Nanosphere shell type lithium iron phosphate composite cathode material and preparation method thereof

Abstract

The application relates to the field of positive electrode materials, in particular to a nanospherical shell type lithium iron phosphate composite positive electrode material and a preparation method thereof; solve the problem of poor cycle performance of the existing lithium iron phosphate positive electrode material; the positive electrode material is composed of tin dioxide as a core, chitosan and polyglycolic acid as a shell, a double-layer nanospherical shell microsphere with a core-shell structure, and is coated on the surface of lithium iron phosphate, so that the rate performance and cycle performance of the positive electrode material are improved; the positive electrode material has good rate performance, can provide sufficient power for new energy vehicles, has excellent cycle stability, can prolong the service life of the battery, reduces the replacement cost, is suitable for large-scale application in an energy storage system, and is helpful to improving energy utilization efficiency and promoting the development of renewable energy.

Description

TECHNICAL FIELD

[0001] The application relates to the field of positive electrode materials, in particular to a nanospherical shell type lithium iron phosphate composite positive electrode material and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have become mainstream products on the market due to their high energy density, long cycle life and low self-discharge rate. The performance of a lithium ion battery depends largely on the performance of its positive electrode material. Lithium iron phosphate, as an important positive electrode material, has good thermal stability and environmental friendliness and has been widely applied to various batteries. However, the lithium iron phosphate material has problems such as low cycle performance in practical application, which limits the application of the battery under large current conditions. Therefore, the application provides a nanospherical shell type lithium iron phosphate composite positive electrode material to improve the above problems and realize a lithium ion battery with higher performance. SUMMARY

[0003] In order to overcome the above technical problems, the purpose of the application is to provide a nanospherical shell type lithium iron phosphate composite positive electrode material and a preparation method thereof, which solves the problem of poor cycle performance of the existing lithium iron phosphate positive electrode material.

[0004] The purpose of the application can be achieved by the following technical solutions.

[0005] In a first aspect, the application provides a nanospherical shell type lithium iron phosphate composite positive electrode material, which comprises the following components by weight:

[0006] 45-90 parts of chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, 4-8 parts of acetylene carbon black, 1.5-3 parts of sodium carboxymethyl cellulose and 0.5-1 part of polyvinyl alcohol;

[0007] The chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate is prepared by the following steps:

[0008] Step A1: lithium hydroxide monohydrate and deionized water are added to a three-necked flask equipped with a stirrer, stirred at 50-100 r / min for 10-20 min, phosphoric acid is added dropwise and stirred magnetically for 8-10 min, cetyltrimethylammonium bromide is added and stirred for 5-10 min, a solution of ferrous sulfate heptahydrate and ascorbic acid is added and stirred for 10-15 min, transferred to a reaction kettle, reacted at 170-180 DEG C for 10-12 h, cooled to 24-26 DEG C, washed with deionized water for 3-5 times after filtration, and dried in a drying oven at 70-80 DEG C for 22-24 h to obtain a lithium iron phosphate precursor powder;

[0009] Step A2: tin dioxide nano powder, deionized water were added into a single neck flask, magnetic stirring for 10-20 min, chloroacetic acid and acetone were added and magnetic stirring for 8-10 min, chitosan powder was added and magnetic stirring for 8-10 min, to obtain a first solution;

[0010] Step A3: the first solution was added into a four-neck flask equipped with reflux condenser, stirrer and thermometer, and placed in an oil bath, and nitrogen was introduced for protection, triethylamine was dissolved in acetone and then added dropwise into the first solution, stirring for 10-20 min, refluxing at 180-190℃ for 4 h, adding glutaraldehyde at 40℃ and reacting for 2 h, evaporating acetone, washing with anhydrous ethanol for 5-7 times, and placing in a drying box for vacuum drying at 60℃ for 12 h, to obtain chitosan / polyglycolic acid coated tin dioxide;

[0011] Reaction principle:

[0012]

[0013] Step A4: lithium iron phosphate precursor powder and deionized water were added into a ball mill tank, ball milling at 400-500 r / min for 15-20 min, chitosan / polyglycolic acid coated tin dioxide was added, mixing at 900-1000 r / min for 4-5 h, transferring to an oven for drying at 80℃, placing in a sintering furnace, introducing nitrogen for protection, calcining at 650-750℃ for 7-8 h, and cooling to 24-26℃, to obtain chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate.

[0014] As a further scheme of the application: the amount ratio of lithium hydroxide monohydrate, deionized water, phosphoric acid, cetyltrimethylammonium bromide, ferrous sulfate heptahydrate and ascorbic acid solution in step A1 is 60-120 mmol: 80-160 mL: 20-40 mmol: 30-60 mmol: 20-40 mmol: 10-20 mL.

[0015] As a further scheme of the application: the molar concentration of the ascorbic acid solution in step A1 is 0.3 mol / L.

[0016] As a further scheme of the application: the amount ratio of tin dioxide nano powder, deionized water, chloroacetic acid, acetone and chitosan powder in step A2 is 0.153-0.306 g: 150-300 mL: 0.3-0.6 g: 0.3-0.6 g: 1.5-3 g.

[0017] As a further scheme of the application: the degree of deacetylation of the chitosan powder in step A2 is 85%.

[0018] As a further scheme of the present application: the amount ratio of the first solution, triethylamine, acetone and glutaraldehyde in step A3 is 150-300 mL: 0.36-0.72 g: 0.72-1.44 g: 0.74-1.48 g.

[0019] As a further scheme of the present application: the amount ratio of the lithium iron phosphate precursor powder, deionized water and chitosan / polyglycolic acid coated tin dioxide in step A4 is 5-10 g: 50-100 mL: 0.55-1.1 g.

[0020] In a second aspect, the present application provides a preparation method of a nanospherical shell type lithium iron phosphate composite positive electrode material, comprising the following steps:

[0021] Step one: according to the weight parts, 45-90 parts of chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, 4-8 parts of acetylene carbon black, 1.5-3 parts of sodium carboxymethyl cellulose and 0.5-1 part of polyvinyl alcohol are weighed and prepared for use; wherein the polyvinyl alcohol is polyvinyl alcohol PVA 1788;

[0022] Step two: the chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, acetylene carbon black, sodium carboxymethyl cellulose and polyvinyl alcohol are ground, then N-methyl pyrrolidone is added to adjust the solid content to 45%-55% and continue to grind, after grinding, coated on an aluminum foil current collector and placed in a constant temperature vacuum drying oven for drying for 8-12 h, placed in a roller compactor for compaction, and finally punched into a circular electrode with a slicing machine to obtain a nanospherical shell type lithium iron phosphate composite positive electrode material.

[0023] The present application has the following advantages:

[0024] The nanospherical shell type lithium iron phosphate composite positive electrode material of the present application has tin dioxide as the core, chitosan and polyglycolic acid as the shell, forming a nanosphere with core-shell structure, coated on the surface of lithium iron phosphate, the tin dioxide has good conductivity, the chitosan contains nitrogen element, which can form a nitrogen-doped carbon layer after calcination, and the polyglycolic acid and chitosan form a network structure together, making the carbon layer formed by carbonization continuous and uniform, improving the reaction kinetics of the material in the charging and discharging process, thereby improving the energy density and cycle stability of the battery.

[0025] The application discloses a nanometer spherical shell type lithium iron phosphate composite positive electrode material, and a preparation method thereof. The lithium iron phosphate precursor powder is prepared from lithium monohydrate, phosphoric acid, cetyltrimethylammonium bromide, ferrous sulfate heptahydrate and ascorbic acid. A water molecule and a hydroxyl protective layer are formed on the surface of the tin dioxide. The carboxyl group in chloroacetic acid reacts with the hydroxyl group in the water molecule protective layer. Chitosan is added. The amino group in the chitosan molecular chain is positively charged, and the carboxyl group in the chloroacetic acid molecule is negatively charged. The two are electrostatically attracted to each other. Triethylamine is used as an acid binding agent to promote the polymerization of chloroacetic acid. After the chloroacetate ion undergoes intermolecular nucleophilic substitution, it gradually reacts and polymerizes to form a polyglycolic acid spherical shell on the surface of the tin dioxide. Glutaraldehyde is used as a crosslinking agent. The amino group in the chitosan molecular chain reacts with the aldehyde group in the glutaraldehyde to cause crosslinking between the chitosan molecular chains. The outer spherical shell structure of the chitosan molecules is compact and stable. The tin dioxide is a kind of excellent conductive material, which can improve the conductivity and stability of the positive electrode material. The crosslinked chitosan has a strong steric shielding effect, which can inhibit the fusion and growth of particles during the calcination process, reduce the particle size, and make the carbon layer formed by carbonization continuous and uniform, and can disperse the tin dioxide nanoparticles to avoid their agglomeration, and ensure the continuity of the electron conduction path. The positive electrode material has high specific capacity and good cycle performance, and is suitable for lithium ion battery scenes with high power and long service life requirements. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be clearly and completely described in combination with the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments of the application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the application.

[0027] Embodiment 1

[0028] The embodiment is a preparation method of a nanometer spherical shell type lithium iron phosphate composite positive electrode material, comprising the following steps.

[0029] Step A1: 60 mmol of lithium monohydrate and 80 mL of deionized water are added to a three-necked flask provided with a stirrer, stirred at 50 r / min for 10 min, 20 mmol of phosphoric acid is added dropwise and stirred magnetically for 8 min, 30 mmol of cetyltrimethylammonium bromide is added and stirred for 5 min, 20 mmol of ferrous sulfate heptahydrate and 10 mL of ascorbic acid solution are added and stirred for 10 min, and then transferred to a reaction kettle, reacted at 170 DEG C for 10 h, cooled to 24 DEG C, filtered and washed with deionized water for 3-5 times, and dried in a drying oven at 70 DEG C for 22 h to obtain lithium iron phosphate precursor powder.

[0030] Step A2: 0.153 g of tin dioxide nano-powder, 150 mL of deionized water were added into a single-necked flask, magnetically stirred for 10 min, 0.3 g of chloroacetic acid and 0.3 g of acetone were added and magnetically stirred for 8 min, 1.5 g of chitosan powder was added and magnetically stirred for 8 min to obtain a first solution;

[0031] Step A3: 150 mL of the first solution was added into a four-necked flask equipped with a reflux condenser, a stirrer and a thermometer, which was placed in an oil bath, and was protected by nitrogen, 0.36 g of triethylamine was dissolved in 0.72 g of acetone and then was added dropwise into the first solution, which was stirred for 10 min, and then was refluxed at 180℃ for 4 h, 0.74 g of glutaraldehyde was added at 40℃ and reacted for 2 h, acetone was evaporated, and the product was washed with anhydrous ethanol for 5 times, and then was placed in a drying box and vacuum dried at 60℃ for 12 h to obtain chitosan / polyglycolic acid coated tin dioxide;

[0032] Step A4: 5 g of lithium iron phosphate precursor powder, 50 mL of deionized water were added into a ball mill tank, which was ball-milled at 400 r / min for 15 min, 0.55 g of chitosan / polyglycolic acid coated tin dioxide was added and mixed at 900 r / min for 4 h, and then was transferred into an oven and dried at 80℃, and then was placed in a sintering furnace and calcined at 650℃ for 7 h under the protection of nitrogen, and then was cooled to 24℃ to obtain chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate;

[0033] Step A5: chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate 45 parts, acetylene carbon black 4 parts, sodium carboxymethyl cellulose 1.5 parts and polyvinyl alcohol 0.5 parts were weighed according to the weight parts, and were prepared for use; wherein the polyvinyl alcohol was polyvinyl alcohol PVA 1788;

[0034] Step A6: chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, acetylene carbon black, sodium carboxymethyl cellulose and polyvinyl alcohol PVA 1788 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 45%, and then was continuously ground, and then was coated on an aluminum foil current collector, and was dried in a constant temperature vacuum drying box for 8 h, and then was placed in a rolling machine and was compacted, and finally was punched into a circular electrode by a slicing machine to obtain a nanospherical shell type lithium iron phosphate composite positive electrode material.

[0035] Example 2:

[0036] The present embodiment is a preparation method of a nanospherical shell type lithium iron phosphate composite positive electrode material, which comprises the following steps:

[0037] Step A1: 90 mmol of lithium hydroxide monohydrate, 120 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred at 75 r / min for 15 min, 30 mmol of phosphoric acid was added by dropwise, stirred magnetically for 9 min, 45 mmol of cetyltrimethylammonium bromide was added, stirred for 7 min, 30 mmol of ferrous sulfate heptahydrate and 15 mL of ascorbic acid solution were added, stirred for 12 min, transferred to a reaction kettle, reacted at 175℃ for 11 h, cooled to 25℃, after suction filtration, washed with deionized water for 4 times, placed in a drying oven at 75℃ for drying for 23 h, to obtain a lithium iron phosphate precursor powder;

[0038] Step A2: 0.223 g of tin dioxide nano powder, 225 mL of deionized water were added to a single-necked flask, stirred magnetically for 15 min, 0.45 g of chloroacetic acid and 0.45 g of acetone were added, stirred magnetically for 9 min, 2.25 g of chitosan powder was added, stirred magnetically for 9 min, to obtain a first solution;

[0039] Step A3: 225 mL of the first solution was added to a four-necked flask equipped with a reflux condenser, a stirrer, a thermometer, placed in an oil bath, protected by nitrogen, 0.54 g of triethylamine was dissolved in 1.08 g of acetone, then added dropwise to the first solution, stirred for 15 min, refluxed at 185℃ for 4 h, 1.11 g of glutaraldehyde was added at 40℃, and reacted for 2 h, acetone was evaporated, washed with anhydrous ethanol for 6 times, placed in a drying box and vacuum dried at 60℃ for 12 h, to obtain chitosan / polyglycolic acid coated tin dioxide;

[0040] Step A4: 7.5 g of lithium iron phosphate precursor powder, 75 mL of deionized water were added to a ball mill jar, ball milled at 450 r / min for 17 min, 0.825 g of chitosan / polyglycolic acid coated tin dioxide was added, mixed at 950 r / min for 4.5 h, transferred to an oven and dried at 80℃, placed in a sintering furnace, protected by nitrogen, calcined at 700℃ for 7.5 h, cooled to 25℃, to obtain chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate;

[0041] Step A5: chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate 67.5 parts, acetylene carbon black 6 parts, sodium carboxymethyl cellulose 2.25 parts and polyvinyl alcohol 0.75 parts were weighed according to the weight parts, and prepared for use; wherein the polyvinyl alcohol is polyvinyl alcohol PVA 1788;

[0042] Step A6: grind the chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, acetylene black, sodium carboxymethyl cellulose and polyvinyl alcohol PVA 1788, then add N-methyl pyrrolidone to adjust the solid content to 50% and continue grinding, after grinding, coat on an aluminum foil current collector, put into a constant temperature vacuum drying oven and dry for 10 h, place in a roller press to compact, and finally use a slicing machine to punch into a circular electrode to obtain a nanospherical shell type lithium iron phosphate composite positive electrode material.

[0043] Example 3:

[0044] The present embodiment is a preparation method of a nanospherical shell type lithium iron phosphate composite positive electrode material, comprising the following steps:

[0045] Step A1: add 120 mmol of lithium hydroxide monohydrate and 160 mL of deionized water into a three-necked flask equipped with a stirrer, stir at 100 r / min for 20 min, add 40 mmol of phosphoric acid and stir magnetically for 10 min, add 60 mmol of cetyltrimethylammonium bromide and stir for 10 min, add 40 mmol of ferrous sulfate heptahydrate and 20 mL of ascorbic acid solution and stir for 15 min, transfer to a reaction kettle, react at 180℃ for 12 h, cool to 26℃, after filtration, wash with deionized water for 5 times, and place in a drying oven to dry at 80℃ for 24 h to obtain lithium iron phosphate precursor powder;

[0046] Step A2: add 0.306 g of tin dioxide nano powder and 300 mL of deionized water into a single-necked flask, magnetically stir for 20 min, add 0.6 g of chloroacetic acid and 0.6 g of acetone and magnetically stir for 10 min, add 3 g of chitosan powder and magnetically stir for 10 min to obtain a first solution;

[0047] Step A3: add 300 mL of the first solution into a four-necked flask equipped with a reflux condenser, a stirrer and a thermometer, place in an oil bath, protect by passing nitrogen, add 0.72 g of triethylamine into 1.44 g of acetone and then drop into the first solution, stir for 20 min, reflux at 190℃ for 4 h, add 1.48 g of glutaraldehyde at 40℃ and react for 2 h, evaporate acetone, wash with anhydrous ethanol for 5-7 times, and place in a drying oven to vacuum dry at 60℃ for 12 h to obtain chitosan / polyglycolic acid coated tin dioxide;

[0048] Step A4: add 10 g of lithium iron phosphate precursor powder and 100 mL of deionized water into a ball mill tank, ball mill at 500 r / min for 20 min, add 1.1 g of chitosan / polyglycolic acid coated tin dioxide, mix at 1000 r / min for 5 h, transfer to an oven and dry at 80℃, place in a sintering furnace, protect by passing nitrogen, and calcine at 750℃ for 8 h, cool to 26℃ to obtain chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate.

[0049] Step A5: 90 parts of chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, 8 parts of acetylene black, 3 parts of sodium carboxymethyl cellulose and 1 part of polyvinyl alcohol were weighed according to the weight parts, and were ready for use; wherein the polyvinyl alcohol was polyvinyl alcohol PVA1788;

[0050] Step A6: chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate, acetylene black, sodium carboxymethyl cellulose and polyvinyl alcohol PVA 1788 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and the grinding was continued, after grinding, it was coated on aluminum foil current collector and put into constant temperature vacuum drying oven for drying for 12h, placed in a roller press for compaction, and finally punched into a circular electrode with a slicing machine, to obtain a nanosphere shell type lithium iron phosphate composite positive electrode material.

[0051] Comparative Example 1

[0052] The present comparative example is a preparation method of a nanosphere shell type lithium iron phosphate composite positive electrode material, comprising the following steps:

[0053] Step A1: 120mmol of lithium hydroxide monohydrate and 160mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred at 100r / min for 20min, 40mmol of phosphoric acid was added by dropwise addition, stirred for 10min, 60mmol of cetyltrimethylammonium bromide was added and stirred for 10min, 40mmol of ferrous sulfate heptahydrate and 20mL of ascorbic acid solution were added and stirred for 15min, transferred to a reaction kettle, reacted at 180℃ for 12h, cooled to 26℃, after filtration, washed with deionized water for 5 times, placed in a drying oven and dried at 80℃ for 24h, to obtain lithium iron phosphate precursor powder;

[0054] Step A2: 0.306g of tin dioxide nano powder and 300mL of deionized water were added to a single-necked flask, magnetically stirred for 20min, 3g of chitosan powder was added and magnetically stirred for 10min, 1.48g of glutaraldehyde was added at 40℃ and reacted for 2h, washed with anhydrous ethanol for 5-7 times, placed in a drying oven and vacuum dried at 60℃ for 12h, to obtain chitosan coated tin dioxide;

[0055] Step A3: 10g of lithium iron phosphate precursor powder and 100mL of deionized water were added to a ball mill tank, ball milled at 500r / min for 20min, 1.1g of chitosan coated tin dioxide was added, mixed at 1000r / min for 5h, transferred to an oven and dried at 80℃, placed in a sintering furnace and protected by nitrogen, calcined at 750℃ for 8h, cooled to 26℃, to obtain chitosan coated tin dioxide composite lithium iron phosphate;

[0056] Step A4: 90 parts of chitosan-coated tin dioxide composite lithium iron phosphate, 8 parts of acetylene black, 3 parts of sodium carboxymethyl cellulose, and 1 part of polyvinyl alcohol were weighed according to the weight parts, and were prepared for use; wherein the polyvinyl alcohol is polyvinyl alcohol PVA 1788;

[0057] Step A5: The chitosan-coated tin dioxide composite lithium iron phosphate, acetylene black, sodium carboxymethyl cellulose, and polyvinyl alcohol PVA 1788 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and the grinding was continued. After grinding, it was coated on an aluminum foil current collector and placed in a constant temperature vacuum drying oven for drying for 12 h, and then was placed in a roller press for compaction. Finally, it was punched into a circular electrode using a slicing machine to obtain a nanospherical shell type lithium iron phosphate composite positive electrode material.

[0058] Comparative Example 2:

[0059] This comparative example is a method for preparing a nanospherical shell type lithium iron phosphate composite positive electrode material, comprising the following steps:

[0060] Step A1: 120 mmol of lithium hydroxide monohydrate and 160 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirred at 100 r / min for 20 min, 40 mmol of phosphoric acid was added dropwise and stirred for 10 min, 60 mmol of cetyltrimethylammonium bromide was added and stirred for 10 min, 40 mmol of ferrous sulfate heptahydrate and 20 mL of ascorbic acid solution were added and stirred for 15 min, then transferred to a reaction kettle and reacted at 180℃ for 12 h, cooled to 26℃, filtered and washed with deionized water for 5 times, and then placed in a drying oven at 80℃ for drying for 24 h to obtain a lithium iron phosphate precursor powder;

[0061] Step A2: 0.306 g of tin dioxide nano powder and 300 mL of deionized water were added to a single-necked flask and magnetically stirred for 20 min, 0.6 g of chloroacetic acid and 0.6 g of acetone were added and magnetically stirred for 10 min to obtain a first solution;

[0062] Step A3: 300 mL of the first solution was added to a four-necked flask equipped with a reflux condenser, a stirrer, and a thermometer, and was placed in an oil bath, and was protected by nitrogen. 0.72 g of triethylamine was dissolved in 1.44 g of acetone and then was added dropwise to the first solution and stirred for 20 min, and then was refluxed at 190℃ for 4 h. The acetone was evaporated, washed with anhydrous ethanol for 5-7 times, and then was placed in a drying oven at 60℃ for vacuum drying for 12 h to obtain polyglycolic acid-coated tin dioxide.

[0063] Step A4: 10 g of lithium iron phosphate precursor powder, 100 mL of deionized water were added to a ball mill tank, ball milling at 500 r / min for 20 min, 1.1 g of polyglycolic acid coated tin dioxide was added, mixing at 1000 r / min for 5 h, transferring to an oven for drying at 80℃, placing in a sintering furnace under nitrogen protection, calcining at 750℃ for 8 h, cooling to 26℃, to obtain polyglycolic acid coated tin dioxide composite lithium iron phosphate;

[0064] Step A5: polyglycolic acid coated tin dioxide composite lithium iron phosphate 90 parts, acetylene black 8 parts, sodium carboxymethyl cellulose 3 parts and polyvinyl alcohol 1 part were weighed according to weight parts, for standby; wherein the polyvinyl alcohol is polyvinyl alcohol PVA 1788;

[0065] Step A6: polyglycolic acid coated tin dioxide composite lithium iron phosphate, acetylene black, sodium carboxymethyl cellulose and polyvinyl alcohol PVA 1788 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55% and continue to grind, after grinding, coated on aluminum foil current collector, dried in a constant temperature vacuum drying oven for 12 h, placed in a roller press for compaction, finally punched into a circular electrode with a slicing machine, to obtain a nanospherical shell type lithium iron phosphate composite positive electrode material.

[0066] Comparative Example 3:

[0067] The present comparative example is a preparation method of a nanospherical shell type lithium iron phosphate composite positive electrode material, comprising the following steps:

[0068] Step A1: 120 mmol of lithium hydroxide monohydrate, 160 mL of deionized water were added to a three-necked flask equipped with a stirrer, stirring at 100 r / min for 20 min, adding 40 mmol of phosphoric acid, stirring for 10 min, adding 60 mmol of cetyltrimethylammonium bromide, stirring for 10 min, adding 40 mmol of ferrous sulfate heptahydrate and 20 mL of ascorbic acid solution, stirring for 15 min, transferring to a reaction kettle, reacting at 180℃ for 12 h, cooling to 26℃, after filtration, washing with deionized water for 5 times, drying in an oven at 80℃ for 24 h, placing in a sintering furnace under nitrogen protection, calcining at 750℃ for 8 h, cooling to 26℃, to obtain lithium iron phosphate powder;

[0069] Step A2: 0.306 g of tin dioxide nano powder, 300 mL of deionized water were added to a single-necked flask, magnetic stirring for 20 min, 0.6 g of chloroacetic acid and 0.6 g of acetone were added, magnetic stirring for 10 min, 3 g of chitosan powder was added, magnetic stirring for 10 min, to obtain a first solution;

[0070] Step A3: 300 mL of the first solution was added to a four-necked flask equipped with a reflux condenser, stirrer, thermometer, and placed in an oil bath, and protected by nitrogen. 0.72 g of triethylamine was dissolved in 1.44 g of acetone and then added dropwise to the first solution, stirred for 20 min, and then refluxed at 190°C for 4 h. 1.48 g of glutaraldehyde was added at 40°C and reacted for 2 h. The acetone was evaporated, washed with anhydrous ethanol for 5-7 times, and then placed in a drying box and dried at 60°C under vacuum for 12 h to obtain chitosan / polyglycolic acid coated tin dioxide;

[0071] Step A4: Lithium iron phosphate powder 90 parts, chitosan / polyglycolic acid coated tin dioxide 5 parts, acetylene black 8 parts, sodium carboxymethyl cellulose 3 parts, and polyvinyl alcohol 1 part were weighed according to the weight parts and prepared for use. The polyvinyl alcohol is polyvinyl alcohol PVA 1788;

[0072] Step A5: The lithium iron phosphate powder, chitosan / polyglycolic acid coated tin dioxide, acetylene black, sodium carboxymethyl cellulose, and polyvinyl alcohol PVA 1788 were ground, then N-methyl pyrrolidone was added to adjust the solid content to 55%, and then the grinding was continued. After grinding, it was coated on an aluminum foil current collector and placed in a constant temperature vacuum drying oven for drying for 12 h, then placed in a roller press for compaction, and finally punched into a circular electrode using a slicing machine to obtain a nanospherical shell type lithium iron phosphate composite cathode material.

[0073] Performance test

[0074] The lithium iron phosphate cathode materials of Examples 1-3 and Comparative Examples 1-3 were assembled using a CR2032 button cell shell, using a lithium sheet as the negative electrode, using a Celgard 2400 battery separator, and adding electrolyte 1M LiPF6 / EC+DEC+EMC (1:1:1, v / v / v) dropwise to obtain a sample battery.

[0075] The sample battery was tested for 0.2C cycle performance at 25°C using a blue light tester: the prepared sample battery was placed in a constant temperature oven at 25°C for charge and discharge test, the voltage range was 2.0V-3.75V, first activated for 1 cycle at 0.1C charge and discharge, then charged and discharged at 0.2C current (constant current charging), and cycled for 100 cycles to obtain the related data of the first discharge specific capacity and the capacity retention rate at the 100th cycle.

[0076] Table 1, 0.2C discharge specific capacity, and capacity retention rate at the 100th cycle data

[0077]

[0078] Referring to the table, according to the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that the cycle performance of chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate is excellent.

[0079] According to the comparison between Example 3 and Comparative Example 1, it can be seen that the capacity retention rate of the positive electrode material obtained by coating tin dioxide with chitosan-polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate is higher than that of the positive electrode material obtained by coating tin dioxide with chitosan and then compounding the coated tin dioxide with lithium iron phosphate, which indicates that the positive electrode material obtained by coating tin dioxide with chitosan-polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate has excellent cycle performance.

[0080] According to the comparison between Example 3 and Comparative Example 2, it can be seen that the capacity retention rate of the positive electrode material obtained by coating tin dioxide with chitosan-polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate is higher than that of the positive electrode material obtained by coating tin dioxide with polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate, which indicates that the positive electrode material obtained by coating tin dioxide with chitosan-polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate has excellent cycle performance.

[0081] According to the comparison between Example 3 and Comparative Example 3, it can be seen that the capacity retention rate of the positive electrode material obtained by coating tin dioxide with chitosan-polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate is higher than that of the positive electrode material obtained by compounding lithium iron phosphate powder with tin dioxide coated with chitosan / polyglycolic acid, which indicates that the positive electrode material obtained by coating tin dioxide with chitosan-polyglycolic acid and then compounding the coated tin dioxide with lithium iron phosphate has excellent cycle performance.

[0082] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0083] The above is only an example and description of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the invention or exceed the scope defined in the present application, which shall be within the protection scope of the present application.

Claims

1. A nanospherical shell-type lithium iron phosphate composite cathode material, characterized in that, The following components are included by weight parts: Chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate 45-90 parts, acetylene carbon black 4-8 parts, sodium carboxymethyl cellulose 1.5-3 parts and polyvinyl alcohol 0.5-1 part; The chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate is prepared by the following steps: Step A1: lithium hydroxide monohydrate, deionized water are added to a three-necked flask and stirred, phosphoric acid is added dropwise and stirred magnetically, cetyltrimethylammonium bromide is added and stirred, ferrous sulfate heptahydrate and ascorbic acid solution are added and stirred, transferred to a reaction kettle and reacted, cooled, filtered and washed with deionized water, and dried to obtain lithium iron phosphate precursor powder; Step A2: tin dioxide nano powder, deionized water are added to a single-necked flask and stirred magnetically, chloroacetic acid and acetone are added and stirred magnetically, chitosan powder is added and stirred magnetically to obtain a first solution; Step A3: the first solution is added to a four-necked flask, placed in an oil bath, and protected by nitrogen, triethylamine is dissolved in acetone and added dropwise to the first solution and stirred, refluxed and reacted, glutaraldehyde is added and reacted, acetone is evaporated, washed with anhydrous ethanol, and vacuum dried to obtain chitosan / polyglycolic acid coated tin dioxide; Step A4: lithium iron phosphate precursor powder, deionized water are added to a ball mill jar and ball milled, chitosan / polyglycolic acid coated tin dioxide is added and mixed, dried, placed in a sintering furnace, protected by nitrogen, calcined for 7-8h, and cooled to obtain chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate.

2. The nanoshell-type lithium iron phosphate composite cathode material according to claim 1, characterized in that, The amount ratio of lithium hydroxide monohydrate, deionized water, phosphoric acid, cetyltrimethylammonium bromide, ferrous sulfate heptahydrate and ascorbic acid solution in step A1 is 60-120mmol:80-160mL:20-40mmol:30-60mmol:20-40mmol:10-20mL.

3. The nanoshell-type lithium iron phosphate composite cathode material of claim 1, wherein the nanoshell-type lithium iron phosphate composite cathode material is represented by the formula: Li1-xFe(1-y)MgyPO4, wherein 0 < x < 1 and 0 < y < 1. The molar concentration of the ascorbic acid solution in step A1 is 0.3mol / L.

4. The nanosphere-type lithium iron phosphate composite cathode material according to claim 1, characterized in that, The amount ratio of tin dioxide nano powder, deionized water, chloroacetic acid, acetone and chitosan powder in step A2 is 0.153-0.306g:150-300mL:0.3-0.6g:0.3-0.6g:1.5-3g.

5. The nanosphere-type lithium iron phosphate composite cathode material according to claim 1, characterized in that, The degree of deacetylation of the chitosan powder in step A2 is 85%.

6. The nanosphere-type lithium iron phosphate composite cathode material according to claim 1, characterized in that, The amount ratio of the first solution, triethylamine, acetone and glutaraldehyde in step A3 is 150-300mL:0.36-0.72g:0.72-1.44g:0.74-1.48g.

7. The nanoshell-type lithium iron phosphate composite cathode material of claim 1, wherein the nanoshell-type lithium iron phosphate composite cathode material is represented by the formula: Li1-xFe(1-y)MgyPO4, wherein 0 < x < 1 and 0 < y < 1. The amount ratio of lithium iron phosphate precursor powder, deionized water and chitosan / polyglycolic acid coated tin dioxide in step A4 is 5-10g:50-100mL:0.55-1.1g.

8. A method for preparing a nanospherical shell type lithium iron phosphate composite cathode material, characterized in that, The method for preparing the nanospherical shell type lithium iron phosphate composite positive electrode material as claimed in any one of claims 1-7 comprises the following steps: Step one: chitosan-polyglycolic acid coated tin dioxide composite lithium iron phosphate 45-90 parts, acetylene carbon black 4-8 parts, sodium carboxymethyl cellulose 1.5-3 parts and polyvinyl alcohol 0.5-1 part are weighed according to weight parts and prepared for use; Step two: grind the lithium iron phosphate coated with tin dioxide-polyglycolic acid-chitosan, acetylene black, sodium carboxymethyl cellulose and polyvinyl alcohol, then add N-methyl pyrrolidone to adjust the solid content and continue to grind, coat on the aluminum foil current collector, put into a constant temperature vacuum drying oven, press in a roller press, and finally punch into a circular electrode with a slicing machine to obtain a nanometer spherical shell type lithium iron phosphate composite positive electrode material.

9. The method for preparing a nanosphere-type lithium iron phosphate composite cathode material according to claim 8, characterized in that, The solid content is adjusted to 45%-55%.

10. The method for preparing a nanosphere-type lithium iron phosphate composite cathode material according to claim 8, characterized in that, The drying time in the constant temperature vacuum drying oven is 8-12h.

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