Modified li5feo4 cathode lithium supplementing additive, preparation method thereof and lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a modified Li5FeO4 positive electrode lithium supplementing additive, a preparation method thereof and a lithium ion battery. The positive electrode lithium supplementing additive comprises a Li5FeO4 core, a porous carbon layer coated outside the Li5FeO4 core, and an Mxene layer coated on the porous carbon layer, and the porosity of the modified Li5FeO4 positive electrode lithium supplementing additive is 5-25%. The lithium ion battery adopting the positive electrode lithium supplementing additive has excellent capacity retention rate and low resistivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a modified Li5FeO4 positive electrode lithium supplement additive, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have many advantages such as high specific energy, good cycle performance, no memory effect, etc. However, when the battery is formed, the negative electrode surface will consume Li + and form a SEI film, resulting in a large loss of lithium ions in the battery system. Therefore, it is of great significance to develop a simple and efficient lithium supplement technology.

[0003] Li5FeO4 is a lithium-rich transition metal oxide with very high specific capacity, which can maximize the delithiation during battery formation and supplement the formation of SEI film on the negative electrode. However, the existing Li5FeO4 material has poor stability and low electronic conductivity, which affects the cycle stability and specific capacity of lithium ion batteries containing Li5FeO4 lithium supplement additive.

[0004] Therefore, it is of great significance to research and develop a modified Li5FeO4 positive electrode lithium supplement additive. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art that the carbon coating has limited improvement effect and the carbon layer coating cannot play a surface protection role. The present application provides a modified Li5FeO4 positive electrode lithium supplement additive, a preparation method thereof and a lithium ion battery. The lithium ion battery using the positive electrode lithium supplement additive has excellent cycle capacity retention rate and low resistivity.

[0006] In order to achieve the above purpose, the first aspect of the present application provides a positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive comprises a Li5FeO4 core, a porous carbon layer coated outside the Li5FeO4 core, and a Mxene layer coated on the porous carbon layer, and the porosity of the modified Li5FeO4 positive electrode lithium supplement additive is 5-25%.

[0007] The second aspect of the present application provides a preparation method of a positive electrode lithium supplement additive, wherein the preparation method comprises:

[0008] (1) mixing iron oxide, carbon source, water and lithium source, ball milling, drying and high temperature sintering treatment to obtain porous carbon coated Li5FeO4; wherein the carbon source comprises one or more of polyvinyl alcohol, polyvinyl butyral ester (PVB), ammonium carbonate and ammonium bicarbonate;

[0009] (2) passing the Mxene powder into deoxygenated deionized water in the presence of inert gas to obtain a suspension, ultrasonicating and centrifuging the suspension, and collecting the supernatant to obtain a MXene dispersion;

[0010] (3) mixing the porous carbon-coated Li5FeO4 and the MXene dispersion, and performing centrifugation and drying treatment to obtain a modified Li5FeO4 positive electrode lithium supplement additive.

[0011] The third aspect of the present application provides a modified Li5FeO4 positive electrode lithium supplement additive prepared by the preparation method described above.

[0012] The fourth aspect of the present application provides a lithium ion battery, which comprises a lithium supplement electrode sheet, the lithium supplement electrode sheet comprising a current collector and a coating layer coated on at least one side of the current collector, wherein the coating layer comprises a positive electrode active material, a conductive agent, a binder and a modified Li5FeO4 positive electrode lithium supplement additive, and the lithium supplement additive is the modified Li5FeO4 positive electrode lithium supplement additive described above.

[0013] Through the above technical solution, the modified Li5FeO4 positive electrode lithium supplement additive obtained by the present application has the synergistic effect of the porous carbon layer and the Mxene layer, which not only increases the conductivity of Li5FeO4, but also further increases the stability of Li5FeO4 due to the double-layer protection effect; the porosity of the porous carbon layer is in the range of 5-25%, which helps to adsorb the electrode liquid on the surface of Li5FeO4, shortens the diffusion path of lithium ions, and further increases the ion conductivity of the material; the lithium ion battery containing the modified Li5FeO4 positive electrode lithium supplement additive has excellent cycle performance and specific capacity.

[0014] The present application uses at least one of polyvinyl alcohol (PVA), polyvinyl butyral ester, ammonium carbonate and ammonium bicarbonate as a carbon source, so that Li5FeO4 becomes a porous structure; then Mxene coating is performed; Mxene is coated on the surface of Li5FeO4 particles, and the modification and coating in sequence can make the coating more uniform and inhibit the oxidation of Li5FeO4. DETAILED DESCRIPTION

[0015] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be interpreted as being approximate. Values that fall within the range of values are included in the disclosed ranges. The ranges and values are approximations that are already "as precise as reasonably possible" to provide a practical conception of the application. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0016] The first aspect of the present application provides a modified Li5FeO4 positive electrode lithium supplement additive, wherein the positive electrode lithium supplement additive comprises a Li5FeO4 core, a porous carbon layer coated outside the Li5FeO4 core, and a Mxene layer coated on the porous carbon layer, and the porosity of the modified Li5FeO4 positive electrode lithium supplement additive is 5-25%.

[0017] The inventors of the present application found that through the synergistic effect of the porous carbon layer and the Mxene layer, not only the conductivity of Li5FeO4 is increased, but also the stability of Li5FeO4 is further increased due to the double-layer protection effect; the porosity of the porous carbon layer in the range of 5-25% helps to adsorb the electrode liquid on the surface of Li5FeO4, reduces the diffusion path of lithium ions, and further increases the ion conductivity of the material; the lithium ion battery containing the modified Li5FeO4 positive electrode lithium supplement additive has excellent cycle performance and specific capacity.

[0018] Further, the present application uses at least one of polyvinyl alcohol (PVA), polyvinyl butyral ester, ammonium carbonate and ammonium bicarbonate as a carbon source, which can be well dispersed on the surface of the Li5FeO4 core, so that the uniformity of the porous carbon coating obtained after heat treatment can be increased, thereby improving the conductivity of the material; at the same time, the use of the above specific carbon source of the present application can also increase the adhesion of Li5FeO4 and MXene; further, the two-dimensional layered structure of MXene can provide a high-conductivity network, better conductivity, make lithium ion more convenient to release, and better protect the inner Li5FeO4 material through the space stereo effect; further, the surface modification of the porous carbon coated Li5FeO4 before coating can make the coating more uniform and inhibit the oxidation of Li5FeO4.

[0019] According to the present application, preferably, the porosity of the porous carbon layer is 6.312-24.864%.

[0020] According to the present application, the size of the pores in the porous carbon layer is 1-100 nm, preferably 1-50 nm, and more preferably 1-25 nm.

[0021] According to the present application, the Mxene has an expression shown in formula (1);

[0022] M n+1 X n T x , formula (1);

[0023] wherein M is a transition metal, X is C and / or N, n is 1 or 2, T x is one or more of -H, -O, -F and -OH;

[0024] Preferably, the Mxene is one or more of Ti3C2T x , Ti2CT x and Ti4N3T x .

[0025] In the present application, it should be noted that the "x" in "Tx" does not have a specific meaning, such as the expression "Ti3C2T x , T x is one or more of -H, -O, -OH, -F and -OH", because due to etching with fluoride, the MXene layer exposure surface (i.e. M surface, M is a transition metal) is always capped with -F, -O, -OH groups (analogous to polymer chain capping), and the MXene surface may be a complex collection of one or more OH, F, O or other capping groups.

[0026] According to the present application, the carbon content is 0.5-5.5wt%, preferably 2.7-4.5wt%, based on the total weight of the positive electrode lithium supplement additive.

[0027] According to the present application, the positive electrode lithium supplement additive further comprises: the porous carbon layer is coated with boron element, and the boron element is derived from boric acid; in the present application, after boron coating, Li2BO3 or amorphous lithium borate or lithium boride can be generated with the surface residual lithium salt (LiOH, Li2CO3), which can reduce residual alkali, reduce pH and appropriately increase capacity. In the present application, the boron content is 0.01-0.5wt%, based on the total weight of the positive electrode lithium supplement additive; the boron element content can be measured by ICP.

[0028] According to the present application, the thickness of the porous carbon layer (carbon coating layer thickness) is 1-50nm, and the thickness of the Mxene layer is 1-10nm; preferably, the thickness of the porous carbon layer (carbon coating layer thickness) is 2.2-25.6nm, and the thickness of the Mxene layer is 1.5-9.3nm.

[0029] The second aspect of the present application provides a preparation method of a positive electrode lithium supplement additive, wherein the preparation method comprises:

[0030] (1) mixing iron oxide, carbon source, water and lithium source, ball milling, drying and high temperature sintering treatment to obtain porous carbon coated Li5FeO4; wherein the carbon source comprises one or more of polyvinyl alcohol, polyvinyl butyral ester, ammonium carbonate and ammonium bicarbonate;

[0031] (2) passing the Mxene powder into deoxygenated water in the presence of inert gas to obtain a suspension, ultrasonic treatment and centrifugal treatment of the suspension, and collecting the supernatant to obtain a MXene dispersion;

[0032] (3) mixing the porous carbon-coated Li5FeO4 and the MXene dispersion liquid, and performing centrifugation and drying treatment to obtain a modified Li5FeO4 positive electrode lithium supplement additive.

[0033] According to the present application, the Ti3AlC2 powder, lithium fluoride and hydrochloric acid are mixed and then subjected to exfoliation treatment to exfoliate the aluminum layer, and then subjected to water washing, centrifugation and drying treatment to obtain the Mxene powder.

[0034] According to the present application, in step (1), preferably, polyvinyl alcohol (PVA) is used as a carbon source, heated in water at 80-100℃, and magnetically stirred at 600-1200rpm to dissolve the PVA in water, and the PVA is mixed with iron oxide at a mass ratio of (8-24):100; a lithium source is added, and the molar ratio of the amount of the lithium source to the amount of the iron oxide is (9-11):1, wet mixing is performed for ball milling, and spray drying is performed to obtain a powdered mixture, wherein the inlet temperature for spray drying is 160-220℃, the outlet temperature is 90-160℃, and the feeding speed is 5-25mL / min; then high-temperature sintering is performed under the protection of inert gas, and the furnace is naturally cooled to room temperature to obtain the porous Li5FeO4 coated with carbon on the surface; wherein the high-temperature sintering refers to increasing the temperature to 700-900℃ at a heating rate of 1-10℃ / min, and maintaining the temperature for 3-10h.

[0035] According to the present application, the lithium source includes LiOH and / or Li2CO3.

[0036] In the present application, the iron oxide can be prepared by the following method:

[0037] Iron chloride, 100mL, 0.5mol / L, iron sulfate / nitric acid 100-150mL, 0.5-1mol / L, is added to 100-300mL ammonium hydroxide, 2-3mol / L, magnetically stirred and dispersed for 20-40 minutes (stirring speed is 400-900rpm / min), ultrasonically treated for 10-20min, and after the red-brown precipitate is completely settled, the supernatant is recovered, and then the precipitate is washed twice, dried at 60℃, transferred into a tube furnace with argon flow, heated to 500-600℃ at a heating rate of 3-10℃ / min, high-temperature sintered for 1-4 hours, and naturally cooled to room temperature to obtain red-brown iron oxide.

[0038] According to the present application, in step (1), the preparation method further includes: dispersing the ethanol solution of the porous carbon-coated Li5FeO4 in a mixed solution of a modifier and ammonia water to perform first modification treatment, and obtaining the first modified porous carbon-coated Li5FeO4.

[0039] According to the present application, preferably, the modifier is methacryloxypropyltrimethoxysilane (MPS).

[0040] According to the present application, preferably, the method of the first modification treatment comprises mixing the modifier, the porous carbon-coated Li5FeO4, ethanol, and ammonia water under stirring, wherein the molar ratio of the amount of ammonia water to the amount of the modifier is 1:(4-8), to obtain the first modified Li5FeO4.

[0041] According to the present application, the conditions of the first modification treatment comprise stirring at a stirring rate of 200-2000 rpm for 24-48 h.

[0042] According to the present application, in step (1), the preparation method further comprises subjecting the first modified Li5FeO4 to a second modification treatment to obtain the second modified Li5FeO4.

[0043] According to the present application, preferably, the conditions of the second modification treatment comprise pre-mixing the first modified Li5FeO4, sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), and water in a three-neck flask at room temperature, stirring for 12-18 h to form a uniform mixed suspension; contacting the suspension, potassium persulfate (KPS), and an emulsifier, and subjecting the potassium persulfate and the emulsifier to a polymerization reaction to become a gel; specifically, the suspension is heated to 60-80 °C, and 2-10 ml of a 20 mg / ml potassium persulfate (KPS) solution is added under a nitrogen / argon atmosphere. Then, the emulsion is slowly added within 15 min, the temperature is raised to 70-80 °C for a polymerization reaction, which lasts for 1-1.5 h, the reaction gel is collected, and then washed by centrifugation with deionized water and ultrasonic dispersion for 30-40 min to obtain a gelatinous dispersion of the second modified Li5FeO4.

[0044] wherein, relative to 120 mL of water, preferably deionized water, the amount of the first modified Li5FeO4 is 10-1000 g, the amount of sodium dodecyl sulfate is 10-100 mg, and the amount of polyvinylpyrrolidone is 0.8-3.6 g.

[0045] According to the present application, the emulsifier comprises one or more of methyl methacrylate (MMA), sodium dodecyl sulfate, water, and potassium hydroxide; preferably, based on 10 g of the first modified Li5FeO4, the amount of methyl methacrylate is 4-8 mL, the amount of sodium dodecyl sulfate is 20-40 mg, and the amount of potassium hydroxide is 30-60 mg; to obtain the second modified Li5FeO4.

[0046] According to the present application, in step (2):

[0047] First, Mxene powder is prepared: Ti3AlC2 powder is slowly added to a mixture of lithium fluoride (LiF) and hydrochloric acid (HCl), wherein the amount of Ti3AlC2 is 0.5-5 g and the amount of lithium fluoride is 0.5-5 g relative to 10-20 mL of hydrochloric acid; then stirring under the exfoliation treatment conditions of a stirring rate of 200-2000 rpm and a temperature of 40-45℃ for 24-28 h to exfoliate the aluminum layer. Then washed with deionized water and centrifuged 1-5 times until the supernatant pH is 5.5-6.5. Finally, the sample is dried in a vacuum at 60-70℃ for 8-10 hours to obtain Mxene powder;

[0048] Second, Mxene colloidal solution is prepared: 100-1000 mg of prepared Mxene powder is passed through argon and introduced into 20-100 mL of oxygen-free deionized water; the suspension obtained in the previous step is ultrasonically treated for 1-2 h and centrifuged at 3500-5000 rpm for 1-2 h to obtain black precipitate and dark green supernatant, and the supernatant is collected for further use.

[0049] In the present application, the Mxene has an expression shown in formula (1);

[0050] M n+1 X n T x , formula (1);

[0051] wherein M is a transition metal, X is C and / or N, n is 1 or 2, T x is one or more of -H, -O, -F and -OH;

[0052] Preferably, the Mxene is one or more of Ti3C2T x , Ti2CT x and Ti4N3T x .

[0053] According to the present application, in step (3), the gel-like porous carbon-coated Li5FeO4 and dark green Mxene dispersion liquid are directly mixed together and stirred for 10-15 minutes. Then the mixture is centrifuged at 5500-6000 r / ppm and then heated to 75-80℃ for drying to collect the dried product.

[0054] According to the present application, in step (3), the preparation method further comprises: after the drying treatment, a heat treatment is performed, wherein the heat treatment conditions include a temperature of 450-500℃ and a time of 4-48 h to remove polymethyl methacrylate to obtain a positive electrode lithium supplement additive.

[0055] The third aspect of the present application provides a modified Li5FeO4 positive electrode lithium supplement additive prepared by the preparation method described above.

[0056] The fourth aspect of the present application provides a lithium ion battery, which comprises a lithium supplement electrode sheet, the lithium supplement electrode sheet comprising a current collector and a coating layer coated on at least one side of the current collector, wherein the coating layer comprises a positive electrode active material, a conductive agent, a binder and a modified Li5FeO4 positive electrode lithium supplement additive, and the lithium supplement additive is the modified Li5FeO4 positive electrode lithium supplement additive described above.

[0057] The present application will be described in detail below through examples.

[0058] In the following examples and comparative examples:

[0059] The porosity and pore size of the modified Li5FeO4 positive electrode lithium supplement additive are measured by a full-automatic high-throughput specific surface area and pore size analyzer;

[0060] The thickness of the porous carbon layer and the MXene layer in the modified Li5FeO4 positive electrode lithium supplement additive is measured by a transmission electron microscope (TEM);

[0061] The various organic material raw materials are commercially available from Aladdin.

[0062] Example 1

[0063] This example aims to illustrate the positive electrode lithium supplement additive prepared by the method of the present application.

[0064] (1) Preparation of iron oxide:

[0065] Iron chloride 100 mL, 0.5 mol / L, iron sulfate 100 mL, 0.5 mol / L, is added to 100 mL ammonium hydroxide 2 mol / L, and after magnetic stirring and dispersion for 20 minutes, the stirring speed is 400 rpm / min, ultrasonic treatment for 10 min, and after standing until the red-brown precipitate is completely recovered, the supernatant is recovered, and then the precipitate is washed twice, dried at 60℃, and then transferred into a tube furnace with argon flow, heated to 600℃ at a heating rate of 3℃ / min, and sintered at high temperature for 1 hour, and then naturally cooled to room temperature to obtain red-brown iron oxide;

[0066] (2) Preparation of porous carbon-coated Li5FeO4:

[0067] Using polyvinyl alcohol (PVA) as a carbon source, the mass ratio of iron oxide: PVA is 100:16, heated in water, 80℃, magnetic stirring, 600rpm, so that PVA is dissolved in water, add lithium source (specifically LiOH), the molar ratio of lithium source and iron oxide is 10:1, wet mixing ball milling, spray drying, get powder mixture, wherein the inlet temperature of spray drying is 160℃, the outlet temperature is 90℃, the feeding speed is 5mL / min. Then high temperature sintering under inert gas protection, natural cooling to room temperature with furnace, wherein the high temperature sintering refers to the heating rate of 1℃ / min to 900℃, and keeping for 3h, get porous carbon coated Li5FeO4;

[0068] (3) Preparation of Mxene nanosheet:

[0069] 3-1) First, prepare Ti3C2Tx(Tx is a functional group, O 2- , F 2- , OH - ):

[0070] Slowly add 0.5g Ti3AlC2 powder sample to a mixture of 0.5g lithium fluoride (LiF) and 10mL 9M hydrochloric acid (HCl), stir at 40℃ for 24 hours to exfoliate the aluminum layer. Then wash with deionized water, centrifuge 3 times until the supernatant pH is 6. Finally, dry the sample in a vacuum at 60℃ for 8 hours to obtain Ti3C2Tx powder.

[0071] 3-2) 100mg of prepared Ti3C2Tx powder is passed through argon and introduced into 20mL of oxygen-free deionized water. The suspension obtained in the previous step is ultrasonicated for 1h, and centrifuged at 3500rpm for 1h to obtain black precipitate and greenish-black Ti3C2Tx dispersion, which is collected for further use;

[0072] (4) Mix the porous carbon coated Li5FeO4 prepared in step (2) and the supernatant prepared in step (3) directly, ball mill for 6h, dry at 75℃, collect the dry material, heat at 400℃ for 18h in argon atmosphere, then take out and crush to obtain the positive electrode lithium supplement additive, marked as S1, and characterize the obtained S1, the results are shown in Table 1.

[0073] Example 2

[0074] This embodiment is to illustrate the positive electrode lithium supplement additive prepared by the method of the application.

[0075] (1) Preparation of iron oxide:

[0076] Iron chloride, 100 mL, 0.5 mol / L, iron nitrate 125 mL, 0.75 mol / L, added to 150 mL ammonium hydroxide 2.5 mol / L, after magnetic stirring dispersion for 30 minutes, wherein the stirring speed is 650 rpm / min, ultrasonic treatment for 15 min, standing until the red-brown precipitate is completely recovered, then the supernatant is washed twice, and after drying at 60℃, it is transferred into a tube furnace with argon flow, heated to 550℃ at a heating rate of 7℃ / min, and sintered at high temperature for 2.5 hours, and then naturally cooled to room temperature to obtain red-brown iron oxide;

[0077] (2) Preparation of porous carbon-coated Li5FeO4:

[0078] Polyvinyl alcohol (PVA) is used as a carbon source, and the mass ratio of iron oxide to PVA is 100:8. Heat in water, 90℃, magnetic stirring, 1000 rpm, so that PVA is dissolved in water, add lithium source (specifically LiOH), the molar ratio of lithium source to iron oxide is 11:1, wet mixing ball milling, spray drying to obtain powdery mixture, wherein the inlet temperature of spray drying is 200℃, the outlet temperature is 120℃, and the feeding speed is 15 mL / min. Then high-temperature sintering under inert gas protection, and natural cooling to room temperature with the furnace, wherein the high-temperature sintering refers to heating to 800℃ at a heating rate of 5℃ / min, and keeping for 6h, to obtain porous carbon-coated Li5FeO4;

[0079] (3) Preparation of Mxene nanosheet:

[0080] 3-1) First, prepare Ti3C2Tx(Tx is a functional group, O 2- , F 2- , OH - ):

[0081] 2.5g Ti3AlC2 powder sample is slowly added to a mixture of 2.5g lithium fluoride (LiF) and 15mL 9M hydrochloric acid (HCl), and stirred at 42℃ for 26 hours to exfoliate the aluminum layer. Then washed with deionized water and centrifuged 4 times until the supernatant pH is 6. Finally, the sample is dried in a vacuum at 60℃ for 9 hours to obtain Ti3C2Tx powder.

[0082] 3-2) 500mg of prepared Ti3C2Tx powder is passed through argon and introduced into 60mL of oxygen-free deionized water. The suspension obtained in the previous step is ultrasonicated for 1.5h, and centrifuged at 4000rpm for 1.5h to obtain black precipitate and dark green Ti3C2Tx dispersion, and the supernatant is collected for further use;

[0083] (4) The porous carbon-coated Li5FeO4 prepared in step (2) and the supernatant (colloidal solution) prepared in step (3) are directly mixed together, the surface carbon-coated porous Li5FeO4 prepared in step (2) and the supernatant prepared in step (3) are directly mixed together, ball milling is performed for 7 h, the dry matter is collected after drying at 75°C, and the dry matter is heated at 450°C for 18 h in an argon atmosphere, then taken out and broken, to obtain a positive electrode lithium supplement additive, marked as S2, and the obtained S2 is characterized, and the results are shown in Table 1.

[0084] Example 3

[0085] This embodiment is to illustrate the positive electrode lithium supplement additive prepared by the method of the present application.

[0086] (1) Preparation of iron oxide:

[0087] Iron chloride, 100 mL, 0.5 mol / L, iron sulfate, 150 mL, 1 mol / L, is added to 150 mL of ammonium hydroxide 3 mol / L, and after magnetic stirring and dispersion for 40 min, the stirring speed is 900 rpm / min, ultrasonic treatment is performed for 20 min, and after standing until the red-brown precipitate is completely recovered, the supernatant is recovered, and then the precipitate is washed twice, dried at 60°C, and then transferred into a tube furnace with argon gas flow, heated to 500°C at a heating rate of 10°C / min, and sintered at high temperature for 4 h, and then naturally cooled to room temperature to obtain red-brown iron oxide;

[0088] (2) Preparation of porous carbon-coated Li5FeO4:

[0089] Polyvinyl alcohol (PVA) is used as a carbon source, and the mass ratio of iron oxide to PVA is 100:24, heated in water, 100°C, magnetic stirring, 1200 rpm, so that the PVA is dissolved in water, lithium source (specifically LiOH) is added, the molar ratio of lithium source to iron oxide is 9:1, wet mixing is performed, spray drying is performed to obtain a powder mixture, wherein the inlet temperature of the spray dryer is 220°C, the outlet temperature is 160°C, and the feeding speed is 25 mL / min. Then high-temperature sintering is performed under inert gas protection, and the furnace is naturally cooled to room temperature, wherein the high-temperature sintering is performed at a heating rate of 10°C / min to 700°C, and the temperature is maintained for 10 h, to obtain porous carbon-coated Li5FeO4;

[0090] (3) Preparation of Mxene nanosheet:

[0091] 3-1) First, Ti3C2Tx (Tx is a functional group, O 2- , F 2- , OH - ) is prepared:

[0092] A 5 g sample of Ti3AlC2 powder was slowly added to a mixture of 5 g lithium fluoride (LiF) and 20 mL of 9 M hydrochloric acid (HC1) and stirred at 45 °C for 28 h to exfoliate the aluminum layer. Then washed with deionized water and centrifuged 5 times until the pH of the Ti3C2Tx dispersion was 6. Finally, the sample was dried in vacuum at 60 °C for 10 h to obtain Ti3C2Tx powder.

[0093] 3-2) 1000 mg of the prepared Ti3C2Tx powder was bubbled through 100 mL of oxygen-free deionized water. The suspension obtained in the previous step was ultrasonicated for 2 h and centrifuged at 5000 rpm for 2 h to obtain a black precipitate and a dark green Ti3C2Tx dispersion, and the supernatant was collected for further use;

[0094] (4) The porous carbon-coated Li5FeO4 prepared in step (2) and the supernatant prepared in step (3) were directly mixed together, ball-milled for 8 h, dried at 75 °C, and then collected. The collected material was heated at 500 °C for 18 h under argon atmosphere, then taken out and crushed to obtain the positive electrode lithium supplement additive, labeled as S3, and S3 was characterized, and the results are shown in Table 1.

[0095] Example 4

[0096] The positive electrode lithium supplement additive was prepared according to the same method as in Example 1, except that in step (2), the prepared porous carbon-coated Li5FeO4 was subjected to the first step of surface modification, specifically:

[0097] After step (2) of Example 1, steps 2-1) and 2-2) were continued:

[0098] 2-1) The porous carbon-coated Li5FeO4 particles were surface modified using methyl methacryloxypropyl trimethoxysilane (MPS). The porous carbon-coated Li5FeO4 was dispersed in a solution of anhydrous ethanol as solvent, and a mixture of NH3H2O and MPS in a ratio of 1:6 as solute, stirred for two days at a speed of 1000 rpm to obtain the first modified porous carbon-coated Li5FeO4

[0099] 2-2) 10 g of MPS modified porous carbon coated Li5FeO4 (first modified porous carbon coated Li5FeO4), 10 mg of sodium dodecyl sulfate (SDS) (first addition), 0.8 g of polyvinylpyrrolidone (PVP), 120 mL of deionized water were pre-mixed in a three-necked flask at room temperature, stirred for 16 h, and then heated to 70 °C after forming a uniform mixed suspension, 8 mL of 20 mg / mL potassium persulfate (KPS) solution was added under a nitrogen / argon atmosphere. Then, an emulsion consisting of 20 mg of sodium dodecyl sulfate (SDS) (second addition), 30 mL of H2O, 6 mL of MMA, and 50 mg of potassium hydroxide was slowly added within 15 min, the temperature was raised to 80 °C for polymerization, which lasted for 1.5 h, and the reaction product colloid was collected, followed by centrifugal washing with deionized water and ultrasonic dispersion for 40 min to obtain second modified porous carbon coated Li5FeO4.

[0100] Step (3) was then performed, and then the second modified porous carbon coated Li5FeO4 prepared in step (2-2) and the supernatant prepared in step (3) were directly mixed together, stirred for 10 min, and then the mixture was centrifuged at 5500 rpm and dried by heating to 75 °C, and then the dried product was collected;

[0101] Step 4-1) was continued:

[0102] 4-1) The obtained positive electrode lithium supplementing additive S1 was heat treated at 450 °C to remove PMMA and obtain the final product positive electrode lithium supplementing additive, marked as S4, and the obtained S4 was characterized, and the results are shown in Table 1.

[0103] Example 5

[0104] The difference from Example 4 is that in the first step of surface modification of the porous carbon coated Li5FeO4 in step 2-1), the molar ratio of the amount of ammonia and methacryloxypropyltrimethoxysilane is 1:4, and the final product positive electrode lithium supplementing additive is obtained, marked as S5, and the obtained S5 is characterized, and the results are shown in Table 1.

[0105] Example 6

[0106] The difference from Example 4 is that in the first step of surface modification of the porous carbon coated Li5FeO4 in step 2-1), the molar ratio of the amount of ammonia and methacryloxypropyltrimethoxysilane is 1:8, and the final product positive electrode lithium supplementing additive is obtained, marked as S6, and the obtained S6 is characterized, and the results are shown in Table 1.

[0107] Example 7

[0108] The difference from Example 4 is that in the surface modification of the prepared porous carbon-coated Li5FeO4 in step (2), the first step of surface modification is not carried out, that is, step 2-1) is not carried out, to obtain the final product of the positive electrode lithium supplement additive, marked as S7, and the obtained S7 is characterized, and the results are shown in Table 1.

[0109] Example 8

[0110] The difference from Example 4 is that in the second step of surface modification of the first modified porous carbon-coated Li5FeO4 in step 2-2), the use amount of methyl methacrylate (MMA) and sodium dodecyl sulfate (SDS) is different; specifically, the use amount of methyl methacrylate is 4 mL, and the total use amount of sodium dodecyl sulfate is 20 mg, wherein sodium dodecyl sulfate is added for the first time 10 mg, and sodium dodecyl sulfate is added for the second time 10 mg; the final product of the positive electrode lithium supplement additive is obtained, marked as S8, and the obtained S8 is characterized, and the results are shown in Table 1.

[0111] Example 9

[0112] The difference from Example 8 is that the use amount of methyl methacrylate and sodium dodecyl sulfate is different; specifically, the use amount of methyl methacrylate is 8 mL, and the total use amount of sodium dodecyl sulfate is 40 mg, wherein sodium dodecyl sulfate is added for the first time 10 mg, and sodium dodecyl sulfate is added for the second time 30 mg; the final product of the positive electrode lithium supplement additive is obtained, marked as S9, and the obtained S9 is characterized, and the results are shown in Table 1.

[0113] Example 10

[0114] The difference from Example 4 is that in the first step of surface modification of the porous carbon-coated Li5FeO4 in step 2-1), the molar ratio of the use amount of ammonia and methyl methacryloxypropyl trimethoxysilane is 1:10; in the second step of surface modification of the first modified porous carbon-coated Li5FeO4 in step 2-2), the use amount of methyl methacrylate and sodium dodecyl sulfate is different; specifically, the use amount of methyl methacrylate is 10 mL, and the total use amount of sodium dodecyl sulfate is 15 mg, wherein sodium dodecyl sulfate is added for the first time 10 mg, and sodium dodecyl sulfate is added for the second time 5 mg; the final product of the positive electrode lithium supplement additive is obtained, marked as S10, and the obtained S10 is characterized, and the results are shown in Table 1.

[0115] Comparative Example 1

[0116] Comparative Example 1 is to illustrate the prepared Li5FeO4 without a Mxene coating layer.

[0117] The positive electrode lithium supplementing additive was prepared according to the same method as in Example 1, except that steps (2), (3) and (4) were not performed, to obtain the final product modified Li5FeO4 positive electrode lithium supplementing additive, marked as DS1, and the obtained DS1 was characterized, and the results are shown in Table 1.

[0118] Comparative Example 2

[0119] Comparative Example 2 is to illustrate the preparation of ordinary modified Li5FeO4+Mxene.

[0120] The modified Li5FeO4 positive electrode lithium supplementing additive was prepared according to the same method as in Example 1, except that polyvinyl alcohol was not used as a carbon source, and other carbon sources such as sucrose were used, and the rest was the same as in Example 1.

[0121] The final product modified Li5FeO4 positive electrode lithium supplementing additive was obtained, marked as DS2, and the obtained DS2 was characterized, and the results are shown in Table 1.

[0122] Comparative Example 3

[0123] Comparative Example 3 is to illustrate the preparation of MXene-coated Li5FeO4, without porous carbon coating.

[0124] The positive electrode lithium supplementing additive was prepared according to the same method as in Example 1, except that step (2) was not performed, i.e., compared with Example 1, the preparation of MXene-coated Li5FeO4 was completed, and no carbon coating was performed.

[0125] The final product modified Li5FeO4 was obtained, marked as DS3, and the obtained DS3 was characterized, and the results are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] As can be seen from the results in Table 1, the specific carbon source used in Examples 1-10 of the present application allows Li5FeO4 to have a porous structure; then Mxene coating is performed; Mxene is coated on the surface of the porous carbon-coated Li5FeO4 particles; secondly, modifying the porous carbon-coated Li5FeO4 first and then performing MXene coating can make the combination of the MXene layer and the porous carbon layer more closely and the coating more uniform; in addition, it should be noted that the more PMMA, the thicker the gel part, and the less the Mxene coating effect.

[0130] Test Example

[0131] The S1-10 and DS1-3 prepared from Examples 1-10 and Comparative Examples 1-3 were used as positive active material additives to prepare soft pack laminated cells, and the amount of S1 was 2.5 wt% compared to the amount of positive electrode (the positive electrode was selected from lithium iron phosphate, and the negative electrode was natural graphite, and the positive electrode was seven layers and the negative electrode was eight layers), and the standard capacity was 1.8 Ah.

[0132] Test method for 500 cycle capacity retention rate: 45℃, 2V-3.8V, 1C charge and discharge cycle 500 tests, record the first discharge capacity data and the discharge capacity data after 500 cycles. 500 cycle capacity retention rate = (discharge capacity data after 500 cycles / first discharge capacity data)*100%.

[0133] Test method for 500 cycle DCR growth rate: in 45℃ cycle, after 500 cycles, adjust the battery capacity to 50% SOC, 1.5C discharge for 30s, record the voltage change value ΔV before and after discharge, R DCR =ΔV / I, I is the 1.5C discharge current value. (The lower the DCR growth rate, the lower the direct current resistance of the battery, and the lower the resistance, the better the battery performance).

[0134] Test method for first cycle charging gram capacity: 45℃, 2V-3.8V, charge at 1C current, record the authorized charging capacity data.

[0135] The results are shown in Table 2.

[0136] Table 2

[0137]

[0138] From the results in Table 2, it can be seen that the lithium ion battery containing the modified Li5FeO4 positive electrode lithium supplementing additive of Examples 1-10 of the present application has excellent cycle performance and excellent first cycle charging gram capacity, in addition, the direct current resistance of the battery of Examples 1-10 is relatively low, indicating that the battery performance is more excellent.

[0139] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A modified Li5FeO4 cathode lithium supplement additive, characterized in that: The positive electrode lithium supplement additive includes a Li5FeO4 core, a porous carbon layer coated outside the Li5FeO4 core, and a Mxene layer coated on the porous carbon layer. The porosity of the modified Li5FeO4 positive electrode lithium supplement additive is 5-25%.

2. The modified Li5FeO4 cathode lithium supplement additive according to claim 1, wherein: The size of the pores in the porous carbon layer is 1-100 nm.

3. The modified Li5FeO4 cathode lithium supplement additive according to claim 2, wherein: The size of the pores in the porous carbon layer is 1-50 nm.

4. The modified Li5FeO4 cathode lithium supplement additive according to claim 1, wherein: The Mxene has an expression as shown in formula (1); M n+1 X n T x , formula (1); Wherein, M is a transition metal, X is C and / or N, n is 1 or 2, T x is one or more of -H, -O, -F and -OH.

5. The modified Li5FeO4 cathode lithium supplement additive according to claim 1, wherein: The Mxene is Ti3C2T x 、Ti2CT x and Ti4N3T x One or more of .

6. The modified Li5FeO4 cathode lithium supplement additive according to any one of claims 1 to 5, wherein: The modified Li5FeO4 positive electrode lithium supplement additive further comprises: boron element coated on the porous carbon layer; and / or, based on the total weight of the modified Li5FeO4 cathode lithium supplement additive, the boron content is 0-0.5wt%; And / or, the thickness of the porous carbon layer is 1-50 nm, and the thickness of the Mxene layer is 1-10 nm.

7. A method for preparing a modified Li5FeO4 cathode lithium supplement additive, characterized in that: The preparation method comprises: (1) mixing iron oxide, a carbon source, water, and a lithium source, and subjecting the mixture to ball milling, drying, and high-temperature sintering to obtain porous carbon-coated Li5FeO4; wherein the carbon source comprises one or more of polyvinyl alcohol, polyvinyl butyral, ammonium carbonate, and ammonium bicarbonate; (2) In the presence of an inert gas, MXene powder is introduced into oxygen-free deionized water to obtain a suspension, the suspension is ultrasonicated and centrifuged, and the supernatant is collected to obtain a MXene dispersion; (3) The porous carbon-coated Li5FeO4 and the MXene dispersion are mixed, and the mixture is centrifuged and dried to obtain a modified Li5FeO4 positive electrode lithium supplement additive.

8. The preparation method according to claim 7, wherein In step (1), the mass ratio of the iron oxide to the carbon source is 100:(8-24); And / or, the molar ratio of the lithium source to the iron oxide is (9-11):1; And / or, the lithium source includes LiOH and / or Li2CO3.

9. The preparation method according to claim 7, wherein The Mxene has an expression as shown in formula (1); M n+1 X n T x , formula (1); Wherein, M is a transition metal, X is C and / or N, n is 1 or 2, T x is one or more of -H, -O, -F and -OH.

10. The preparation method according to claim 7, wherein The Mxene is Ti3C2T x 、Ti2CT x and Ti4N3T x One or more of .

11. The preparation method according to claim 7, wherein In step (1), the preparation method further comprises: subjecting the porous carbon-coated Li5FeO4 to a first modification treatment to obtain a first modified porous carbon-coated Li5FeO4.

12. The preparation method according to claim 11, wherein The first modification treatment method includes: mixing a modifier, the porous carbon-coated Li5FeO4, ethanol, and ammonia water under stirring conditions to obtain a first modified porous carbon-coated Li5FeO4.

13. The preparation method according to claim 12, wherein The modifier is methacryloxypropyltrimethoxysilane.

14. The preparation method according to claim 11, wherein The preparation method further includes: subjecting the first modified porous carbon-coated Li5FeO4 to a second modification treatment to obtain a second modified porous carbon-coated Li5FeO4.

15. The preparation method according to claim 14, wherein The conditions of the second modification treatment include: mixing the first modified porous carbon-coated Li5FeO4, sodium lauryl sulfate, polyvinyl pyrrolidone and water to obtain a suspension; contacting the suspension, potassium persulfate and an emulsifier to carry out a polymerization reaction to obtain the second modified porous carbon-coated Li5FeO4.

16. The preparation method according to claim 15, wherein The second modified porous carbon-coated Li 5 FeO 4 is washed and then subjected to ultrasonic dispersion treatment to obtain a colloidal dispersion of the second modified porous carbon-coated Li 5 FeO 4 .

17. The preparation method according to claim 7, wherein In step (3), the preparation method further comprises: performing a heat treatment after drying to remove the polymethyl methacrylate to obtain a positive electrode lithium supplement additive.

18. The preparation method according to claim 17, wherein The heat treatment conditions include: temperature of 450-500° C. and time of 4-24 hours.

19. The preparation method according to claim 12, wherein The conditions of the first modification treatment include: stirring at a stirring rate of 200-2000 rpm for 24-48 hours; And / or, the molar ratio of ammonia water to the modifier is 1:(4-8).

20. The preparation method according to claim 15, wherein The emulsifier includes one or more of methyl methacrylate, sodium lauryl sulfate, water and potassium hydroxide.

21. The preparation method according to claim 20, wherein Based on 10 g of the first modified porous carbon-coated Li 5 FeO 4 , the amount of methyl methacrylate used is 4-8 mL, the amount of sodium lauryl sulfate used is 20-40 mg, and the amount of potassium hydroxide used is 30-60 mg.

22. The preparation method according to claim 15, wherein The polymerization reaction conditions include: temperature of 70-80° C. and time of 1-5 hours.

23. A modified Li5FeO4 positive electrode lithium supplement additive prepared by the preparation method according to any one of claims 7 to 22.

24. A lithium-ion battery comprising a lithium-supplementing electrode sheet, wherein the lithium-supplementing electrode sheet comprises a current collector and a dressing layer coated on at least one side of the current collector, wherein: The dressing layer comprises a positive electrode active material, a conductive agent, a binder and a modified Li5FeO4 positive electrode lithium replenishing additive, wherein the lithium replenishing additive is the modified Li5FeO4 positive electrode lithium replenishing additive according to any one of claims 1-6 or 23.

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