CN107316974B - Preparation method of nano-silver composite lithium iron phosphate cathode material - Google Patents
Preparation method of nano-silver composite lithium iron phosphate cathode material Download PDFInfo
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Abstract
The invention discloses a preparation method of a nano-silver composite lithium iron phosphate anode material. And then washing with a water-alcohol mixed solution to remove ascorbic acid or carbonizing the ascorbic acid by high-temperature treatment at 300-700 ℃ in a protective atmosphere to obtain the nano-silver composite lithium iron phosphate anode material. After the modification by the method, the conductivity of the lithium iron phosphate positive electrode material is obviously improved, and the specific capacity, the cycling stability and the rate capability are obviously improved. The initial discharge specific capacity of the nano-silver modified lithium iron phosphate can reach 163mAh/g, and the capacity is not attenuated after 80 cycles. The specific capacity reaches 95mAh/g under the 5C multiplying power. The method adopted by the invention is simple, easy to operate, easy for industrial production, relatively low in energy consumption and less in environmental pollution.
Description
Technical Field
The invention relates to a preparation method of nano-silver modified lithium iron phosphate, and the synthesized nano-silver composite lithium iron phosphate material can be used as a lithium ion battery anode material for manufacturing various types of lithium ion batteries.
Background
Along with the progress and development of human society, the consumption of energy by people is continuously increased. The existing non-renewable energy mainly comprising fossil energy is continuously consumed, so that the environment is adversely affected, and the sustainable development of economy and society is undoubtedly limited in the near future. Therefore, people are striving to find new clean and recyclable energy sources. Energy storage devices represented by lithium ion batteries have attracted much attention. Among various factors affecting the performance of the lithium ion battery, the positive electrode material of the lithium ion battery is a key factor affecting and even determining the performance of the lithium ion battery. Lithium iron phosphate in the commercialized lithium ion battery anode material is considered to be one of the lithium ion battery anode materials with ideal prospects due to the advantages of readily available raw materials, low price, higher working voltage, stable discharge voltage, high safety performance, environmental friendliness, good thermal stability and the like. But due to the characteristics of the structure and the composition of the lithium iron phosphate, the electronic conductivity of the lithium iron phosphate is (10)～9～10～10S/cm) and lithium ion diffusion coefficient (1.8X 10)～14cm2the/S) is low, directly results in poor specific capacity and rate charge-discharge performance, and limits the application of the material. At present, a plurality of methods can improve the electrochemical performance of the lithium iron phosphate anode material, wherein the method of compounding the lithium iron phosphate anode material with metal nano particles is a simple and effective method. The nano silver with excellent conductivity is often selected by researchers as a complexing agent of the lithium iron phosphate anode material, and the electrochemical performance of the material is improved under the condition that the lattice structure of the lithium iron phosphate is not changed. For example, patent CN103531801A (pending) discloses that the first discharge specific capacity of the modified silver powder composite lithium iron phosphate can reach 168mAh/g, and the cycle performance is significantly improved. Patent CN101635349A (effective) discloses that a silver compound and a raw material for preparing lithium iron phosphate are mixed in a solvent, a reducing agent is added, vacuum drying is performed, and high-temperature heat treatment is performed in vacuum to obtain a lithium iron phosphate/silver/carbon composite cathode material. The highest discharge specific capacity of the lithium iron phosphate composite anode material obtained by the method can reach 169.1mAh/g, and the lithium iron phosphate composite anode material has good cycling stability. Patent CN104577117AThe method is characterized in that silver nanowires with a certain mass percentage are added into positive and negative electrode slurry, so that the conductivity of the lithium ion battery is improved, the internal resistance of the battery is reduced, and the rate capability of the lithium ion battery is greatly improved.
Disclosure of Invention
The invention aims to solve the technical problem that the lithium iron phosphate serving as the lithium ion battery anode material has low electronic conductivity and lithium ion diffusion coefficient and directly causes poor specific capacity and rate charging and discharging performance, and provides a simple and effective method for improving the electrochemical performance of the lithium iron phosphate.
In order to solve the technical problems, the invention adopts the following technical scheme:
a preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) fully mixing lithium iron phosphate and silver nitrate in a mortar, and dropwise adding a small amount of ethanol for pre-grinding;
(2) adding ascorbic acid into the mixture pre-ground in the step (1), fully mixing and then continuing to grind, so that the reaction is fully carried out to obtain a reaction product;
(3) post-treatment method a: and (3) dispersing the reaction product obtained in the step (2) into a solvent by using a mixed solution of deionized water and ethanol as the solvent for soaking, removing ascorbic acid in the product, separating a solid-phase product by using a high-speed centrifuge after soaking, washing, centrifuging, and drying the solid-phase product in a vacuum drying oven to obtain the nano-silver composite lithium iron phosphate material.
Post-treatment method B: and (3) placing the reaction product obtained in the step (2) into a tubular furnace, and carbonizing ascorbic acid by high-temperature treatment under the protection of inert gas to obtain the carbon-coated nano silver composite lithium iron phosphate material.
The mass ratio of the silver nitrate to the lithium iron phosphate is 1-10: 100, 0.3mL of ethanol needs to be added dropwise based on 1g of lithium iron phosphate, and the pre-grinding time is 10-30 min; the grinding method employed in the present invention is not limited to the manual grinding, but also includes mechanical grinding such as ball milling and the like.
The mass ratio of the ascorbic acid to the silver nitrate is 1-3: 1; and (3) adding ascorbic acid in the step (2), fully mixing, and continuously grinding for 30-60 min.
The volume ratio of the deionized water to the ethanol in the mixed solution of the deionized water and the ethanol adopted in the step (3) is 1: 1-10; and soaking the reaction product in a solvent for 10-30 min.
And (3) centrifuging for 10-30 min by adopting a high-speed centrifuge under the condition of 10000-15000 r/min to separate a solid-phase product, and repeating the washing and centrifuging processes for 2-3 times.
And (3) drying the obtained solid-phase product in a vacuum drying oven at 50-60 ℃ for 12-24 h.
The inert gas is nitrogen or argon; the high-temperature treatment is carried out at a high temperature of 300-700 ℃ for 1-2 h.
The principle of the invention is as follows: on the basis of lithium iron phosphate, the silver nitrate and the ascorbic acid are ground together, so that on one hand, the silver nitrate is fully reduced by the ascorbic acid to generate nano silver, and on the other hand, the generated nano silver is uniformly dispersed in a lithium iron phosphate material and well combined with a lithium iron phosphate crystal; dissolving ascorbic acid in a hydroalcoholic solution by a post-treatment method A, and simultaneously separating the nano-silver/lithium iron phosphate composite material by a high-speed centrifuge; and C, carbonizing the ascorbic acid at high temperature by using a post-treatment method B to obtain the nano silver/lithium iron phosphate composite material coated with the carbon material, so as to achieve the purpose of improving the electronic conductivity and the lithium ion diffusion coefficient of the material.
Compared with other methods, the method has the beneficial technical effects that: the invention takes the lithium iron phosphate material as the base, and prepares the nano silver with good binding property with the lithium iron phosphate by mixing and grinding with silver salt and ascorbic acid. After the modification by the method, the conductivity of the lithium iron phosphate positive electrode material is obviously improved, and the specific capacity, the cycling stability and the rate capability are obviously improved.
The nano-silver composite lithium iron phosphate cathode material is prepared through a solid-phase chemical reaction and a post-treatment process, and electrochemical tests prove that the nano-silver modified lithium iron phosphate cathode material has obviously improved conductivity, obviously improved specific capacity, cycle stability and rate capability, has a first discharge specific capacity of 163mAh/g after detection, has no capacity attenuation after 80 cycles, has a specific capacity of 95mAh/g under a 5C rate, and has good rate capability. In addition, the method adopted by the invention is simple, easy to operate, easy for industrial production, relatively low in energy consumption and less in environmental pollution. Therefore, the method has obvious advantages in process method and performance improvement effect compared with other methods.
Drawings
Fig. 1 is SEM images of (a) lithium iron phosphate and (b) the lithium iron phosphate/nano silver composite positive electrode material prepared in example 2 of the present invention.
Fig. 2 shows XRD spectra of (a) lithium iron phosphate, (b) lithium iron phosphate/nano silver composite positive electrode materials prepared in examples 2 and 4 of the present invention.
Fig. 3 is a first discharge specific capacity curve of (a) lithium iron phosphate, (b) the lithium iron phosphate/nano silver composite positive electrode material prepared in embodiment 2 and (c) embodiment 4 of the present invention.
Fig. 4 (a) shows rate capability of lithium iron phosphate, (b) lithium iron phosphate/nano silver composite positive electrode materials prepared in embodiments 2 and 4 of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples. It is to be understood that the following examples are illustrative only and are not intended to limit the scope of the invention, which is to be given numerous insubstantial modifications and adaptations by those skilled in the art based on the teachings set forth above.
Example 1
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.01g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, pre-grinding the mixture for 30 minutes after the lithium iron phosphate and the silver nitrate are fully mixed by a spoon, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.03g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 60 minutes to fully react to obtain a corresponding reaction product;
(3) the reaction product obtained was placed in about 30mL of a 1:1, shaking and shaking uniformly, standing for 30 minutes to fully dissolve ascorbic acid in a reaction product, centrifuging for 30 minutes at 15000 r/min by adopting a high-speed centrifuge with a cooling function, taking out an upper layer solution, separating a solid-phase product, and washing off the ascorbic acid; this washing centrifugation process was repeated 3 times; and placing the obtained solid-phase product in a vacuum drying oven, and drying for 12 hours at the temperature of 60 ℃ to obtain the lithium iron phosphate/nano silver composite anode material.
The obtained lithium iron phosphate/nano silver composite material is used as a positive electrode material, is assembled into a half-cell and is subjected to electrochemical test, and the result shows that the first discharge specific capacity of the lithium iron phosphate/nano silver composite positive electrode material reaches 140mAh/g, which is obviously superior to that of the selected commercial lithium iron phosphate positive electrode material of 128 mAh/g.
Example 2
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.02g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, fully mixing the lithium iron phosphate and the silver nitrate with a spoon, pre-grinding for 30 minutes, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.06g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 60 minutes to fully react to obtain a corresponding reaction product;
(3) the reaction product obtained was placed in about 30mL of a 1:1, shaking and shaking uniformly, standing for 30 minutes to fully dissolve ascorbic acid in a reaction product, centrifuging for 30 minutes at 15000 r/min by adopting a high-speed centrifuge with a cooling function, taking out an upper layer solution, separating a solid-phase product, and washing off the ascorbic acid; this washing centrifugation process was repeated 3 times; and placing the obtained solid-phase product in a vacuum drying oven, and drying for 12 hours at the temperature of 60 ℃ to obtain the lithium iron phosphate/nano silver composite anode material.
Fig. 1 (b) is an SEM image of the lithium iron phosphate/nano silver composite prepared in this embodiment, and it can be seen from the SEM image that the original shape of the lithium iron phosphate is substantially maintained after the lithium iron phosphate is compounded with silver.
Fig. 2 (b) is an XRD spectrum of the lithium iron phosphate/nano silver composite prepared in this example, and it can be determined from the spectrum that only the phases of lithium iron phosphate and silver are present in the composite.
Fig. 3 (b) is a first specific discharge capacity curve of the lithium iron phosphate/nano silver composite positive electrode material prepared in this embodiment, and a map shows that the first specific discharge capacity can reach 156 mAh/g.
Fig. 4 (b) is a rate performance curve of the lithium iron phosphate/nano silver composite anode material prepared in this embodiment, and a graph shows that the composite material in this embodiment has good rate performance.
Example 3
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.01g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, pre-grinding the mixture for 30 minutes after the lithium iron phosphate and the silver nitrate are fully mixed by a spoon, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.03g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 60 minutes to fully react to obtain a corresponding reaction product;
(3) transferring the obtained reaction product into a porcelain boat, placing the porcelain boat into a tube furnace, introducing argon for half an hour, heating to 500 ℃, and keeping the temperature for 1 hour; and then cooling to room temperature to obtain the nano silver/lithium iron phosphate anode material compounded with the carbon material, wherein the whole heat treatment process is carried out under the protection of argon.
The obtained lithium iron phosphate/nano silver composite material is used as a positive electrode material, a half cell is assembled and subjected to electrochemical test, and the result shows that the first discharge specific capacity of the lithium iron phosphate/nano silver composite positive electrode material reaches 142 mAh/g.
Example 4
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.02g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, fully mixing the lithium iron phosphate and the silver nitrate with a spoon, grinding for 30 minutes, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.06g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 60 minutes to fully react to obtain a corresponding reaction product;
(3) transferring the obtained reaction product into a porcelain boat, placing the porcelain boat into a tube furnace, introducing argon for half an hour, heating to 500 ℃, and keeping the temperature for 1 hour; and then cooling to room temperature to obtain the nano silver/lithium iron phosphate anode material compounded with the carbon material, wherein the whole heat treatment process is carried out under the protection of argon.
Fig. 2 (c) is an XRD spectrum of the lithium iron phosphate/nano silver composite prepared in this example, and it can be determined from the spectrum that only the phases of lithium iron phosphate and silver are present in the composite.
Fig. 3 (c) is a first specific discharge capacity curve of the lithium iron phosphate/nano silver composite anode material prepared in this embodiment, and a map shows that the first specific discharge capacity can reach 163 mAh/g.
Fig. 4 (c) is a rate performance curve of the lithium iron phosphate/nano silver composite anode material prepared in this embodiment, and a graph shows that the composite material in this embodiment has good rate performance.
Example 5
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.1g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, fully mixing the lithium iron phosphate and the silver nitrate with a spoon, pre-grinding for 25 minutes, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.1g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 45 minutes to fully react to obtain a corresponding reaction product;
(3) the reaction product obtained was placed in about 30mL of a 1: 10, shaking and shaking uniformly in a mixed solvent of deionized water and ethanol, standing for 30 minutes to fully dissolve ascorbic acid in a reaction product, centrifuging for 25 minutes at 10000 rpm by adopting a high-speed centrifuge with a cooling function, taking out an upper layer solution, separating a solid-phase product, and washing off the ascorbic acid; this washing centrifugation process was repeated 3 times; and placing the obtained solid-phase product in a vacuum drying oven, and drying for 24 hours at the temperature of 50 ℃ to obtain the lithium iron phosphate/nano silver composite anode material.
The obtained lithium iron phosphate/nano silver composite material is used as a positive electrode material, a half battery is assembled and subjected to electrochemical test, and the result shows that the first discharge specific capacity of the lithium iron phosphate/nano silver composite positive electrode material reaches 130 mAh/g.
Example 6
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.05g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, pre-grinding the mixture for 10 minutes after the lithium iron phosphate and the silver nitrate are fully mixed by a spoon, and dripping 0.2ml of ethanol in the grinding process;
(2) weighing 0.1g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 35 minutes to fully react to obtain a corresponding reaction product;
(3) the reaction product obtained was placed in about 30mL of a 1: 5, shaking and shaking uniformly in a mixed solvent of deionized water and ethanol, keeping still for 30 minutes to fully dissolve ascorbic acid in a reaction product, centrifuging for 10 minutes at 12000 r/min by adopting a high-speed centrifuge with a cooling function, taking out an upper layer solution, separating a solid-phase product, and washing off the ascorbic acid; this washing centrifugation process was repeated 2 times; and placing the obtained solid-phase product in a vacuum drying oven, and drying for 20 hours at the temperature of 55 ℃ to obtain the lithium iron phosphate/nano silver composite anode material.
The obtained lithium iron phosphate/nano silver composite material is used as a positive electrode material, a half battery is assembled and subjected to electrochemical test, and the result shows that the first discharge specific capacity of the lithium iron phosphate/nano silver composite positive electrode material reaches 136 mAh/g.
Example 7
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.03g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, fully mixing the lithium iron phosphate and the silver nitrate with a spoon, pre-grinding for 15 minutes, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.045g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 50 minutes to fully react to obtain a corresponding reaction product;
(3) transferring the obtained reaction product into a porcelain boat, placing the porcelain boat into a tube furnace, introducing argon for half an hour, heating to 300 ℃, and keeping the temperature for 2 hours; and then cooling to room temperature to obtain the nano silver/lithium iron phosphate anode material compounded with the carbon material, wherein the whole heat treatment process is carried out under the protection of argon.
The obtained lithium iron phosphate/nano silver composite material compounded with the carbon material is used as a positive electrode material, a half battery is assembled, and an electrochemical test is carried out, so that the result shows that the first discharge specific capacity of the lithium iron phosphate/nano silver composite positive electrode material reaches 143 mAh/g.
Example 8
A preparation method of a nano-silver composite lithium iron phosphate anode material comprises the following steps:
(1) weighing 1g of lithium iron phosphate and 0.08g of silver nitrate, pouring the lithium iron phosphate and the silver nitrate into a mortar, mixing the lithium iron phosphate and the silver nitrate fully by using a spoon, pre-grinding for 20 minutes, and dropwise adding 0.2ml of ethanol in the grinding process;
(2) weighing 0.2g of ascorbic acid, adding the ascorbic acid into the ground mixture, fully mixing by using a medicine spoon, and keeping grinding for 40 minutes to fully react to obtain a corresponding reaction product;
(3) transferring the obtained reaction product into a porcelain boat, placing the porcelain boat into a tube furnace, introducing argon for half an hour, heating to 700 ℃, and keeping the temperature for 1 hour; and then cooling to room temperature to obtain the nano silver/lithium iron phosphate anode material compounded with the carbon material, wherein the whole heat treatment process is carried out under the protection of argon.
The obtained lithium iron phosphate/nano silver composite material compounded with the carbon material is used as a positive electrode material, a half battery is assembled, electrochemical tests are carried out, and the result shows that the first discharge specific capacity of the lithium iron phosphate/nano silver composite positive electrode material reaches 132 mAh/g.
The invention can be realized by all the listed raw materials, the upper limit value and the lower limit value of all the raw materials and the interval value of all the process parameters (such as rotating speed, temperature, time and the like) of the invention, and the invention can be realized by all the upper limit value and the lower limit value of the process parameters and the interval value of all the process parameters, and the embodiments are not listed.
In summary, it can be seen that the preparation method provided by the invention can prepare a high-quality lithium iron phosphate/nano silver composite material, and compared with the selected single lithium iron phosphate positive electrode material, the electrochemical performance of the prepared composite positive electrode material is remarkably improved; in addition, the preparation method has the advantages of simple process, easy operation, low energy consumption and easy amplification for industrial production.
The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. A preparation method of a nano-silver composite lithium iron phosphate anode material is characterized by comprising the following steps:
(1) fully mixing lithium iron phosphate and silver nitrate in a mortar, and dropwise adding a proper amount of ethanol for pre-grinding;
(2) adding ascorbic acid into the mixture pre-ground in the step (1), fully mixing and then continuing to grind, so that the reaction is fully carried out to obtain a reaction product;
(3) dispersing the reaction product obtained in the step (2) into a solvent by using a mixed solution of deionized water and ethanol as the solvent for soaking, removing ascorbic acid in the product, separating a solid-phase product by using a high-speed centrifuge after soaking, washing, centrifuging, and drying the solid-phase product in a vacuum drying oven to obtain the nano-silver composite lithium iron phosphate material; the mass ratio of silver nitrate to lithium iron phosphate in the step (1) is 1-10: 100, 0.3mL of ethanol needs to be added dropwise based on 1g of lithium iron phosphate, and the pre-grinding time is 10-30 min;
the mass ratio of the ascorbic acid to the silver nitrate is 1-3: 1; and (3) adding ascorbic acid in the step (2), fully mixing, and continuing to grind for 30-60 min.
2. The preparation method of the nano-silver composite lithium iron phosphate cathode material according to claim 1, characterized by comprising the following steps: and (3) placing the reaction product obtained in the step (2) into a tubular furnace, and carbonizing ascorbic acid by high-temperature treatment under the protection of inert gas to obtain the carbon-coated nano silver composite lithium iron phosphate material.
3. The preparation method of the nano-silver composite lithium iron phosphate cathode material according to claim 1, characterized by comprising the following steps: the volume ratio of the deionized water to the ethanol in the mixed solution of the deionized water and the ethanol adopted in the step (3) is 1: 1-10; and soaking the reaction product in a solvent for 10-30 min.
4. The preparation method of the nano-silver composite lithium iron phosphate cathode material according to claim 1, characterized by comprising the following steps: and (3) centrifuging for 10-30 min by adopting a high-speed centrifuge under the condition of 10000-15000 r/min to separate a solid-phase product, and repeating the washing and centrifuging processes for 2-3 times.
5. The preparation method of the nano-silver composite lithium iron phosphate cathode material according to claim 1, characterized by comprising the following steps: and (3) drying the obtained solid-phase product in a vacuum drying oven at 50-60 ℃ for 12-24 h.
6. The preparation method of the nano-silver composite lithium iron phosphate cathode material according to claim 2, characterized by comprising the following steps: the inert gas is nitrogen or argon; the high-temperature treatment is carried out at a high temperature of 300-700 ℃ for 1-2 h.
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