Fast-charging lithium-ion batteries and their preparation methods

Abstract

This invention provides a fast-charging lithium-ion battery and its preparation method, relating to the field of lithium battery technology. The preparation method of the fast-charging lithium-ion battery includes: S1, preparation of the positive electrode: granulating lithium iron phosphate to obtain granulated lithium iron phosphate, using the granulated lithium iron phosphate to prepare a positive electrode slurry; preparing the positive electrode slurry into an electrode sheet; surface-treating at least one side of the electrode sheet using lithium titanium phosphate nanowires to obtain the positive electrode sheet; S2, preparation of the negative electrode sheet; S3, preparation of the fast-charging lithium-ion battery. The lithium-ion battery of this invention has superior fast-charging performance.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a fast-charging lithium-ion battery and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in various fields due to their advantages such as light weight, high energy density, no memory effect, long cycle life, and environmental friendliness. However, with the development of technology, higher demands are being placed on the fast-charging performance of lithium-ion batteries. The Society of Automotive Engineers (SAE) believes that compared to internal combustion engine vehicles, the limited driving range and long charging time of electric vehicles (EVs) cause range anxiety for drivers and hinder the development of potential users. Therefore, the U.S. Department of Energy has identified ultra-fast charging (XFC) as a key challenge to ensure the large-scale adoption of electric vehicles.

[0003] The internal structure of a lithium-ion battery consists of four parts: the negative electrode material, the electrolyte, the separator, and the positive electrode material. Currently, most lithium-ion batteries use graphite as the negative electrode material and lithium-containing compounds as the positive electrode material. However, the charge / discharge performance and rate capability of existing lithium-ion batteries are inadequate and cannot meet future market demands for faster charging speeds. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a fast-charging lithium-ion battery and its preparation method, solving the technical problems of poor charge / discharge performance and rate performance of existing lithium-ion batteries.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] On one hand, the present invention provides a method for preparing a fast-charging lithium-ion battery, comprising the following steps:

[0009] S1, Preparation of the positive electrode

[0010] Lithium iron phosphate is granulated to obtain granulated lithium iron phosphate, and a positive electrode slurry is prepared using the granulated lithium iron phosphate; the positive electrode slurry is prepared into an electrode sheet; at least one side of the electrode sheet is surface-treated using lithium titanium phosphate nanowires to obtain the positive electrode sheet.

[0011] S2, Preparation of the negative electrode

[0012] Fast-charging graphite is selected to prepare the negative electrode slurry, and the negative electrode slurry is made into a negative electrode sheet;

[0013] S3. Preparation of fast-charging lithium-ion batteries

[0014] A fast-charging lithium-ion battery is prepared by forming a core with the separator, the positive electrode, and the negative electrode, with the coated side of the separator facing the positive electrode, and injecting an organosilicon electrolyte into the core.

[0015] Granulated lithium iron phosphate (LFP) is prepared by granulation. The morphology of granulated LFP consists of large LFP particles with several small LFP particles attached to them. On the one hand, granulated LFP only requires carbon black as a conductive agent, and the carbon black can be uniformly mixed between the large and small particles to achieve better conductive contact. On the other hand, the granulated LFP particles can form a contact between one large LFP particle and multiple small LFP particles, which is more conducive to the transport and diffusion of lithium ions. Thirdly, after being made into an electrode, the granulated LFP particles can better absorb and store electrolyte.

[0016] Using a single-sided coated separator and an organosilicon electrolyte, with the coated side of the separator facing the positive electrode, ensures good adhesion between the separator and the positive electrode, improves ionic conductivity, and reduces battery impedance. The organosilicon electrolyte has high ionic conductivity, good thermal stability, excellent SEI film-forming performance, and high voltage and high rate performance.

[0017] Preferably, the method for preparing the positive electrode sheet includes the following steps:

[0018] (1) The granulated lithium iron phosphate, carbon black, PVDF and solvent are mixed in a certain weight ratio to prepare a positive electrode slurry;

[0019] (2) The positive electrode slurry is sequentially coated, baked and rolled to obtain an electrode sheet;

[0020] (3) Mix lithium titanium phosphate nanowires and organic adhesive at a mass ratio of 1:(20-100), add them to a spraying machine, set the speed of the electrode through the nozzle of the spraying machine to 0.8-1.5 m / min, set the spraying pressure of the spraying machine to 0.1-0.8 MPa, and set the spraying range to the coating width of the electrode. Perform surface treatment on the electrode to obtain a positive electrode.

[0021] Positive electrodes were prepared by surface modification of the electrode sheet using lithium titanium phosphate nanowires via a spray coating process. Spraying lithium titanium phosphate nanowires onto the electrode surface enhances the contact and coating effect between lithium titanium phosphate and the active material particles (lithium iron phosphate) on the electrode surface. Furthermore, the loose structure formed by the winding of the lithium titanium phosphate nanowires during the spray coating process increases the adhesion between the positive electrode and the separator, while also improving the liquid absorption and retention effect of the positive electrode, eliminating polarization, and improving rate performance. Since lithium titanium phosphate and lithium iron phosphate have the same crystal structure, they have a synergistic effect in increasing the electronic conductivity and lithium-ion transport rate of the positive electrode material. Moreover, the small diameter of the lithium titanium phosphate nanowire structure reduces the diffusion distance of lithium ions when in close contact with the active material particles on the electrode surface, thereby increasing the lithium-ion diffusion rate.

[0022] Preferably, the preparation method satisfies at least one of the following conditions:

[0023] The amount of granulated lithium iron phosphate is 95-99 parts, carbon black is 1-4 parts, and PVDF is 1-4 parts.

[0024] The method for preparing granulated lithium iron phosphate includes sintering large lithium iron phosphate particles with a particle size distribution D50 of 0.2-2 μm and small lithium iron phosphate particles with a D50 of 0.02-0.1 μm at 350-500℃ for 3-6 hours.

[0025] The mass ratio of lithium iron phosphate particles with a D50 of 0.2–2 μm to lithium iron phosphate particles with a D50 of 0.02–0.1 μm is 1:(3–20).

[0026] The coating method includes coating the positive electrode slurry onto the positive electrode current collector, controlling the double-sided coating surface density to be 350–420 g / m². 2 ;

[0027] The organic adhesive is selected from at least one of gelatin, carrageenan, xanthan gum, and agar.

[0028] Preferably, the solvent is NMP, and the preparation method of the positive electrode slurry includes dissolving the PVDF in NMP, stirring under vacuum for 3-6 hours to obtain a PVDF solution with a mass fraction of 3%-8%; mixing the granulated lithium iron phosphate and carbon black dry for 0.5-2 hours, then adding the PVDF solution and stirring under vacuum for 4-6 hours; finally, adding an appropriate amount of NMP according to the slurry viscosity, stirring under vacuum for 0.5-1.5 hours, and then allowing it to stand under vacuum for 0.5-2 hours to defoam, thus obtaining the positive electrode slurry.

[0029] Preferably, the method for preparing the negative electrode sheet includes the following steps:

[0030] (1) A negative electrode slurry is prepared by combining fast-charging graphite, carbon black, lithium-ionized CMC, modified SBR and deionized hydrate slurry;

[0031] (2) The negative electrode slurry is sequentially coated, baked, rolled and cut to obtain a negative electrode sheet.

[0032] Using fast-charging graphite to prepare negative electrode slurry has advantages in rate performance, volume expansion, and prevention of electrode rebound due to the smaller grain size, lower degree of graphitization, and lower degree of crystal orientation of fast-charging graphite.

[0033] Preferably, the preparation method satisfies at least one of the following conditions:

[0034] The fast-charging graphite content is 95-99 parts, the carbon black content is 0.5-1.5 parts, the lithiated CMC content is 0.8-2 parts, and the modified SBR content is 1-2.5 parts;

[0035] The fast-charging graphite is artificial graphite with a particle size distribution D50 of 6–11 μm and a specific surface area of ​​1.3–4 m². 2 / g, with a graphitization degree of 93.8%–94.2% and an OI value of 2.8–3.2;

[0036] The coating method includes coating the negative electrode slurry onto the negative electrode current collector, controlling the double-sided coating surface density to be 180–230 g / m². 2 .

[0037] Preferably, the method for preparing the negative electrode slurry includes dissolving the lithium-ionized CMC in deionized water and stirring under vacuum for 4-6 hours to obtain a CMC slurry with a mass fraction of 0.8%-1.8%; mixing the fast-charging graphite and carbon black dry for 1.5-2.5 hours, then adding the CMC slurry and stirring under vacuum for 3-6 hours; continuing to add the SBR and stirring under vacuum at low speed for 0.5-1.5 hours; finally, adding deionized water according to the slurry viscosity, stirring under vacuum for 0.5-1.5 hours, and then allowing it to stand under vacuum for 0.5-2 hours to remove bubbles to obtain the negative electrode slurry.

[0038] Preferably, the diaphragm is a PTFE diaphragm with a porosity of 45% to 55%, coated on one side with an alumina and PVDF coating, and a thickness of 12+3 μm.

[0039] Preferably, the preparation method satisfies at least one of the following conditions:

[0040] The organosilicon electrolyte is composed of 1.2M LiPF6 / EC:DMC (1:1 in vol.), and the incorporation ratio of polysiloxane oligomers is 10% to 30%.

[0041] The method for preparing a fast-charging lithium-ion battery further includes: sequentially subjecting the core to baking, hot pressing, ultrasonic welding, top and side sealing, baking, liquid injection, standing, pressure formation, aging, venting and sealing, and capacity testing.

[0042] Secondly, the present invention provides a fast-charging lithium-ion battery prepared by the preparation method described in the first aspect, wherein the fast-charging lithium-ion battery has a 4C constant current charge ratio of 95.0%-99.0%, a 6C constant current charge ratio of 95.0%-97.0%, an 8C constant current charge ratio of 92.0%-94.0%, and a capacity retention rate of 97%-99% after 500 6C / 1C fast charging cycles.

[0043] (III) Beneficial Effects

[0044] This invention provides a fast-charging lithium-ion battery and its preparation method. Compared with the prior art, it has the following advantages:

[0045] 1. The method for preparing a fast-charging lithium-ion battery of the present invention includes granulating lithium iron phosphate to prepare granulated lithium iron phosphate. The morphology of granulated lithium iron phosphate consists of large lithium iron phosphate particles with several small lithium iron phosphate particles attached to them. On the one hand, granulated lithium iron phosphate only requires carbon black as a conductive agent, and the carbon black can be uniformly mixed between the large and small particles to achieve better conductive contact. On the other hand, the granulated lithium iron phosphate particles can form a contact between a large lithium iron phosphate particle and multiple small lithium iron phosphate particles, which is more conducive to the transport and diffusion of lithium ions. Thirdly, after the granulated lithium iron phosphate particles are made into electrode sheets, they can better absorb and store electrolyte.

[0046] 2. The preparation method of the fast-charging lithium-ion battery of the present invention includes preparing a positive electrode by surface modification of an electrode sheet using lithium titanium phosphate nanowires through a spraying process. By spraying lithium titanium phosphate nanowires onto the electrode surface, the contact and coating effect between lithium titanium phosphate and the active material particles of lithium iron phosphate on the electrode surface is enhanced. Furthermore, the nanowires of lithium titanium phosphate, through the spraying process, form a loose structure, which increases the adhesion between the positive electrode sheet and the separator, and also increases the liquid absorption and retention effect of the positive electrode sheet, eliminating polarization and improving rate performance. Since lithium titanium phosphate and lithium iron phosphate have the same crystal structure, they have a synergistic effect in increasing the electronic conductivity of the positive electrode material and the lithium-ion transport rate. Moreover, the small diameter of the lithium titanium phosphate nanowire structure reduces the diffusion distance of lithium ions when in close contact with the active material particles on the electrode surface, thereby increasing the lithium-ion diffusion rate.

[0047] 3. The preparation method of the fast-charging lithium-ion battery of the present invention includes the preparation of negative electrode slurry using fast-charging graphite. Since the fast-charging graphite has a smaller grain size, a lower degree of graphitization, and a smaller degree of crystal orientation, it has more advantages in terms of rate performance, volume expansion, and prevention of electrode rebound.

[0048] 4. The preparation method of the fast-charging lithium-ion battery of the present invention includes using a high-porosity single-sided coated separator and an organosilicon electrolyte. The coated side of the separator faces the positive electrode, which can ensure good adhesion between the separator and the positive electrode sheet. The high porosity of the separator can more effectively promote the absorption and penetration of the electrolyte by the separator, improve the ionic conductivity, and reduce the impedance of the battery. The organosilicon electrolyte has high ionic conductivity, good thermal stability, excellent SEI film formation performance, and high voltage and high rate performance. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a schematic diagram of the surface treatment device for the positive electrode sheet prepared in Example 1;

[0051] 1-Heater; 2-Powder coating; 3-Angle control valve; 4-Wind shield;

[0052] Figure 2 A planar SEM image of the positive electrode sheet prepared in Example 1;

[0053] Figure 3 A cross-sectional SEM image of the positive electrode sheet prepared in Example 1;

[0054] Figure 4 Cyclic voltammetry (CV) curves of the positive electrode coin cell prepared in Example 1;

[0055] Figure 5 This is a comparison XRD pattern of the negative electrode fast-charging graphite and conventional graphite in Example 1. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0058] Example 1

[0059] This embodiment provides a fast-charging lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode comprises the following raw materials in parts by weight: 97.2 parts granulated lithium iron phosphate, 1 part conductive carbon black, and 1.8 parts PVDF copolymer. The negative electrode comprises the following raw materials in parts by weight: 96.5 parts fast-charging graphite, 0.7 parts conductive carbon black, 1 part lithium-ionized CMC, and 1.8 parts modified SBR. The separator is a PTFE separator with a porosity of 48%, coated with alumina and PVDF on one side, and a thickness of 12±3 μm. The electrolyte is 1.2M LiPF6 / EC:DMC (1:1 in vol.), with a polysiloxane oligomer incorporation ratio of 15%.

[0060] The preparation method of a fast-charging lithium-ion battery includes the following steps:

[0061] S1, Preparation of the positive electrode

[0062] The specified amount of PVDF was dissolved in NMP and stirred under vacuum for 4 hours to obtain a PVDF slurry with a mass fraction of 5%. The specified amount of granulated lithium iron phosphate and conductive carbon black were mixed and dry-mixed for 1 hour, and then the PVDF slurry was added to it and stirred under vacuum for 4.5 hours. Finally, an appropriate amount of NMP was added according to the viscosity of the slurry, and the mixture was stirred under vacuum for 1 hour and then allowed to stand under vacuum for 1 hour to remove bubbles to obtain the positive electrode slurry.

[0063] The preparation process of granulated lithium iron phosphate involves sintering large lithium iron phosphate particles with a D50 of 0.2–2 μm and small lithium iron phosphate particles with a D50 of 0.02–0.1 μm at 425℃ for 5 hours. The mass ratio of lithium iron phosphate particles with a D50 of 0.2–2 μm to those with a D50 of 0.02–0.1 μm is 1:3.

[0064] The prepared positive electrode slurry was coated onto the positive electrode current collector ((15+1+1)μm double-sided carbon-coated aluminum foil), and the areal density of the double-sided coating was controlled at 380g / m². 2 Large-rolled electrode sheets are obtained through baking and rolling.

[0065] like Figure 1 Lithium titanium phosphate nanowires and carrageenan particles were mixed at a mass ratio of 1:50 and added to the feed inlet of the thermal spraying machine. The electrode conveying roller was turned on and the speed through the nozzle of the thermal spraying machine was set to 1.0 m / min. Simultaneously, the compressed air and heater switches of the thermal spraying machine were turned on, and the pressure was adjusted to 0.6 MPa. The heating temperature was set to 140℃. The angle control valve was adjusted to set the spraying range to the electrode coating width. Once the entire roll of electrode had passed through the nozzle of the thermal spraying machine, one side of the large roll of electrode was treated. The above operation was repeated to treat the other side of the electrode. After surface treatment, the large roll of electrode was slit to prepare positive electrode sheets. The planar SEM of the prepared positive electrode sheets is shown below. Figure 2 Cross-sectional SEM, such as Figure 3 The cyclic voltammetry (CV) curves of the prepared positive electrode coin cell are as follows: Figure 4 .

[0066] S2, Preparation of the negative electrode

[0067] The specified amount of lithium-ionized CMC was dissolved in deionized water and stirred under vacuum for 4 hours to obtain a CMC slurry with a mass fraction of 1.2%. The specified amount of graphite and conductive carbon black were mixed and dry-mixed for 1.8 hours, and then the CMC slurry was added to it and stirred under vacuum for 4 hours. The specified amount of SBR was then added and stirred under vacuum at low speed for 1 hour. Finally, an appropriate amount of deionized water was added according to the viscosity of the slurry, and the mixture was stirred under vacuum for 1 hour and then allowed to stand under vacuum for 1.2 hours to remove bubbles, thus obtaining the negative electrode slurry.

[0068] The prepared negative electrode slurry was coated onto the negative electrode current collector (6μm copper foil), and the surface density of the double-sided coating was controlled at 200g / m². 2 Large rolled electrode sheets are baked, rolled, and slit to obtain negative electrode sheets;

[0069] S3, Battery Assembly

[0070] The positive and negative electrode sheets and the separator are wound into a core, wherein the single-sided coated side of the separator faces the positive electrode sheet, the separator is a PTFE separator with a porosity of 45%, and is coated with alumina and PVDF coatings on one side with a thickness of 12+3μm. The core is then processed through baking, hot pressing, ultrasonic welding, top and side sealing, baking, liquid injection, standing, pressure formation, aging, venting and double sealing, and capacity testing to produce a lithium-ion battery.

[0071] Example 2

[0072] This embodiment provides a fast-charging lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode comprises the following raw materials in parts by weight: 96.5 parts granulated lithium iron phosphate, 1.5 parts conductive carbon black, and 2 parts PVDF copolymer. The negative electrode comprises the following raw materials in parts by weight: 96 parts fast-charging graphite, 1 part conductive carbon black, 1 part lithium-ionized CMC, and 2 parts modified SBR. The separator is a PTFE separator with a porosity of 52%, coated with alumina and PVDF on one side, and a thickness of 12±3 μm. The electrolyte is 1.2M LiPF6 / EC:DMC (1:1 in vol.), with a polysiloxane oligomer incorporation ratio of 20%.

[0073] The preparation method of a fast-charging lithium-ion battery includes the following steps:

[0074] S1, Preparation of the positive electrode

[0075] (1) Dissolve the amount of PVDF in NMP and stir under vacuum for 5 hours to obtain a PVDF slurry with a mass fraction of 6%; mix the amount of granulated lithium iron phosphate and conductive carbon black and dry mix for 2 hours, then add the PVDF slurry and stir under vacuum for 5 hours; finally, add an appropriate amount of NMP according to the viscosity of the slurry, stir under vacuum for 0.7 hours, and then let it stand under vacuum to defoam for 1.5 hours to obtain the positive electrode slurry.

[0076] The preparation process of granulated lithium iron phosphate involves sintering large particles with a D50 of 0.2–2 μm and small particles with a D50 of 0.02–0.1 μm at 375 °C for 3 h. The mass ratio of lithium iron phosphate particles with a D50 of 0.2–2 μm to those with a D50 of 0.02–0.1 μm is 1:15.

[0077] (2) Coat the positive electrode slurry prepared above onto the positive electrode current collector ((15+1+1)μm double-sided carbon-coated aluminum foil), and control the surface density of the double-sided coating to be 400g / m². 2 Large-rolled electrode sheets are obtained through baking and rolling.

[0078] (3) Mix lithium titanium phosphate nanowires and xanthan gum particles at a mass ratio of 1:30 and add them to the feed port of the thermal spraying machine. Turn on the electrode conveying roller and set the speed through the nozzle of the thermal spraying machine to 1.2 m / min. At the same time, turn on the compressed air and heater switches of the thermal spraying machine, adjust the pressure to 0.8 MPa, and the heating temperature to 180℃. Adjust the angle control valve to set the spraying range to the electrode coating width setting. Once the entire roll of electrode has passed through the nozzle of the thermal spraying machine, the treatment of one side of the large roll of electrode is complete. Repeat the above operation to treat the other side of the electrode. After the surface treatment is completed, the large roll of electrode is slit to prepare positive electrode sheets.

[0079] S2, Preparation of the negative electrode

[0080] (1) Dissolve the specified amount of lithium-ionized CMC in deionized water and stir under vacuum for 5 hours to obtain a CMC slurry with a mass fraction of 1.5%; mix the specified amount of graphite and conductive carbon black and dry mix for 2.2 hours, then add the CMC slurry and stir under vacuum for 4.5 hours; continue to add the specified amount of SBR and stir under vacuum at low speed for 1.2 hours; finally, add an appropriate amount of deionized water according to the viscosity of the slurry, stir under vacuum for 0.8 hours, and then let it stand under vacuum to defoam for 1.5 hours to obtain the negative electrode slurry.

[0081] (2) Coat the prepared negative electrode slurry onto the negative electrode current collector (6μm copper foil), controlling the double-sided coating surface density to be 210g / m². 2 Large rolled electrode sheets are baked, rolled, and slit to obtain negative electrode sheets;

[0082] S3, Battery Assembly

[0083] The positive and negative electrode sheets and the separator are wound into a core, wherein the single-sided coated side of the separator faces the positive electrode sheet, the separator is a PTFE separator with a porosity of 50%, and is coated with alumina and PVDF coatings on one side with a thickness of 12+3μm. The core is then processed through baking, hot pressing, ultrasonic welding, top and side sealing, baking, liquid injection, standing, pressure formation, aging, venting and double sealing, and capacity testing to produce a lithium-ion battery.

[0084] Example 3

[0085] This embodiment provides a fast-charging lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode comprises the following raw materials in parts by weight: 98 parts granulated lithium iron phosphate, 0.8 parts conductive carbon black, and 1.2 parts PVDF copolymer. The negative electrode comprises the following raw materials in parts by weight: 97 parts fast-charging graphite, 0.5 parts conductive carbon black, 1.1 parts lithium-ionized CMC, and 1.4 parts modified SBR. The separator is a PTFE separator with a porosity of 45%, coated with alumina and PVDF on one side, and a thickness of 12±3 μm. The electrolyte is 1.2M LiPF6 / EC:DMC (1:1 in vol.), with a polysiloxane oligomer incorporation ratio of 25%.

[0086] The preparation method of a fast-charging lithium-ion battery includes the following steps:

[0087] S1, Preparation of the positive electrode

[0088] (1) Dissolve the amount of PVDF in NMP and stir under vacuum for 4.5 h to obtain a PVDF slurry with a mass fraction of 4%; mix the amount of granulated lithium iron phosphate and conductive carbon black and dry mix for 1.5 h, then add the PVDF slurry and stir under vacuum for 6 h; finally, add an appropriate amount of NMP according to the viscosity of the slurry, stir under vacuum for 1.2 h, and then let it stand under vacuum to defoam for 1.8 h to obtain the positive electrode slurry.

[0089] The preparation process of granulated lithium iron phosphate involves sintering large particles with a D50 of 0.2–2 μm and small particles with a D50 of 0.02–0.1 μm at 475 °C for 6 h. The mass ratio of lithium iron phosphate particles with a D50 of 0.2–2 μm to those with a D50 of 0.02–0.1 μm is 1:20.

[0090] (2) Coat the positive electrode slurry prepared above onto the positive electrode current collector ((15+1+1)μm double-sided carbon-coated aluminum foil), and control the surface density of the double-sided coating to be 415g / m². 2 Large-rolled electrode sheets are obtained through baking and rolling.

[0091] (3) Mix lithium titanium phosphate nanowires and agar particles at a mass ratio of 1:75 and add them to the feed port of the thermal spraying machine. Turn on the electrode conveying roller and set the speed through the nozzle of the thermal spraying machine to 1.5 m / min. At the same time, turn on the compressed air and heater switches of the thermal spraying machine, adjust the pressure to 0.3 MPa, and the heating temperature to 120℃. Adjust the angle control valve to set the spraying range to the electrode coating width setting. Once the entire roll of electrode has passed through the nozzle of the thermal spraying machine, the treatment of one side of the large roll of electrode is complete. Repeat the above operation to treat the other side of the electrode. After the surface treatment is completed, the large roll of electrode is slit to prepare positive electrode sheets.

[0092] S2, Preparation of the negative electrode

[0093] (1) Dissolve the specified amount of lithium-ionized CMC in deionized water and stir under vacuum for 5.5 h to obtain a CMC slurry with a mass fraction of 1.8%; mix the specified amount of graphite and conductive carbon black and dry mix for 2.5 h, then add the CMC slurry and stir under vacuum for 5 h; continue to add the specified amount of SBR and stir under vacuum at low speed for 0.8 h; finally, add an appropriate amount of deionized water according to the viscosity of the slurry, stir under vacuum for 1.2 h, and then let it stand under vacuum to defoam for 1.8 h to obtain the negative electrode slurry.

[0094] (2) Coat the negative electrode slurry prepared above onto the negative electrode current collector (6μm copper foil), and control the double-sided coating surface density to be 220g / m². 2 Large rolled electrode sheets are baked, rolled, and slit to obtain negative electrode sheets;

[0095] S3, Battery Assembly

[0096] The positive and negative electrode sheets and the separator are wound into a core, wherein the separator is coated on one side facing the positive electrode sheet, the separator is a PTFE separator with a porosity of 55%, and coated on one side with aluminum oxide and PVDF with a thickness of 12+3μm. The core is then processed through baking, hot pressing, ultrasonic welding, top and side sealing, baking, liquid injection, standing, pressure formation, aging, venting and double sealing, and capacity testing to produce a lithium-ion battery.

[0097] Comparative Example 1

[0098] The difference between this comparative example and Example 1 is that lithium iron phosphate particles with a particle size distribution D50 of 0.2 to 2 μm were used without granulation to replace the granulated lithium iron phosphate in Example 1. Otherwise, the comparison is the same as in Example 1.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 1 is that, in the preparation method of the fast-charging lithium-ion battery, lithium titanium phosphate nanowires are not included when preparing the positive electrode sheet; otherwise, it is the same as Example 1.

[0101] Comparative Example 3

[0102] This comparative example differs from Example 1 in that conventional graphite is used instead of the fast-charging graphite of Example 1; otherwise, they are the same as in Example 1. The XRD comparison images of the fast-charging graphite and conventional graphite are shown below. Figure 5 .

[0103] Comparative Example 4

[0104] The difference between this comparative example and Example 1 is that a membrane with a porosity of 30% is used instead of the membrane in Example 1; otherwise, they are the same as in Example 1.

[0105] Comparative Example 5

[0106] The difference between this comparative example and Example 1 is that lithium iron phosphate electrolyte is used instead of the electrolyte in Example 1, while the rest is the same as in Example 1.

[0107] Comparative Example 6

[0108] The difference between this comparative example and Example 1 is that, in the preparation method of the fast-charging lithium-ion battery, when preparing the positive electrode sheet, lithium titanium phosphate nanowires and carrageenan particles are mixed at a mass ratio of 1:50 and coated onto the active layer surface of the electrode sheet instead of the spraying process in Example 1. The rest is the same as in Example 1.

[0109] Depend on Figure 2 It can be seen that, after Figure 1 The apparatus shown demonstrates the preparation of a positive electrode by surface treatment of an electrode sheet. Lithium titanium phosphate nanowires uniformly coat the active particles of lithium iron phosphate on the electrode surface, and the coating exhibits a loose structure, which effectively improves rate performance. Figure 3 It can be seen that granulated lithium iron phosphate particles have a tighter contact within the positive electrode, and conductive carbon black can effectively fill the pores, forming a better conductive network, which can also effectively improve rate performance; Figure 4 As can be seen from the CV spectrum, in addition to a pair of redox peaks for lithium iron phosphate, there are also three pairs of redox peaks for lithium titanium phosphate with good symmetry at low potentials. This indicates that after electrode surface treatment, the lithium titanium phosphate nanowires effectively coated the surface-active particles, and that lithium titanium phosphate also participated in the electrochemical reaction during charge and discharge, playing a role in improving capacity and rate performance. Figure 5 It is known that fast-charging graphite has smaller grain size, lower graphitization degree, and lower crystal orientation than conventional graphite. Therefore, the fast-charging lithium-ion battery of this invention has excellent rate performance, smaller volume expansion, and can prevent electrode rebound.

[0110] The fast-charging lithium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-6 were placed in a cycle test chamber for rate performance and service life testing. The results are shown in Table 1.

[0111] Table 1. Performance test results of fast-charging lithium-ion batteries in Examples 1-3 and Comparative Examples 1-6

[0112]

[0113] As can be seen from Table 1, the lithium-ion batteries prepared by granulation of lithium iron phosphate, surface treatment of the electrode sheet using lithium titanium phosphate nanowires to prepare the positive electrode sheet, and the use of fast-charging graphite, high-porosity separator and organosilicon electrolyte have lower battery impedance and better fast-charging capability.

[0114] The test results of Example 1 and Comparative Example 2 show that the fast-charging lithium-ion battery cannot achieve good performance without either lithium titanium phosphate or lithium iron phosphate. This indicates that lithium titanium phosphate and lithium iron phosphate have a synergistic effect in increasing the electronic conductivity of the cathode material and the lithium-ion transport rate.

[0115] As can be seen from the test results of Example 1 and Comparative Example 6, the fast-charging lithium-ion battery prepared by coating the active layer surface of the electrode with a mixture of lithium titanium phosphate nanowires and carrageenan particles at a mass ratio of 1:50 cannot achieve good performance. This is because the preparation method of the fast-charging lithium-ion battery of the present invention uses lithium titanium phosphate nanowires to modify the surface of the electrode through a spraying process to prepare the positive electrode. By spraying lithium titanium phosphate nanowires on the surface of the electrode, the contact and coating effect between lithium titanium phosphate and the active material particles lithium iron phosphate on the electrode surface is enhanced. Moreover, the nanowires of lithium titanium phosphate formed by the spraying process form a loose structure, which can increase the adhesion between the positive electrode and the separator, and also increase the liquid absorption and retention effect of the positive electrode, eliminate polarization, and improve the rate performance.

[0116] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0117] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0118] The present invention has been illustrated with the above embodiments to describe the detailed process flow of the present invention. However, the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a fast-charging lithium-ion battery, characterized in that, Includes the following steps: Lithium iron phosphate is granulated to obtain granulated lithium iron phosphate, and the granulated lithium iron phosphate is then made into an electrode sheet. A positive electrode is obtained by surface treatment of at least one side of the electrode using lithium titanium phosphate nanowires. A separator, a negative electrode, and a positive electrode are rolled into a core, with the coated side of the separator facing the positive electrode. An organosilicon electrolyte is injected into the core to prepare a fast-charging lithium-ion battery. The method for preparing granulated lithium iron phosphate includes sintering lithium iron phosphate particles with a particle size distribution D50 of 0.2-2 μm and lithium iron phosphate particles with a D50 of 0.02-0.1 μm at 350-500℃ for 3-6 h. The organosilicon electrolyte is composed of 1.2M LiPF6 / EC:DMC, with the polysiloxane oligomer incorporation ratio of 10% to 30%. The positive electrode is obtained by spraying lithium titanium phosphate nanowires onto the surface of the electrode. The spraying range is the coating width of the electrode.

2. The preparation method according to claim 1, characterized in that, The method for preparing the positive electrode sheet includes the following steps: (1) The granulated lithium iron phosphate, carbon black, PVDF and solvent are mixed in a certain weight ratio to prepare a positive electrode slurry; (2) The positive electrode slurry is sequentially coated, baked, and rolled to obtain an electrode sheet; (3) Mix lithium titanium phosphate nanowires and organic adhesive at a mass ratio of 1:(20-100), add them to a spraying machine, set the speed of the electrode through the nozzle of the spraying machine to 0.8-1.5 m / min, set the spraying pressure of the spraying machine to 0.1-0.8 MPa, and set the spraying range to the coating width of the electrode. Perform surface treatment on the electrode to obtain a positive electrode.

3. The preparation method according to claim 2, characterized in that, The preparation method satisfies at least one of the following conditions: The amount of granulated lithium iron phosphate is 95-99 parts, carbon black is 1-4 parts, and PVDF is 1-4 parts. The mass ratio of lithium iron phosphate particles with a D50 of 0.2–2 μm to lithium iron phosphate particles with a D50 of 0.02–0.1 μm is 1:(3–20). The coating method includes coating the positive electrode slurry onto the positive electrode current collector, controlling the double-sided coating surface density to be 350–420 g / m². 2 ; The organic adhesive is selected from at least one of gelatin, carrageenan, xanthan gum, and agar.

4. The preparation method according to claim 2, characterized in that, The solvent is NMP. The preparation method of the positive electrode slurry includes dissolving the PVDF in NMP and stirring under vacuum for 3-6 hours to obtain a PVDF solution with a mass fraction of 3%-8%; mixing the granulated lithium iron phosphate and carbon black dry for 0.5-2 hours, then adding the PVDF solution and stirring under vacuum for 4-6 hours; finally, adding an appropriate amount of NMP according to the slurry viscosity, stirring under vacuum for 0.5-1.5 hours, and then allowing it to stand under vacuum for 0.5-2 hours to defoam, thus obtaining the positive electrode slurry.

5. The preparation method according to claim 1, characterized in that, The method for preparing the negative electrode sheet includes the following steps: (1) A negative electrode slurry is prepared by combining fast-charging graphite, carbon black, lithium-ionized CMC, modified SBR and deionized hydrate slurry; (2) The negative electrode slurry is sequentially coated, baked, rolled and cut to obtain a negative electrode sheet.

6. The preparation method according to claim 5, characterized in that, The preparation method satisfies at least one of the following conditions: The fast-charging graphite content is 95-99 parts, the carbon black content is 0.5-1.5 parts, the lithiated CMC content is 0.8-2 parts, and the modified SBR content is 1-2.5 parts; The fast-charging graphite is artificial graphite with a particle size distribution D50 of 6–11 μm and a specific surface area of ​​1.3–4 m². 2 / g, with a graphitization degree of 93.8%–94.2% and an OI value of 2.8–3.2; The coating method includes coating the negative electrode slurry onto the negative electrode current collector, controlling the double-sided coating surface density to be 180–230 g / m². 2 .

7. The preparation method according to claim 5, characterized in that, The method for preparing the negative electrode slurry includes dissolving the lithium-ionized CMC in deionized water and stirring under vacuum for 4–6 hours to obtain a CMC slurry with a mass fraction of 0.8%–1.8%; mixing the fast-charging graphite and carbon black dry for 1.5–2.5 hours, then adding the CMC slurry and stirring under vacuum for 3–6 hours; continuing to add the modified SBR and stirring under vacuum at low speed for 0.5–1.5 hours; finally, adding deionized water according to the slurry viscosity, stirring under vacuum for 0.5–1.5 hours, and then allowing it to stand under vacuum for 0.5–2 hours to remove bubbles to obtain the negative electrode slurry.

8. The preparation method according to claim 1, characterized in that, The diaphragm is a PTFE diaphragm with a porosity of 45% to 55%, coated on one side with alumina and PVDF coatings, and a thickness of 12+3μm.

9. The preparation method according to claim 1, characterized in that, The method for preparing a fast-charging lithium-ion battery further includes: sequentially subjecting the core to baking, hot pressing, ultrasonic welding, top and side sealing, baking, liquid injection, standing, pressure formation, aging, venting and sealing, and capacity testing.

10. A fast-charging lithium-ion battery prepared by the preparation method according to any one of claims 1-9, characterized in that, The fast-charging lithium-ion battery has a 4C constant current charge ratio of 95.0%-99.0%, a 6C constant current charge ratio of 95.0%-97.0%, an 8C constant current charge ratio of 92.0%-94.0%, and a capacity retention rate of 97%-99% after 500 6C / 1C fast charging cycles.

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