Lithium battery positive electrode material, positive electrode sheet and lithium-ion battery

Abstract

The present disclosure provides a lithium battery positive electrode material, comprising a positive electrode material body and filler particles filled within the positive electrode material body. The positive electrode material body comprises an inner core and a coating layer coated on the inner core. The inner core comprises first-stage particles, and the filler particles comprise second-stage particles. The present disclosure also provides a method for preparing a positive electrode plate, a positive electrode plate, and a lithium battery. The positive electrode material disclosed herein, when used in a lithium battery, can reduce thermal diffusion of the plate and can also regulate thermal diffusion of the plate as needed.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium batteries, and in particular to a lithium battery positive electrode material, a positive electrode sheet, and a lithium ion battery. Background Art

[0002] With the rapid popularization of electric vehicles, power battery technology is constantly developing and updating. There is a possibility of short circuit in power batteries during use. When a short circuit occurs, the battery's electrical energy is converted into heat energy and stored inside the battery, causing thermal runaway. The concentrated burst and release of energy in a short period of time may cause smoke, leakage, and even fire and explosion. NCM (nickel cobalt manganese oxide) and NCA (nickel cobalt aluminum oxide) have been used as cathode materials for lithium-ion batteries due to their high specific capacity and high voltage. However, NCM or NCX can experience runaway when triggered by relatively low levels of heat. Lithium-ion batteries made with these materials have poor thermal stability and safety. When an NCX positive electrode plate experiences thermal runaway, the large amount of heat it releases is transferred to the adjacent NCX positive electrode plate. The adjacent plate will also experience thermal runaway due to the external heat, generating heat that then spreads to the adjacent plate, causing thermal runaway to propagate within the plate stack. The spread of thermal runaway increases the probability of accidents such as smoke, leakage, and even fire and explosion, reducing the thermal stability and safety of the lithium battery. In this process, a key step to prevent the spread of thermal runaway is to prevent the conduction and diffusion of heat between adjacent plates. The olivine structure of LFP (lithium iron phosphate) and LMFP (lithium manganese iron phosphate) provides excellent safety, but they also suffer from issues such as low compaction, a low voltage platform, and low specific capacity. LMO (lithium manganese oxide) offers advantages such as a high voltage platform and good thermal stability, but also has a low specific capacity. Summary of the Invention

[0003] The first object of the present disclosure is to provide a lithium battery positive electrode material that takes both safety performance and energy density into consideration.

[0004] The second object of the present disclosure is to provide a method for preparing a lithium battery positive electrode sheet containing the above-mentioned lithium battery positive electrode material.

[0005] The third object of the present invention is to provide a positive electrode sheet containing the above-mentioned lithium battery positive electrode material.

[0006] The fourth object of the present disclosure is to provide a lithium-ion battery containing the above-mentioned positive electrode sheet.

[0007] To achieve the above-mentioned object, the present disclosure provides a lithium battery positive electrode material in a first aspect, the lithium battery positive electrode material comprising a positive electrode material body and filler particles filled between the positive electrode material bodies, the positive electrode material body comprising a core and a coating layer coated on the surface of the core; the core comprising first-stage particles, the filler particles comprising second-stage particles; the D90 of the first-stage particles being greater than the D90 of the second-stage particles;

[0008] The first-stage particles include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide, the coating layer includes at least one of lithium iron phosphate, lithium manganese iron phosphate and lithium manganate; the filling particles include at least one of lithium iron phosphate, lithium manganese iron phosphate and lithium manganate.

[0009] D90 refers to the particle size corresponding to when the cumulative particle size distribution percentage of the sample reaches 90%. Its physical meaning is that the volume of particles smaller than it accounts for 90% of the total particle volume of the sample.

[0010] Optionally, the nickel content of the first-stage particles is ≥70%.

[0011] Optionally, the first-stage particles include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide with a layered structure.

[0012] Optionally, the second-stage particles include lithium iron phosphate and / or lithium iron manganese phosphate; the filling particles further include third-stage particles, and the third-stage particles include lithium iron manganese phosphate and / or lithium manganate.

[0013] Optionally, the filling particles further include fourth-stage particles, and the fourth-stage particles include lithium manganese iron phosphate and / or lithium manganate.

[0014] Optionally, the thickness d of the coating layer satisfies 1 μm<d≤15 μm; preferably, the thickness d of the coating layer satisfies 11 μm≤d≤15 μm.

[0015] Optionally, the mass ratio of the first-stage particles, the second-stage particles, the third-stage particles and the fourth-stage particles is 1:(0.053-0.445):(0.0111-0.0769):(0.0136-0.0734).

[0016] Optionally, the cathode material body is stacked in a face-centered cubic manner, and the D of the first-stage particles is 90 The second-stage particles have a D 90 The D of the third-level particles is 4 μm~8.68 μm. 90 The D of the fourth-level particles is 2.25 μm~4.725 μm. 90 It is 1.77μm~3.71μm.

[0017] A second aspect of the present disclosure provides a method for preparing a lithium battery positive electrode sheet comprising the above-mentioned lithium battery positive electrode material, the method comprising the following steps:

[0018] S1: mixing and dispersing the first-stage particles and the coating layer material in a solvent to form a mixed solution;

[0019] S2: mixing the mixed liquid, drying it to obtain a powder, and crushing the powder to form a mixture;

[0020] S3: crushing the mixture to obtain a positive electrode material body;

[0021] S4: The positive electrode material body and the filling particles are mixed, and then mixed with a conductive agent and a binder, coated, and rolled to obtain a positive electrode sheet.

[0022] A third aspect of the present disclosure provides a positive electrode plate containing a lithium battery positive electrode material.

[0023] Optionally, the longitudinal thermal diffusion rate of the positive electrode plate n ≤0.5 mm / s.

[0024] A fourth aspect of the present disclosure provides a lithium-ion battery, which is loaded with the above-mentioned positive electrode sheet.

[0025] The present disclosure also provides a method for measuring the thermal diffusion performance of a pole piece, the method comprising the following steps:

[0026] Step 1: stacking the fully charged electrodes to be tested to form an electrode stack;

[0027] Step 2: stacking fully charged initiation cells on the upper surface of the electrode stack to obtain a measurement sample;

[0028] Step 3: inserting a steel needle vertically into the fully charged trigger cell of the test sample until the topmost electrode of the electrode stack experiences thermal runaway, and measuring the time interval from the thermal runaway of the first electrode to the thermal runaway of the second electrode below the first electrode;

[0029] Step 4: Calculate the thermal diffusion rate ν of the fully charged electrode to be tested according to the following formula (2);

[0030] (2)

[0032] In formula (2), d represents the thickness interval between the topmost electrode and any electrode below the topmost electrode, Δt represents the time interval.

[0033] The above-mentioned first pole piece can be selected from any pole piece in the pole piece stack except the lowest pole piece away from the upper surface. For example, the above-mentioned first pole piece can be selected from the top pole piece in the pole piece stack, or a pole piece in the middle of the pole piece stack; the above-mentioned second pole piece can be selected from any pole piece below the above-mentioned first pole piece, such as the lowest pole piece away from the upper surface.

[0034] Optionally, the fully-charged triggering cell is a high-nickel cell (nickel content ≥ 80%).

[0035] Optionally, d The thickness of the fully charged triggering cell is 5-10 mm.

[0036] Optionally, the length of the steel needle is 2-4 mm, the needling speed of the steel needle is 0.5-2 mm / s, and the pre-load force of the steel needle is 1-3 N.

[0037] Optionally, the method for measuring the time interval is that the topmost electrode and the bottom electrode of the electrode stack are respectively electrically connected to a temperature measuring device, and the temperature measuring device continuously measures the temperature of the electrode and calculates the temperature rise rate of the electrode. When the temperature rise rate is above 30 °C / s, it is defined as thermal runaway of the electrode, and the time when the thermal runaway occurs is recorded.

[0038] Optionally, the method includes setting a plurality of thermal runaway measurement points along the thickness direction of the pole piece stack, and the thickness intervals of the thermal runaway measurement points are greater than 5 mm.

[0039] The present disclosure also provides the application of the measurement method in evaluating the safety performance of lithium battery pole pieces.

[0040] Through the above technical solution, the positive electrode material provided by the present invention has higher compaction density, energy density and average voltage when made into a positive electrode, and reduces the thermal diffusion of the electrode, thereby improving the thermal stability and safety performance of the lithium battery, and can also regulate the thermal diffusion of the electrode as needed.

[0041] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0043] Figure 1 It is a model diagram of the positive electrode material disclosed in the present invention. DETAILED DESCRIPTION

[0044] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0045] refer to Figure 1 Model diagram, the first aspect of the present disclosure provides a lithium battery positive electrode material, the lithium battery positive electrode material comprising a positive electrode material body and filling particles filled between the positive electrode material bodies, the positive electrode material body comprising a core and a coating layer coated on the surface of the core; the core comprises first-stage particles, the filling particles comprise second-stage particles; the D90 of the first-stage particles is greater than the D90 of the second-stage particles;

[0046] The first-stage particles are lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide, the material of the coating layer is at least one of lithium iron phosphate, lithium manganese iron phosphate and lithium manganate; the material of the filling particles is at least one of lithium iron phosphate, lithium manganese iron phosphate and lithium manganate.

[0047] The above “the first-stage particles are lithium nickel cobalt manganate and / or lithium nickel cobalt aluminum oxide” means that the first-stage particles can be lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, or lithium nickel cobalt manganate and lithium nickel cobalt aluminum oxide.

[0048] The present disclosure reduces the heat diffusion between the positive electrode plates by coating the surface of the lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide core with high specific capacity and high voltage characteristics with an olivine structure material such as lithium iron phosphate, lithium iron manganese phosphate and lithium manganese oxide, thereby preventing the spread of thermal runaway, reducing the probability of smoke, leakage, and even fire and explosion accidents, and improving the thermal stability and safety of the lithium battery. In the scheme of the present disclosure, by arranging filler particles between the positive electrode material bodies, the compaction density, energy density and average voltage of the lithium battery can be increased, and the thermal stability can be further improved. The positive electrode material provided by the present disclosure, when used in a lithium battery, can increase the battery's average voltage, capacity, compaction density, safety and reduce heat diffusion between the plates.

[0049] According to the present disclosure, as an embodiment, the nickel content of the first-stage particles is ≥70%. First-stage particles with a nickel content of ≥70% can enable lithium battery positive electrode materials to have higher specific capacity and voltage.

[0050] According to the present disclosure, as an embodiment, the first-stage particles are lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide with a layered structure.

[0051] According to the present disclosure, as an embodiment, the material of the second-stage particles is lithium iron phosphate and / or lithium iron manganese phosphate; the filling particles also include third-stage particles, and the material of the third-stage particles is lithium iron manganese phosphate and / or lithium manganate; preferably, the filling particles also include fourth-stage particles, and the material of the fourth-stage particles is lithium iron manganese phosphate and / or lithium manganate.

[0052] According to the present disclosure, the thickness of the coating layer is 0.1-15 μm; preferably, the thickness of the coating layer is 1-15 μm; further preferably, the thickness of the coating layer is 11-15 μm. When the thickness of the coating layer is less than 0.1 μm, the longitudinal thermal diffusion rate of the electrode made of the positive electrode material is n When the thickness d of the coating layer is 1<d≤15, the longitudinal thermal diffusion rate of the electrode made of the positive electrode material can be reduced. n ≤0.5 mm / s. Among them, when the thickness d of the coating layer satisfies 1μm<d≤11μm, the longitudinal thermal diffusion rate of the electrode made of the positive electrode material can be calculated using the formula ν=-0.05d+0.55; when the thickness of the coating layer satisfies d When the thickness is ≥11 μm, the electrode piece made of the positive electrode material can be prevented from thermal diffusion in the longitudinal direction, that is, the longitudinal thermal diffusion rate of the electrode piece made of the positive electrode material is reduced to n “Longitudinal thermal diffusion” refers to the thermal diffusion between the positive electrode plates. This disclosure uses the longitudinal thermal diffusion rate n Indicates the heat diffusion capacity between the positive electrode plates.

[0053] According to the present disclosure, as an embodiment, the mass ratio of the first-stage particles, the second-stage particles, the third-stage particles and the fourth-stage particles is 1:(0.053-0.445):(0.0111-0.0769):(0.0136-0.0734).

[0054] According to the present disclosure, the positive electrode material body can be stacked in a face-centered cubic manner, the D90 of the first-level particles can be 10~15μm, the D90 of the second-level particles can be 4~8.68μm, the D90 of the third-level particles can be 2.25~4.725μm, and the D90 of the fourth-level particles can be 1.77~3.71μm.

[0055] When the D of the first-level particles, second-level particles, third-level particles and fourth-level particles 90 When the thickness of the and coating layers are respectively within the above ranges, optimal thermal stability, safety and energy density can be achieved.

[0056] A second aspect of the present disclosure provides a method for preparing a positive electrode sheet for a lithium battery, the method comprising the following steps:

[0057] S1: mixing and dispersing the first-stage particles and the coating layer material in a solvent to form a mixed solution;

[0058] S2: mixing the mixed liquid with a blender, drying the mixed liquid to obtain a powder, and crushing the powder to form a mixture;

[0059] S3: grinding the mixture by jet milling to obtain a positive electrode material body;

[0060] S4: The positive electrode material body, the second-stage particles, the third-stage particles and the fourth-stage particles are mixed, and then mixed with the conductive agent and the binder, coated, and rolled to obtain the positive electrode sheet.

[0061] The fluid velocity of the above-mentioned air flow milling treatment is controlled at 10-30m / s. When lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide is not completely coated or the coating thickness is too low, when the heat is large enough, thermal diffusion between the positive electrode material particles will occur, which can be reduced to the point of blocking the thermal diffusion between the particles by controlling the thickness of the coating layer. The coating thickness is related to the amount of coating material used. The coating thickness can be controlled by regulating the amount of coating material used, and the thermal diffusion between the positive electrode material particles and the thermal diffusion between the positive electrode plates can be further regulated. Specifically, the amount of coating material used can be adjusted during the positive electrode material preparation process.

[0062] A third aspect of the present disclosure provides a positive electrode sheet comprising the aforementioned lithium battery positive electrode material. The positive electrode sheet may further comprise a positive electrode current collector, a conductive agent, and a positive electrode binder, all of which may be conventionally used in the art. The positive electrode sheet provided by the present disclosure can be prepared using conventional methods in the art, which will not be further described here.

[0063] A fourth aspect of the present disclosure provides a lithium-ion battery equipped with the aforementioned positive electrode sheet. The lithium-ion battery comprises a housing, a battery cell loaded within the housing, and an electrolyte. The battery cell comprises the aforementioned positive electrode sheet, negative electrode sheet, and a separator. The negative electrode sheet and separator may be conventionally used in the art. The lithium-ion battery provided by the present disclosure can be prepared using conventional methods in the art, which will not be described in detail here.

[0064] The fifth aspect of the present invention provides a longitudinal heat diffusion rate between pole pieces. n A measuring method comprising the following steps:

[0065] Step 1: stacking the fully charged electrodes to be tested to form an electrode stack;

[0066] Step 2: stacking fully charged initiation cells on the upper surface of the electrode stack to obtain a measurement sample;

[0067] Step 3: A steel needle is vertically inserted into the fully charged trigger cell of the test sample until the topmost electrode of the electrode stack experiences thermal runaway, and the time interval from the thermal runaway of the first electrode to the thermal runaway of the second electrode below the first electrode is measured;

[0068] Step 4: Calculate the thermal diffusion rate ν of the fully charged electrode to be tested according to the following formula (2);

[0069] (2)

[0070] In formula (2), d represents the thickness interval between the topmost electrode and any electrode below the topmost electrode, Δt represents the time interval.

[0071] The above-mentioned first pole piece can be selected from any pole piece in the pole piece stack except the lowest pole piece away from the upper surface. For example, the above-mentioned first pole piece can be selected from the top pole piece in the pole piece stack, or a pole piece in the middle of the pole piece stack; the above-mentioned second pole piece can be selected from any pole piece below the first pole piece, such as the lowest pole piece away from the upper surface.

[0072] In the scheme disclosed herein, a steel needle is inserted vertically into the battery cell to trigger thermal runaway of the battery cell. After thermal runaway of the battery cell is triggered, a large amount of heat is released, and part of the heat diffuses to the topmost electrode of the electrode stack. When the material of the electrode stack is a low-heat-inducing material such as NCX (lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide), the topmost electrode of the electrode stack will thermally runaway, and part of the heat generated by the thermal runaway will diffuse to the adjacent lower electrode. The lower electrode will also cause its own thermal runaway due to the external heat, generate heat, and then diffuse to the adjacent electrode, thereby causing thermal runaway to propagate in the electrode stack. The propagation rate of thermal runaway depends on the rate and amount of heat transferred to the lower electrode after the upper electrode thermally runs away, that is, the propagation rate of thermal runaway can reflect the thermal diffusion performance between the electrodes. Specifically, the thermal diffusion performance between the electrodes can be expressed by formula (2), where d represents the distance that thermal runaway propagates, Δt represents the time for thermal runaway to propagate, d and Δt The difference is actually the propagation rate of thermal runaway, which can be used to reflect the thermal diffusion performance between the pole pieces. Specifically, the thermal diffusion rate n express.

[0073] The longitudinal heat diffusion rate between the pole pieces disclosed in the present invention nThe measurement method, when used to evaluate the composite cathode materials formed by the combination of lithium iron phosphate, lithium manganese iron phosphate and / or lithium manganate with NCX, can truly reflect the effect of lithium iron phosphate, lithium manganese iron phosphate and / or lithium manganate in improving the thermal stability and safety of the materials. If the effect of improving the thermal stability is very good, the propagation rate of thermal runaway will be very slow. Δt The method for measuring the thermal diffusion performance of a pole piece disclosed in the present invention is simple to operate and has accurate measurement results.

[0074] The present disclosure proposes a method for the longitudinal heat diffusion rate between pole pieces. n The measurement method is to measure the thermal diffusion rate n It can be shown whether the material according to the first aspect of the present disclosure can improve the thermal diffusion performance between pole pieces.

[0075] Optionally, the fully charged triggering cell is a high-nickel cell. By using a high-nickel cell, it is ensured that the heat generated by the triggering thermal runaway of the cell can diffuse to the topmost electrode of the electrode stack, thereby causing thermal runaway, and thus the thermal runaway can propagate in the electrode stack.

[0076] Optionally, the thickness of the topmost electrode and the bottom electrode is 5-10mm apart; the thickness of the fully charged trigger cell is 5-10mm. The thickness of the topmost electrode and the bottom electrode is 5-10mm apart to prevent the impact of thermal radiation and to indicate that the temperature rise is due to heat generated by thermal runaway.

[0077] Optionally, the length of the steel needle is 2-4 mm, the needling speed of the steel needle is 0.5-2 mm / s, and the pre-load force of the steel needle is 1-3 N.

[0078] Optionally, the method for measuring the time interval is that the topmost electrode and the bottom electrode of the electrode stack are respectively electrically connected to a temperature measuring device, and the temperature measuring device continuously measures the temperature of the electrode and calculates the temperature rise rate of the electrode. When the temperature rise rate is above 30 °C / s, thermal runaway occurs in the electrode, and the time when thermal runaway occurs is recorded.

[0079] The temperature measuring device may be a thermocouple, which may be arranged at the topmost pole piece and the bottom pole piece of the pole piece stack to continuously measure the temperature of the pole pieces.

[0080] Optionally, multiple thermal runaway measurement points are set along the thickness direction of the pole piece stack, and the thickness interval of the thermal runaway measurement points is greater than 5mm. By setting multiple thermal runaway measurement points, the longitudinal heat diffusion rate between multiple pole pieces can be obtained simultaneously. n The measurement data can be used to more accurately evaluate the thermal diffusion performance between the pole pieces.

[0081] The sixth aspect of the present disclosure provides the application of the measurement method described in the fifth aspect for evaluating the safety performance of lithium battery pole pieces.

[0082] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0083] Unless otherwise specified, the materials, reagents, instruments and equipment used in the embodiments of the present disclosure can be obtained from commercial sources.

[0084] Example 1

[0085] S1: Lithium nickel cobalt manganese oxide (nickel content of lithium nickel cobalt manganese oxide is 80% by mass) with a D90 of 12 μm is mixed with lithium iron phosphate coating material and dispersed in N-methyl pyrrolidone to form a mixed solution;

[0086] S2: Mechanically stirring the mixture at room temperature for 30 minutes using a four-planetary mixer, and then stirring under vacuum for 2 hours. The mixture is then dried using a blower to obtain a powder, which is then ground to form a mixture.

[0087] S3: The mixture was subjected to a jet milling process with the fluid velocity controlled at 20 m / s to prepare a positive electrode material body. The thickness of the coating layer of the positive electrode material body is shown in Table 1;

[0088] S4: The positive electrode material body, the second-level particles of lithium iron phosphate with a D90 of 5.6μm, the third-level particles of lithium iron manganese phosphate with a D90 of 3.15μm, and the fourth-level particles of lithium manganese oxide with a D90 of 2.48μm are mixed and compacted. In the obtained lithium battery positive electrode material, the mass ratio of the first-level particles: the second-level particles: the third-level particles: the fourth-level particles is shown in Table 1.

[0089] Example 2

[0090] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 is that the D90 of the second-level particles is 8.4 μm, the D90 of the third-level particles is 2.5 μm, and the D90 of the fourth-level particles is 1.9 μm. In addition, the thickness of the coating layer and the mass ratio of the first-level particles: the second-level particles: the third-level particles: the fourth-level particles are different, as shown in Table 1.

[0091] Example 3

[0092] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 is that the thickness of the coating layer and the mass ratio of the first-stage particles: the second-stage particles: the third-stage particles: the fourth-stage particles are different, as shown in Table 1.

[0093] Example 4

[0094] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 is that the first-stage particles were changed to lithium nickel cobalt aluminum oxide with a D90 of 12 μm, as shown in Table 1.

[0095] Example 5

[0096] The positive electrode material was prepared by the method of Example 1, except that the coating layer material was changed to lithium manganese iron phosphate (LMFP).

[0097] Example 6

[0098] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 was that the third-stage particles and the fourth-stage particles were not used, but the total mass of the positive electrode material was the same.

[0099] Example 7

[0100] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 is that the thickness of the coating layer and the mass ratio of the first-stage particles: the second-stage particles: the third-stage particles: the fourth-stage particles are different, as shown in Table 1.

[0101] Example 8

[0102] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 is that the thickness of the coating layer and the mass ratio of the first-stage particles: the second-stage particles: the third-stage particles: the fourth-stage particles are different, as shown in Table 1.

[0103] Example 9

[0104] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 is the thickness of the coating layer, as shown in Table 1.

[0105] Example 10

[0106] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 was that the D 90 The D of the second-stage particles is 10 μm. 90 The D of the third-level particles is 4 μm. 90 The D of the fourth-order particles is 2.25 μm. 90 is 1.77μm; the mass ratios of first-level particles: second-level particles: third-level particles: and fourth-level particles are different.

[0107] Example 11

[0108] The positive electrode material was prepared by the method of Example 1. The difference from Example 1 was that the D 90 The second-stage particles have a D of 15 μm.90 The D of the third-level particles is 8.68 μm. 90 The D of the fourth-order particles is 4.725 μm. 90 is 3.71μm; the mass ratios of first-level particles: second-level particles: third-level particles: and fourth-level particles are different.

[0109] Comparative Example 1

[0110] The positive electrode material was prepared by the method of Example 1, except that no coating layer material was used.

[0111] The positive electrode materials prepared in Examples 1-11 and Comparative Example 1 were used to prepare positive electrode sheets, and further to prepare lithium-ion batteries. The specific methods are as follows:

[0112] (1) Preparation of positive electrode sheet:

[0113] A positive electrode slurry is prepared, which includes a positive electrode material, a conductive agent (carbon nanotubes CNT and carbon black SP), a binder-PVDF and a solvent NMP, and the positive electrode material: CNT: SP: PVDF: NMP = 100:1.2:0.3:2.5:55;

[0114] A 12 μm aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was applied on both sides of the aluminum foil. After drying, a double-sided positive electrode sheet was obtained. The double-sided positive electrode sheet was rolled, slit and die-cut to obtain a positive electrode sheet to be used.

[0115] (2) Preparation of negative electrode sheet:

[0116] Natural graphite is mixed with binder CMC, binder SBR, and water in a mass ratio of 100:1.5:2.5:3:130 to obtain a negative electrode slurry; the negative electrode slurry is coated on both sides of a 6-μm-thick copper foil, and after baking at 110°C to remove water, a negative electrode active material layer is formed on the copper foil, which is then rolled and slit to obtain a double-sided negative electrode sheet.

[0117] (3) Assembly of full battery:

[0118] The above-mentioned positive electrode sheets, negative electrode sheets and PE separators are stacked in a Z-shaped stacking manner to assemble into battery cells in one direction. The hot-pressed battery cells are placed in a battery shell, and the electrolyte is injected under vacuum according to the injection coefficient of 2.8g / Ah. The shell is sealed and then subjected to high-temperature aging, formation, aging, and capacity separation before vacuum sealing to produce a long-cell battery with a length of 500mm and a width of 12mm.

[0119] Test Example 1

[0120] Longitudinal thermal diffusion rate of the positive electrode sheets prepared from the positive electrode materials prepared in Examples 1-11 and Comparative Example 1 n The measurement method is as follows:

[0121] Step 1: Stack the fully charged positive electrode sheets to be tested to form a sheet stack, with the thickness of the top positive electrode sheet and the bottom positive electrode sheet separated by 5.0-6.0 mm.

[0122] Step 2: stacking fully charged initiation cells on the upper surface of the positive electrode stack to obtain a measurement sample, wherein the thickness of the fully charged initiation cells is 4.0-5.0 mm, placing the measurement sample in an aluminum-plastic film, injecting liquid, and encapsulating;

[0123] Step 3: A steel needle is vertically inserted into the measurement sample until the top positive electrode of the electrode stack thermally runs away, and the time interval from the thermal runaway of the top positive electrode to the thermal runaway of the bottom positive electrode of the electrode stack is measured. The length of the steel needle is 3 mm, the needle penetration speed of the steel needle is 1 mm / s, and the preload force of the steel needle is 2 N.

[0124] The time interval is measured in the following manner: the topmost positive electrode sheet and the bottommost positive electrode sheet of the electrode sheet stack are electrically connected to a temperature measuring device, respectively. The temperature measuring device continuously measures the temperature of the positive electrode sheet and calculates the temperature rise rate of the positive electrode sheet. When the temperature rise rate is above 30 °C / s, it indicates that thermal runaway has occurred in the positive electrode sheet, and the time when thermal runaway occurs is recorded.

[0125] Step 4: Calculate the thermal diffusion rate ν of the fully charged positive electrode to be tested according to formula (2);

[0126] (2)

[0128] In formula (2), d represents the thickness interval, Δt represents the time interval.

[0129] Specifically, the preparation method of the above-mentioned electrode stack includes: charging the above-mentioned full battery to 4.25V and a cut-off current of 0.05C using a 1 / 3C constant current and constant voltage method, and then disassembling the battery in a glove box, taking out the fully charged positive electrode sheet, washing off the electrolyte with dimethyl carbonate (DMC), and after drying, stacking the positive electrode sheets in sequence to obtain the electrode stack to be tested.

[0130] Specifically, the preparation method of the fully-charged triggering cell includes: taking a normal battery, charging it to 4.25V using a 1 / 3C constant current and constant voltage method with a cut-off current of 0.05C, and obtaining a fully-charged triggering cell.

[0131] Place the fully charged initiating cell on the electrode stack to be tested, wrap it with aluminum-plastic film, and inject an appropriate amount of electrolyte into the interior. Refill the electrolyte according to the injection coefficient of 2.3g / Ah. The capacity is calculated according to the battery capacity before disassembly, and then vacuum seal it.

[0132] The test results are shown in Table 1.

[0133] Table 1

[0134]

[0135] Comparing the thermal diffusion rates of Example 1 and Comparative Example 1 in Table 1, when the positive electrode material of Comparative Example 1 does not contain a coating layer, the thermal diffusion rate between the pole pieces is 0.52 mm / s. At this time, the particle accumulation only contributes to the compaction of the pole pieces, but does not improve the thermal diffusion rate of the pole pieces. At this time, the longitudinal thermal diffusion rate of the pole pieces of this material is consistent with that of pure NCX. Therefore, the technical solution of the present application reduces the thermal diffusion of the pole pieces, thereby improving the thermal stability and safety performance of the lithium battery. It can be seen from Examples 1-3 and 9 that as the amount of coating material and the thickness of the coating layer gradually increase, the longitudinal thermal diffusion rate of the pole pieces made of the positive electrode material gradually decreases, indicating that the thermal diffusion between the pole pieces can be reduced by coating, and the thermal diffusion performance between the pole pieces can be regulated as needed by adjusting the amount of coating material and the thickness of the coating layer.

[0136] The preferred embodiments of the present disclosure are described in detail above. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0137] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0138] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A lithium battery positive electrode material, characterized in that The lithium battery positive electrode material comprises a positive electrode material body and filling particles filled between the positive electrode material bodies, wherein the positive electrode material body comprises a core and a coating layer coated on the surface of the core; the thickness d of the coating layer satisfies 11 μm≤d≤15 μm; the core comprises first-level particles, and the filling particles comprise second-level particles; the D of the first-level particles 90 Greater than the D of the second-stage particles 90 ; The first-stage particles include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide, and the coating layer includes at least one of lithium iron phosphate and lithium manganese iron phosphate; The second stage particles include lithium iron phosphate and / or lithium iron manganese phosphate; The filling particles further include third-level particles and fourth-level particles; the third-level particles include lithium iron manganese phosphate and / or lithium manganate; the fourth-level particles include lithium iron manganese phosphate and / or lithium manganate; The mass ratio of the first-stage particles, the second-stage particles, the third-stage particles, and the fourth-stage particles is 1:(0.053-0.445):(0.0111-0.0769):(0.0136-0.0734); The cathode material is stacked in a face-centered cubic manner, and the D 90 The second-stage particles have a D 90 The D of the third-level particles is 4 μm~8.68 μm. 90 The D of the fourth-level particles is 2.25 μm~4.725 μm. 90 It is 1.77μm~3.71μm.

2. The lithium battery positive electrode material according to claim 1, characterized in that The nickel content of the first-stage particles is ≥70%.

3. The lithium battery positive electrode material according to claim 1, characterized in that The first-stage particles include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide in a layered structure.

4. A method for preparing a lithium battery positive electrode sheet comprising the lithium battery positive electrode material according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1: mixing and dispersing the first-stage particles and the coating layer material in a solvent to form a mixed solution; S2: mixing the mixed liquid, drying it to obtain a powder, and crushing the powder to form a mixture; S3: crushing the mixture to obtain a positive electrode material body; S4: The positive electrode material body and the filling particles are mixed, and then mixed with a conductive agent and a binder, coated, and rolled to obtain a positive electrode sheet.

5. A positive electrode plate, characterized in that: The positive electrode sheet contains the lithium battery positive electrode material according to any one of claims 1 to 3.

6. The positive electrode sheet according to claim 5, characterized in that: The longitudinal thermal diffusion rate of the positive electrode sheet ν ≤0.5 mm / s.

7. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 5 or 6.

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