Secondary battery, method of manufacturing the same, and electric device

Abstract

The present application provides a secondary battery comprising an anode sheet, a cathode sheet, a separator installed between the anode sheet and the cathode sheet, and an electrolyte comprising an electrolyte salt and a solvent, wherein the anode sheet comprises an anode current collector and an anode film layer installed on at least one surface of the anode current collector, the anode film layer comprises a first particle, the first particle comprises a first lithium iron manganese phosphate salt particle, the first average particle size s1 of the first particle is 120 to 600 nm, and wherein the manganese leaching amount of the secondary battery is ≤50 ppm.

Description

Technology Field

[0001] Cross-reference

[0002] This application claims priority to Chinese patent application No. 202410027059.3, filed on January 8, 2024, titled “Secondary battery, method of manufacturing the same and electric device,” which is incorporated by reference in its entirety into this application.

[0003] Technology field

[0004] This application relates to the field of secondary battery technology, and in particular to secondary batteries, methods for manufacturing the same, and electrical devices. Background Technology

[0005] As a positive electrode active material for lithium-ion batteries, lithium manganese iron phosphate offers a higher voltage platform, theoretical energy density, theoretical specific capacity, and lower cost compared to lithium iron phosphate. However, lithium manganese iron phosphate has a more significant issue with high-temperature (at 60°C) storage performance compared to lithium iron phosphate.

[0006] Therefore, it is necessary to provide an anode active material containing a lithium iron manganese phosphate salt having superior high-temperature storage performance.

[0007] This application is made in consideration of the aforementioned problem, and its purpose is to provide a secondary battery and an electric device having superior high-temperature storage performance.

[0008] The inventor has discovered that the above-described objective can be realized by using the technical solution of the present application.

[0009] According to the first aspect of the present application, a secondary battery is provided, which is

[0010] It comprises an anode sheet, a cathode sheet, a separator installed between the anode sheet and the cathode sheet, and an electrolyte containing an electrolyte salt and a solvent, and

[0011] The anode sheet comprises an anode current collector and an anode film layer installed on at least one surface of the anode current collector, and

[0012] The anode film layer comprises a first particle, the first particle comprises a first lithium iron manganese phosphate salt particle, and the first average particle size s1 of the first particle is 120 to 600 nm, and

[0013] Here, the manganese leaching amount of the secondary battery is ≤50 ppm.

[0014] The secondary battery of the present application has superior high-temperature storage performance. In addition, the secondary battery of the present application also has superior high-temperature cycle performance.

[0015] In any embodiment, the anode film layer further comprises a second particle, the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese iron phosphate particle, the first average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese iron phosphate particle is ≤ 1.5.

[0016] When the positive electrode film layer further comprises a second particle, wherein the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese iron phosphate particle, and the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese iron phosphate particle is ≤ 1.5, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, and better high-temperature cycle performance.

[0017] In any embodiment, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first particles is 60% to 98%, and the area ratio of the second particles is 2% to 40%.

[0018] In any embodiment, the anode film layer further comprises a first lithium iron phosphate salt particle, and the first average particle size s2' of the first lithium iron phosphate salt particle satisfies 500 nm ≤ s2' ≤ 3000 nm.

[0019] When the anode film layer further comprises first lithium iron phosphate particles and the first average particle size s2' of the first lithium iron phosphate particles satisfies 500nm≤s2'≤3000nm, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, and a higher solid content of the anode slurry.

[0020] In any embodiment, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 98%, and the area ratio of the first lithium iron phosphate particles is 2% to 30%.

[0021] In any embodiment, the anode film layer further comprises a third particle, the third particle comprises a second lithium iron phosphate particle and / or a third lithium manganese iron phosphate particle, the first average particle size s3 of the third particle satisfies 30 nm ≤ s3 ≤ 200 nm, and the Mn / Fe molar ratio of the third lithium manganese iron phosphate particle is ≤ 1.5.

[0022] In any embodiment, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first particles is 70% to 97%; the area ratio of the second particles is 2% to 25%; and the area ratio of the third particles is 1% to 10%.

[0023] In any embodiment, the anode film layer further comprises lithium iron phosphate particles, and the primary average particle size s3' of the lithium iron phosphate particles satisfies 30nm ≤ s3' ≤ 200nm.

[0024] When the positive electrode film layer further comprises lithium iron phosphate particles and the primary average particle size s3' of the lithium iron phosphate particles satisfies 30nm≤s3'≤200nm, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, and better high-temperature cycle performance.

[0025] In any embodiment, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 97%; the area ratio of the first lithium iron phosphate particles is 2% to 25%; and the area ratio of the second lithium iron phosphate particles is 1% to 10%.

[0026] In any embodiment, the first manganese iron lithium salt particle has the molecular formula Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1 having, where Q1 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m1≤1.15, x1>0, r1>0, 0.9≤x1+r1≤1, 0.95≤y1≤1, 3.5≤j1≤4, 0≤q1≤0.1, and / or

[0027] The lithium manganese iron phosphate particles have the molecular formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2having, where Q2 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m2≤1.15, x2>0, r2>0, r2 / x2≤1.5; 0.9≤x2+r2≤1, 0.95≤y2≤1, 3.5≤j2≤4, 0≤q2≤0.1, and / or

[0028] The trimanganese iron lithium salt particles have the molecular formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3 having, where Q3 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m3≤1.15, x3>0, r3>0, r3 / x3≤1.5; 0.9≤x3+r3≤1, 0.95≤y3≤1, 3.5≤j3≤4, 0≤q3≤0.1, and / or

[0029] The above-mentioned first lithium iron phosphate salt particle has the molecular formula Li m4 Fe x4 P y4 O j4 Q4 q4 having, where Q4 comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m4≤1.15, 0.9≤x4≤1, 0.95≤y4≤1, 3.5≤j4≤4, 0<q4≤0.1, and / or

[0030] The above-mentioned lithium iron phosphate particles have the molecular formula Li m5 Fe x5 P y5 O j5 Q5 q5It has, where Q5 includes at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and 0.95≤m5≤1.15, 0.9≤x5≤1, 0.95≤y5≤1, 3.5≤j5≤4, 0≤q5≤0.1.

[0031] In any embodiment, Q4 in the first lithium iron phosphate salt particle comprises at least one of Ti, V, Mg, and Nb, and when calculated based on the total weight of the first lithium iron phosphate salt particle, the content of Ti, V, Mg and / or Nb is 1,000 to 10,000 ppm.

[0032] In any embodiment, the specific surface area (BET) of the first lithium iron phosphate salt particle is 3 m 2 / g to 8m 2 / g is.

[0033] The specific surface area (BET) of the lithium iron phosphate particles is 3 m² 2 / g to 8m 2 When / g, the secondary battery of the present application has a lower manganese leaching amount, a higher solid content of the anode slurry, and a higher anode sheet compression density.

[0034] In any embodiment, when calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is Cx4 weight%, where 0.8≤Cx4≤2.0.

[0035] In any embodiment, when calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is Cx4 weight%, and the ratio z4 of the specific surface area of ​​the first lithium iron phosphate particles to Cx4 satisfies 1.5≤z4≤8.5.

[0036] In any embodiment, the specific surface area of ​​the lithium iron manganese phosphate particle is 5 m² 2 / g to 12m 2 / g is.

[0037] In any embodiment, when calculated based on the total weight of the lithium manganese iron phosphate particles, the carbon content of the lithium manganese iron phosphate particles is Cx2 weight%, where 0.8≤Cx2≤2.0.

[0038] In any embodiment, the primary average particle size s1' of the first lithium iron manganese phosphate particle is 150 to 210 nm, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 870 nm ≤ s2' ≤ 3000 nm, and / or the primary average particle size s3' of the second lithium iron phosphate particle satisfies 60 nm ≤ s3' ≤ 200 nm.

[0039] In any embodiment, the capacity ratio η of the first lithium iron phosphate salt particle is ≥ 88%, and said η is

[0040] A battery having lithium iron phosphate particles as a positive electrode active material is defined as being charged and discharged twice with a constant current of rate 0.1C in a voltage range of 2.0V to 3.75V, and then charged and discharged once with a constant current of rate 1C. In the charge-discharge test at rate 1C, a capacity value of discharge voltage 3.2V is taken and recorded as C1, and a capacity value of discharge voltage 2.0V is taken and recorded as C2, where η=C1 / C2, and the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA.

[0041] In any embodiment, the first lithium iron phosphate salt particle is

[0042] (a) The Dv10 of the first lithium iron phosphate salt particles is ≥0.2 μm;

[0043] (b) The Dv50 of the first lithium iron phosphate salt particles is 0.5 to 5 μm;

[0044] (c) The Dv90 of the first lithium iron phosphate salt particle is ≤10 μm;

[0045] (d) The Dv99 of the first lithium iron phosphate salt particle is ≤12 μm;

[0046] (e) The powder compression density of the first lithium iron phosphate salt particles under a pressure of 3 tons is ≥2.25 g / cm³ 3 thing;

[0047] (f) The powder resistivity of the first lithium iron phosphate particles is 60 Ω·cm, satisfying at least one of these conditions.

[0048] In any embodiment, the aspect ratio of the second lithium iron phosphate particle is ≥1.3.

[0049] When the aspect ratio of the lithium iron phosphate particles is ≥1.3, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, better high-temperature cycle performance, and higher capacity per gram.

[0050] In any embodiment, the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the second iron phosphate lithium salt particle is ≥1.03.

[0051] When the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the lithium iron phosphate particles is ≥1.03, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, better high-temperature cycle performance and higher capacity per gram.

[0052] In any embodiment, the first lithium iron phosphate salt particles are mainly

[0053] A raw material is provided containing at least a lithium source, an iron source, a phosphorus, a selective carbon film-forming agent, a selective carbon source, and a selective modifier, and is obtained by a manufacturing method that performs at least two sintering steps, wherein,

[0054] The primary sintering temperature is 500℃ to 760℃, and optionally 550℃ to 720℃;

[0055] The secondary sintering temperature is 700°C to 800°C, and optionally 720°C to 780°C.

[0056] In any embodiment, the first lithium iron phosphate salt particles are mainly

[0057] A raw material is provided containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film-forming agent, and a modifier, and is obtained by a manufacturing method that performs at least two sintering steps, wherein,

[0058] The carbon content of the material after the first sintering is 0.01 wt% to 0.79 wt%, and optionally 0.05 wt% to 0.4 wt%;

[0059] The carbon content of the material after secondary sintering is 0.8 wt% to 2.0 wt%, and optionally 1.0 wt% to 1.6 wt%.

[0060] In any embodiment, the method for manufacturing the first lithium iron phosphate salt particles

[0061] The method includes the step of performing a first grinding after performing the first sintering above, and performing a second grinding after performing the second sintering above, wherein,

[0062] The Dv50 of the product after the first grinding is 300 nm to 1200 nm, and optionally 400 nm to 1100 nm;

[0063] The Dv50 of the product after the second grinding is 500 nm to 5000 nm, and optionally 700 nm to 2500 nm.

[0064] According to a second aspect of the present application, an electric device comprising a secondary battery according to a first aspect of the present application is provided. Brief explanation of the drawing

[0065] FIG. 1 is a schematic diagram of a secondary battery according to one embodiment of the present application. FIG. 2 is an exploded view of a secondary battery according to one embodiment of the present application shown in FIG. 1. FIG. 3 is a schematic diagram of a battery module according to one embodiment of the present application. FIG. 4 is a schematic diagram of a battery pack according to one embodiment of the present application. FIG. 5 is an exploded view of a battery pack according to one embodiment of the present application shown in FIG. 4. FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to one embodiment of the present application. FIG. 7 is a scanning electron microscope image of a first lithium iron phosphate salt particle with a primary particle size indicated according to one embodiment of the present application. Specific details for implementing the invention

[0066] In the following, embodiments of the secondary battery, the method for manufacturing the same, and the electrical device of the present application are described in detail and disclosed with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of known matters and redundant descriptions of structures that are identical in actual form may be omitted. This is intended to avoid making the following description unnecessarily verbose and to aid the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0067] The “range” disclosed in this application is limited in the form of lower and upper limits, and a given range is limited by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. A range limited in this way may include or not include end values ​​and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is expected that they are understood as ranges of 60 to 110 and 80 to 120. Furthermore, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4 and 5 are listed, the ranges described below may all be expected to be 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the value range “a to b” represents an abbreviated expression of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numeric range “0 to 5” means that all real numbers between “0 to 5” are already listed in this application, and “0 to 5” appears merely as an abbreviation for such numeric combinations. Additionally, if a specific parameter is an integer ≥ 2, this parameter is disclosed as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] Unless otherwise specified, all embodiments and optional embodiments of the present application may be combined with one another to form a new technical solution.

[0069] Unless otherwise specified, all technical features of the present application and selectable technical features may be combined with each other to form a new technical solution.

[0070] Unless otherwise specified, all steps of the present application may be performed sequentially, may be performed randomly, and preferably sequentially. For example, the method comprises steps (a) and (b), which indicates that the method may comprise steps (a) and (b) performed sequentially and steps (b) and (a) performed sequentially. For example, the aforementioned method may further comprise step (c), which indicates that step (c) may be added to the method in any order, and for example, the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0071] Unless otherwise specified, the terms “comprehensive” and “include” as used in this application are open forms and may also be closed forms. For example, the terms “comprehensive” and “include” may indicate that other unlisted components may be further included or included, or that only the listed components may be included or included.

[0072] Unless otherwise specified, the term “or” in this application is inclusive. For example, the phrase “A or B” indicates “A, B or both A and B”. More specifically, any one of the following conditions satisfies “A or B”: A is true (or exists) and B is false (or absent); A is false (or absent) and B is true (or exists); or A and B are both true (or exist).

[0073] As a cathode active material for lithium-ion batteries, lithium iron manganese phosphate offers a higher voltage platform, theoretical energy density, theoretical specific capacity, and lower cost compared to lithium iron phosphate. However, lithium iron manganese phosphate has a more poor high-temperature (at 60°C) storage performance compared to lithium iron phosphate. Therefore, there is a need to provide a cathode active material containing lithium iron manganese phosphate that possesses superior high-temperature storage performance.

[0074] Based on this, the present application proposes a technical solution for solving the aforementioned technical problem.

[0075] According to the first aspect of the present application, a secondary battery is provided, which is

[0076] It comprises an anode sheet, a cathode sheet, a separator installed between the anode sheet and the cathode sheet, and an electrolyte containing an electrolyte salt and a solvent, and

[0077] The anode sheet comprises an anode current collector and an anode film layer installed on at least one surface of the anode current collector, and

[0078] The anode film layer comprises a first particle, the first particle comprises a first lithium iron manganese phosphate salt particle, and the first average particle size s1 of the first particle is 120 to 600 nm, and

[0079] Here, the manganese leaching amount of the secondary battery is ≤50 ppm.

[0080] Lithium manganese iron phosphate exhibits superior ionic and electronic conductivity, which is significantly influenced by particle size. When a material contains lithium manganese iron phosphate with larger particle sizes, solid-phase lithium ion transport is more severely restricted, and the electron transport pathway during electrochemical reactions is lengthened, resulting in a significant decrease in the material's capacity per gram and kinetic performance. Research findings indicate that the surface of lithium manganese iron phosphate materials is highly oxidizable during the charged state. Furthermore, due to the Yarn-Taylor effect, surface oxygen atoms are prone to side reactions with protons in the electrolyte, leading to manganese leaching and electrolyte loss. Therefore, the particle size of lithium manganese iron phosphate particles must be designed to avoid containing excessive small particles; in other words, the fine powder content must be controlled to a lower level. Experimental results revealed that the surface activity of small particles with a size of less than 120 nm increases significantly. By using a lithium iron manganese phosphate salt with a lower manganese leaching amount and selecting an optimized particle size, the secondary battery of the present application has superior high-temperature storage performance and superior high-temperature cycle performance.

[0081] In some embodiments, the first average particle size s1 of the first particle may be 140 to 500 nm. In some embodiments, the first average particle size s1 of the first particle may be 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, 350 nm, 400 nm, 450 nm, 480 nm, 490 nm, 500 nm, 550 nm, 600 nm, or a range consisting of any two of the above first average particle sizes or a value within this range.

[0082] In this application, the term "primary average particle size" refers to the average value of the primary particle sizes of all particles, where the primary particle size refers to the longest distance connecting two points on the edge in a cross-sectional view.

[0083] The primary average particle size of the first particle can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. Taking the lithium manganese iron phosphate particles as an example, the electrode sheet is cut perpendicular to the face of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of the lithium manganese iron phosphate particles is statistically analyzed using long-axis statistics. Specifically, the total number of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm can be statistically determined from the scanning electron microscope image, and the sum of the primary particle sizes of the lithium manganese iron phosphate particles with a primary particle size greater than 10 nm can be statistically determined. The primary average particle size of the lithium manganese iron phosphate particles = primary particle size of the total lithium manganese iron phosphate particles / total number of lithium manganese iron phosphate particles. Here, in the first particle size statistical process, particles with 0 < first particle size ≤ 10 nm are excluded from the statistical range.

[0084] In some embodiments, the manganese leaching amount of the secondary battery is ≤48 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤45 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤40 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤38 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤37 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤35 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤33 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤31 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤30 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤28 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤25 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤24 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤20 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤18 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤17 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤16 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤15 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤14 ppm. In some embodiments, the manganese leaching amount of the secondary battery is ≤12 ppm.

[0085] In some embodiments, the manganese leaching amount refers to the manganese leaching amount after 100 cycles at 25°C.

[0086] The manganese leaching amount can be measured using methods and instruments known in the art. For example, it can be performed by referring to the ICP test procedure: after 100 cycles at 25°C, remove the fully charged cell and disassemble it in a glove box; remove the anode sheet from the drying chamber and carefully scrape off 1g of material from the center of the electrode sheet using a ceramic knife, ensuring that the entire active material layer is scraped off to avoid variations in manganese content due to different thicknesses; seal it in a sealed bag and send it to the laboratory. Prepare an electronic balance, a heating plate, a 150ml quartz beaker, a watch glass, a funnel, a 100ml volumetric flask, tongs (heat-resistant gloves), a sampling spoon, a dust-free bag, etc.; check that the calibration date of the electronic balance is within its validity period; if the validity period has expired, it cannot be used and requires recalibration; connect the power so that the heating plate can normally heat up to 250°C; and weigh 0.2000±0.005g of powder into the beaker; Acidification treatment: Prepare a dilute sulfuric acid solution with a volume ratio of 1:4 (concentrated sulfuric acid:ultrapure water = 1:4); add 20 ml of the prepared dilute sulfuric acid solution to a beaker; preheat by operating a heating plate and, once the temperature reaches 250°C, place the sample in the beaker and decompose it for 30 minutes, then cover the mouth of the beaker with a quartz cover to reduce the evaporation of the acidic solution; after the sample decomposition is complete for 30 minutes, remove the sample and cool it to room temperature; transfer the decomposed sample to a 100 ml glass volumetric flask and dilute it; then perform the ICP standard test procedure: the test instrument temperature is 22±2℃ and the humidity is <60%; select the trace element method as the test method; and run the calibration standard: determine the standard curve using the prepared standard solution; select Mn as the element; and finally, obtain the Mn elution amount through the test.

[0087] In some embodiments, the anode film layer further comprises a second particle, the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese iron phosphate particle, the first average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese iron phosphate particle is ≤ 1.5.

[0088] In a specific embodiment, as shown in the scanning electron microscope image of the first lithium iron phosphate salt particle of FIG. 7, the line segment indicated by the double arrow within the particle is the primary particle size defined in the present application.

[0089] In some embodiments, the second particle is a primary particle.

[0090] In this document, “primary particles” refer to particles that lack distinct aggregation interfaces in particle scanning electron microscope images but may contain fine pores and point or line defects; the difference lies in the smallest unit of powder particles that lack structures such as accumulation and aggregation.

[0091] The primary average particle size of the second particles can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. As an example, the electrode sheet is cut perpendicular to the face of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of the second particles is statistically analyzed using long-axis statistics. Specifically, the total number of second particles with a primary particle size greater than 80 nm can be statistically analyzed from the scanning electron microscope image, and the sum of the primary particle sizes of the second particles with a primary particle size greater than 80 nm can be statistically analyzed, and the primary average particle size of the second particles = the primary particle size of the total second particles / the total number of second particles. Here, in the primary particle size statistical process, particles with 0 < primary particle size ≤ 80 nm are excluded from the statistical range.

[0092] By setting the primary average particle size of the second particle to 500 nm to 3000 nm, the particle can be maintained at an appropriate micrometer dimension, thereby avoiding interfacial side reactions and processing difficulties that occur when nano-sizing the particle, and avoiding a decrease in kinetic performance caused by the particle being too large; furthermore, it is advantageous for stirring the slurry containing the second particle and improving the solid content, thereby improving the processing problem of the cell and further improving the volumetric energy density of the battery; additionally, it is possible to avoid the cell's capacity development being affected by the normal extraction and insertion of lithium ions due to the carbon coating being too high.

[0093] When the anode film layer further comprises a second particle, wherein the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese iron phosphate particle, and the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese iron phosphate particle is ≤ 1.5, dense accumulation can be achieved by mixing a portion of the larger second particle into the lithium manganese iron phosphate material; at the same time, since the large particle component is a lithium iron phosphate or a lithium manganese iron phosphate with a lower Mn / Fe molar ratio, the kinetic performance of the material is superior compared to a lithium manganese iron phosphate with a larger particle and, after the second particle cracks during the cycling process, there is no manganese element inside the particle or the manganese element content is lower, thus mitigating the problem of electrolyte oxidation due to the oxidative properties of the corresponding material and the problem of damage to the cathode SEI film due to manganese leaching, so that the secondary battery of the present application has lower manganese It is designed to have a higher yield, superior high-temperature storage performance, and superior high-temperature cycle performance.

[0094] In some embodiments, the primary average particle size of the second particle is 250 nm, 300 nm, 350 nm, 400 nm, 440 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 730 nm, 750 nm, 780 nm, 800 nm, 830 nm, 850 nm, 870 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 2000 nm, 2100 nm, 2200 nm, 2300 nm, 2400 nm, 2500 nm, 2600 nm, 2700 nm, 2800 nm, 2900 nm, It may be a range consisting of 3000nm, 3500nm, 4000nm, or any two of the aforementioned first-order average particle sizes, or a value within this range.

[0095] In some embodiments, the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3500 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 4000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 300 nm ≤ s2 ≤ 3500 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 650 nm ≤ s2 ≤ 2500 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 650 nm ≤ s2 ≤ 3000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 650 nm ≤ s2 ≤ 4000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 700 nm ≤ s2 ≤ 3000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 700 nm ≤ s2 ≤ 4000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 800 nm ≤ s2 ≤ 3000 nm. In some embodiments, the primary average particle size s2 of the second particle satisfies 700 nm ≤ s2 ≤ 4000 nm.

[0096] In some embodiments, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first particles is 60% to 98%, and the area ratio of the second particles is 2% to 40%.

[0097] In some embodiments, the area ratio of the first particles is 70% to 98% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the first particles is 65%, 70%, 72%, 74%, 75%, 97%, and 98%.

[0098] In some embodiments, the area ratio of the second particles is 2% to 30% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the second particles is a range consisting of 2%, 23%, 25%, 30%, or any two of the above-mentioned area ratios, or a value within this range.

[0099] The respective areas of the first and second particles can be obtained by statistically analyzing the cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratio is obtained by dividing each area by the total area.

[0100] In some embodiments, the second particle does not contain the second manganese iron lithium salt particle.

[0101] In some embodiments, the anode film layer further comprises first lithium iron phosphate particles, and the first average particle size s2' of the first lithium iron phosphate particles satisfies 500 nm ≤ s2' ≤ 3000 nm.

[0102] In some embodiments, the first lithium iron phosphate salt particle is a primary particle.

[0103] By setting the primary average particle size of the first lithium iron phosphate particles to 500 nm to 3000 nm, the particles can be maintained at appropriate micrometer dimensions, thereby avoiding interfacial side reactions and processing difficulties that occur when nano-sizing the particles, and avoiding a decrease in kinetic performance caused by the particles being too large; furthermore, it is advantageous for stirring the slurry containing the first lithium iron phosphate particles and improving the solid content, thereby improving the processing problems of the cell and further improving the volumetric energy density of the battery; additionally, it is possible to avoid the effect on the cell's capacity development caused by the density being too high due to the carbon coating, which affects the normal extraction and insertion of lithium ions.

[0104] When the anode film layer further includes first lithium iron phosphate particles and the first average particle size s2' of the first lithium iron phosphate particles satisfies 500nm ≤ s2' ≤ 3000nm, dense accumulation can be achieved by mixing some of the first large particles of lithium iron phosphate with the lithium manganese phosphate material, and at the same time, since the large particle component is lithium iron phosphate, the kinetic performance of the material is superior compared to the large particles of lithium manganese phosphate, and since there are no manganese elements inside the particles after the large particles of lithium iron phosphate are cracked during the cycling process, the problem of electrolyte oxidation due to the oxidative properties of the corresponding material and the problem of damage to the negative electrode SEI film due to manganese leaching are mitigated, thereby enabling the secondary battery of the present application to have a lower manganese leaching amount, superior high-temperature storage performance, superior high-temperature cycle performance, and a higher solid content of the anode slurry.

[0105] In some embodiments, the primary average particle size of the first lithium iron phosphate salt particle is 250 nm, 300 nm, 350 nm, 400 nm, 440 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 730 nm, 750 nm, 780 nm, 800 nm, 830 nm, 850 nm, 870 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 2000 nm, 2100 nm, 2200 nm, 2300 nm, 2400 nm, 2500 nm, 2600 nm, 2700 nm, 2800 nm, 2900 nm, It may be a range consisting of 3000nm, 3500nm, 4000nm, or any two of the aforementioned first-order average particle sizes, or a value within this range.

[0106] In some embodiments, the primary average particle size s2' of the first lithium iron phosphate salt particle satisfies 500 nm ≤ s2' ≤ 3500 nm.

[0107] When the primary average particle size s2' of the first lithium iron phosphate salt particles satisfies 500nm≤s2'≤3500nm, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, and a higher solid content of the cathode slurry.

[0108] In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particles satisfies 500 nm ≤ s2' ≤ 4000 nm.

[0109] When the primary average particle size s2' of the first lithium iron phosphate salt particles satisfies 500nm≤s2'≤4000nm, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, and a higher solid content of the cathode slurry.

[0110] In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 300 nm ≤ s2' ≤ 3500 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 500 nm ≤ s2' ≤ 3000 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 650 nm ≤ s2' ≤ 2500 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 650 nm ≤ s2' ≤ 3000 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 650 nm ≤ s2' ≤ 4000 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 700 nm ≤ s2' ≤ 3000 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 700 nm ≤ s2' ≤ 4000 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 800 nm ≤ s2' ≤ 3000 nm. In some embodiments, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 800 nm ≤ s2' ≤ 4000 nm.

[0111] In some embodiments, the first lithium iron phosphate salt particles are single-crystal particles and / or polycrystalline particles.

[0112] In this application, the term "single crystal" refers to a crystal with a complete structure grown from a single crystal nucleus. The single crystal of this application is a single whole in the scanning electron microscope image field of view, and there are no crystal boundaries within the single crystal.

[0113] In some embodiments, the single crystal of the present application may have microdefects such as internal micropores, small amounts of dots and planes, or small amounts of particles adhering to each other on the surface of a single particle.

[0114] In this application, the term "polycrystalline" refers to a crystal formed by the random combination of orientations of small single-crystal grains, and has crystal boundaries within the crystal.

[0115] In some embodiments, the number of single-crystal particles is 90% or more based on the total number of particles of the first lithium iron phosphate salt. By controlling the number of single-crystal particles within the above-described range, the proportion of single-crystal particles is higher compared to polycrystalline and secondary aggregates, and the blockage of crystal boundaries for lithium ions is smaller, which is advantageous for further improving the lithium ion transport rate and the kinetic performance of the secondary battery.

[0116] The primary average particle size of the lithium iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. As an example, the electrode sheet is cut perpendicular to the surface of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of the lithium iron phosphate particles is statistically analyzed using long-axis statistics. Specifically, the total number of lithium iron phosphate particles with a primary particle size greater than 80 nm can be statistically determined from the scanning electron microscope image, and the sum of the primary particle sizes of the lithium iron phosphate particles with a primary particle size greater than 80 nm can be statistically determined. The primary average particle size of the lithium iron phosphate particles = the primary particle size of the total lithium iron phosphate particles / the total number of lithium iron phosphate particles. Here, in the first particle size statistical process, particles with 0 < first particle size ≤ 80 nm are excluded from the statistical range.

[0117] In some embodiments, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 98%, and the area ratio of the first lithium iron phosphate particles is 2% to 30%.

[0118] In some embodiments, the area ratio of lithium iron manganese phosphate particles is 70% to 98% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of lithium iron manganese phosphate particles is 65%, 70%, 72%, 74%, 75%, 97%, and 98%.

[0119] In some embodiments, the area ratio of the first lithium iron phosphate salt particles is 2% to 30% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the first lithium iron phosphate salt particles is a range consisting of 2%, 23%, 25%, 30%, or any two of the above-mentioned area ratios, or a value within this range.

[0120] The respective areas of the first lithium iron phosphate particles and the second lithium iron phosphate particles can be obtained by statistically analyzing the cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratio is obtained by dividing each area by the total area.

[0121] In some embodiments, the second particle does not include the first lithium iron phosphate salt particle.

[0122] In some embodiments, the anode film layer further comprises lithium iron manganese phosphate particles, and the primary average particle size s2'' of the lithium iron manganese phosphate particles satisfies 500 nm ≤ s2'' ≤ 3000 nm.

[0123] In some embodiments, the lithium manganese iron phosphate particles are primary particles.

[0124] By setting the primary average particle size of the lithium manganese iron phosphate particles to 500 nm to 3000 nm, the particles can be maintained at appropriate micrometer dimensions, thereby avoiding interfacial side reactions and processing difficulties that occur when nano-sizing the particles, and avoiding a decrease in kinetic performance caused by the particles being too large; furthermore, it is advantageous for stirring the slurry containing the lithium manganese iron phosphate particles and improving the solid content, thereby improving the processing problems of the cell and further improving the volumetric energy density of the battery; additionally, it is possible to avoid the effect on the cell's capacity development caused by the density being too high due to the carbon coating, which affects the normal extraction and insertion of lithium ions.

[0125] When the anode film layer further comprises lithium manganese iron phosphate particles and the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 500nm ≤ s2'' ≤ 3000nm, dense accumulation can be achieved by mixing some large particles of lithium manganese iron phosphate with the lithium manganese iron phosphate material, and at the same time, since the large particle component is lithium manganese iron phosphate with a lower Mn / Fe molar ratio, the kinetic performance of the material is superior compared to lithium manganese iron phosphate with large particles having a higher Mn / Fe molar ratio, and after the large particles of lithium manganese iron phosphate are cracked during the cycling process, the manganese element content inside the particles is lower, so the problem of electrolyte oxidation due to the oxidative properties of the corresponding material and the problem of damage to the anode SEI film due to manganese leaching are mitigated, thereby enabling the secondary battery of the present application to have a lower manganese leaching amount, superior high-temperature storage performance, and superior high-temperature cycling performance.

[0126] In some embodiments, the primary average particle size of the lithium iron manganese phosphate particles is 250 nm, 300 nm, 350 nm, 400 nm, 440 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 730 nm, 750 nm, 780 nm, 800 nm, 830 nm, 850 nm, 870 nm, 900 nm, 950 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 2000 nm, 2100 nm, 2200 nm, 2300 nm, 2400 nm, 2500 nm, 2600 nm, 2700 nm, 2800 nm, It may be a range consisting of 2900nm, 3000nm, 3500nm, 4000nm, or any two of the above-mentioned first-order average particle sizes, or a value within this range.

[0127] In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 500 nm ≤ s2'' ≤ 3500 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 500 nm ≤ s2'' ≤ 4000 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 300 nm ≤ s2'' ≤ 3500 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 500 nm ≤ s2'' ≤ 3000 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 650 nm ≤ s2'' ≤ 2500 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 650 nm ≤ s2'' ≤ 3000 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 650 nm ≤ s2'' ≤ 4000 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 700 nm ≤ s2'' ≤ 3000 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 700 nm ≤ s2'' ≤ 4000 nm. In some embodiments, the primary average particle size s2'' of the lithium manganese iron phosphate particles satisfies 800 nm ≤ s2'' ≤ 3000 nm. In some embodiments, the primary average particle size s2'' of the lithium iron manganese phosphate particles satisfies 700nm ≤ s2'' ≤ 4000nm.

[0128] In some embodiments, the lithium iron manganese phosphate particles are single-crystal particles and / or polycrystalline particles.

[0129] In some embodiments, the number of single-crystal particles is 90% or more based on the total number of particles of the lithium iron manganese phosphate particles. By controlling the number of single-crystal particles within the above-described range, the proportion of single-crystal particles is higher compared to polycrystalline and secondary aggregates, and the blockage of crystal boundaries for lithium ions is smaller, which is advantageous for further improving the lithium ion transport rate and the kinetic performance of the secondary battery.

[0130] The primary average particle size of the lithium manganese iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. As an example, the electrode sheet is cut perpendicular to the face of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of the lithium manganese iron phosphate particles is statistically analyzed using long-axis statistics. Specifically, the total number of lithium manganese iron phosphate particles with a primary particle size greater than 80 nm can be statistically determined from the scanning electron microscope image, and the sum of the primary particle sizes of the lithium manganese iron phosphate particles with a primary particle size greater than 80 nm can be statistically determined. The primary average particle size of the lithium manganese iron phosphate particles = primary particle size of the total lithium manganese iron phosphate particles / total number of lithium manganese iron phosphate particles. Here, in the first particle size statistical process, particles with 0 < first particle size ≤ 80 nm are excluded from the statistical range.

[0131] In some embodiments, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 98%, and the area ratio of the second lithium iron manganese phosphate particles is 2% to 30%.

[0132] In some embodiments, the area ratio of lithium iron manganese phosphate particles is 70% to 98% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of lithium iron manganese phosphate particles is 65%, 70%, 72%, 74%, 75%, 97%, and 98%.

[0133] In some embodiments, the area ratio of the lithium iron manganese phosphate particles is 2% to 30% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the lithium iron manganese phosphate particles is a range consisting of 2%, 23%, 25%, 30%, or any two of the above-mentioned area ratios, or a value within this range.

[0134] The respective areas of the first lithium iron manganese phosphate particles and the second lithium iron manganese phosphate particles can be obtained by statistically analyzing the cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratio is obtained by dividing each area by the total area.

[0135] In some embodiments, the anode film layer further comprises a third particle, the third particle comprises a second lithium iron phosphate particle and / or a third lithium manganese iron phosphate particle, the first average particle size s3 of the third particle satisfies 30 nm ≤ s3 ≤ 200 nm, and the Mn / Fe molar ratio of the third lithium manganese iron phosphate particle is ≤ 1.5.

[0136] By increasing the amount of ultrafine particles in the anode film layer, space utilization can be further improved, and the ultrafine particles can be adjusted to a gap between intermediate lithium iron phosphate particles and ultra-large lithium iron phosphate particles / lithium iron phosphate particles, thereby further improving the volume energy density, that is, further improving the compression density of the electrode sheet. Compared to lithium iron phosphate with an ultrafine Mn / Fe molar ratio, lithium iron phosphate with a lower Mn / Fe molar ratio has some loss in the voltage platform, but the capacity per gram and surface stability, especially surface stability, are significantly improved. In contrast, lithium iron phosphate with an ultrafine Mn / Fe molar ratio is difficult to form a superior coating and has stronger oxidative properties on the surface in the charged state. At the same time, due to the Yarn-Taylor effect, the specific surface energy of the overlapping small particles is high, which leads to prominent manganese leaching problems and reduced battery cycle life. The secondary battery of the present application exhibits superior cycle life and capacity per gram by controlling the first lithium iron phosphate particles to a more appropriate particle size and incorporating fewer ultrafine powders and ultra-large particles. Furthermore, the secondary battery of the present application ensures superior compression density by increasing the lithium iron phosphate material with a lower large particle lithium iron phosphate / Mn / Fe molar ratio and the lithium iron phosphate material with a lower small particle lithium iron phosphate / Mn / Fe molar ratio in the anode film layer. In the case of the anode active material, inferred through an ideal dense accumulation model, to achieve superior compression density, the material must contain some large particles and ultrafine powders to form a dense accumulation, thereby achieving superior high-temperature cycle performance while having a higher anode sheet compression density.

[0137] In some embodiments, the anode film layer further comprises lithium iron phosphate particles, and the primary average particle size s3' of the lithium iron phosphate particles satisfies 30nm ≤ s3' ≤ 100nm.

[0138] In some embodiments, the anode film layer further comprises lithium iron phosphate particles, and the primary average particle size of the lithium iron phosphate particles may be a range consisting of 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or any two primary average particle sizes described above, or a value within this range.

[0139] The primary average particle size of the third particle can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. As an example, the electrode sheet is cut perpendicular to the face of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of the third particle is statistically analyzed using long-axis statistics. Specifically, the total number of third particles with a primary particle size greater than 10 nm can be statistically analyzed from the scanning electron microscope image, and the sum of the primary particle sizes of third particles with a primary particle size greater than 10 nm can be statistically analyzed, and the primary average particle size of the third particle = the primary particle size of the total third particle / the total number of third particles. Here, in the primary particle size statistical process, particles with a primary particle size of 0 < primary particle size ≤ 10 nm are excluded from the statistical range.

[0140] In some embodiments, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first particles is 70% to 97%; the area ratio of the second particles is 2% to 25%; and the area ratio of the third particles is 1% to 10%.

[0141] In some embodiments, the area ratio of the first particle is 70% to 97% based on the total area of ​​the primary particle of the anode film layer. In some embodiments, the area ratio of the first particle is 65%, 70%, 72%, 74%, 75%, 97%, and 98% based on the total area of ​​the primary particle of the anode film layer. In some embodiments, the area ratio of the first particle is 65% to 74% based on the total area of ​​the primary particle of the anode film layer.

[0142] In some embodiments, the area ratio of the second particle is 2% to 25% based on the total area of ​​the primary particle of the anode film layer. In some embodiments, the area ratio of the second particle is 2%, 23%, 25%, 30%, or any two of the above-mentioned area ratios, or a value within this range. In some embodiments, the area ratio of the second particle is 23% to 25% based on the total area of ​​the primary particle of the anode film layer.

[0143] In some embodiments, the area ratio of the third particle is 1% to 10% based on the total area of ​​the primary particle of the anode film layer. In some embodiments, the area ratio of the third particle is a range consisting of 1%, 3%, 5%, 10%, or any two of the above-mentioned area ratios, or a value within this range.

[0144] The respective areas of the first, second, and third particles can be obtained by statistically analyzing the cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratio is obtained by dividing each area by the total area.

[0145] In some embodiments, the third particle does not contain the third manganese iron lithium salt particle.

[0146] In some embodiments, the anode film layer further comprises lithium iron phosphate particles, and the primary average particle size s3' of the lithium iron phosphate particles satisfies 30nm ≤ s3' ≤ 200nm.

[0147] By increasing the amount of small amounts of ultrafine particles in the anode film layer, space utilization can be further improved. The ultrafine particles can be adjusted to a gap between intermediate-sized lithium iron manganese phosphate particles and ultra-large lithium iron phosphate particles, thereby further enhancing volumetric energy density, that is, further improving the compression density of the electrode sheet. Compared to ultrafine lithium iron phosphate, although some losses exist in the voltage platform, the capacity per gram and surface stability, particularly surface stability, are significantly improved. In contrast, lithium iron manganese phosphate materials with a higher ultrafine Mn / Fe molar ratio are difficult to form a superior coating and exhibit stronger oxidative properties on the surface during charging. Furthermore, due to the Yarn-Taylor effect, the specific surface energy of the overlapping small particles is high, leading to prominent manganese leaching problems and reduced battery cycle life. The secondary battery of the present application controls the lithium iron manganese phosphate particles to a more appropriate particle size and includes fewer ultrafine powders and ultra-large particles, thereby the material exhibits superior cycle life and capacity per gram. Furthermore, the secondary battery of the present application ensures superior compression density by increasing the large particle lithium iron phosphate and small particle lithium iron phosphate materials in the anode film layer. In the case of the anode active material, inferred through an ideal dense accumulation model, to achieve superior compression density, the material must contain some large particles and ultrafine powder to form a dense accumulation, thereby achieving superior high-temperature cycle performance while having a higher anode sheet compression density. When the anode film layer further comprises second lithium iron phosphate particles, and the primary average particle size s3' of the second lithium iron phosphate particles satisfies 30nm ≤ s3' ≤ 200nm, the secondary battery of the present application has a lower manganese leaching amount, superior high-temperature storage performance, and superior high-temperature cycle performance.

[0148] In some embodiments, the anode film layer further comprises lithium iron phosphate particles, and the primary average particle size s3' of the lithium iron phosphate particles satisfies 30nm ≤ s3' ≤ 100nm.

[0149] In some embodiments, the anode film layer further comprises lithium iron phosphate particles, and the primary average particle size of the lithium iron phosphate particles may be a range consisting of 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or any two primary average particle sizes described above, or a value within this range.

[0150] The primary average particle size of lithium iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. As an example, the electrode sheet is cut perpendicular to the surface of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of the lithium iron phosphate particles is statistically analyzed using long-axis statistics. Specifically, the total number of lithium iron phosphate particles with a primary particle size greater than 10 nm can be statistically determined from the scanning electron microscope image, and the sum of the primary particle sizes of lithium iron phosphate particles with a primary particle size greater than 10 nm can be statistically determined. The primary average particle size of the lithium iron phosphate particles = the primary particle size of the total lithium iron phosphate particles / the total number of lithium iron phosphate particles. Here, in the first particle size statistical process, particles with 0 < first particle size ≤ 10 nm are excluded from the statistical range.

[0151] In some embodiments, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 97%; the area ratio of the first lithium iron phosphate particles is 2% to 25%; and the area ratio of the second lithium iron phosphate particles is 1% to 10%.

[0152] In some embodiments, the area ratio of the lithium manganese iron phosphate particles is 70% to 97% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the lithium manganese iron phosphate particles is 65%, 70%, 72%, 74%, 75%, 97%, and 98% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the lithium manganese iron phosphate particles is 65% to 74% based on the total area of ​​the primary particles of the anode film layer.

[0153] In some embodiments, the area ratio of the first lithium iron phosphate particles is 2% to 25% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the first lithium iron phosphate particles is a range consisting of 2%, 23%, 25%, 30%, or any two of the above-mentioned area ratios, or a value within this range. In some embodiments, the area ratio of the first lithium iron phosphate particles is 23% to 25% based on the total area of ​​the primary particles of the anode film layer.

[0154] In some embodiments, the area ratio of the second lithium iron phosphate salt particles is 1% to 10% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the second lithium iron phosphate salt particles based on the total area of ​​the primary particles of the anode film layer is a range consisting of 1%, 3%, 5%, 10%, or any two of the above-mentioned area ratios, or a value within this range.

[0155] The respective areas of the lithium manganese phosphate particles, lithium iron phosphate particles, and lithium iron phosphate particles can be obtained by statistically analyzing the cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratios are obtained by dividing each area by the total area.

[0156] In some embodiments, the third particle does not include the second lithium iron phosphate particle.

[0157] In some embodiments, the anode film layer further comprises lithium iron manganese phosphate particles, and the primary average particle size s3'' of the lithium iron manganese phosphate particles satisfies 30 nm ≤ s3'' ≤ 200 nm.

[0158] By increasing the amount of ultrafine particles in the anode film layer, space utilization can be further improved. The ultrafine particles can be adjusted to a gap between intermediate lithium iron phosphate particles and ultra-large lithium iron phosphate particles / lithium iron phosphate particles, thereby further improving the volume energy density, that is, further improving the compression density of the electrode sheet. Compared to lithium iron phosphate with a lower ultrafine Mn / Fe molar ratio, lithium iron phosphate with a higher ultrafine Mn / Fe molar ratio exhibits some loss in the voltage platform, but the capacity per gram and surface stability, particularly surface stability, are significantly improved. In contrast, lithium iron phosphate with a higher ultrafine Mn / Fe molar ratio is difficult to form a superior coating and has stronger oxidative properties on the surface in the charged state. At the same time, due to the Yarn-Taylor effect, the specific surface energy of the overlapping small particles is high, leading to prominent manganese leaching problems and reduced battery cycle life. The secondary battery of the present application exhibits superior cycle life and capacity per gram by controlling the first lithium iron phosphate particles to a more appropriate particle size and incorporating fewer ultrafine powders and ultra-large particles. Furthermore, the secondary battery of the present application ensures superior compression density by increasing the lithium iron phosphate material with a lower large particle lithium iron phosphate / Mn / Fe molar ratio and the lithium iron phosphate material with a lower small particle Mn / Fe molar ratio in the anode film layer. In the case of the anode active material, inferred through an ideal dense accumulation model, to achieve superior compression density, the material must contain some large particles and ultrafine powders to form a dense accumulation, thereby achieving superior high-temperature cycle performance while having a higher anode sheet compression density.

[0159] In some embodiments, the anode film layer further comprises lithium iron manganese phosphate particles, and the primary average particle size s3'' of the lithium iron manganese phosphate particles satisfies 30nm ≤ s3'' ≤ 100nm.

[0160] In some embodiments, the anode film layer further comprises lithium iron manganese phosphate particles, and the primary average particle size of the lithium iron manganese phosphate particles may be a range consisting of 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or any two primary average particle sizes described above, or a value within this range.

[0161] The primary average particle size of lithium manganese iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be tested using a scanning electron microscope and long-axis statistics. As an example, the electrode sheet is cut perpendicular to the face of the anode sheet using an argon ion beam to expose the cross-section, the cross-section is photographed with a scanning electron microscope, and the particle size of lithium manganese iron phosphate particles is statistically analyzed using long-axis statistics. Specifically, the total number of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm can be statistically determined from the scanning electron microscope image, and the sum of the primary particle sizes of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm can be statistically determined. The primary average particle size of lithium manganese iron phosphate particles = primary particle size of total lithium manganese iron phosphate particles / total number of lithium manganese iron phosphate particles. Here, in the first particle size statistical process, particles with 0 < first particle size ≤ 10 nm are excluded from the statistical range.

[0162] In some embodiments, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 97%; the area ratio of the second lithium iron manganese phosphate particles is 2% to 25%; and the area ratio of the third lithium iron manganese phosphate particles is 1% to 10%.

[0163] In some embodiments, the area ratio of the lithium manganese iron phosphate particles is 70% to 97% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the lithium manganese iron phosphate particles is 65%, 70%, 72%, 74%, 75%, 97%, and 98% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the lithium manganese iron phosphate particles is 65% to 74% based on the total area of ​​the primary particles of the anode film layer.

[0164] In some embodiments, the area ratio of the lithium manganese iron phosphate particles based on the total area of ​​the primary particles of the anode film layer is 2% to 25%. In some embodiments, the area ratio of the lithium manganese iron phosphate particles based on the total area of ​​the primary particles of the anode film layer is a range consisting of 2%, 23%, 25%, 30%, or any two of the above-mentioned area ratios, or a value within this range. In some embodiments, the area ratio of the lithium manganese iron phosphate particles based on the total area of ​​the primary particles of the anode film layer is 23% to 25%.

[0165] In some embodiments, the area ratio of the lithium iron tertian phosphate particles is 1% to 10% based on the total area of ​​the primary particles of the anode film layer. In some embodiments, the area ratio of the lithium iron tertian phosphate particles is a range consisting of 1%, 3%, 5%, 10%, or any two of the above-mentioned area ratios, or a value within this range based on the total area of ​​the primary particles of the anode film layer.

[0166] The respective areas of the first lithium manganese iron phosphate particles, the second lithium manganese iron phosphate particles, and the third lithium manganese iron phosphate particles can be obtained by statistically analyzing the cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratio is obtained by dividing each area by the total area.

[0167] In some embodiments, the first manganese iron lithium salt particle has the molecular formula Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1 having, where Q1 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m1≤1.15, x1>0, r1>0, 0.9≤x1+r1≤1, 0.95≤y1≤1, 3.5≤j1≤4, 0≤q1≤0.1, and / or

[0168] The lithium manganese iron phosphate particles have the molecular formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 having, where Q2 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m2≤1.15, x2>0, r2>0, r2 / x2≤1.5; 0.9≤x2+r2≤1, 0.95≤y2≤1, 3.5≤j2≤4, 0≤q2≤0.1, and / or

[0169] The trimanganese iron lithium salt particles have the molecular formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3having, where Q3 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m3≤1.15, x3>0, r3>0, r3 / x3≤1.5; 0.9≤x3+r3≤1, 0.95≤y3≤1, 3.5≤j3≤4, 0≤q3≤0.1, and / or

[0170] The above-mentioned first lithium iron phosphate salt particle has the molecular formula Li m4 Fe x4 P y4 O j4 Q4 q4 having, where Q4 comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m4≤1.15, 0.9≤x4≤1, 0.95≤y4≤1, 3.5≤j4≤4, 0<q4≤0.1, and / or

[0171] The above-mentioned lithium iron phosphate particles have the molecular formula Li m5 Fe x5 P y5 O j5 Q5 q5 It has, where Q5 includes at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and 0.95≤m5≤1.15, 0.9≤x5≤1, 0.95≤y5≤1, 3.5≤j5≤4, 0≤q5≤0.1.

[0172] In some embodiments, the first manganese iron lithium salt particle has the molecular formula Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1It has, where m1 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x1+r1 can be 0.9, 1.0, y1 can be 0.95, 0.98, 1.00, j1 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, and q1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1. In some embodiments, r1 / x1≥1.5.

[0173] In some embodiments, the lithium manganese iron phosphate particles have the molecular formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 It has, where m2 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x2+r2 can be 0.9, 1.0, y2 can be 0.95, 0.98, 1.00, j2 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, and q2 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1. In some embodiments, r2 / x2≤1.5. In some embodiments, 0≤r2 / x2≤1.5. In some embodiments, 0.43≤r2 / x2≤1.5.

[0174] When the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is ≤1.5 (i.e., r2 / x2 ≤ 1.5), the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, and a higher capacity per gram.

[0175] In some embodiments, the lithium iron manganese phosphate particles are of the molecular formula Li m3 Fe x3 Mn r3P y3 O j3 Q3 q3 It has, where m3 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x3+r3 can be 0.9, 1.0, y3 can be 0.95, 0.98, 1.00, j3 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, and q3 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1. In some embodiments, r3 / x3≤1.5. In some embodiments, 0≤r3 / x3≤1.5. In some embodiments, 0.43≤r3 / x3≤1.5.

[0176] When the Mn / Fe molar ratio of the lithium iron manganese phosphate particles is ≤1.5 (i.e., r3 / x3 ≤ 1.5), the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, higher capacity per gram, higher solid content of the anode slurry, and higher compression density of the anode sheet.

[0177] In some embodiments, the first lithium iron phosphate salt particle has the molecular formula Li m4 Fe x4 P y4 O j4 Q4 q4 It has, where m4 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x4 can be 0.9, 1.0, y4 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, j4 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, and q4 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0178] In some embodiments, the lithium iron phosphate particles have the molecular formula Li m5 Fe x5 P y5 O j5 Q5 q5 It has, where m5 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, x5 can be 0.9, 1.0, y5 can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, j5 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, and q5 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0179] Modifying lithium iron phosphate particles and / or lithium iron phosphate particles with Q4 and / or Q5 elements helps to improve the ion transport capacity of the cathode active material. The aforementioned elements can form vacant sites within the particle crystal lattice or alter the length of interatomic bonds, thereby facilitating the movement of lithium ions within the crystal lattice, effectively improving the conductivity of the particles themselves and enhancing the kinetic performance of the cathode active material. In this application, the modification may specifically be represented by doping and / or coating.

[0180] In some embodiments, Q4 in the first lithium iron phosphate particles comprises at least one of Ti, V, Mg, and Nb, and when calculated based on the total weight of the first lithium iron phosphate particles, the content of Ti, V, Mg and / or Nb is 1,000 to 10,000 ppm.

[0181] In some embodiments, when calculated based on the total weight of the first lithium iron phosphate particles, the content of Q4 in the first lithium iron phosphate particles is a range consisting of 1000 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm, 8500 ppm, 9000 ppm, 9500 ppm, 10000 ppm, or any two of the above-mentioned contents of Q4, or a value within this range.

[0182] The content of Q4, for example, the content of Ti, in the lithium iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be tested by referring to GB / T 33822-2017.

[0183] Conventional lithium iron phosphate particles generally have a low content of modifying elements or no modifying elements are added. Increasing the content of Q4 element in the first lithium iron phosphate particles helps to further enhance the body phase ion transport capacity of the first lithium iron phosphate particles and improve their kinetic performance. However, as the content of Q4 element increases further, the body phase ion transport capacity may not continue to increase, and it may occupy the positions of lithium ions, which may affect the output of capacity per gram. The range of Q4 element in this application helps to further obtain superior kinetic performance and capacity per gram.

[0184] In some embodiments, Q4 in the first lithium iron phosphate particles contains Ti, and when calculated based on the total weight of the first lithium iron phosphate particles, the content of Ti is 1,000 to 10,000 ppm, and optionally 2,500 to 6,000 ppm.

[0185] In some embodiments, Q4 in the first lithium iron phosphate particles contains V, and when calculated based on the total weight of the first lithium iron phosphate particles, the content of V is 1000 to 10000 ppm, and optionally 2500 to 6000 ppm.

[0186] In some embodiments, Q4 in the first lithium iron phosphate particles contains Nb, and when calculated based on the total weight of the first lithium iron phosphate particles, the content of Nb is 1,000 to 10,000 ppm, and optionally 2,500 to 6,000 ppm.

[0187] When calculated based on the total weight of the first lithium iron phosphate particles, when the Ti content in the first lithium iron phosphate particles is 2500 to 6000 ppm, further appropriately increasing the Ti content in the first lithium iron phosphate particles helps to further improve the body phase ion transport capacity of the first lithium iron phosphate particles, thereby enabling the secondary battery of the present application to have superior high-temperature storage performance and a higher capacity per gram.

[0188] In some embodiments, the specific surface area of ​​the first lithium iron phosphate salt particle is 3 m² 2 / g to 8m 2 / g is.

[0189] In some embodiments, the specific surface area (BET) of the first lithium iron phosphate salt particle is 3 m 2 / g, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 4.6m 2 / g, 5m 2 / g, 5.5m 2 / g, 6m 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, 8.5m 2 / g, 9m 2 / g, 9.5m 2 / g, 10m2 / g, 10.5m 2 / g, 11m 2 / g, 11.5m 2 / g, 12m 2 / g or a range consisting of any two BETs described above, or a value within this range.

[0190] In this application, the term "specific surface area" or "BET" refers to the total surface area of ​​a particle per unit mass, and in this application, the BET of the lithium iron phosphate particles is related to factors such as the primary average particle size of the lithium iron phosphate particles, carbon content, density of the carbon coating, degree of bonding between the carbon and the particle, and porosity of the particle.

[0191] The specific surface area (BET) of the particles can be measured using methods and instruments known in the art. For example, it can be tested according to the gas adsorption method by referring to GB / T 19587-2017. As an example, lithium iron phosphate particles are taken as a sample and placed in a sample tube, the sample tube is immersed in liquid nitrogen at -196°C, and the amount of nitrogen adsorbed on the solid surface is measured at different pressures from 0.05 to 0.30 relative pressures, the amount of single molecular layer adsorption of the sample is calculated according to the BET multilayer adsorption theory and formula, and the specific surface area of ​​the sample is obtained.

[0192] The BET of the lithium iron phosphate particles is too high, increasing particle absorption performance and affecting the processing performance of the mixed anode slurry. However, the BET of the lithium iron phosphate particles is too low, reducing its capacity per gram. The BET of the lithium iron phosphate particles is 3m 2 / g to 8m 2 By controlling it within / g, it is advantageous to further balance the processing performance and solid content of the anode slurry, thereby improving the processing problems of the cell and further improving the volumetric energy density of the battery.

[0193] The specific surface area of ​​the lithium iron phosphate particles is 3 m² 2 / g to 8m2 When / g, by introducing larger particles smaller than BET, the specific surface energy of the cathode active material can be reduced, and the spontaneous aggregation and polymerization of the material after the dispersion process can be slowed down, thereby reducing the viscosity of the slurry and enabling a higher solid content. At the same time, as the specific surface area of ​​the cathode active material decreases, the corresponding active reaction area decreases, which can reduce side reactions of the electrode under high voltage, and the specific surface area of ​​the lithium iron phosphate particles is lower, and at the same time, the water absorption of the entire material is reduced, moisture is reduced, and side reactions of the battery during the charge-discharge process can be reduced, thereby enabling the secondary battery of the present application to have a lower manganese leaching amount, a higher solid content of the cathode slurry, and a higher cathode sheet compression density.

[0194] In some embodiments, the specific surface area of ​​the first lithium iron phosphate salt particle is 3 m² 2 / g to 6m 2 / g is.

[0195] The specific surface area (BET) of the lithium iron phosphate particles is 3 m² 2 / g to 6m 2 When / g, the secondary battery of the present application has superior high-temperature storage performance, superior high-temperature cycle performance, and a higher compression density of the anode sheet.

[0196] In some embodiments, when calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is Cx4 weight%, where 0.8≤Cx4≤2.0.

[0197] When 0.8≤Cx4≤2.0, controlling the carbon content of the large-particle lithium iron phosphate salt within a certain range allows for the control of the conductivity and coating integrity of the large-particle lithium iron phosphate salt material. As the carbon content increases, the kinetic performance improves, the conductivity of the particles improves, and the coating integrity improves, thereby reducing side reactions on the material surface. However, excessively high carbon content increases the specific surface area of ​​the material, thereby degrading cycle performance. Furthermore, high carbon coating results in some excess carbon in the form of suspended carbon or inefficient coating, which degrades the processing performance of the material and has a greater impact on the solid content of the material's slurry. The range of carbon content in this application helps to further obtain superior kinetic performance and processing performance.

[0198] In some embodiments, when calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is a range consisting of 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any two of the above-mentioned carbon contents, or a value within this range.

[0199] In some embodiments, when calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is Cx4 weight%, where 0.8≤Cx4≤1.2.

[0200] When calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is Cx4 weight% and 0.8≤Cx4≤1.2, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, higher solid content of the anode slurry, better high-temperature cycle performance, and higher compression density of the anode sheet.

[0201] In some embodiments, the carbon contained in the first lithium iron phosphate salt particle is coated on the surface of the particle. In some embodiments, the carbon contained in the first lithium iron phosphate salt particle is inserted into the particle. In some embodiments, a portion of the carbon contained in the first lithium iron phosphate salt particle is coated on the surface of the particle, and a portion is inserted into the particle.

[0202] In some embodiments, the ratio z4 of the specific surface area of ​​the first lithium iron phosphate salt particle to Cx4 satisfies 1.5≤z4≤8.5. In some embodiments, the ratio z4 of the specific surface area of ​​the first lithium iron phosphate salt particle to Cx4 satisfies 3≤z4≤6.

[0203] In some embodiments, z4 may be a range consisting of 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5, 3.75, 3.8, 4, 4.2, 4.3, 4.5, 4.58, 4.8, 4.98, 5, 5.3, 5.42, 5.5, 5.71, 5.8, 5.83, 6, 6.3, 6.5, 6.7, 6.8, 7, 7.3, 7.5, 7.8, 7.9, 8, 8.3, 8.5, 8.6, or any two of the above-mentioned z4 values ​​or a value within this range.

[0204] The ratio z4 of the specific surface area (BET) of the first lithium iron phosphate particles and Cx4 can characterize the uniformity and density of the carbon contained in the first lithium iron phosphate particles. When the primary average particle size and carbon content of the first lithium iron phosphate particles remain unchanged, the lower the ratio z4, the higher the coverage utilization of carbon within the particles, the less suspended carbon there is, and the more uniform and dense the carbon contained in the first lithium iron phosphate particles becomes. Improving the uniformity and density of the contained carbon is advantageous for further improving the kinetic performance and capacity per gram of the first lithium iron phosphate particles, but the carbon density is too high, which affects the insertion and extraction of lithium ions and may affect the kinetic performance and capacity per gram of the secondary battery to some extent. The ratio range z4 of the present application is advantageous for the carbon contained in the first iron phosphate lithium salt particles to have appropriate uniformity and density, is advantageous for improving the conductivity of the particle surface, and is advantageous for further improving the capacity per gram and kinetic performance of the secondary battery.

[0205] In some embodiments, the ratio z4 of the specific surface area of ​​the first lithium iron phosphate salt particle to Cx4 satisfies 3.8≤z4≤5.

[0206] When the ratio z4 of the specific surface area of ​​the first lithium iron phosphate salt particles to Cx4 satisfies 3.8≤z4≤5, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, higher solid content of the anode slurry, better high-temperature cycle performance, and higher compression density of the anode sheet.

[0207] In some embodiments, the primary average particle size s1 of the first particle is 120 to 600 nm, the primary average particle size s2 of the second particle satisfies 650 nm ≤ s2 ≤ 3000 nm, and / or the primary average particle size s3 of the third particle satisfies 30 nm ≤ s3 ≤ 100 nm.

[0208] In some embodiments, the primary average particle size s1' of the first lithium iron manganese phosphate particles is 120 to 600 nm, the primary average particle size s2' of the first lithium iron phosphate particles satisfies 650 nm ≤ s2' ≤ 3000 nm, and / or the primary average particle size s3' of the second lithium iron phosphate particles satisfies 30 nm ≤ s3' ≤ 100 nm.

[0209] In some embodiments, the primary average particle size s1' of the first lithium iron manganese phosphate particles is 150 to 210 nm, the primary average particle size s2' of the first lithium iron phosphate particles satisfies 650 nm ≤ s2' ≤ 3000 nm, and / or the primary average particle size s3' of the second lithium iron phosphate particles satisfies 30 nm ≤ s3' ≤ 100 nm.

[0210] In some embodiments, the primary average particle size s1' of the first lithium iron manganese phosphate particle is 150 to 210 nm, the primary average particle size s2' of the first lithium iron phosphate particle satisfies 870 nm ≤ s2' ≤ 3000 nm, and / or the primary average particle size s3' of the second lithium iron phosphate particle satisfies 60 nm ≤ s3' ≤ 200 nm.

[0211] In some embodiments, the primary average particle size s1' of the first lithium iron manganese phosphate salt particle is 120 to 600 nm, the primary average particle size s2'' of the second lithium iron manganese phosphate salt particle satisfies 650 nm ≤ s2'' ≤ 3000 nm, and / or the primary average particle size s3'' of the third lithium iron manganese phosphate salt particle satisfies 30 nm ≤ s3'' ≤ 100 nm.

[0212] In some embodiments, the primary average particle size s1' of the first lithium iron manganese phosphate salt particle is 150 to 210 nm, the primary average particle size s2'' of the second lithium iron manganese phosphate salt particle satisfies 650 nm ≤ s2'' ≤ 3000 nm, and / or the primary average particle size s3'' of the third lithium iron manganese phosphate salt particle satisfies 30 nm ≤ s3'' ≤ 100 nm.

[0213] In some embodiments, the capacity ratio η of the first lithium iron phosphate salt particle is ≥ 88%, and η is

[0214] A battery having lithium iron phosphate particles as a positive electrode active material is defined as being charged and discharged twice with a constant current of rate 0.1C in a voltage range of 2.0V to 3.75V, and then charged and discharged once with a constant current of rate 1C. In the charge-discharge test at rate 1C, a capacity value of discharge voltage 3.2V is taken and recorded as C1, and a capacity value of discharge voltage 2.0V is taken and recorded as C2, where η=C1 / C2, and the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA.

[0215] In some embodiments, η may be a range consisting of 88%, 88.1%, 89%, 90%, 90.1%, 91%, 92%, 92.2%, 93%, 94%, 94.1%, 94.5%, 95%, 95.1% or any two of the above-mentioned η values, or a value within this range.

[0216] The η value of the lithium iron phosphate particles can be measured using methods and instruments known in the art. As an example, a button battery is first manufactured, and the specific manufacturing process of the button battery is as follows: 2.0000 g of lithium iron phosphate particles are mixed with 0.1111 g of conductive carbon black and 0.1111 g of polyvinylidene fluoride, then 2.5 g of the organic solvent N-methylpyrrolidone is added and mixed sufficiently uniformly to form a slurry. The slurry is coated onto aluminum foil with a coating thickness of 140 micrometers, dried under vacuum at 120°C for 2 hours, and punched into a circular sheet with a diameter of 13 mm using a punch. A positive electrode sheet is obtained by purifying at 10 MPa using a purification press and maintaining vacuum insulation at 120°C for 12 hours. The weight of the positive electrode sheet is weighed, wherein the loading amount of lithium iron phosphate particles is 11 to 12 mg. A button battery is assembled in a glove box protected by argon gas, the metal lithium sheet is used as the negative electrode, the electrolyte is a mixed solvent of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) in a volume ratio of 1:1, the electrolyte is LiPF6, and the separator is a Celgard 2400 microporous polyethylene membrane.

[0217] The manufactured button battery is tested for electrical performance in a LAND tester. Specifically, the button battery is charged and discharged twice with a constant current of rate 0.1C in a voltage range of 2.0V to 3.75V, and then charged and discharged once with a constant current of rate 1C. In the charge-discharge test at rate 1C, a capacitance value of discharge voltage 3.2V is taken and recorded as C1, and a capacitance value of discharge voltage 2.0V is taken and recorded as C2, so η=C1 / C2. Here, the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA.

[0218] The capacity ratio η of the first lithium iron phosphate particles can reflect kinetic performance and platform maintenance performance, and can be controlled by adjusting the primary average particle size, carbon content, ratio of carbon source and carbon film agent, and the modifier and its content of the first lithium iron phosphate particles. The first lithium iron phosphate particles of the present application have an η value of ≥88% and possess superior kinetic performance. At the same time, when the η value is higher, superior power performance can be maintained even when the secondary battery is discharged at a low state of charge (SOC); that is, a battery with a high η value has a smaller voltage drop value when discharged at a high current in a low power state.

[0219] In some embodiments, the aspect ratio of the lithium iron phosphate particles is ≥1.1. In some embodiments, the aspect ratio of the lithium iron phosphate particles is ≥1.3.

[0220] When the aspect ratio of the lithium iron phosphate particles is ≥1.3, the crystallinity of the material is superior, so that the secondary battery of the present application has superior high-temperature storage performance, lower manganese leaching amount, superior high-temperature cycle performance, and higher capacity per gram.

[0221] In the present application, the term "major axis ratio" refers to the ratio of the major axis diameter to the minor axis diameter of a primary particle, with the major axis diameter set to a and the minor axis diameter to b, and the major axis ratio = a / b; this parameter is generally used to express the shape of the particle and can be used to measure its sphericity.

[0222] The aspect ratio of lithium iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be tested using the following method: a cold-pressed electrode sheet is taken, and the electrode sheet is cut to expose a cross-section by directing an Ar ion beam perpendicularly to the direction facing the electrode sheet, and an image is obtained using a scanning electron microscope. Then, the scanning electron microscope image of the electrode sheet cross-section is analyzed using image software to measure the major aspect a and minor aspect b of the particles, and their ratio, i.e., the aspect ratio of the particles, is obtained.

[0223] In some embodiments, the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the second lithium iron phosphate salt particle is ≥0.98. In some embodiments, the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the second lithium iron phosphate salt particle is ≥1.03. In some embodiments, the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the second lithium iron phosphate salt particle is ≥1.08.

[0224] When the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the lithium iron phosphate particles is ≥1.03, the crystallinity of the material is superior; furthermore, a higher W value indicates that there is more exposure of the (020) crystal plane, which is more advantageous for the extraction and insertion of lithium ions, thereby enabling the secondary battery of the present application to have superior high-temperature storage performance, lower manganese leaching amount, superior high-temperature cycle performance, and a higher capacity per gram.

[0225] (020) The ratio W of the crystal plane diffraction peak intensity and (211) the crystal plane diffraction peak intensity can be measured using methods and instruments known in the art. For example, it can be tested using the following method:

[0226] The ratio of the diffraction peak intensity of the lithium iron phosphate particles is tested using X-rays, and the lithium iron phosphate particles are placed on an X-ray diffraction (Shimadz XRD-7000 model) test platform using a copper target X-ray diffraction, the scan start angle is set to 10°, the end angle to 90°, and the step length to 0.013, and then the test is started to obtain the diffraction pattern of the lithium iron phosphate particles within the diffraction angle range of 10° to 90°, and the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity is calculated according to the diffraction pattern.

[0227] In some embodiments, the specific surface area of ​​the second lithium iron phosphate salt particle is 11 m² 2 / g to 14m 2 / g. In some embodiments, the specific surface area of ​​the lithium iron phosphate particles is 11 m² 2 / g to 12m 2 / g. In some embodiments, the specific surface area of ​​the lithium iron phosphate particles is 12 m² 2 / g to 14m 2 / g is.

[0228] In some embodiments, when calculated based on the total weight of the second lithium iron phosphate particles, the carbon content of the second lithium iron phosphate particles is Cx5 weight%, and the ratio z5 of the specific surface area of ​​the second lithium iron phosphate particles to Cx5 satisfies 8≤z5≤11. In some embodiments, 8.1≤z5≤10.4. In some embodiments, when calculated based on the total weight of the second lithium iron phosphate particles, the carbon content of the second lithium iron phosphate particles is Cx5 weight%, and the ratio z5 of the specific surface area of ​​the second lithium iron phosphate particles to Cx5 is a range consisting of 8.1, 8.9, 10.4, or any two of the above-mentioned z5s, or a value within this range.

[0229] In some embodiments, the carbon contained in the lithium iron phosphate particles is coated on the surface of the particles. In some embodiments, the carbon contained in the lithium iron phosphate particles is inserted into the particles. In some embodiments, a portion of the carbon contained in the lithium iron phosphate particles is coated on the surface of the particles, and a portion is inserted into the particles.

[0230] In some embodiments, the specific surface area of ​​the first lithium iron manganese phosphate particle is 8 to 20 m² 2 / g. In some embodiments, the specific surface area of ​​the lithium iron manganese phosphate particles is 10 to 20 m² 2 / g is.

[0231] In some embodiments, the specific surface area of ​​the first iron manganese phosphate lithium salt particle is 8 m² 2 / g, 9m 2 / g, 10m 2 / g, 10.5m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g, 19 m 2 / g, 20 m 2 / g or a range consisting of any two specific surface areas as described above, or a value within this range.

[0232] In some embodiments, the specific surface area of ​​the first lithium iron manganese phosphate particle is 10 to 18 m² 2 / g. In some embodiments, the specific surface area of ​​the lithium iron manganese phosphate particles is 10 to 17 m² 2 / g is.

[0233] The specific surface area of ​​the lithium manganese iron phosphate particles is 10 m² 2 / g to 17m 2When / g, the secondary battery of the embodiment of the present application has superior high-temperature storage performance, lower manganese leaching amount, superior high-temperature cycle performance, and higher compression density of the anode sheet.

[0234] In some embodiments, when calculated based on the total weight of the first manganese iron lithium salt particles, the carbon content of the first manganese iron lithium salt particles is Cx1 weight%, where 1.2≤Cx1≤1.8.

[0235] In some embodiments, when calculated based on the total weight of the first lithium iron manganese phosphate particles, the carbon content of the lithium iron manganese phosphate particles is Cx1 weight%, where Cx1 is a range consisting of 1.2, 1.3, 1.4, 1.5, 1.6, 1.65, 1.7, 1.8 or any two of the above-mentioned Cx1s, or a value within this range.

[0236] In some embodiments, the carbon contained in the first manganese iron lithium salt particles is coated on the surface of the particles. In some embodiments, the carbon contained in the first manganese iron lithium salt particles is inserted into the particles. In some embodiments, a portion of the carbon contained in the first manganese iron lithium salt particles is coated on the surface of the particles, and a portion is inserted into the particles.

[0237] In some embodiments, the ratio z1 of the specific surface area of ​​the first manganese iron lithium salt particle to Cx1 satisfies 7 ≤ z1 ≤ 13. In some embodiments, the ratio z of the specific surface area of ​​the first manganese iron lithium salt particle to Cx1 satisfies 7.1 ≤ z1 ≤ 12.5. In some embodiments, the ratio z1 of the specific surface area of ​​the first manganese iron lithium salt particle to Cx is a range consisting of 7, 7.1, 7.3, 7.5, 7.6, 7.9, 8.3, 8.6, 8.8, 9.1, 9.3, 9.4, 12.5, 13 or any two of the above-mentioned z1s, or a value within this range.

[0238] In some embodiments, the specific surface area of ​​the lithium iron manganese phosphate particles is 5 m² 2 / g to 12m 2 / g is.

[0239] In some embodiments, the specific surface area (BET) of the lithium iron manganese phosphate particles is 5 m 2 / g, 5.5m 2 / g, 6m 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, 8.5m 2 / g, 9m 2 / g, 9.5m 2 / g, 10m 2 / g, 10.5m 2 / g, 11m 2 / g, 11.5m 2 / g, 12m 2 / g or a range consisting of any two BETs described above, or a value within this range.

[0240] In some embodiments, when calculated based on the total weight of the lithium manganese iron phosphate particles, the carbon content of the lithium manganese iron phosphate particles is Cx2 weight%, where 0.8≤Cx2≤2.0.

[0241] In some embodiments, when calculated based on the total weight of the lithium manganese iron phosphate particles, the carbon content of the lithium manganese iron phosphate particles is a range consisting of 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any two of the above-mentioned carbon contents, or a value within this range.

[0242] In some embodiments, the specific surface area of ​​the lithium iron manganese phosphate particles is 15 m² 2 / g to 30m 2 / g is.

[0243] In some embodiments, the specific surface area (BET) of the lithium iron manganese phosphate particles is 15 m 2 / g, 15.5m 2 / g, 16m 2 / g, 16.5m 2 / g, 17m 2 / g, 17.5m 2 / g, 18m 2 / g, 18.5m 2 / g, 19m 2 / g, 19.5m 2 / g, 20m 2 / g, 20.5m 2 / g, 21m 2 / g, 21.5m 2 / g, 22m 2 / g, 22.5m 2 / g, 23m 2 / g, 23.5m 2 / g, 24m 2 / g, 24.5m 2 / g, 25m 2 / g, 25.5m 2 / g, 26m 2 / g, 26.5m 2 / g, 27m 2 / g, 27.5m 2 / g, 28m 2 / g, 28.5m 2 / g, 29m 2 / g, 29.5m 2 / g, 30m 2 / g or a range consisting of any two BETs described above, or a value within this range.

[0244] In some embodiments, when calculated based on the total weight of the lithium manganese iron phosphate particles, the carbon content of the lithium manganese iron phosphate particles is Cx3 weight%, where 0.8≤Cx3≤2.0.

[0245] In some embodiments, when calculated based on the total weight of the lithium manganese iron phosphate particles, the carbon content of the lithium manganese iron phosphate particles is a range consisting of 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.15 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any two of the above-mentioned carbon contents, or a value within this range.

[0246] In some embodiments, the first lithium iron phosphate salt particles are

[0247] (a) The Dv10 of the first lithium iron phosphate salt particles is ≥0.2 μm;

[0248] (b) The Dv50 of the first lithium iron phosphate salt particles is 0.5 to 5 μm;

[0249] (c) The Dv90 of the first lithium iron phosphate salt particle is ≤10 μm;

[0250] (d) The Dv99 of the first lithium iron phosphate salt particle is ≤12 μm;

[0251] (e) The powder compression density of the first lithium iron phosphate salt particles under a pressure of 3 tons is ≥2.25 g / cm³ 3 thing;

[0252] (f) The powder resistivity of the first lithium iron phosphate particles is 60 Ω·cm, satisfying at least one of these conditions.

[0253] In this application, the term "Dv10" refers to the particle size corresponding to when the percentage of the volume-cumulative particle size distribution among the particles reaches 10%.

[0254] In this application, the term "Dv90" refers to the particle size corresponding to when the percentage of volume-cumulative particle size distribution among the particles reaches 90%.

[0255] In this application, the term "Dv99" refers to the particle size corresponding to when the percentage of volume-cumulative particle size distribution among the particles reaches 99%.

[0256] In this application, the term "powder compression density" refers to the density of a rolled material having a constant density and strength, formed by the powder moving and deforming during an external compression process, thereby filling larger voids, increasing the contact area between particles, generating atomic attraction, and enhancing mechanical connections between particles; the unit is g / cm³ 3 am.

[0257] In some embodiments, the Dv10 of the first lithium iron phosphate salt particle is <Dv50.

[0258] In some embodiments, the Dv90 of the first lithium iron phosphate salt particle is >Dv50.

[0259] In some embodiments, the Dv50 of the first lithium iron phosphate salt particles may be a range consisting of 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1700 nm, 1900 nm, 2000 nm, 2300 nm, 2500 nm, 2700 nm, 2900 nm, 3000 nm, 3200 nm, 3400 nm, 3600 nm, 3800 nm, 4000 nm, 4200 nm, 4400 nm, 4600 nm, 4800 nm, 5000 nm, or the Dv50 of any two of the products after secondary grinding described above, or a value within this range. there is.

[0260] The Dv10, Dv50, Dv90, and Dv99 of the lithium iron phosphate particles can be measured using methods and instruments known in the art. For example, with reference to GB / T19077.1-2016, they can be measured using a laser particle size analyzer (Malvern Master Size 3000).

[0261] At different pressures, the powder compression density of the first lithium iron phosphate particles can be measured using methods and instruments known in the art. For example, it can be measured using a compression density instrument by referring to GB / T 24533-2009. Specifically, a certain amount of lithium iron phosphate particles is placed in a special compression mold (based on mold diameter), which has a metal circular sheet above and below the hollow center of the mold. The lithium iron phosphate particles are placed between the metal circular sheets, a metal cylinder is placed on the top, the mold is placed in a compression density instrument, and different pressures (e.g., 3T) are set. The thickness of the lithium iron phosphate particles can be read from the instrument at different pressures. The powder compression density of the lithium iron phosphate particles is given by ρ=m / v, where v=(S×H), m is the mass of the lithium iron phosphate particles, S is the bottom area of ​​the mold, and H is the thickness of the lithium iron phosphate particles after compression.

[0262] The powder resistivity of the first lithium iron phosphate salt particles can be measured using methods and instruments known in the art. For example, it can be measured using a powder resistivity instrument (Suzhou Lattice, ST2722 type) with reference to GB / T 33822-2017. Specifically, a certain amount of lithium iron phosphate salt particles (e.g., 1 g) is weighed and added to the supply chamber of the powder resistivity instrument, and a pressure of 8 MPa is applied to test the forward resistivity and reverse resistivity of the lithium iron phosphate salt particles, respectively, and the average value of both is used as the powder resistivity of the lithium iron phosphate salt particles.

[0263] By ensuring that the first lithium iron phosphate salt particle satisfies at least one of (a) to (f), the first lithium iron phosphate salt particle can be made to more effectively realize the technical effects of the present application.

[0264] In some embodiments, the first lithium iron phosphate salt particles are mainly

[0265] A raw material is provided containing at least a lithium source, an iron source, a phosphorus, a selective carbon film-forming agent, a selective carbon source, and a selective modifier, and is obtained by a manufacturing method that performs at least two sintering steps, wherein,

[0266] The primary sintering temperature is 500℃ to 760℃, and optionally 550℃ to 720℃;

[0267] The secondary sintering temperature is 700°C to 800°C, and optionally 720°C to 780°C.

[0268] In some embodiments, the primary sintering temperature may be a range consisting of 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, 650°C, 680°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, or any two primary sintering temperatures described above, or a value within this range; the secondary sintering temperature may be a range consisting of 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any two secondary sintering temperatures described above, or a value within this range.

[0269] In some embodiments, the heating rate of the first sintering and the second sintering is independently 2°C / min to 20°C / min.

[0270] In some embodiments, the heating rate of the first sintering and the second sintering is independently 2°C / min, 5°C / min, 7°C / min, 10°C / min, 13°C / min, 15°C / min, 17°C / min, or 20°C / min.

[0271] In some embodiments, the isothermal sintering time for the first sintering is 1 hour to 6 hours. In some embodiments, the isothermal sintering time for the first sintering may be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or 6 hours.

[0272] In some embodiments, the isothermal sintering time for the secondary sintering is 2 hours to 12 hours. In some embodiments, the isothermal sintering time for the secondary sintering may be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours.

[0273] Compared to traditional manufacturing methods that utilize high temperatures to achieve particle growth, the first lithium iron phosphate particles of the embodiments of the present application are sintered twice, and controlling the sintering temperature twice is advantageous for producing the first lithium iron phosphate particles having the first average particle size and specific surface area of ​​the present application. Additionally, controlling the heating rate, sintering temperature, and isothermal sintering time of the first and / or second sintering helps reduce side reactions, thereby better producing the first lithium iron phosphate particles of the present application. Furthermore, in conventional high-temperature sintering processes, the carbon coating layer on the particle surface is prone to cracking, which reduces the integrity of the carbon coating. In the present application, large particles are synthesized at low temperatures, which is advantageous for improving the consistency and uniformity of the surface carbon coating.

[0274] In some embodiments, the first lithium iron phosphate salt particles are mainly

[0275] A raw material is provided containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film-forming agent, and a modifier, and is obtained by a manufacturing method that performs at least two sintering steps, wherein,

[0276] The carbon content of the material after the first sintering is 0.01 wt% to 0.79 wt%, and optionally 0.05 wt% to 0.4 wt%;

[0277] The carbon content of the material after secondary sintering is 0.8 wt% to 2.0 wt%, and optionally 1.0 wt% to 1.6 wt%.

[0278] In some embodiments, the carbon content of the material after the first sintering may be a range consisting of 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.20 wt%, 0.25 wt%, 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt%, 0.50 wt%, 0.55 wt%, 0.60 wt%, 0.65 wt%, 0.70 wt%, 0.75 wt%, 0.79 wt%, or any two of the above-mentioned carbon contents, or a value within this range; The carbon content of the material after the second sintering may be a range consisting of 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, or any two of the above-mentioned carbon contents, or a value within this range.

[0279] In the manufacturing method of the embodiment of the present invention, a carbon source is added before the first sintering to effectively reduce trivalent iron in the raw material, thereby improving the purity and stability of the product. Additionally, by controlling the first sintering temperature and the carbon content of the intermediate after the first sintering within the aforementioned ranges, it helps to increase the primary particle size of the lithium iron phosphate particle precursor obtained after the first sintering. Specifically, a lower carbon content during the first sintering process is advantageous for reducing the blocking effect of the carbon layer on the growth process of the lithium iron phosphate particles and is advantageous for crystal growth of the lithium iron phosphate particle precursor at a lower temperature. At the same time, this is advantageous for the solid-state diffusion reaction between the modifier that can be added and the lithium iron phosphate material, which is advantageous for realizing a higher concentration of metal ion modification. By controlling the secondary sintering temperature and the carbon content of the material after sintering within the aforementioned range, the surface of the first lithium iron phosphate salt particles is better coated with carbon to help form a uniform and dense carbon coating layer, which is advantageous for improving the surface conductivity of the first lithium iron phosphate salt particles and improving their kinetic performance and capacity per gram.

[0280] In some embodiments, a raw material containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a modifier, and a carbon film-forming agent is provided, and at least two sintering steps are performed.

[0281] In some embodiments, based on the atomic moles of each element, the mixing ratio of lithium source, iron source, and phosphorus satisfies Fe:P=(0.96-0.985):1 and Li:Fe=(1.0-0.95):1.1.

[0282] In some embodiments, based on the atomic moles of each element, the mixing ratio of iron source to phosphorus satisfies Fe:P=0.96:1, Fe:P=0.965:1, Fe:P=0.97:1, Fe:P=0.975:1, Fe:P=0.98:1, or Fe:P=0.985:1.

[0283] In some embodiments, based on the atomic moles of each element, the mixing ratio of the lithium source and the iron source satisfies Li:Fe=1.0:1.1, Li:Fe=0.99:1.1, Li:Fe=0.98:1.1, Li:Fe=0.97:1.1, Li:Fe=0.96:1.1, or Li:Fe=0.95:1.1.

[0284] In some embodiments, the weight ratio of the carbon source to the carbon film agent is (9 to 0.25):1. In some embodiments, the weight ratio of the carbon source to the carbon film agent may optionally be 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 0.8:1, 0.5:1, or 0.25:1.

[0285] In some embodiments, the lithium source is a compound containing lithium. In some embodiments, the lithium source comprises at least one of lithium dihydrogen phosphate, lithium oxalate, lithium carbonate, lithium oxide, lithium hydroxide, and lithium acetate. In some embodiments, the lithium source comprises lithium carbonate.

[0286] In some embodiments, the iron source is a compound containing iron. In some embodiments, the iron source comprises at least one of iron hydroxide, ferrous chloride, ferric oxide, iron phosphate, ferrous pyrophosphate, ferrous oxalate, iron powder, ferric nitrate, triiron tetroxide, and iron hydroxide. In some embodiments, the iron source comprises ferric oxide.

[0287] In some embodiments, the phosphorus is a compound containing phosphorus. In some embodiments, the phosphorus comprises at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. In some embodiments, the phosphorus comprises phosphoric acid.

[0288] In some embodiments, the carbon source comprises at least one of citric acid, glucose, sucrose, starch, fructose, and lactose. In some embodiments, the carbon source comprises glucose.

[0289] In some embodiments, the carbon film-forming agent comprises at least one of polyethylene glycol, polyaniline, polyacrylonitrile, polyvinylpyrrolidone, and polyvinyl alcohol. In some embodiments, the carbon film-forming agent comprises polyaniline.

[0290] In some embodiments, the modifier comprises at least one of titanium dioxide, vanadium pentoxide, n-butyl titanate, ammonium metavanadate, niobium ethanolate, niobium oxalate, niobium pentoxide, magnesium hydroxide, and magnesium nitrate. In some embodiments, the modifier comprises titanium dioxide.

[0291] By using raw materials in the above-described ratio, it is advantageous to form the first lithium iron phosphate salt particles of the present application.

[0292] In some embodiments, the method for manufacturing the first lithium iron phosphate salt particles

[0293] The method includes the step of performing a first grinding after performing the first sintering above, and performing a second grinding after performing the second sintering above, wherein,

[0294] The Dv50 of the product after the first grinding is 300 nm to 1200 nm, and optionally 400 nm to 1100 nm;

[0295] The Dv50 of the product after the second grinding is 500 nm to 5000 nm, and optionally 700 nm to 2500 nm.

[0296] In this application, the term "Dv50" refers to the particle size corresponding to when the percentage of volume-cumulative particle size distribution among the particles reaches 50%.

[0297] In some embodiments, the Dv50 of the product after primary grinding may be a range consisting of 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, or any two of the Dv50s of the products after primary grinding described above, or a value within this range.

[0298] In some embodiments, the Dv50 of the product after secondary grinding may be a range consisting of 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1700nm, 1900nm, 2000nm, 2300nm, 2500nm, 2700nm, 2900nm, 3000nm, 3200nm, 3400nm, 3600nm, 3800nm, 4000nm, 4200nm, 4400nm, 4600nm, 4800nm, 5000nm, or any two of the above-mentioned Dv50s of the products after secondary grinding, or a value within this range.

[0299] In some embodiments, the crushing includes one or more of mechanical crushing, grinding, sand milling, and airflow crushing.

[0300] The Dv50 of the particles can be measured using methods and instruments commonly used in the field. For example, referring to GB / T19077.1-2016, it can be measured using a laser particle size analyzer (Malvern Master Size 3000).

[0301] Controlling the Dv50 of the product after the first grinding within the aforementioned range is advantageous for reducing the growth-blocking effect of the added carbon source and the modifying element that may be added to the first lithium iron phosphate particle precursor crystal, and helps in producing a lithium iron phosphate particle precursor of micrometers. By controlling the Dv50 value of the product after the second grinding within the aforementioned range, the present application helps in obtaining a first lithium iron phosphate particle having a first average particle size.

[0302] According to a second aspect of the present application, an electric device comprising a secondary battery according to a first aspect of the present application is provided.

[0303] In addition, the secondary battery and electric device according to the present application will be described below with appropriate reference to the drawings.

[0304] In one embodiment of the present application, a secondary battery is provided.

[0305] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process, active ions are reciprocally inserted into and removed from the positive and negative electrode sheets. The electrolyte serves to conduct ions between the positive and negative electrode sheets. The separator is installed between the positive and negative electrode sheets and primarily serves to prevent short circuits between them, while simultaneously allowing ions to pass through.

[0306] [Positive Sheet]

[0307] The anode sheet includes an anode current collector and an anode film layer installed on at least one surface of the anode current collector.

[0308] As an example, the positive current collector has two opposing surfaces in its own thickness direction, and the positive film layer is disposed on either or both of the two opposing surfaces of the positive current collector.

[0309] In some embodiments, the positive current collector may use a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0310] In some embodiments, the anode film layer optionally further comprises an adhesive. As an example, the adhesive may comprise at least one of polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluoroacrylate resin.

[0311] In some embodiments, the anode film layer optionally further comprises a conductive agent. As an example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers.

[0312] In some embodiments, an anode sheet can be manufactured by the following method: the above-mentioned components used to manufacture an anode sheet, such as an anode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form an anode slurry; the anode slurry is coated onto an anode current collector, and an anode sheet can be obtained through processes such as drying and cold pressing.

[0313] [Cathode Sheet]

[0314] The cathode sheet comprises a cathode current collector and a cathode film layer installed on at least one surface of the cathode current collector, and the cathode film layer comprises a cathode active material.

[0315] As an example, the cathode current collector has two opposing surfaces in its own thickness direction, and the cathode film layer is installed on either or both of the two opposing surfaces of the cathode current collector.

[0316] In some embodiments, the negative current collector may use a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0317] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of solid silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of solid tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. Such negative electrode active materials may be used individually or in combination of two or more types.

[0318] In some embodiments, the cathode film layer optionally further comprises a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0319] In some embodiments, the cathode film layer optionally further comprises a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers.

[0320] In some embodiments, the cathode film layer optionally further comprises other auxiliary agents such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0321] In some embodiments, a cathode sheet can be manufactured through the following method. The above-described components used to manufacture a cathode sheet, such as a cathode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a cathode slurry, and the cathode slurry is applied to a cathode current collector and a cathode sheet can be obtained through processes such as drying and cold pressing.

[0322] [Electrolyte]

[0323] The electrolyte serves to conduct ions between the anode sheet and the cathode sheet. The present application does not have specific limitations on the type of electrolyte and may be selected as needed. For example, the electrolyte may be in a liquid state, a gel state, or a completely solid state.

[0324] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0325] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis(trifluoro)methanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0326] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethylmethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, tetramethylene sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0327] In some embodiments, the electrolyte optionally further comprises additives. For example, the additives may include a negative electrode film forming additive and a positive electrode film forming additive, and may further include additives that improve specific performance of the battery, such as an additive that improves the overcharge performance of the battery, or an additive that improves the high or low temperature performance of the battery.

[0328] [Separator]

[0329] In some embodiments, the secondary battery further comprises a separator. The present application does not have any particular limitations on the type of separator and any known porous structure separator with excellent chemical and mechanical stability may be used.

[0330] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multilayer composite thin film, and is not particularly limited. If the separator is a multilayer composite thin film, the material of each layer may be the same or different, and is not particularly limited.

[0331] In some embodiments, the anode sheet, cathode sheet, and separator can be manufactured into an electrode assembly through a winding process or a lamination process.

[0332] In some embodiments, the secondary battery may include an outer casing. This outer casing may be used to seal and package the electrode assembly and electrolyte described above.

[0333] In some embodiments, the exterior member of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior member of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be a plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate, for example.

[0334] In the present application, the shape of the secondary battery is not particularly limited and may be cylindrical, square, or any other shape. For example, FIG. 1 is a secondary battery (5) with a square structure as an example.

[0335] In some embodiments, referring to FIG. 2, the outer member may include a case (51) and a cover plate (53). Here, the case (51) may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity. The case (51) has an opening communicating with the receiving cavity, and the cover plate (53) may be installed as a cover over the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly (52) through a winding process or a lamination process. The electrode assembly (52) is sealed and packaged within the receiving chamber. The electrolyte is infiltrated into the electrode assembly (52). The number of electrode assemblies (52) included in the secondary battery (5) may be one or more, and a person skilled in the art may select according to actual demand.

[0336] In some embodiments, the secondary battery may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or multiple, and the specific number may be selected according to the application and capacity of the battery module by a person with ordinary knowledge of the art.

[0337] FIG. 3 is a battery module (4) as an example. Referring to FIG. 3, in the battery module (4), a plurality of secondary batteries (5) may be installed by being arranged sequentially along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary way. Additionally, the plurality of secondary batteries (5) may be secured through fastening members.

[0338] Optionally, the battery module (4) may further include a case having a receiving space for accommodating a plurality of secondary batteries (5).

[0339] In some embodiments, the above-described battery module may be assembled into a battery pack, and the number of battery modules included in the battery pack may be one or multiple, and the specific number may be selected by a person with ordinary knowledge in the art according to the application and capacity of the battery pack.

[0340] FIGS. 4 and FIGS. 5 are examples of a battery pack (1). Referring to FIGS. 4 and FIGS. 5, the battery pack (1) may include a battery box and a plurality of battery modules (4) installed in the battery box. The battery box includes an upper box body (2) and a lower box body (3), and the upper box body (2) may be covered and installed on the lower box body (3) to form a closed space used to accommodate the battery modules (4). The plurality of battery modules (4) may be arranged within the battery box in any manner.

[0341] In addition, the present application further provides an electric device, said electric device comprising at least one of a secondary battery, a battery module, or a battery pack provided in the present application. The secondary battery, battery module, or battery pack may be used as a power source for said electric device and may also be used as an energy storage unit for said electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0342] As for the above electrical device, a secondary battery, a battery module, or a battery pack can be selected depending on the usage demand.

[0343] FIG. 6 is an electric device as an example. This electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the requirements of this electric device for high power output and high energy density of a secondary battery, a battery pack or a battery module may be used.

[0344] Another example of such a device could be a mobile phone, tablet, or laptop. These devices generally require lightweight design and can use secondary batteries as a power source.

[0345] Examples

[0346] The following describes embodiments of the present application. The embodiments described below are illustrative and are intended only for interpreting the present application and should not be understood as a limitation thereof. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in literature of the art or in the product descriptions. Where the manufacturer of the reagents or equipment used is not specified, they are all general products available on the market.

[0347] Example 1

[0348] (1) Preparation of anode slurry:

[0349] Preparation of lithium iron phosphate particles:

[0350] Lithium carbonate, diiron trioxide, phosphoric acid, glucose, titanium dioxide (based on the total weight of the lithium iron phosphate salt particles, the amount of titanium dioxide added satisfies a titanium content of 5,000 ppm in the lithium iron phosphate salt particles obtained by preparation), and polyaniline were each weighed. Here, the weight ratios of the Li, Fe, and P elements satisfied Fe:P=0.968:1 and Li:Fe=1:0.98, and the weight ratio of glucose to polyaniline satisfied glucose:polyaniline=1:2. The amount of glucose added satisfied the requirement that the carbon content accounted for 0.15% of the weight of the lithium iron phosphate salt precursor after the completion of the first sintering. Water was added to the above-described materials to obtain a mixture slurry.

[0351] The mixture slurry was uniformly mixed using a ball mill and ground using a sand mill to obtain a slurry with a solid content of 38% and a Dv50 of 0.40 μm, and spray-dried (the negative pressure of the high-speed spray dryer was -650 to -200 Pa, the inlet temperature was 300°C to 360°C, and the outlet temperature was 100°C to 140°C). The dried reaction product was charged into a sintering furnace to perform primary sintering, with the heating rate controlled at 5°C / min, the holding temperature at 650°C, and the holding time at 4 hours. After cooling the material, it was ground using a mechanical mill to obtain a powder.

[0352] Glucose as a carbon source and polyaniline as a carbon film-forming agent were added to the obtained powder, and then mixed with water to obtain a material with a solid content of 40%. Here, the amounts of glucose and polyaniline added satisfied the requirement that the carbon content of the product after secondary sintering be 1.2% (based on the total weight of the lithium iron phosphate salt particles), and the weight ratio of glucose to polyaniline satisfied glucose:polyaniline = 1:2. A slurry was obtained by processing using a ball mill and a sand mill, and the Dv50 of the insoluble matter in the slurry was 550 nm. Spray drying was performed (the negative pressure of the high-speed spray dryer was -650 to -200 Pa, the inlet temperature was 300°C to 360°C, and the outlet temperature was 100°C to 140°C). The dried reactant was loaded into a sintering furnace and subjected to secondary low-temperature sintering (controlled heating rate to 5℃ / min, sintering temperature to 750℃, and sintering time to 4 hours). After the material was cooled, it was ground twice to obtain a primary average particle size of 870 nm, and after re-magnification, lithium iron phosphate particles were obtained, with a carbon content of 1.2% and a Ti element content of 5000 ppm in the lithium iron phosphate particles.

[0353] A cathode active material was obtained by mixing lithium iron phosphate particles (related parameters as shown in Table 1) and lithium manganese iron phosphate particles (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-001-001, related parameters as shown in Table 2) according to the area ratio listed in Table 4, and the above-described mixed cathode active material, conductive carbon black, adhesive polyvinylidene fluoride, and dispersant PVP were mixed in a weight percentage of 93:4.0:2.5:0.5, N-methylpyrrolidone was added, and after sufficient mixing, stirring, and dispersion, a cathode slurry was prepared.

[0354] (2) Manufacture of anode sheet:

[0355] The viscosity of the above-described slurry, which has been uniformly mixed and stirred, is adjusted to 8,000 to 20,000 mPa·s until no layer separation of the slurry occurs, and the slurry is applied to the surface of a substrate Al foil at a rate of 420 mg / 1,540 mm using a double-sided dual-control coating machine. 2 After coating, the anode sheet was finally obtained through drying, cold pressing, slitting, and sheet forming.

[0356] (3) Manufacture of the cathode sheet:

[0357] Synthetic graphite, conductive agent carbon black, adhesive styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) are uniformly mixed in a weight percentage of 95:1.0:2.0:2.0, deionized water is added, and after stirring and dispersion, a cathode slurry is obtained, and the cathode slurry is 211 mg / 1540 mm 2 A cathode sheet was obtained by coating a copper foil substrate, drying, cold pressing, cutting, and sheet manufacturing.

[0358] (4) Manufacturing of the battery:

[0359] A positive electrode sheet, a separator, and a negative electrode sheet are stacked in sequence, and the separator must be capable of separating the negative and positive electrodes. The layers are then wound to obtain a bare cell, the bare cell is placed into an outer casing, an electrolyte is injected, and a final lithium-ion battery is obtained through processes such as packaging, formation, and evacuation.

[0360] Example 2

[0361] Example 2 differs from Example 1 mainly in that the primary average particle size of the lithium manganese iron phosphate particles is 210 nm and the specific surface area is 12 m². 2 / g, the carbon content is 1.4 wt%, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is CPP-001-002 (Guangdong Bangpu Cycle Technology Co., Ltd.).

[0362] Example 3

[0363] Example 3 differs from Example 2 mainly in that the primary average particle size of the lithium manganese iron phosphate particles is 120 nm and the specific surface area is 15 m² 2 / g, the carbon content is 1.65 wt%, and this lithium iron manganese phosphate particle was purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is SH-LMFP-1.

[0364] Example 4

[0365] Example 4 differs from Example 2 mainly in that the primary average particle size of the lithium manganese iron phosphate particles is 600 nm and the specific surface area is 10 m² 2 / g, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is SH-LMFP-2.

[0366] Example 5

[0367] Example 5 differs from Example 2 mainly in that the primary average particle size of the lithium iron phosphate particles is 250 nm and the specific surface area is 9.5 m². 2 It is / g.

[0368] Example 6

[0369] Example 6 differs from Example 2 mainly in that the primary average particle size of the lithium iron phosphate particles is 300 nm and the specific surface area is 7.5 m². 2 It is / g.

[0370] Example 7

[0371] Compared to Example 2, Example 7 differs mainly in that the primary average particle size of the lithium iron phosphate particles is 4000 nm and the specific surface area is 4.5 m². 2 It is / g.

[0372] Example 8

[0373] Example 8 differs from Example 2 mainly in that the primary average particle size of the lithium iron manganese phosphate particles is 480 nm and the specific surface area is 11 m² 2 / g, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is CPP-001-003.

[0374] Example 9

[0375] Example 9 differs from Example 2 mainly in that the primary average particle size of the lithium iron phosphate particles is 3000 nm and the specific surface area is 5 m² 2 It is / g.

[0376] Example 10

[0377] Example 10 differs from Example 2 mainly in that the primary average particle size of the lithium iron phosphate particles is 3500 nm and the specific surface area is 4.6 m². 2 It is / g.

[0378] Example 11

[0379] Example 11 differs from Example 2 mainly in that the primary average particle size of the lithium iron phosphate particles is 500 nm and the specific surface area is 7 m² 2 It is / g.

[0380] Example 12

[0381] Example 12 differs from Example 2 mainly in that the specific surface area of ​​the lithium manganese iron phosphate particles is 17 m² 2 / g, the carbon content is 1.8 wt%, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is CPP-001-005.

[0382] Example 13

[0383] Example 13 differs from Example 2 mainly in that the specific surface area of ​​the lithium manganese iron phosphate particles is 10 m² 2 / g, the carbon content is 1.2 wt%, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is CPP-001-009.

[0384] Example 14

[0385] Example 14 differs from Example 2 mainly in that the specific surface area of ​​the lithium iron phosphate particles is 5.5 m² 2 It is / g and has a carbon content of 1.15 wt%.

[0386] Example 15

[0387] Example 15 differs from Example 2 mainly in that the specific surface area of ​​the lithium iron phosphate particles is 5 m² 2 It is / g and has a carbon content of 1.2 wt%.

[0388] Example 16

[0389] Example 16 differs from Example 2 mainly in that the titanium content of the lithium iron phosphate particles is 2500 ppm.

[0390] Example 17

[0391] The difference between Example 17 and Example 2 is mainly that the titanium content of the lithium iron phosphate particles is 6000 ppm.

[0392] Example 18

[0393] Example 18 differs from Example 2 mainly in that titanium dioxide was replaced with vanadium pentoxide and the specific surface area of ​​the lithium iron phosphate particles was 8 m² 2 It is / g.

[0394] Example 19

[0395] The difference between Example 19 and Example 2 is that titanium dioxide was mainly replaced with niobium pentoxide.

[0396] Example 20

[0397] Example 20 differs from Example 2 mainly in that the specific surface area of ​​the lithium iron phosphate particles is 3 m² 2 It is / g, and the carbon content is 0.8 wt%.

[0398] Example 21

[0399] Example 21 differs from Example 2 mainly in that the specific surface area of ​​the lithium iron phosphate particles is 12 m² 2 It is / g and has a carbon content of 1.4% by weight.

[0400] Example 22

[0401] Example 22 differs from Example 2 mainly in that the primary average particle size of the lithium manganese iron phosphate particles is 500 nm and the specific surface area is 10.5 m². 2 / g, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is CPP-001-013.

[0402] Example 23

[0403] Example 23 differs from Example 2 mainly in that the primary average particle size of the lithium manganese iron phosphate particles is 140 nm and the specific surface area is 20 m² 2 / g, and these lithium manganese iron phosphate particles were purchased from Guangdong Bangpu Cycle Technology Co., Ltd., and the product number is CPP-001-026.

[0404] Example 24

[0405] Example 24 differs from Example 2 mainly in that the area ratio of the lithium iron manganese phosphate particles is 70% and the area ratio of the lithium iron phosphate particles is 30%.

[0406] Example 25

[0407] Example 25 differs from Example 2 mainly in that the area ratio of the lithium iron manganese phosphate particles is 98% and the area ratio of the lithium iron phosphate particles is 2%.

[0408] Example 26

[0409] Example 26 differs from Example 2 mainly in that the titanium content of the lithium iron phosphate particles is 1000 ppm.

[0410] Example 27

[0411] The difference between Example 27 and Example 2 is mainly that the titanium content of the lithium iron phosphate particles is 10,000 ppm.

[0412] Example 28

[0413] (1) Preparation of anode slurry:

[0414] The source / manufacturing method of the lithium manganese phosphate particles and the lithium iron phosphate particles was the same as in Example 2.

[0415] The lithium iron phosphate particles were purchased from XTC New Energy Materials (Xiamen) Co., Ltd., with product number CPF-014-001, and the relevant parameters are as shown in Table 3.

[0416] A cathode active material was obtained by mixing lithium manganese phosphate particles, lithium iron phosphate particles, and lithium iron phosphate particles according to the area ratios listed in Table 4, and the above-described mixed cathode active material, conductive carbon black, adhesive polyvinylidene fluoride, and dispersant PVP were mixed in a weight percentage of 93:4.0:2.5:0.5, N-methylpyrrolidone was added, and after sufficient mixing, stirring, and dispersion, a cathode slurry was prepared.

[0417] (2) Manufacture of anode sheet:

[0418] It was exactly the same as Example 2.

[0419] (3) Manufacture of the cathode sheet:

[0420] It was exactly the same as Example 2.

[0421] (4) Manufacturing of the battery:

[0422] It was exactly the same as Example 2.

[0423] Example 29

[0424] The difference between Example 29 and Example 28 is that the area ratio of the lithium iron manganese phosphate particles is 70%, the area ratio of the lithium iron phosphate particles is 25%, and the area ratio of the lithium iron phosphate particles is 5%.

[0425] Example 30

[0426] The difference between Example 30 and Example 28 is that the area ratio of the lithium iron manganese phosphate particles is mainly 65%, the area ratio of the lithium iron phosphate particles is 25%, and the area ratio of the lithium iron phosphate particles is 10%.

[0427] Example 31

[0428] The difference between Example 31 and Example 28 is that the area ratio of the lithium iron manganese phosphate particles is mainly 74%, the area ratio of the lithium iron phosphate particles is 25%, and the area ratio of the lithium iron phosphate particles is 1%.

[0429] Example 32

[0430] Example 32 differs from Example 28 mainly in that the primary average particle size of the lithium iron phosphate particles is 30 nm and the specific surface area is 14 m² 2 / g, and these lithium iron phosphate particles were purchased from XTC New Energy Materials (Xiamen) Co., Ltd., and the product number is XW-LFP-1.

[0431] Example 33

[0432] Example 33 differs from Example 28 mainly in that the primary average particle size of the lithium iron phosphate particles is 200 nm and the specific surface area is 11 m² 2 / g, and these lithium iron phosphate particles were purchased from XTC New Energy Materials (Xiamen) Co., Ltd., and the product number is XW-LFP-2.

[0433] Example 34

[0434] Example 34 is different from Example 28 in that the major aspect ratio of the lithium iron phosphate particles is 1.3, and the ratio of the (020) crystal plane diffraction peak intensity to the (211) crystal plane diffraction peak intensity is W=1.03, and these lithium iron phosphate particles were purchased from XTC New Energy Materials (Xiamen) Co., Ltd. and the product number is XW-LFP-3.

[0435] Example 35

[0436] Example 35 is different from Example 28 in that the major aspect ratio of the lithium iron phosphate particles is 1.3, and the ratio of the (020) crystal plane diffraction peak intensity to the (211) crystal plane diffraction peak intensity of the lithium iron phosphate particles is W=1.08, and these lithium iron phosphate particles were purchased from XTC New Energy Materials (Xiamen) Co., Ltd. and the product number is XW-LFP-4.

[0437] Example 36

[0438] Example 36 differs from Example 28 in that the primary lithium iron phosphate particles were replaced with secondary lithium iron phosphate particles (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-010-01; related parameters as shown in Table 2) and the secondary lithium iron phosphate particles were replaced with tertiary lithium iron phosphate particles (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-100-05; related parameters as shown in Table 3); the area ratio of the primary lithium iron phosphate particles is 75%, the area ratio of the secondary lithium iron phosphate particles is 23%, and the area ratio of the tertiary lithium iron phosphate particles is 2%.

[0439] Example 37

[0440] Example 37 differs from Example 36 mainly in that the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is 0.67 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-010-03; relevant parameters are as shown in Table 2).

[0441] Example 38

[0442] The difference between Example 38 and Example 36 is mainly that the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is 0.43 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-010-07; related parameters are as shown in Table 2) and the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is 1.5 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-100-06; related parameters are as shown in Table 3).

[0443] Example 39

[0444] Example 39 differs from Example 38 mainly in that the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is 0.67 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-100-067; relevant parameters are as shown in Table 3).

[0445] Example 40

[0446] The difference in Example 40 compared to Example 2 is that the lithium iron phosphate first was replaced with lithium iron phosphate particles (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-010-01; related parameters are as shown in Table 2).

[0447] Example 41

[0448] Example 41 differs from Example 40 mainly in that the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is 0.43 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-010-043; related parameters are as shown in Table 2).

[0449] Comparative Example 1

[0450] The difference between Comparative Example 1 and Example 2 is that Comparative Example 1 mainly does not contain lithium iron phosphate particles.

[0451] Comparative Example 2

[0452] Comparative Example 2 differs from Example 28 mainly in that it does not contain lithium iron phosphate particles.

[0453] Comparative Example 3

[0454] Comparative Example 3 differs from Example 40 mainly in that the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is 4 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-010-40; related parameters are as shown in Table 2).

[0455] Comparative Example 4

[0456] The difference between Comparative Example 4 and Example 40 is that the lithium manganese iron phosphate diphosphate was replaced with lithium manganese iron phosphate particles having a Mn / Fe molar ratio of 4 (purchased from Guangdong Bangpu Cycle Technology Co., Ltd., product number CPP-100-40; related parameters are as shown in Table 3).

[0457] C. Battery Performance Test

[0458] 1) Primary average particle size

[0459] Lithium manganese iron phosphate particles:

[0460] The electrode sheet was cut perpendicular to the face of the electrode sheet using an argon ion beam to expose the cross-section, the cross-section was photographed using a scanning electron microscope, and the longest axis of the lithium manganese iron phosphate particles was statistically analyzed using the long axis statistics method. Here, "primary average particle size" refers to the average value of the primary particle sizes of all particles, and the value is equal to the value obtained by dividing the total particle size value by the total number of particles. Here, the primary particle size refers to the longest distance connecting two points at the edge in the cross-sectional image. Specifically, the total number of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm in the scanning electron microscope image can be statistically analyzed, and the sum of the primary particle sizes of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm can be statistically analyzed, and the primary average particle size of the lithium manganese iron phosphate particles = primary particle size of the total lithium manganese iron phosphate particles / total number of lithium manganese iron phosphate particles. Here, in the particle size statistics process described above, particles with a first average particle size of 10 nm or less are excluded from the statistical range.

[0461] Lithium iron phosphate particles:

[0462] The electrode sheet was cut perpendicular to the face of the electrode sheet using an argon ion beam to expose the cross-section, the cross-section was photographed using a scanning electron microscope, and the longest axis of the lithium iron phosphate particles was statistically analyzed using the long axis statistics method. Here, "primary average particle size" refers to the average value of the primary particle sizes of all particles, and the value is equal to the value obtained by dividing the total particle size value by the total number of particles. Here, the primary particle size refers to the longest distance connecting two points at the edge in the cross-sectional image. Specifically, the total number of lithium iron phosphate particles with a primary particle size greater than 80 nm in the scanning electron microscope image can be statistically analyzed, and the sum of the primary particle sizes of lithium iron phosphate particles with a primary particle size greater than 80 nm can be statistically analyzed, and the primary average particle size of the lithium iron phosphate particles = primary particle size of the total lithium iron phosphate particles / total number of lithium iron phosphate particles. Here, in the particle size statistics process described above, particles with a first average particle size of 80 nm or less are excluded from the statistical range.

[0463] Lithium manganese iron phosphate particles:

[0464] The electrode sheet was cut perpendicular to the face of the electrode sheet using an argon ion beam to expose the cross-section, the cross-section was photographed using a scanning electron microscope, and the longest axis of the lithium manganese iron phosphate particles was statistically analyzed using the long axis statistics method. Here, "primary average particle size" refers to the average value of the primary particle sizes of all particles, and the value is equal to the value obtained by dividing the total particle size value by the total number of particles. Here, the primary particle size refers to the longest distance connecting two points at the edge in the cross-sectional image. Specifically, the total number of lithium manganese iron phosphate particles with a primary particle size greater than 80 nm in the scanning electron microscope image can be statistically analyzed, and the sum of the primary particle sizes of lithium manganese iron phosphate particles with a primary particle size greater than 80 nm can be statistically analyzed, and the primary average particle size of the lithium manganese iron phosphate particles = primary particle size of the total lithium manganese iron phosphate particles / total number of lithium manganese iron phosphate particles. Here, in the particle size statistics process described above, particles with a first average particle size of 80 nm or less are excluded from the statistical range.

[0465] Lithium iron phosphate particles:

[0466] The electrode sheet was cut perpendicular to the face of the electrode sheet using an argon ion beam to expose the cross-section, the cross-section was photographed using a scanning electron microscope, and the longest axis of the lithium iron phosphate particles was statistically analyzed using the long axis statistics method. Here, "primary average particle size" refers to the average value of the primary particle sizes of all particles, and the value is equal to the value obtained by dividing the total particle size value by the total number of particles. Here, the primary particle size refers to the longest distance connecting two points at the edge in the cross-sectional image. Specifically, the total number of lithium iron phosphate particles with a primary particle size greater than 10 nm in the scanning electron microscope image can be statistically analyzed, and the sum of the primary particle sizes of lithium iron phosphate particles with a primary particle size greater than 10 nm can be statistically analyzed, and the primary average particle size of the lithium iron phosphate particles = primary particle size of the total lithium iron phosphate particles / total number of lithium iron phosphate particles. Here, in the particle size statistics process described above, particles with a first average particle size of 10 nm or less are excluded from the statistical range.

[0467] Lithium manganese iron phosphate particles:

[0468] The electrode sheet was cut perpendicular to the face of the electrode sheet using an argon ion beam to expose the cross-section, the cross-section was photographed using a scanning electron microscope, and the longest axis of the lithium manganese iron phosphate particles was statistically analyzed using the long axis statistics method. Here, "primary average particle size" refers to the average value of the primary particle sizes of all particles, and the value is equal to the value obtained by dividing the total particle size value by the total number of particles. Here, the primary particle size refers to the longest distance connecting two points at the edge in the cross-sectional image. Specifically, the total number of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm in the scanning electron microscope image can be statistically analyzed, and the sum of the primary particle sizes of lithium manganese iron phosphate particles with a primary particle size greater than 10 nm can be statistically analyzed, and the primary average particle size of lithium manganese iron phosphate particles = primary particle size of total lithium manganese iron phosphate particles / total number of lithium manganese iron phosphate particles. Here, in the particle size statistics process described above, particles with a first average particle size of 10 nm or less are excluded from the statistical range.

[0469] 2) Dv50

[0470] Referring to GB / T19077.1-2016, the Dv50 value was measured using a laser particle size analyzer (Malvern Master Size 3000). In addition, the Dv10, Dv90, and Dv99 of the present application were measured in the same manner.

[0471] 3) Specific surface area

[0472] The specific surface area is tested by gas adsorption and according to the GB / T19587-2017 test standard, specifically as follows: lithium iron phosphate particles / lithium manganese iron phosphate particles are taken as a sample, the sample tube is immersed in liquid nitrogen at -196°C, and the amount of nitrogen adsorbed on the solid surface at different pressures is measured under relative pressures of 0.05 to 0.30, the amount of single molecular layer adsorption of the sample is determined according to the BET multilayer adsorption theory and formula, and the specific surface area of ​​the material is calculated.

[0473] 4) Carbon content

[0474] After burning lithium iron phosphate particles / lithium manganese iron phosphate particles using a high-frequency induction furnace, the carbon content was tested by infrared absorption, and the specific test procedure was in accordance with the standard GB / T 20123-2006 / ISO 15350:2000.

[0475] 5) Content of Q element (e.g., Ti element) in the lithium iron phosphate particles

[0476] The Q element content in the lithium iron phosphate particles was tested according to GB / T 33822-2017.

[0477] 6) Area ratio

[0478] The respective areas of the monolithic manganese iron phosphate lithium salt particles, monolithic iron phosphate lithium salt particles, distalic manganese iron phosphate lithium salt particles, distalic iron phosphate lithium salt particles, and trilithic manganese iron phosphate lithium salt particles were obtained by statistically analyzing cross-sectional scanning electron microscope images of the electrode sheet obtained with Avizo 3D software, and the corresponding area ratios were obtained by dividing each area by the total area.

[0479] 7) Ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity

[0480] The ratio of the diffraction peak intensity of the lithium iron phosphate particles was tested using X-rays, and the lithium iron phosphate particles were placed on an X-ray diffraction (Shimadz XRD-7000 model) test platform using a copper target X-ray diffraction, the scan start angle was set to 10°, the end angle to 90°, and the step length to 0.013, and then the test was started to obtain the diffraction pattern of the lithium iron phosphate particles within the diffraction angle range of 10° to 90°, and the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity was calculated according to the diffraction pattern.

[0481] 8) Janggyeongbi

[0482] The major-aspect ratio is the ratio of the major axis diameter to the minor axis diameter of a primary particle, with the major axis diameter set to a and the minor axis diameter to b, and the major-aspect ratio = a / b; this parameter is commonly used to describe the shape of the particle and can be used to measure its sphericity.

[0483] Test method: A cold-pressed electrode sheet was taken, and the sheet was cut perpendicular to the face of the electrode sheet using an Ar ion beam to expose the cross-section, and an image was obtained using a scanning electron microscope. Subsequently, the scanning electron microscope image of the electrode sheet cross-section was analyzed using image software to measure the major axis a and minor axis b of the particles, and their ratio, i.e., the major axis ratio of the particles, was obtained.

[0484] 9) Capacity ratio η of the first lithium iron phosphate salt particles of the Examples and Comparative Examples when discharged to 3.2V and 2.0V, respectively

[0485] First, a button battery was manufactured, and the specific manufacturing process of the button battery is as follows: 2.0000 g of lithium iron phosphate particles were mixed with 0.1111 g of conductive carbon black and 0.1111 g of polyvinylidene fluoride, then 2.5 g of the organic solvent N-methylpyrrolidone was added and mixed sufficiently uniformly to form a slurry. The slurry was coated onto aluminum foil with a coating thickness of 140 micrometers, dried under vacuum at 120°C for 2 hours, and punched into a circular sheet with a diameter of 13 mm using a punch. The material was purified at 10 MPa using a purification press and maintained under vacuum at 120°C for 12 hours to obtain an anode sheet. The weight of the anode sheet was weighed, wherein the loading amount of lithium iron phosphate particles was 11 to 12 mg. A button battery was assembled in a glove box protected by argon gas, with a metallic lithium sheet as the negative electrode, an electrolyte consisting of a 1:1 volume ratio of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) mixed solvent, an electrolyte consisting of LiPF6, and a separator consisting of a Celgard 2400 microporous polyethylene membrane.

[0486] The manufactured button battery is tested for electrical performance in a LAND tester. Specifically, the button battery is charged and discharged twice with a constant current of rate 0.1C in a voltage range of 2.0V to 3.75V, and then charged and discharged once with a constant current of rate 1C. In the charge-discharge test at rate 1C, a capacitance value of discharge voltage 3.2V is taken and recorded as C1, and a capacitance value of discharge voltage 2.0V is taken and recorded as C2, so η=C1 / C2. Here, the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA.

[0487] 10) Manganese leaching amount

[0488] After 100 cycles at 25°C, the fully charged cell was removed and disassembled in a glove box. The anode sheet was removed from the drying chamber, and 1g of material was carefully scraped from the center of the electrode sheet using a ceramic knife, ensuring that the entire active material layer was scraped to avoid variations in manganese content due to different thicknesses. The sample was then sealed in a sealed bag and sent to the laboratory. An electronic balance, a heating plate, a 150ml quartz beaker, a watch glass, a funnel, a 100ml volumetric flask, tongs (heat-resistant gloves), a sampling spoon, a dust-free bag, etc. were prepared; it was checked that the calibration date of the electronic balance was within its expiration date; if the expiration date had passed, it could not be used and required recalibration; the power was connected to ensure that the heating plate could normally reach 250°C; and 0.2000±0.005g of powder was weighed into the beaker. Acidification treatment: A dilute sulfuric acid solution was prepared with a volume ratio of 1:4 (concentrated sulfuric acid:ultrapure water = 1:4); 20 ml of the prepared dilute sulfuric acid solution was added to a beaker; the heating plate was preheated and, after the temperature reached 250°C, the sample was placed in the beaker and decomposed for 30 minutes, and a quartz cover was placed over the mouth of the beaker to reduce the evaporation of the acid solution; after the sample decomposition was completed for 30 minutes, the sample was removed and cooled to room temperature; the decomposed sample was transferred to a 100 ml glass volumetric flask and diluted. Then, the test was performed according to the ICP standard test procedure: the test instrument temperature was 22±2°C and the humidity was <60%; the trace element method was selected as the test method; and the calibration standard was executed: a standard curve was determined using the prepared standard solution; the element was selected as Mn; and finally, the Mn elution amount was obtained through the test.

[0489] 11) Anode slurry solid content

[0490] An electronic balance (precision 0.0001), an oven, and a glass drying tray were prepared. An 8 to 10 g anode slurry sample was taken and spread evenly on the sample tray, and the mass of the slurry before drying was recorded as A. The oven door was closed and heating was applied. As heating occurred, the internal temperature of the oven continuously increased, reaching 130°C over 5 hours. After drying, the sample was cooled inside the oven and removed; the mass of the dried slurry was recorded, and the dried mass was recorded as B after drying several times until the sample mass became constant. Slurry solid content = (B / A) × 100%.

[0491] 12) Electrode sheet compression density

[0492] The "electrode sheet compression density" referred to in this application means the "ultimate compression density" of the electrode sheet, and the test method thereof is as follows:

[0493] A double-sided coated electrode sheet was cold-pressed using a rolling mill, and the elongation of the cold-pressed electrode sheet was tested while simultaneously evaluating the flexibility of the cold-pressed electrode sheet.

[0494] By increasing the pressure of the rolling mill, electrode sheets with different compression densities are obtained. As the pressure increases, the compression density of the electrode sheet increases, the elongation of the electrode sheet increases, and the flexibility of the electrode sheet decreases. If the elongation of the electrode sheet is too high, it is easy to cause warping of the electrode sheet, and if the flexibility of the electrode sheet is too low, it is easy to cause brittle fracture of the electrode sheet. Therefore, the compression density that is smaller than when the elongation of the electrode sheet is 6% or when the number of flexibility folds of the electrode sheet is 3 is defined as the ultimate compression density.

[0495] Compressive density was calculated as the weight of the single-sided anode layer divided by the volume of the anode layer.

[0496] 13) Capacity per gram

[0497] The specific detection procedure is briefly described as follows: (1) The battery was placed in a 40°C oven environment and left undisturbed for 2 hours until the battery temperature was maintained at 40°C. (2) The battery was discharged to 2.0V with a constant current of 1 / 3C. (3) Waited for 5 minutes. (4) The battery was charged to 4.1V with a constant current of 1 / 3C, and then charged at a constant voltage of 4.1V until the cutoff current became 0.05C. (5) Waited for 5 minutes. (6) The battery was discharged to 2.0V with a constant current of 1 / 3C. At this stage, the actual cell capacity is tested, and the capacity per gram of the battery can be calculated by combining the mass of the positive electrode active material, where capacity per gram = capacity / mass of positive electrode active material.

[0498] 14) High-temperature storage performance

[0499] High-temperature storage performance was characterized by detecting the time it takes for the battery capacity to decay to 80% of the initial value by storing it in a fully charged state (charged to 4.1V) at 60°C.

[0500] 1. It was left for 10 minutes and discharged to 2V with a constant current of 0.33Cn (Cn is the battery capacity at 40℃ and 1 / 3C).

[0501] 2. It was left for 10 minutes, charged to 4.1V with a constant current of 0.33Cn, and then charged with a constant voltage so that the cutoff current was 0.02Cn.

[0502] 3. After leaving it for 2 hours, storing it at 60°C for 30 days, removing it, and testing the reversible capacity of the cell.

[0503] The specific detection procedure is briefly described as follows: (1) The battery was placed in a 40°C oven environment and left to stand for 2 hours until the battery temperature was maintained at 40°C. (2) It was discharged to 2.0V with a constant current of 1 / 3C. (3) It was waited for 5 minutes. (4) It was charged to 4.1V with a constant current of 1 / 3C, and then charged at a constant voltage of 4.1V until the cutoff current became 0.05C. (5) It was waited for 5 minutes. (6) It was discharged to 2.0V with a constant current of 1 / 3C. At this stage, the actual cell capacity was tested.

[0504] 4. The cell was tested regularly until its reversible capacity decayed to 80% of its initial value.

[0505] 15) High-temperature cycle performance

[0506] High-temperature cycle performance was characterized by detecting the number of cycles at which the battery capacity decayed to 80% of the initial value using a 1C / 1C cycle at 60°C.

[0507] The specific procedure is briefly described as follows: (1) The battery was placed in a 45°C oven and left to stand for 2 hours until the battery temperature was maintained at 25°C. (2) The battery was charged to 3.65V with a constant current of 1C, continued to charge at a constant voltage, and cut off until the charging current was less than 0.05C. (3) Waited for 5 minutes. (4) The battery was discharged to 2.5V with a constant current of 1C. (5) Waited for 5 minutes. Steps (2) through (5) constitute one charge-discharge cycle of the battery, and steps (2) through (5) were repeated until the battery capacity was reduced to 80% of the initial value.

[0508] 16) Mn / Fe molar ratio

[0509] The test method for the Mn molar ratio can be performed using methods and instruments known in the field, and examples are as follows: the molar content of the Mn element and the Fe element can be tested by referring to the chemical analysis method of lithium iron phosphate according to the national standard GB T33822-2017, and the molar ratio of Mn in the material can be calculated.

[0510] C. Analysis of test results for each example and comparative example

[0511] According to the method described above, batteries of each example and comparative example were manufactured and various performance parameters were measured. Refer to Tables 1 to 3 for the positive active material parameters, refer to Table 4 for the area ratio, and refer to Table 5 for the performance test results.

[0512] Table 1: Relevant parameters of the first particle

[0513]

[0514]

[0515] Table 2: Relevant parameters of the second particle

[0516]

[0517]

[0518]

[0519]

[0520]

[0521] Table 3: Relevant parameters of the third particle

[0522]

[0523]

[0524]

[0525] Table 4: Area ratios of the first, second, and third particles

[0526]

[0527]

[0528]

[0529] Table 5: Performance Test Results

[0530]

[0531]

[0532]

[0533] As can be seen from the results described above, the secondary batteries of Examples 1 to 41 are all

[0534] It comprises an anode sheet, a cathode sheet, a separator installed between the anode sheet and the cathode sheet, and an electrolyte containing an electrolyte salt and a solvent, and

[0535] The anode sheet comprises an anode current collector and an anode film layer installed on at least one surface of the anode current collector, and

[0536] The anode film layer comprises a first particle, the first particle comprises a first lithium iron manganese phosphate salt particle, and the first average particle size s1 of the first particle is 120 to 600 nm, and

[0537] Here, the manganese leaching amount of the secondary battery is ≤50 ppm.

[0538] As can be seen from the comparison between Examples 1 to 41 and Comparative Examples 1 to 4, the secondary battery of the embodiments of the present application has superior high-temperature storage performance. In addition, the secondary battery of the embodiments of the present application also has superior high-temperature cycle performance.

[0539] As can be seen from the comparison between Examples 1 to 41 and Comparative Examples 1 to 3, when the anode film layer further comprises a second particle, and the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese phosphate particle, and the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese phosphate particle is ≤ 1.5, the secondary battery of the present application example has a lower manganese leaching amount, better high-temperature storage performance, and better high-temperature cycle performance.

[0540] As can be seen from the comparison between Examples 36 to 41 and Comparative Example 3, when the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is ≤1.5, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, and a higher capacity per gram.

[0541] As can be seen from the comparison between Examples 1 to 41 and Comparative Examples 1 to 2 and 4, when the anode film layer further comprises a second particle, and the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese phosphate particle, and the primary average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese phosphate particle is ≤ 1.5, the secondary battery of the present application example has a lower manganese leaching amount, better high-temperature storage performance, and better high-temperature cycle performance.

[0542] As can be seen from the comparison between Examples 36 to 39 and Comparative Example 4, when the Mn / Fe molar ratio of the lithium manganese iron phosphate particles is ≤1.5, the secondary battery of the present application has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, higher capacity per gram, higher solid content of the anode slurry, and higher compression density of the anode sheet.

[0543] As can be seen from the comparison between Examples 2, 9, and 11 and Examples 5 to 6, when the anode film layer further comprises first lithium iron phosphate salt particles and the first average particle size s2' of the first lithium iron phosphate salt particles satisfies 500 nm ≤ s2' ≤ 3000 nm, the secondary battery of the present application embodiment has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, and a higher solid content of the anode slurry.

[0544] As can be seen from the comparison between Examples 2, 9, 10 to 11 and Examples 5 to 6, when the anode film layer further comprises first lithium iron phosphate salt particles and the first average particle size s2' of the first lithium iron phosphate salt particles satisfies 500 nm ≤ s2' ≤ 3500 nm, the secondary battery of the present application embodiment has a lower manganese leaching amount, better high-temperature storage performance, better high-temperature cycle performance, and a higher solid content of the anode slurry.

[0545] As can be seen from the comparison between Examples 2, 7, 9, 10 to 11 and Examples 5 to 6, when the anode film layer further comprises first lithium iron phosphate salt particles and the first average particle size s2' of the first lithium iron phosphate salt particles satisfies 500 nm ≤ s2' ≤ 4000 nm, the secondary battery of the present application example has a lower manganese leaching amount, better high-temperature storage performance, and a higher solid content of the anode slurry.

[0546] As can be seen from the comparison between Example 2 and Examples 28 to 35, when the anode film layer further comprises lithium iron phosphate particles and the primary average particle size s3' of the lithium iron phosphate particles satisfies 30nm ≤ s3' ≤ 200nm, the secondary battery of the present application embodiment has a lower manganese leaching amount, better high-temperature storage performance, and better high-temperature cycle performance.

[0547] As can be seen from the comparison of Examples 2, 16 to 17 and Examples 26 to 27, when calculated based on the total weight of the first lithium iron phosphate salt particles, the secondary battery of the present application has superior high-temperature storage performance and a higher capacity per gram when the Ti content in the first lithium iron phosphate salt particles is 2500 to 6000 ppm.

[0548] As can be seen from the comparison of Examples 2, 14 to 15, 18, 20 and Example 21, the specific surface area of ​​the first lithium iron phosphate salt particles is 3m 2 / g to 8m 2 When / g, the secondary battery of the embodiment of the present application has a lower manganese elution amount, a higher solid content of the anode slurry, and a higher anode sheet compression density. .

[0549] As can be seen from the comparison of Examples 2, 10 to 11, 16 and Example 17, the specific surface area of ​​the first lithium iron phosphate salt particles is 3 m² 2 / g to 6m 2 When / g, the secondary battery of the embodiment of the present application has superior high-temperature storage performance, superior high-temperature cycle performance, and a higher compression density of the anode sheet.

[0550] As can be seen from the comparison of Examples 2, 14 to 15, 20 and Example 21, when calculated based on the total weight of the first lithium iron phosphate salt particles, the carbon content of the first lithium iron phosphate salt particles is Cx4 wt% and 0.8≤Cx4≤1.2, the secondary battery of the present application example has better high-temperature storage performance, lower manganese leaching amount, higher solid content of the anode slurry, better high-temperature cycle performance, and higher compression density of the anode sheet.

[0551] As can be seen from the comparison of Examples 2, 14 to 15, 20 and Example 21, when the ratio z4 of Cx4 to the specific surface area of ​​the first lithium iron phosphate salt particles satisfies 3.8≤z4≤5, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, higher solid content of the anode slurry, better high-temperature cycle performance, and higher compression density of the anode sheet.

[0552] As can be seen from the comparison between Examples 34 and 35 and Example 28, when the aspect ratio of the lithium iron phosphate particles is ≥1.3, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, better high-temperature cycle performance, and higher capacity per gram.

[0553] As can be seen from the comparison between Examples 34 and 35 and Example 28, when the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the lithium iron phosphate particles is ≥1.03, the secondary battery of the present application has better high-temperature storage performance, lower manganese leaching amount, better high-temperature cycle performance and higher capacity per gram.

[0554] As can be seen from the comparison between Examples 2, 12 to 13 and Example 23, the specific surface area of ​​the lithium iron manganese phosphate particles is 10 m² 2 / g to 17m 2 When / g, the secondary battery of the embodiment of the present application has superior high-temperature storage performance, lower manganese leaching amount, superior high-temperature cycle performance, and higher compression density of the anode sheet.

[0555] It must be explained that the present application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiments having substantially the same configuration as the technical concept and exhibiting the same functional effects within the scope of the technical solution of the present application are included within the technical scope of the present application. Furthermore, within the scope without departing from the gist of the present application, those skilled in the art may make various modifications to the embodiments, and other forms configured by combining some components of the embodiments are included within the scope of the present application. Explanation of the symbols

[0556] 1 battery pack, 2 upper box body, 3 lower box body, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 top cover assembly.

Claims

Claim 1 A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator installed between the positive electrode sheet and the negative electrode sheet, and an electrolyte comprising an electrolyte salt and a solvent, wherein the positive electrode sheet comprises a positive current collector and a positive film layer installed on at least one surface of the positive current collector, wherein the positive film layer comprises a first particle, wherein the first particle comprises a first lithium iron manganese phosphate salt particle, and the primary average particle size s1 of the first particle is 120 to 600 nm, and wherein the manganese leaching amount of the secondary battery is ≤50 ppm. Claim 2 A secondary battery according to claim 1, wherein the anode film layer further comprises a second particle, the second particle comprises a first lithium iron phosphate particle and / or a second lithium manganese iron phosphate particle, the first average particle size s2 of the second particle satisfies 500 nm ≤ s2 ≤ 3000 nm, and the Mn / Fe molar ratio of the second lithium manganese iron phosphate particle is ≤ 1.

5. Claim 3 A secondary battery according to paragraph 2, wherein, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first particles is 60% to 98% and the area ratio of the second particles is 2% to 40%. Claim 4 A secondary battery according to any one of claims 1 to 3, wherein the anode film layer further comprises a first lithium iron phosphate salt particle, and the primary average particle size s2' of the first lithium iron phosphate salt particle satisfies 500 nm ≤ s2' ≤ 3000 nm. Claim 5 A secondary battery according to any one of claims 2 to 4, wherein, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate particles is 70% to 98% and the area ratio of the first lithium iron phosphate particles is 2% to 30%. Claim 6 A secondary battery according to any one of claims 2 to 5, wherein the anode film layer further comprises a third particle, the third particle comprises a second lithium iron phosphate particle and / or a third lithium manganese iron phosphate particle, the primary average particle size s3 of the third particle satisfies 30 nm ≤ s3 ≤ 200 nm, and the Mn / Fe molar ratio of the third lithium manganese iron phosphate particle is ≤ 1.

5. Claim 7 A secondary battery according to claim 6, wherein, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first particles is 70% to 97%; the area ratio of the second particles is 2% to 25%; and the area ratio of the third particles is 1% to 10%. Claim 8 A secondary battery according to any one of claims 2 to 7, wherein the anode film layer further comprises second lithium iron phosphate salt particles, and the primary average particle size s3' of the second lithium iron phosphate salt particles satisfies 30nm ≤ s3' ≤ 200nm. Claim 9 A secondary battery according to any one of claims 6 to 8, wherein, based on the total area of ​​the primary particles of the anode film layer, the area ratio of the first lithium iron manganese phosphate salt particles is 70% to 97%; the area ratio of the first lithium iron phosphate salt particles is 2% to 25%; and the area ratio of the second lithium iron phosphate salt particles is 1% to 10%. Claim 10 In any one of claims 1 to 9, the first manganese iron lithium salt particle is of the molecular formula Li m1 Fe x1 Mn r1 P y1 O j1 Q1 q1 It has, wherein Q1 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m1≤1.15, x1>0, r1>0, 0.9≤x1+r1≤1, 0.95≤y1≤1, 3.5≤j1≤4, 0≤q1≤0.1, and / or the lithium iron manganese phosphate particle has the molecular formula Li m2 Fe x2 Mn r2 P y2 O j2 Q2 q2 It has, wherein Q2 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m2≤1.15, x2>0, r2>0, r2 / x2≤1.5; 0.9≤x2+r2≤1, 0.95≤y2≤1, 3.5≤j2≤4, 0≤q2≤0.1, and / or the tri-element lithium manganese phosphate salt particles have the molecular formula Li m3 Fe x3 Mn r3 P y3 O j3 Q3 q3 It has, wherein Q3 comprises at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m3≤1.15, x3>0, r3>0, r3 / x3≤1.5; 0.9≤x3+r3≤1, 0.95≤y3≤1, 3.5≤j3≤4, 0≤q3≤0.1, and / or the first lithium iron phosphate salt particle has the molecular formula Li m4 Fe x4 P y4 O j4 Q4 q4 It has, wherein Q4 comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.95≤m4≤1.15, 0.9≤x4≤1, 0.95≤y4≤1, 3.5≤j4≤4, 0<q4≤0.1, and / or the lithium iron phosphate particle has the molecular formula Li m5 Fe x5 P y5 O j5 Q5 q5 A secondary battery having, wherein Q5 comprises at least one of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and 0.95≤m5≤1.15, 0.9≤x5≤1, 0.95≤y5≤1, 3.5≤j5≤4, and 0≤q5≤0.

1. Claim 11 A secondary battery according to claim 10, wherein the Q4 in the first lithium iron phosphate salt particle comprises at least one of Ti, V, Mg, and Nb, and when calculated based on the total weight of the first lithium iron phosphate salt particle, the content of Ti, V, Mg, and / or Nb is 1,000 to 10,000 ppm. Claim 12 In any one of paragraphs 2 to 11, the specific surface area of ​​the first lithium iron phosphate salt particle is 3 m² 2 / g to 8m 2 / g, secondary battery. Claim 13 A secondary battery according to any one of claims 2 to 12, wherein, when calculated based on the total weight of the first lithium iron phosphate particles, the carbon content of the first lithium iron phosphate particles is Cx4 weight%, where 0.8≤Cx4≤2.

0. Claim 14 In any one of paragraphs 2 to 13, the specific surface area of ​​the lithium iron manganese phosphate particles is 5 m² 2 / g to 12m 2 / g, secondary battery. Claim 15 A secondary battery according to any one of claims 2 to 14, wherein, when calculated based on the total weight of the lithium manganese iron phosphate particles, the carbon content of the lithium manganese iron phosphate particles is Cx2 weight%, where 0.8≤Cx2≤2.

0. Claim 16 A secondary battery according to any one of claims 1 to 15, wherein the primary average particle size s1' of the first lithium iron manganese phosphate salt particle is 150 to 210 nm, the primary average particle size s2' of the first lithium iron phosphate salt particle satisfies 870 nm ≤ s2 ≤ 3000 nm, and / or the primary average particle size s3' of the second lithium iron phosphate salt particle satisfies 60 nm ≤ s3' ≤ 200 nm. Claim 17 A secondary battery according to any one of claims 2 to 16, wherein the capacity ratio η of the first lithium iron phosphate salt particle is ≥ 88%, and η is defined as charging and discharging a battery having the first lithium iron phosphate salt particle as a positive electrode active material twice with a constant current of rate 0.1C in a voltage range of 2.0V to 3.75V, followed by charging and discharging once with a constant current of rate 1C, wherein in the charge-discharge test at rate 1C, a capacity value at a discharge voltage of 3.2V is taken and recorded as C1, and a capacity value at a discharge voltage of 2.0V is taken and recorded as C2, and η = C1 / C2, wherein the charging process includes constant voltage charging, the constant voltage is 3.75V, and the constant voltage cutoff current is 50μA. Claim 18 In any one of claims 2 to 17, the first lithium iron phosphate particles are: (a) the Dv10 of the first lithium iron phosphate particles is ≥0.2 μm; (b) the Dv50 of the first lithium iron phosphate particles is 0.5 to 5 μm; (c) the Dv90 of the first lithium iron phosphate particles is ≤10 μm; (d) the Dv99 of the first lithium iron phosphate particles is ≤12 μm; and (e) the powder compression density of the first lithium iron phosphate particles under a pressure of 3 tons is ≥2.25 g / cm³ 3 A secondary battery satisfying at least one of the following: (f) the powder resistivity of the first lithium iron phosphate salt particles is 60 Ω·cm. Claim 19 A secondary battery according to any one of claims 6 to 18, wherein the aspect ratio of the second lithium iron phosphate particle is ≥1.

3. Claim 20 A secondary battery according to any one of claims 6 to 19, wherein the ratio W of the (020) crystal plane diffraction peak intensity and the (211) crystal plane diffraction peak intensity of the second lithium iron phosphate salt particle is ≥1.

03. Claim 21 A secondary battery according to any one of claims 2 to 20, wherein the first lithium iron phosphate salt particles are obtained by a manufacturing method comprising providing a raw material mainly containing at least a lithium source, an iron source, a phosphorus, a carbon film-forming agent, a carbon source, and a modifier, and performing at least two sintering steps, wherein the first sintering temperature is 500°C to 760°C; and the second sintering temperature is 700°C to 800°C. Claim 22 In claim 21, the first lithium iron phosphate salt particles are obtained by a manufacturing method comprising providing a raw material mainly containing at least a lithium source, an iron source, a phosphorus source, a carbon source, a carbon film-forming agent, and a modifier, and performing at least two sintering steps, wherein the carbon content of the material after the first sintering is 0.01 wt% to 0.79 wt%; and the carbon content of the material after the second sintering is 0.8 wt% to 2.0 wt%, a secondary battery. Claim 23 A secondary battery according to claim 21 or 22, wherein the method for manufacturing the first lithium iron phosphate salt particles comprises the steps of performing a first grinding after performing the first sintering, and performing a second grinding after performing the second sintering, wherein the Dv50 of the product after the first grinding is 300 nm to 1200 nm; and the Dv50 of the product after the second grinding is 500 nm to 5000 nm. Claim 24 An electric device comprising a secondary battery according to any one of claims 1 to 23.

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