provides a lithium ion battery, which comprises the negative electrode plate.
In the present invention, the preparation method of the lithium ion battery may be conventional in the art, and for example, includes the following steps: liPF of 1mol/L 6 The mixed solvent is prepared by mixing ethyl carbonate, dimethyl carbonate and methyl ethyl carbonate with the volume ratio of 1:1:1, a polypropylene microporous membrane is adopted as a diaphragm, a metal lithium sheet is adopted as a counter electrode, and the electrode prepared from the stearate coated pre-lithiated silica composite material is assembled into a button cell in an inert gas glove box system filled with argon, so that the lithium ion battery is prepared.
On the basis of conforming to the common knowledge in the field, the above preferred conditions can be arbitrarily combined to obtain the preferred examples of the invention.
The reagents and materials used in the present invention are commercially available.
The invention has the positive progress effects that:
(1) The method generates LiBO by reacting boric acid or phosphoric acid with the residual lithium compound on the surface of the precursor of the raw material of the pre-lithiated silica material 2 /B 2 O 3 Or Li (lithium) 3 PO 4 /P 2 O 5 The method comprises the steps of carrying out a first treatment on the surface of the On the one hand, the reaction can greatly reduce the content of residual alkali in the precursor of the raw material of the pre-lithiated silica material; on the other hand, liBO produced by the reaction 2 Or Li (lithium) 3 PO 4 Presentation in organic electrolyteThe electrochemical inertia can well isolate the direct contact between electrolyte and pre-lithiated silica material, and LiBO 2 Or Li (lithium) 3 PO 4 Is a fast ion conductor, is favorable for Li + Provides a new idea for solving the gas production problem of the pre-lithiated silica material; in addition, liBO 2 And B 2 O 3 ，Li 3 PO 4 And P 2 O 5 All are high-viscosity substances, can be mutually adsorbed, and are firmly adsorbed on the surface of the pre-lithiated silica material.
(2) The invention firstly uses LiBO 2 /B 2 O 3 Or Li (lithium) 3 PO 4 /P 2 O 5 The coating layer is applied to the pre-lithiated silica material, and the LiBO of the outer layer 2 /B 2 O 3 Or Li (lithium) 3 PO 4 /P 2 O 5 The coating layer can isolate air and/or water, and can greatly solve the problem that the pre-lithiated silica material is easy to react to generate H under an alkaline aqueous solution system 2 Poor water resistance is unfavorable for stable slurry, influences the processing performance such as uniform coating and the like, and further causes the problem of unsatisfactory final battery performance, and the coating layer can isolate the contact between the electrolyte and the pre-lithiated silica material, so that the occurrence of side reaction is reduced. In addition, liBO 2 Or Li (lithium) 3 PO 4 Is a fast ion conductor, is favorable for Li + Is embedded and released in LiBO 2 And B 2 O 3 、Li 3 PO 4 And P 2 O 5 All are high-viscosity substances, can be mutually adsorbed, and are firmly adsorbed on the surface of the pre-lithiated silica material. The pre-lithiated silica composite material prepared by the invention not only can well inhibit gas production, but also has better electrochemical performance.
Drawings
Fig. 1 is an XRD pattern of the prelithiated silicon composite material prepared in example 2.
Detailed Description
The invention is further illustrated by means of the following examples, which are not intended to limit the scope of the invention. The experimental methods, in which specific conditions are not noted in the following examples, were selected according to conventional methods and conditions, or according to the commercial specifications.
Example 1
A pre-lithiated silica composite material and a preparation method thereof:
step one: 150g boric acid was added to the ethanol solution and dispersed by sonication until completely dissolved. Wherein the water content of the ethanol is below 0.1%, and the boiling point is 78.3 ℃.
Step two: 1kg of a pre-lithiated silica material raw material precursor is added into the solution, then water bath heating is carried out, stirring is carried out at a speed of 1000r/min until alcohol is completely evaporated, and the evaporation rate of the solvent is 10mL/min. The preparation method of the pre-lithiated silica material raw material precursor comprises the following steps: (1) carbon coating: placing the silicon oxide into a tube furnace, heating to 800 ℃ under argon atmosphere, introducing acetylene (argon: acetylene=9:1), and preserving heat for 1 hour to obtain a carbon-coated silicon oxide material SiO@C;
(2) Etching: soaking SiO@C into 0.2M hydrogen fluoride solution, continuously stirring the solution for 2 hours, filtering and repeatedly washing with deionized water for 4 times to obtain a carbon-coated silica material SiO@void@C with a core-void shell structure;
(3) Lithium absorption: immersing SiO@void@C into a lithium-containing organic solution, sucking lithium, wherein the lithium-containing organic substance is phenyl lithium, the solvent is diethyl ether, continuously stirring the solution for 4 hours under an argon atmosphere, and filtering to obtain a carbon-coated silicon oxide material SiO@void@C@Li after sucking lithium; wherein the mass ratio of SiO@void@C to the lithium-containing organic solution is 1:3, a step of; in the lithium-containing organic solution, the mass fraction of the lithium-containing organic matters is 30-50%;
(4) And (3) heat treatment: placing the SiO@void@C@Li subjected to alcohol washing treatment into a tube furnace, heating to 500 ℃ under argon atmosphere, preserving heat for 1 hour, automatically cooling to room temperature, and sieving with a 300-mesh sieve to obtain a pre-lithiated silica material raw material precursor Si/Li which is insoluble in water and has residual alkali content of 5.5 percent 2 SiO 3 @void@C；
Step three: placing the reactant obtained in the second step into a crucible, placing the crucible into a molybdenum wire furnace, heating to 500 ℃ at a heating rate of 5 ℃/min under argon atmosphere, and preserving heat for 4 hours to obtain the catalystTo the final LiBO 2 /B 2 O 3 Coating the pre-lithiated silica composite material.
Example 2
The only difference from example 1 is that: the mass of boric acid in the first step is 100g.
Example 3
The only difference from example 1 is that: the mass of boric acid in the first step is 200g.
Example 4
The only difference from example 1 is that: the temperature of heating in step three was 550 ℃.
Example 5
The only difference from example 1 is that: the temperature of heating in step three was 600 ℃.
Example 6
The only difference from example 1 is that: and in the third step, the heat preservation time is 5 hours.
Example 7
The only difference from example 1 is that: and in the third step, the heat preservation time is 6 hours.
Example 8
The only difference from example 1 is that: the solvent in the first step is ethyl acetate, and the specific steps are as follows:
step one: 150g boric acid was added to the ethyl acetate solution and dispersed by sonication until completely dissolved. Wherein the water content of the ethyl acetate is below 0.1%, and the boiling point is 77 ℃.
Example 9
The only difference from example 1 is that: in the first step, the solvent is toluene, and the method concretely comprises the following steps:
step one: 150g boric acid was added to the toluene solution and dispersed by sonication until completely dissolved. Wherein the water content of toluene is below 0.1%, and the boiling point is 110.6 ℃.
Example 10
The only difference from example 1 is that: the method for removing the solvent in the second step is rotary evaporation, and the evaporation rate of the solvent is 3mL/min.
Example 11
The only difference from example 1 is that: in the first step, the raw material is phosphoric acid, which is specifically as follows:
step one: 130g of phosphoric acid was added to the ethanol solution and dispersed by sonication until completely dissolved. Wherein the water content of the ethanol is below 0.1%, and the boiling point is 78.3 ℃.
Comparative example 1
The only difference from example 1 is that: and (5) canceling the first step.
Comparative example 2
The only difference from example 1 is that: the mass of boric acid in the first step was 50g.
Comparative example 3
The only difference from example 1 is that: the mass of boric acid in the first step is 250g.
Effect examples
The amount of residual alkali contained in the precursor of the raw material of the pre-lithiated silicone material prepared by the preparation method of the precursor of the raw material of the pre-lithiated silicone material in the steps two of examples 1 to 10 and comparative examples 1 to 3, and the amount of residual alkali in the pre-lithiated silicone composite material were tested. The testing method comprises the following steps: first, 10g of a pre-lithiated silicone material raw material precursor is added to 100ml of deionized water and stirred for 30min. And then suction filtration is carried out to obtain a supernatant. 10ml of the supernatant was placed in a conical flask. Then 2 drops of methyl orange indicator were added to the conical flask and the solution immediately turned yellow. Then slowly dripping hydrochloric acid with the mass concentration (0.1M) of the known substance, simultaneously continuously shaking the conical flask by the right hand in the clockwise direction to fully mix the solution, and watching the color change of the solution in the conical flask by eyes. With the dropwise addition of hydrochloric acid, OH in the Erlenmeyer flask - The concentration gradually decreases. Finally, when 1 drop of hydrochloric acid was added, the solution became orange-red and did not fade after half a minute. Stopping titration, accurately recording the scale of the liquid level of the burette solution, and accurately obtaining the volume of hydrochloric acid for titration. And then calculating the residual alkali content in the precursor of the raw material of the pre-lithiated silica material to be measured according to the related metering relation.
Wherein, the metering relation is divided into the following three steps: (1) C (a) ×v (a) =c (B) ×v (B), wherein a (Acid) is an Acid, B (Base) is a pre-lithiated silicone material raw material precursor, C is a mass concentration of a or B, and V is a volume of a or B, to calculate a concentration of residual alkali contained in the pre-lithiated silicone material raw material precursor.
(2) The mass of the residual alkali contained in the pre-lithiated silicone material raw material precursor is calculated from the concentrations of n=c×v and m=n×m and the residual alkali contained in the pre-lithiated silicone material raw material precursor.
(3) The amount of residual alkali contained in the pre-lithiated silicone material raw material precursor=the mass of residual alkali contained in the pre-lithiated silicone material raw material precursor in step (2)/(the mass of the pre-lithiated silicone material raw material precursor).
Pole pieces were prepared from the pre-lithiated silicon oxygen negative electrode composites obtained in examples 1-10 and comparative examples 1-3 according to the methods described above, and assembled into button cells. The assembled battery was tested for first reversible capacity, first coulombic efficiency, and 100 cycles capacity retention.
The test conditions were: the charge-discharge potential was 0.01V-1.5V, the first three rounds were activated with a current density of 0.1A/g, and then the cyclic test was conducted with a current density of 0.5A/g, and the test results are shown in Table 1.
The pre-lithiated silicon oxygen negative electrode composites obtained in examples 1-10 and comparative examples 1-3 were subjected to a gassing test under the following conditions: the pre-lithiated silica anode composite material and water are mixed according to the following ratio of 1:10 was added to a beaker, stirred for 30min, then added to a test tube, left to stand for 3h,6h,12h,24h,48h,60h,72h, and the change in scale was observed, and the results are shown in Table 1.
The pre-lithiated silicon oxygen negative electrode composites obtained in examples 1 to 10 and comparative examples 1 to 3 were subjected to the minimum film thickness test, and the results obtained are shown in table 1. The test method of the thinnest film thickness comprises the following steps: the coating is first observed by TEM at low magnification (e.g. 500nm scale) to see if it is complete, then the place where the coating is thinnest is found, and observed at high magnification (e.g. 20nm scale) to determine the thinnest film thickness. The inventors found that the thinnest film thickness is related to the gas production performance in the research and development process, and that the effect of no gas production can be achieved when the film thickness of the pre-lithiated silicon-oxygen negative electrode composite material is the thinnest film thickness, and those skilled in the art can understand that other thicker thicknesses of the pre-lithiated silicon-oxygen negative electrode composite material can also achieve the effect of no gas production.
The pre-lithiated silicon oxygen negative electrode composites obtained in examples 1 to 10 and comparative examples 1 to 3 were subjected to an average film thickness test, and the results obtained are shown in table 1. The test method of the average film thickness comprises the following steps: the method comprises the steps of firstly observing TEM at a low multiplying power (such as a scale of 500 nm) to see whether a coating layer is complete, then observing 5-10 points of the pre-lithiated silicon-oxygen negative electrode composite material at a high multiplying power (such as a scale of 20 nm), determining the film thickness, and then obtaining the average film thickness by taking an average value.
TABLE 1
| Example | First reversible capacity (mAh +. g） | First coulombic efficiency （%） | Capacity retention of 100 cycles （%） | The thinnest film thickness （nm） | Average film thickness （nm） | Residual alkali content in the pre-lithiated silica composite material （%） | Gas production |
| Example 1 | 1308.3 | 89.5 | 85 | 10 | 35 | 1.25 | No production for 24 hours Air flow |
| Example 2 | 1378.5 | 90 | 80 | 5 | 22 | 2.14 | No production for 12 hours Air flow |
| Example 3 | 1188.4 | 88 | 74 | 15 | 45 | 1.02 | No production for 48 hours Air flow |
| Example 4 | 1285.4 | 89 | 83 | 12 | 41 | 1.23 | No production for 24 hours Air flow |
| Example 5 | 1181.3 | 88 | 80 | 15 | 50 | 1.26 | No production for 48 hours Air flow |
| Example 6 | 1237.5 | 89 | 82 | 13 | 44 | 1.27 | No production for 24 hours Air flow |
| Example 7 | 1174.3 | 88 | 80 | 16 | 53 | 1.25 | No production for 48 hours Air flow |
| Example 8 | 1380.5 | 89.5 | 85 | 9.5 | 36 | 1.25 | No production for 24 hours Air flow |
| Example 9 | 1374.8 | 89.5 | 85 | 9 | 38 | 1.25 | No production for 24 hours Air flow |
| Examples 10 | 1301.9 | 89.5 | 85 | 10 | 35 | 1.25 | No production for 24 hours Air flow |
| Examples 11 | 1308.3 | 90.3 | 83 | 11 | 35 | 1.46 | No production for 24 hours Air flow |
| Comparative example 1 | 1430.5 | 91 | 70 | 0 | 0 | 5.23 | No gas is produced in 3 hours |
| Comparative example 2 | 1394.3 | 90.5 | 75 | 0 | 15 | 3.53 | No gas is produced in 6 hours |
| Comparative example 3 | 1098.5 | 87 | 68 | 19 | 65 | 0.97 | Producing gas for 60 hours |
In Table 1, 3h non-gassing means 0-3h non-gassing, 3h-6h gassing; the non-gas production in 6 hours means 0-6 hours of non-gas production and 6-9 hours of gas production; the non-gas production for 12h means 0-12h of non-gas production and 12-24 h of gas production; the 24h non-gas production means 0-24h non-gas production and 24-48 h gas production; the 48h non-gas production means 0-48h non-gas production and 48-72 h gas production; the gas generation in 60 hours means that no gas is generated in 0-60 hours, and the gas is generated after 60 hours.
The residual alkali contained in the precursor of the raw material of the pre-lithiated silica material can be obviously reduced by increasing the amount of boric acid or phosphoric acid, but the residual alkali amount remains basically unchanged when the amount of phosphoric acid or boric acid is continuously increased, because the raw material absorbs a certain amount of CO from the air 2 Formation of Li 2 CO 3 So that the alkalinity is increased, i.e. the final residual alkali approximately remains unchanged at about 1%.
FIG. 1 shows the XRD pattern of the composite material obtained in example 2, and LiBO not detected on the XRD pattern of the composite material obtained in example 2 because the coating amount is small and the thickness of the coating layer is not large 2 /B 2 O 3 A phase.
Examples 1-3, comparative examples 1-3 show that an increase in boric acid content increases the coating thickness, and although the occurrence of gassing can be better suppressed, an increase in the coating amount leads to deterioration of the battery performance.
Examples 1, 4 and 5 show that an increase in the heat treatment temperature increases the coating thickness, in particular B 2 O 3 The increase in the content can also suppress the occurrence of gas production, but B 2 O 3 Is a non-conductive material, and an increase in the content thereof may cause deterioration of the battery performance.
Examples 1, 6 and 7 show that an increase in the heat treatment time leads to an increase in the coating thickness, in particular B 2 O 3 The increase in the content can also suppress the occurrence of gas production, but B 2 O 3 Is a non-conductive material, and an increase in the content thereof may cause deterioration of the battery performance.
Examples 1, 8, 9 comparative demonstrate that the solvent has little effect on the inhibition of gassing effect and electrochemical properties. But ethanol is somewhat better from an environmental and cost standpoint: the cost of the ethanol is lower and the ethanol is nontoxic; toluene and ethyl acetate are more expensive and toluene is also toxic in particular. Ethanol is therefore preferred.
Examples 1 and 10 are comparative to demonstrate that spin steaming and water bath agitation drying have little effect on the inhibition of gassing and electrochemical properties. However, the rotary evaporation has the advantages that a negative pressure is provided in the process, the evaporation rate of the solvent is faster, but the water bath stirring evaporation is longer, and the reaction is more complete.
Claims (9)
1. The preparation method of the pre-lithiated silica composite material is characterized by comprising the following steps of:
mixing a pre-lithiated silica material raw material precursor with an acid solution, and performing heat treatment to obtain the pre-lithiated silica composite material;
wherein the acid solution is boric acid solution or phosphoric acid solution;
wherein the mass ratio of the acid in the acid solution to the raw material precursor of the pre-lithiated silica material is (0.13-0.15): 1, a step of;
wherein, the residual alkali content in the precursor of the raw material of the pre-lithiated silica material is 3-6%; the residual alkali amount contained in the pre-lithiated silica material raw material precursor refers to the mass ratio of alkali generated by the reaction of lithium remained after pre-lithiation of the silica material and water to the pre-lithiated silica material raw material precursor;
wherein the temperature of the heat treatment is 500-550 ℃; the heat treatment time is 4-5h;
the pre-lithiated silica composite material is of a core-shell structure, and the core-shell structure comprises an inner core and an outer shell;
the inner core is made of a pre-lithiated silica material; the pre-lithiated silicone material comprises a carbon-coated silicone material having a porous structure; the structure of the carbon-coated silica material with the porous structure is a hollow structure of a core-a gap-a shell;
the shell is LiBO 2 /B 2 O 3 Coating or Li 3 PO 4 /P 2 O 5 A coating layer;
the average film thickness of the shell is 35-45nm.
2. The method of preparing a pre-lithiated silicone composite material of claim 1, wherein the shell has a thinnest film thickness of 5 to 16nm.
3. The method of preparing a pre-lithiated silicone composite material of claim 2, wherein the shell has a thinnest film thickness of 8.5-14nm;
and/or the average film thickness of the shell is 36nm, 38nm, 41nm or 44nm.
4. The method of preparing a pre-lithiated silicone composite material of claim 1, wherein the acid solution comprises an acid and a solvent;
and/or, the residual alkali content of the pre-lithiated silica material raw material precursor is 4% -5.8%;
and/or, after said mixing, before said heat treatment, further comprising a step of removing the solvent;
and/or, the atmosphere of the heat treatment is an inert atmosphere;
and/or the heating rate in the heat treatment is 1-20 ℃/min.
5. The method of preparing a pre-lithiated silicone composite material of claim 4, wherein the solvent is ethanol, ethyl acetate, or toluene;
and/or the acid and the solvent can be mixed and dispersed to prepare the acid solution;
and/or, the residual alkali content of the pre-lithiated silica material raw material precursor is 5.5%;
and/or the solvent is removed by rotary evaporation or evaporation;
and/or the atmosphere of the heat treatment is argon atmosphere;
and/or, the temperature of the heat treatment is 530-550 ℃;
and/or the heating rate in the heat treatment is 4-6 ℃/min.
6. A pre-lithiated silicone composite material prepared by the method of any one of claims 1-5.
7. Use of a pre-lithiated silicone composite material according to any one of claims 1 to 5 and claim 6 in an electrode material.
8. A negative electrode sheet, characterized in that it is made of the pre-lithiated silica composite material according to any one of claims 1 to 5 or claim 6.
9. A lithium ion battery comprising the negative electrode tab of claim 8.
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