Phosphate-based positive electrode material, preparation method thereof, positive electrode sheet, and battery

Abstract

The application discloses a phosphate-based positive electrode material, a preparation method thereof, a positive electrode sheet and a battery. The preparation method of the phosphate-based positive electrode material comprises the following steps: preparing a solid-phase precursor material, pre-sintering the solid-phase precursor material at 300-400 DEG C for 5-10 hours, adding a second carbon source containing a benzene ring and phosphorus elements to perform ball milling mixing, increasing the temperature to a preset temperature at a rate of 15-20 DEG C / min, and then keeping the temperature for 4-8 hours; decreasing the temperature to 20-30 DEG C at a rate of 3-5 DEG C / min, adding a third carbon source to perform ball milling mixing, increasing the temperature to the preset temperature at a rate of 0.5-1.5 DEG C / min, and then keeping the temperature for 8-10 hours; decreasing the temperature to 20-30 DEG C at a rate of 0.5-1.5 DEG C / min, and obtaining the phosphate-based positive electrode material. According to the embodiment of the application, the cycle stability and electronic conductivity of the phosphate-based positive electrode material can be effectively improved.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery material technology, and particularly relates to a phosphate-based cathode material, its preparation method, cathode sheet, and battery. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x LiFePO4 (LiFePO4) is a novel phosphate-based lithium-ion battery cathode material formed by doping a certain proportion of manganese (Mn) onto lithium iron phosphate (LiFePO4). By doping with manganese, the advantageous characteristics of both iron and manganese are effectively combined. Furthermore, manganese and iron are both located in the fourth period of the periodic table and are adjacent to each other, possessing similar ionic radii and some chemical properties; therefore, doping does not significantly affect the original structure. Consequently, LiFePO4's high-voltage platform can deliver higher energy density, comparable to LiFePO4 in cycle life and safety performance, and superior to LiFePO4 in low-temperature performance. LiFePO4 shares the same advantages as LiFePO4: low cost, high safety, high thermal stability, no spontaneous combustion after needle penetration or overcharging, long lifespan, and no risk of explosion. It can be said to combine the advantages of both LiFePO4 and LiFePO4 while also compensating for the low energy density of LiFePO4, thus being hailed as an "upgraded version of LiFePO4."

[0003] As is well known, phosphate-based lithium-ion battery materials (such as lithium manganese iron phosphate) have two major drawbacks: low intrinsic conductivity and low lithium-ion diffusion coefficient, which greatly limit the practical application of phosphate-based materials. Summary of the Invention

[0004] This application provides a phosphate-based cathode material and its preparation method, cathode sheet, and battery, which can improve the internal crystallinity of particles, the density of coating, and prevent the dissolution of manganese, thereby effectively improving the cycle stability and electronic conductivity of the phosphate-based cathode material.

[0005] In one aspect, embodiments of this application provide a method for preparing a phosphate-based cathode material, comprising: preparing a solid-phase precursor material from raw materials containing an iron source, a phosphorus source, a manganese source, a lithium source, and a first carbon source; placing the solid-phase precursor material in an inert atmosphere or a reducing atmosphere and pre-sintering it at 300–400°C for 5–10 h to obtain a first semi-finished product; ball-milling the first semi-finished product and a second carbon source containing a benzene ring and phosphorus elements, and then, in an inactive atmosphere, increasing the temperature at a rate of 15–20°C / min. After being heated to the preset temperature, the temperature is maintained for 4–8 hours, and then lowered to 20–30℃ at a rate of 3–5℃ / min to obtain the second semi-finished product. The preset temperature is T1, where 600℃≤T1≤700℃. The material containing the second semi-finished product and the third carbon source is ball-milled and mixed. In an inactive atmosphere, the temperature is increased to the preset temperature at a rate of 0.5–1.5℃ / min and maintained for 8–10 hours, and then lowered to 20–30℃ at a rate of 0.5–1.5℃ / min to obtain the phosphate-based cathode material.

[0006] In any embodiment of this application, the second carbon source includes at least one of the following substances:

[0007]

[0008] In any embodiment of this application, the second carbon source accounts for 0.1 wt% to 10.0 wt% of the total mass of the phosphate-based cathode material.

[0009] In any embodiment of this application, the first carbon source accounts for 0.95wt% to 2wt% of the total mass of the phosphate-based cathode material.

[0010] In any embodiment of this application, the third carbon source accounts for 0.5wt% to 3.0wt% of the total mass of the phosphate-based cathode material.

[0011] In any embodiment of this application, in the step of placing the solid precursor material in an inert atmosphere or a reducing atmosphere, the heating rate is 5 to 10 °C / min.

[0012] In any embodiment of this application, in the step of ball milling and mixing the materials containing the second semi-finished product and the third carbon source, the preset temperature is T2, 700°C. <T2≤800℃。

[0013] In any embodiment of this application, in the step of preparing a solid-phase precursor material from raw materials containing an iron source, a phosphorus source, a manganese source, a lithium source, and a first carbon source, the iron source includes at least one of FeCl3, Fe(NO3)3, Fe2O3, and FeSO4.

[0014] In any embodiment of this application, the phosphorus source includes at least one of (NH4)3PO4, LiH2PO4, and H3PO4.

[0015] In any embodiment of this application, the manganese source includes at least one of MnO2, Mn(NO3)2, MnSO4 and Mn3(PO4)2.

[0016] In any embodiment of this application, the lithium source includes at least one of Li2O, Li2CO3, LiH2PO4, LiOH, CH3COOLi, and LiNO3.

[0017] In any embodiment of this application, the first carbon source is an organic carbon source, which includes at least one of fructose, glucose, and sucrose.

[0018] In any embodiment of this application, in the step of ball milling and mixing the material containing the second semi-finished product and the third carbon source, the third carbon source is an inorganic carbon source, which includes at least one of graphite, Ketjen black, carbon nanotubes, and graphene.

[0019] In any embodiment of this application, in the step of preparing a solid-phase precursor material from raw materials containing an iron source, a phosphorus source, a manganese source, a lithium source, and a first carbon source, the raw materials further include a dopant element source; the dopant element source includes an oxide or soluble salt of at least one element selected from Ti, Mg, V, and Nb; the dopant element source accounts for 0.3wt% to 1.5wt% of the total mass of the phosphate-based cathode material.

[0020] In any embodiment of this application, the inactive atmosphere is independently selected from at least one of nitrogen, helium, argon and neon.

[0021] In any embodiment of this application, the inert atmosphere includes at least one of helium, argon and neon, and the reducing atmosphere includes at least one of H2 / N2 and CO / N2.

[0022] In any embodiment of this application, the chemical formula of the phosphate-based cathode material is LiMn. x Fe y M z PO4 / C, where M is the dopant element, 0 <x<1,0<y<1,0≤z<0.08,x+y+z=1。

[0023] Secondly, this application provides a phosphate-based cathode material obtained using the above-described preparation method.

[0024] Thirdly, embodiments of this application provide a positive electrode sheet, which includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a phosphate-based positive electrode material obtained by the above-described preparation method or the above-described phosphate-based positive electrode material.

[0025] Fourthly, embodiments of this application provide a battery including the aforementioned positive electrode sheet.

[0026] The phosphate-based cathode material, its preparation method, cathode sheet, and battery of this application embodiment can be nucleated by low-temperature sintering, and then carbon coated by an extremely fast heating rate, so that the benzene ring in the carbon source forms sp2 carbon. At the same time, the phosphorus element in the carbon source coordinates with the manganese and iron on the nucleation surface formed by low-temperature sintering. Finally, carbon coating is carried out at an extremely slow heating rate to improve the crystallinity of the overall material, thereby effectively improving the cycle stability and electronic conductivity of the phosphate-based cathode material. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the coordination process during ball milling mixing of the second semi-finished product and the third carbon source;

[0029] Figure 2 This is a transmission electron scanning microscope image of the phosphate-based cathode material in Example 1. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of this application, the solution of this application will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0031] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of this application, and not all embodiments.

[0032] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the phosphate-based cathode material, its preparation method, cathode sheet, and battery of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0038] Unless otherwise specified, this application uses conventional testing methods or testing methods recommended by the instrument.

[0039]

Preparation Method

[0040] A method for preparing a phosphate-based cathode material includes: S1. preparing a solid-phase precursor material from raw materials containing an iron source, a phosphorus source, a manganese source, a lithium source, and a first carbon source; S2. placing the solid-phase precursor material in an inert atmosphere or a reducing atmosphere and pre-sintering it at 300–400°C for 5–10 h to obtain a first semi-finished product; S3. ball-milling the first semi-finished product and a second carbon source containing a benzene ring and phosphorus, and heating the mixture at a rate of 15–20°C / min to a preset temperature in an inactive atmosphere. After heating to the desired temperature, maintain the temperature for 4–8 hours, then lower the temperature to 20–30°C at a rate of 3–5°C / min to obtain the second semi-finished product. The preset temperature is T1, where 600°C ≤ T1 ≤ 700°C. S4. Ball mill the material containing the second semi-finished product and the third carbon source. In an inactive atmosphere, heat the mixture to the preset temperature at a rate of 0.5–1.5°C / min, maintain the temperature for 8–10 hours, then lower the temperature to 20–30°C at a rate of 0.5–1.5°C / min to obtain the phosphate-based cathode material. In step S1, the carbon source provides a reducing atmosphere and also acts as a coating layer, improving the electrochemical performance of the phosphate-based cathode material. Step S1 includes drying a mixture containing an iron source, phosphorus source, manganese source, lithium source, first carbon source, and solvent to obtain a solid-phase precursor material. In step S2, pre-sintering under these conditions can form a semi-finished product with poor crystallinity, resulting in uncoordinated manganese and iron on the surface. In step S3, carbon coating is performed using an extremely rapid heating rate, causing the benzene rings in the carbon source to form sp2 carbon. Simultaneously, phosphorus in the carbon source coordinates with uncoordinated manganese and iron. On one hand, the high degree of graphitization of sp2 carbon improves the electronic conductivity of the material; on the other hand, the coordination of phosphorus with manganese and iron improves the density of the coating and prevents manganese leaching. In step S4, carbon coating is performed with an extremely slow heating rate, which increases the internal crystallinity of the material, thereby improving the overall crystallinity of the material.

[0041] In some embodiments, the second carbon source includes at least one of the following substances:

[0042]

[0043] like Figure 1 As shown, in step S4, the phosphorus element in the second carbon source forms coordination with the uncoordinated manganese and iron, which can improve the density of the coating and prevent the manganese element from dissolving.

[0044] In some embodiments, the second carbon source accounts for 0.1 wt% to 10.0 wt% of the total mass of the phosphate-based cathode material. Within this range, the cycle stability and electronic conductivity of the phosphate-based cathode material can be better improved. Optionally, the amount of the second carbon source added is independently selected from any value or a range between 0.10 wt%, 0.20 wt%, 0.30 wt%, 0.40 wt%, 0.50 wt%, 0.60 wt%, 0.70 wt%, 0.80 wt%, 0.90 wt%, 0.91 wt%, 0.98 wt%, 1.00 wt%, 2.00 wt%, 3.00 wt%, 4.00 wt%, 5.00 wt%, 6.00 wt%, 7.00 wt%, 8.00 wt%, 9.00 wt%, and 10.00 wt%.

[0045] In some embodiments, the first carbon source accounts for 0.95 wt% to 5 wt% of the total mass of the phosphate-based cathode material. Optionally, the amount of the first carbon source added is independently selected from any value or a range between 0.95 wt%, 0.97 wt%, 1.00 wt%, 1.02 wt%, 1.05 wt%, 1.10 wt%, 1.50 wt%, 2.00 wt%, 3.00 wt%, 4.00 wt%, and 5.00 wt%.

[0046] In some embodiments, the third carbon source accounts for 0.5 wt% to 3.0 wt% of the total mass of the phosphate-based cathode material. Optionally, the amount of the third carbon source added is independently selected from any value or a range between 0.50 wt%, 0.60 wt%, 0.70 wt%, 0.75 wt%, 0.76 wt%, 0.80 wt%, 0.90 wt%, 1.00 wt%, 2.00 wt%, and 3.00 wt%.

[0047] In some embodiments, during the step of placing the solid precursor material in an inert or reducing atmosphere, the heating rate is 5–10 °C / min. Optionally, the heating rate is independently selected from any value of 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, or a range between any two.

[0048] In some embodiments, in the step of ball milling and mixing the first semi-finished product and the second carbon source containing benzene rings and phosphorus, the preset temperature is T1, 600℃≤T1≤700℃. Within this range, phosphorus can better coordinate inwards with uncoordinated manganese and iron, while also avoiding the formation of impurity phases.

[0049] In some embodiments, in the step of ball-milling and mixing the material containing the second semi-finished product and the third carbon source, the preset temperature is T2, where 700 °C < T2 ≤ 800 °C. Within this range, the crystallinity inside the material can be better improved, thereby enhancing the crystallinity of the overall material.

[0050] In some embodiments, in the step of preparing the solid-phase precursor material from the raw materials containing an iron source, a phosphorus source, a manganese source, a lithium source, and a first carbon source, the iron source includes at least one of FeCl3, Fe(NO3)3, Fe2O3, and FeSO4. The iron source also includes their respective hydrates that exist at room temperature. For example, the iron source can also include FeSO4·7H2O.

[0051] In some embodiments, the phosphorus source includes at least one of (NH4)3PO4, LiH2PO4, and H3PO4.

[0052] In some embodiments, the manganese source includes at least one of MnO2, Mn(NO3)2, MnSO4, and Mn3(PO4)2. The manganese source also includes their respective hydrates that exist at room temperature. For example, the manganese source can also include Mn3(PO4)2·3H2O.

[0053] In some embodiments, the lithium source includes at least one of Li2O, Li2CO3, LiH2PO4, LiOH, CH3COOLi, and LiNO3. The lithium source also includes their respective hydrates that exist at room temperature. For example, the lithium source can also include LiOH·H2O.

[0054] In some embodiments, step S1 includes drying the mixed solution containing an iron source, a phosphorus source, a manganese source, a lithium source, a first carbon source, and a solvent to obtain the solid-phase precursor material, and the solvent includes at least one of water, ethanol, and acetone.

[0055] In some embodiments, in the step of preparing the solid-phase precursor material from the raw materials containing an iron source, a phosphorus source, a manganese source, a lithium source, and a first carbon source, the raw materials further include a doping element source; the doping element source includes oxides or soluble salts of at least one element selected from Ti, Mg, V, and Nb; the doping element source accounts for 0.3 wt% to 1.5 wt% of the total mass of the phosphate-based cathode material. Optionally, the addition amount of the doping element source is independently selected from any value of 0.3 wt%, 0.5 wt%, 0.7 wt%, 1.0 wt%, 1.1 wt%, 1.​​​​​In some embodiments, the inert atmosphere includes at least one of helium, argon, and neon, and the reducing atmosphere includes at least one of H2 / N2 and CO / N2. It is possible to promote the formation of vacancies on the material surface, thereby exposing the uncoordinated Mn / Fe, which is more conducive to the binding of the phosphorus-containing carbon source.

[0058] In some embodiments, the chemical formula of the phosphate-based cathode material is LiMn x Fe y M z PO4 / C, where M is a doping element, 0 < x < 1, 0 < y < 1, 0 ≤ z < 0.08, and x + y + z = 1. When the raw materials in step S1 do not contain doping elements, the chemical formula of the phosphate-based cathode material is LiMn x Fe y PO4 / C, 0 < x < 1, 0 < y < 1, and x + y = 1; when the raw materials in step S1 contain doping elements, the chemical formula of the phosphate-based cathode material is LiMn x Fe y M z PO4 / C, where M is a doping element, 0 < x < 1, 0 < y < 1, 0 < z < 0.08, and x + y + z = 1.

[0059]

Phosphate-based cathode material

[0060] A phosphate-based cathode material obtained by using the above preparation method.

[0061]

Positive electrode plate

[0062] A positive electrode plate, which includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes the above phosphate-based cathode material or the phosphate-based cathode material obtained by the above preparation method. For example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive current collector.

[0063] In some embodiments, the positive electrode film layer includes the phosphate-based cathode material obtained by the preparation method of the first aspect of the present application embodiment and / or the phosphate-based cathode material of the second aspect of the present application embodiment. However, the positive electrode film layer used in the positive electrode plate of the present application does not exclude other positive electrode active materials other than the above phosphate-based cathode material and / or the phosphate-based cathode material obtained by the preparation method. For example, other positive electrode active materials can use the positive electrode active materials for lithium-ion batteries well-known in the art, including but not limited to LiCoO2, lithium manganate, ternary positive electrode materials, etc. These other positive electrode film layers can be used alone or in combination of two or more.

[0064] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] In some embodiments, this application does not impose any particular limitation on the type of positive electrode binder. For example, the positive electrode binder may include at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0066] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. An example of a polymer substrate may be polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0067] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0068] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a conductive undercoating layer (e.g., composed of a conductive agent and a binder) sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0069]

Battery

[0070] A battery comprising the aforementioned positive electrode plate.

[0071] In some embodiments, the battery is a lithium-ion battery, including a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, lithium ions repeatedly insert and extract between the positive and negative electrodes, while the electrolyte acts as a conductor between them. The battery of this application can be applied to energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in various fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0072] Example 1

[0073] (1) Weigh 1 mol LiNO3, 0.4 mol Fe(NO3)3, 1 mol NH4H2PO4, 0.6 mol Mn(NO3)2, 5% of the weight of the finished product glucose (first carbon source), and 500 mL of water. Mix them evenly, add 0.5% of the weight of the finished product magnesium nitrate, and mix again to obtain a mixed solution. Heat and stir until the water evaporates, then crush the solution to obtain a solid precursor material.

[0074] (2) The solid precursor material is placed in a sintering furnace and heated to 350°C for 8 hours under a nitrogen atmosphere at a heating rate of 8°C / min. After the material is cooled to 25°C, it is taken out and crushed to obtain the first semi-finished product.

[0075] (3) Add 2 wt% of the finished product weight of triphenylphosphine (second carbon source) to the first semi-finished product obtained in step (2), ball mill and dry it, then place it in a tube furnace, heat it to 700°C at a rate of 15°C / min and hold it for 5 hours under a nitrogen atmosphere, and then cool it to 25°C at a rate of 3°C / min to obtain the second semi-finished product.

[0076] (4) Add 0.8 wt% of Ketjen black (third carbon source) to the second semi-finished product obtained in step (3), ball mill and dry, then place in a tube furnace, heat to 750℃ at a rate of 0.5℃ / min under a nitrogen atmosphere and hold at that temperature for 10 h, then cool to 25℃ at a rate of 0.5℃ / min to obtain LiMn 0.6 Fe 0.3947 Mg 0.0053 PO4 / C.

[0077] Example 2

[0078] The experimental procedure is the same as in Example 1, except that magnesium nitrate in step (1) is not added, resulting in LiMn. 0.6 Fe 0.4 PO4 / C.

[0079] Comparative Example 1

[0080] The experimental procedure is the same as in Example 1, except that the heating and cooling rates in step (3) are changed. Specifically, the heating rate in step (3) is replaced with 5℃ / min and the cooling rate is replaced with 10℃ / min, to obtain LiMn. 0.6 Fe 0.3947 Mg 0.0053 PO4 / C.

[0081] Comparative Example 2

[0082] The experimental procedure was the same as in Example 1, except that the carbon source in step (3) was changed. Specifically, 2 wt% of the finished product triphenylphosphine was replaced with 2 wt% of the finished product tetradecylphosphonic acid and 1.38 g of NH4H2PO4 (the same molar amount of P contained in the original triphenylphosphine) to obtain LiMn. 0.6 Fe 0.3947 Mg 0.0053 PO4 / C.

[0083] Comparative Example 3

[0084] The experimental procedure was the same as in Example 1, except that the carbon source in step (3) was changed. Specifically, 2 wt% of the finished product triphenylphosphine was replaced with 2 wt% of the finished product 3,4,9,10-perylenetetracarboxylic dianhydride and 1.38 g NH4H2PO4 (the same molar amount of P contained in the original triphenylphosphine) to obtain LiMn. 0.6 Fe 0.3947 Mg 0.0053 PO4 / C.

[0085] Comparative Example 4

[0086] The experimental procedure was the same as in Example 1, except that the carbon source in step (3) was changed. Specifically, 2 wt% of the finished product's triphenylphosphine was replaced with 2 wt% of the finished product's n-hexadecane and 1.38 g of NH4H2PO4 (the same molar amount of P contained in the original triphenylphosphine) to obtain LiMn. 0.6 Fe 0.3947 Mg 0.0053 PO4 / C.

[0087] Comparative Example 5

[0088] The experimental procedure is the same as in Example 1, except that the heating and cooling rates in step (4) are changed. Specifically, the heating rate in step (4) is replaced with 5℃ / min and the cooling rate is replaced with 10℃ / min to obtain LiMn. 0.6 Fe 0.3947 Mg 0.0053 PO4 / C.

[0089] Data Analysis:

[0090] The cathode materials from Examples 1-2 and Comparative Examples 1-5 were assembled into lithium secondary batteries, and the assembly method is as follows:

[0091] Inside the glove box, the coin cells were assembled sequentially in the following order: negative electrode shell, spring contact, steel sheet, lithium sheet, separator, positive electrode sheet, and positive electrode shell. During the process, 10 μL of electrolyte was injected, and then the coin cells were sealed using a sealing machine. Electrochemical performance tests were then conducted on these seven coin cell sets. The assembled lithium secondary batteries were then subjected to electrochemical performance testing according to industry standard testing methods. The results are shown in the table below.

[0092]

[0093]

[0094] As can be seen from Examples 1 and 2, the electrochemical performance and high-temperature storage performance of magnesium-doped lithium iron phosphate are both higher than those of undoped lithium manganese iron phosphate. This indicates that doping elements have a significant impact on the electrochemistry of lithium manganese iron phosphate, mainly because doping elements alter the one-dimensional diffusion channels of lithium ions within the crystal structure, thereby reducing migration resistance.

[0095] As can be seen from Example 1 and Comparative Examples 1 and 5, the sintering process has an effect on the crystal structure, which is beneficial to the electrochemical performance of the material under certain slow cooling conditions. The main reason is that during the slow cooling process, the temperature compensates for the defects in the incompletely crystallized crystal structure, improves the stability of the crystal, and thus provides better electrochemical performance and high-temperature storage performance.

[0096] As can be seen from Examples 1 and Comparative Examples 2, 3, and 4, the special characteristics of the second coated carbon source structure affect the material properties. If the second coated carbon source does not contain phosphorus, as shown in Comparative Example 3, its carbon source fails to coordinate with the iron and manganese on the surface to form a dense coated conductive carbon layer; if the second coated carbon source does not contain benzene rings, as shown in Comparative Example 2, even with the influence of phosphorus coordination, the degree of graphitization is far worse than in Example 1; if the second coated carbon source does not contain both phosphorus and benzene rings, as shown in Comparative Example 4, the degree of graphitization is low and the coating density is poor, resulting in the worst electrochemical and high-temperature performance.

[0097] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A method for producing a phosphate-based positive electrode material, characterized by, The application relates to a preparation method of a phosphate-based positive electrode material. The raw material containing an iron source, a phosphorus source, a manganese source, a lithium source and a first carbon source is used to prepare a solid-phase precursor material; The solid-phase precursor material is placed in an inert atmosphere or a reducing atmosphere, and is pre-sintered at 300-400 DEG C for 5-10 h to obtain a first semi-product; The first semi-product and a second carbon source containing a benzene ring and a phosphorus element are ball-milled and mixed, and then are heated to a preset temperature at a rate of 15-20 DEG C / min in an inactive atmosphere, and are kept at the preset temperature for 4-8 h, and then are cooled to 20-30 DEG C at a rate of 3-5 DEG C / min to obtain a second semi-product, wherein the preset temperature is T1, and 600 DEG C<=T1<=700 DEG C; The material containing the second semi-product and a third carbon source is ball-milled and mixed, and then is heated to a preset temperature at a rate of 0.5-1.5 DEG C / min in an inactive atmosphere, and is kept at the preset temperature for 8-10 h, and then is cooled to 20-30 DEG C at a rate of 0.5-1.5 DEG C / min to obtain the phosphate-based positive electrode material, wherein the preset temperature is T2, and 700 DEG C 2. The production method according to claim 1, characterized by, The second carbon source comprises at least one of the following substances:

3. The preparation method according to claim 1, characterized in that, The second carbon source accounts for 0.1wt%-10.0wt% of the total mass of the phosphate-based positive electrode material; And / or, the first carbon source accounts for 0.95wt%-5wt% of the total mass of the phosphate-based positive electrode material; And / or, the third carbon source accounts for 0.5wt%-3.0wt% of the total mass of the phosphate-based positive electrode material.

4. The method of claim 1, wherein, In the step of placing the solid-phase precursor material in an inert atmosphere or a reducing atmosphere, the heating rate is 5-10 DEG C / min; And / or, in the step of ball-milling and mixing the material containing the second semi-product and the third carbon source, the preset temperature is T2, and 700 DEG C 5. The preparation method according to claim 1, characterized in that, In the step of preparing the solid-phase precursor material from the raw material containing the iron source, the phosphorus source, the manganese source, the lithium source and the first carbon source, the iron source comprises at least one of FeCl3, Fe(NO3)3, Fe2O3 and FeSO4; And / or, the phosphorus source comprises at least one of (NH4)3PO4, LiH2PO4 and H3PO4; And / or, the manganese source comprises at least one of MnO2, Mn(NO3)2, MnSO4 and Mn3(PO4)2; And / or, the lithium source comprises at least one of Li2O, Li2CO3, LiH2PO4, LiOH, CH3COOLi and LiNO3; And / or, the first carbon source is an organic carbon source, and the organic carbon source comprises at least one of fructose, glucose and sucrose; And / or, in the step of ball-milling and mixing the material containing the second semi-product and the third carbon source, the third carbon source is an inorganic carbon source, and the inorganic carbon source comprises at least one of graphite, Ketjen black, carbon nanotube and graphene; And / or, the inert atmosphere comprises at least one of helium, argon and neon, and the reducing atmosphere comprises at least one of H2 / N2 and CO / N2; And / or, the inactive atmosphere comprises at least one of nitrogen, helium, argon and neon.

6. The method of claim 1, wherein, In the step of preparing the solid-phase precursor material from the raw material containing the iron source, the phosphorus source, the manganese source, the lithium source and the first carbon source, the raw material further comprises a doping element source; The doping element source comprises an oxide or soluble salt of at least one element selected from Ti, Mg, V and Nb; The doping element source accounts for 0.3wt%-1.5wt% of the total mass of the phosphate-based positive electrode material.

7. The production method according to any one of claims 1 to 6, characterized by, The phosphate-based positive electrode material has a chemical formula of LiMn x Fe y M z PO4 / C, wherein M is a doping element, 0 < x < 1, 0 < y < 1, 0 ≤ z < 0.08, and x + y + z = 1.

8. A phosphate-based positive electrode material, characterized by, The phosphate-based positive electrode material obtained by the preparation method of any one of claims 1-7.

9. A positive electrode sheet characterized by comprising: The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the phosphate-based positive electrode material obtained by the preparation method of any one of claims 1-7 or the phosphate-based positive electrode material of claim 8.

10. A battery, characterized by The positive electrode tab of claim 9.

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