A method for determining the thermal safety of high-nickel ternary cathode materials

Abstract

The present application discloses a method for determining the thermal safety of a high-nickel ternary cathode material, which is used to predict the thermal safety of the high-nickel ternary cathode material, thereby improving the efficiency of determining the performance of the high-nickel ternary cathode material. The method includes: obtaining a cross-section of the high-nickel ternary cathode material; wherein, the high-nickel ternary cathode material is a secondary particle composed of primary particles; determining the quantity parameter β of the primary particles on any line segment passing through the center of the cross-section, and / or, the edge number parameter α of the primary particles on the cross-section; wherein, the endpoints of the line segment are located at the edge of the cross-section, and β is obtained by the following formula: β = N / L, where N is the number of primary particles on the line segment and L is the length of the line segment, and α is obtained by the following formula: α = M / S, where M is the sum of the edge numbers of all the primary particles on the cross-section and S is the area of the cross-section; determining the thermal safety of the high-nickel ternary cathode material according to β and / or α.

Description

Technical Field

[0001] This application relates to the technical field of new energy batteries, and particularly to a method for determining the thermal safety of high-nickel ternary cathode materials. Background Art

[0002] At present, ternary cathode materials are gradually being put into the market due to their good performance of lithium ion extraction and insertion and stable structure. For the structural stability of cathode materials, generally, the cathode materials are first tested for structural stability for a set period of time. Then, the cathode materials are assembled into lithium batteries, and the stability of the lithium batteries is tested to determine the thermal safety after the lithium batteries are put into market use. However, the above stability (i.e., thermal safety) test has problems such as long test cycle, low efficiency, and high cost; thus, there is a lack of a method for pre-judging the thermal safety of the prepared materials. Summary of the Invention

[0003] This application provides a method for determining the thermal safety of high-nickel ternary cathode materials, which is used to pre-judge the thermal safety of high-nickel ternary cathode materials, thereby improving the efficiency of determining the performance of high-nickel ternary cathode materials.

[0004] In a first aspect, this application provides a method for determining the thermal safety of high-nickel ternary cathode materials, including:

[0005] Obtain a cross-section of the high-nickel ternary cathode material; wherein, the high-nickel ternary cathode material is a secondary particle composed of primary particles;

[0006] Determine the number parameter β of the primary particles on any line segment passing through the center of the cross-section, and / or, the edge number parameter α of the primary particles on the cross-section; wherein, the endpoints of the line segment are located on the edge of the cross-section, and β is obtained by the following formula: β = N / L, where N is the number of primary particles on the line segment, L is the length of the line segment, the length unit is micrometer, and α is obtained by the following formula: α = M / S, where M is the sum of the edge numbers of all the primary particles on the cross-section, S is the area of the cross-section, and the area unit is square micrometer;

[0007] Determine the thermal safety of the high-nickel ternary cathode material according to β and / or α.

[0008] Embodiments of this application determine the thermal safety of high-nickel ternary cathode materials by determining the intrinsic properties of high-nickel ternary cathode materials: the number of edges and the number of primary particles on the cross-section of high-nickel ternary cathode materials, avoiding the problem of low efficiency caused by the existing technology of testing the stability (thermal safety) of all prepared high-nickel ternary cathode materials one by one.

[0009] A possible implementation, where the cross-section is the maximum cross-section passing through the center of the high-nickel ternary cathode material.

[0010] A possible implementation, determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes:

[0011] When the value of β is less than 2.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

[0012] A possible implementation, determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes:

[0013] When the value of α is less than 7.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

[0014] A possible implementation, determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes:

[0015] When the product of α and β is less than 12.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

[0016] A possible implementation, determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes:

[0017] When the ratio of α to β is less than 6.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

[0018] A possible implementation, the molecular formula of the high-nickel ternary cathode material is: Li x Ni a Co b Mn c Al d M 1-a-b-c-d O 2 ; where M is at least one of Zr, Mo, Ca, Mg, Ba, B, Ti, Sr, Nb, Y, and W, 1 < x < 1.2, 0.8 ≤ a < 0.95, 0 < b < 0.2, 0 ≤ c < 0.2, 0 ≤ d < 0.2, 0 ≤ 1 - a - b - c - d < 0.06; and c and d are not both 0.

[0019] A possible implementation, the high-nickel ternary cathode material is obtained by the following method:

[0020] By performing high-temperature sintering treatment on a mixture of a high-nickel ternary precursor and a lithium source; where the molecular formula of the high-nickel ternary precursor is: Ni x Co y Mn z Al P (OH)2 or Ni x Co y Mn z Al P CO 3 where 0.8 ≤ x < 0.95, 0 < y < 0.2, 0 ≤ z < 0.2, 0 ≤ p < 0.2, and z and p are not both 0;

[0021] When the high-nickel ternary cathode material contains the doping element M, a mixture of the high-nickel ternary precursor, a lithium source, and a doping source corresponding to the doping element is subjected to high-temperature sintering treatment.

[0022] In a second aspect, the present application provides a high-nickel ternary cathode material, comprising:

[0023] The high-nickel ternary cathode material is a secondary particle composed of primary particles, and a cross-section passing through the midpoint of the high-nickel ternary cathode material satisfies at least the following requirements: α < 7, and / or, β < 2; where

[0024] β is a quantity parameter of the primary particles on any line segment passing through the cross-section, the endpoints of the line segment are located at the edge of the cross-section, and β is obtained by the following formula: β = N / L, where N is the number of the primary particles on the line segment, L is the length of the line segment, and the unit of the length is micrometer; α is obtained by the following formula: α = M / S, where M is the total number of the sides of each primary cross-section on the cross-section, S is the area of the cross-section, and the unit of the area is square micrometer.

[0025] In the embodiment of the present application, a high-nickel ternary cathode material with a cross-section satisfying α < 7, and / or, β < 2 is proposed. Since under the foregoing conditions, the stress between the primary particles in the high-nickel ternary cathode material is effectively relieved, the thermal safety of the high-nickel ternary cathode material is effectively improved, that is, the stability of the high-nickel ternary cathode material at high temperature is significantly improved.

[0026] In a possible implementation manner, α × β < 12.

[0027] In a possible implementation manner, α / β < 6.

[0028] In a possible implementation manner, the molecular formula of the high-nickel ternary cathode material is:

[0029] Li x Ni a Co b Mn c Al d M 1-a-b-c-d O 2; wherein, M is at least one of Zr, Mo, Ca, Mg, Ba, B, Ti, Sr, Nb, Y, and W, 1 < x < 1.2, 0.8 ≤ a < 0.95, 0 < b < 0.2, 0 ≤ c < 0.2, 0 ≤ d < 0.2, 0 ≤ 1 - a - b - c - d < 0.06; and c and d are not both 0.

[0030] In a possible implementation manner, the critical temperature at which the high-nickel ternary cathode material undergoes a phase change is not less than 212 °C, and the phase change indicates a change from a layered structure to a rock-salt phase structure in the high-nickel ternary cathode material. Description of the Drawings

[0031] Figure 1 It is a schematic flow chart of a method for determining the thermal safety of a high-nickel ternary cathode material provided by an embodiment of the present application;

[0032] Figure 2 It is a schematic diagram for determining α and β on the cross-section of Example 3 - 4 provided by an embodiment of the present application. Detailed Embodiments

[0033] In view of the lack of a method for determining the thermal safety of ternary cathode materials in the prior art, the present application proposes a method for determining the thermal safety of high-nickel ternary cathode materials: by determining the number of sides of primary particles on the cross-section of the high-nickel ternary cathode material, and / or the number of primary particles on a line segment passing through the center of the cross-section in any direction, the thermal safety of the high-nickel ternary cathode material is determined; thereby avoiding the problem of low efficiency in determining the performance of cathode materials caused by conducting thermal stability tests on all cathode materials and the lithium batteries where the cathode materials are located.

[0034] It should be noted that this method can be used to predict the thermal safety of high-nickel ternary cathode materials prepared with different preparation parameters and / or different batches, so as to preliminarily screen out high-nickel ternary cathode materials that meet the thermal safety requirements, and / or exclude high-nickel ternary cathode materials that obviously do not meet the thermal safety requirements.

[0035] Furthermore, good thermal safety in the embodiments of the present application means that the corresponding high-nickel ternary cathode material reduces safety risks in actual applications; that is, after applying the corresponding high-nickel ternary cathode material to a lithium battery, it does not cause high-temperature aggregation inside the material due to chemical reactions (mainly redox reactions) occurring inside the high-nickel ternary cathode material, resulting in a phase change of the material, causing the internal structure of the high-nickel ternary cathode material to collapse, releasing lattice oxygen, and even causing problems such as combustion, fire, and explosion with the electrolyte and its decomposition products.

[0036] To better understand the above technical solution, the technical solution of the present application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific features in the embodiments of the present application are detailed descriptions of the technical solution of the present application, rather than limitations on the technical solution of the present application. Without conflict, the technical features in the embodiments of the present application and the embodiments can be combined with each other.

[0037] Please refer to Figure 1 , the present application proposes a method for determining the thermal safety of a high-nickel ternary cathode material to judge the thermal safety of the high-nickel ternary cathode material. The method specifically includes the following implementation steps:

[0038] Step 101: Obtain a cross-section of the high-nickel ternary cathode material.

[0039] Among them, the high-nickel ternary cathode material is a secondary particle composed of primary particles.

[0040] Specifically, the molecular formula of the high-nickel ternary cathode material is: Li x Ni a Co b Mn c Al d M 1-a-b-c-d O 2 ; where M is at least one of Zr, Mo, Ca, Mg, Ba, B, Ti, Sr, Nb, Y, and W, 1 < x < 1.2, 0.8 ≤ a < 0.95, 0 < b < 0.2, 0 ≤ c < 0.2, 0 ≤ d < 0.2, 0 ≤ 1 - a - b - c - d < 0.06; and c and d are not both 0 at the same time.

[0041] Furthermore, in an embodiment of the present application, when the high-nickel ternary cathode material contains both manganese element and aluminum element, that is, when both c and d are not 0, c + d < 0.2, and d < 0.06.

[0042] Furthermore, the high-nickel ternary cathode material can be obtained by mixing a lithium source with a high-nickel ternary precursor and performing a high-temperature sintering treatment. And when the high-nickel ternary cathode material contains a doping element M, a mixture of the high-nickel ternary precursor, the lithium source, and a doping source corresponding to the doping element is subjected to a high-temperature sintering treatment.

[0043] In the embodiment of the present application, the high-nickel ternary precursor and the molecule are: Ni x Co y Mn z Al P (OH) 2 , or Ni x Co y Mn z Al P CO 3。

[0044] Among them, x, y, z, and p are each selected from: 0.8 ≤ x < 0.95, 0 < y < 0.2, 0 ≤ z < 0.2, 0 ≤ p < 0.2, and z and p are not both 0 at the same time.

[0045] In an embodiment of the present application, in the high-nickel ternary precursor Ni x Co y Mn z Al P (OH) 2 , or Ni x Co y Mn z Al P CO 3 In, when both z and p are not 0, z + p < 0.2, and p < 0.06.

[0046] Step 102: Determine the number parameter β of the primary particles on any central line segment passing through the cross-section, and / or the edge number parameter α of the primary particles on the cross-section.

[0047] Among them, the endpoints of the line segment are located on the edge of the cross-section, and β is obtained by the following formula: β = N / L, where N is the number of primary particles on the line segment, L is the length of the line segment, the length unit is micrometer, and α is obtained by the following formula: α = M / S, where M is the sum of the edge numbers of all the primary particles on the cross-section, and S is the area of the cross-section, and the area unit is square micrometer.

[0048] The number of edges of the primary particles on the above cross-section corresponds to the grain boundaries of the primary particles. That is, the number of edges of the primary particles is the number of edges with a non-zero angle on the grain boundary forming the primary particles. And on the cross-section, for adjacent primary particles with overlapping grain boundaries, only one of the overlapping grain boundary edges is recorded. Based on the above rules, the number of edges of all the primary particles on the cross-section of the secondary sphere can be determined by size measurement software.

[0049] Specifically, for the secondary particles composed of primary particles, the more fully the primary particles grow, the better the thermal stability of the secondary particles, and correspondingly, the better the thermal safety.

[0050] Therefore, in the embodiment of the present application, the growth situation of the primary particles inside the secondary particles (high-nickel ternary cathode material) is determined by β.

[0051] Further, when the high-nickel ternary cathode material is applied to a lithium battery, along with the deintercalation and intercalation of lithium ions, the primary particles exhibit corresponding volume shrinkage and expansion phenomena. Therefore, for the internal defects of the secondary particles, that is, on the premise that the primary particles are not spherical, the more sides the primary particles have, the less significant the stress concentration phenomenon during the shrinkage and expansion of the primary particles, and thus the better the thermal stability of the high-nickel ternary cathode material. Correspondingly, the thermal safety is also better.

[0052] Therefore, in the embodiment of the present application, by determining α, the stress condition of the primary particles in the secondary particles is determined.

[0053] After determining β, and / or, α, step 103 can be executed.

[0054] Step 103: Determine the thermal safety of the high-nickel ternary cathode material according to β and / or α.

[0055] In an embodiment of the present application, the cross-section is a cross-section passing through the center of the high-nickel ternary cathode material. Correspondingly, when the value of β is less than 2.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good; preferably, the value of β is less than 1.5. And / or, when the value of α is less than 7.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good; preferably, α < 5.0. And / or, when the product of α and β is less than 12.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good; preferably, α*β < 5.0. And / or, when the ratio of α to β is less than 6.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good; preferably, α / β < 4.0.

[0056] Further, β can be the average of the quantity parameters on multiple line segments in different directions on the same cross-section.

[0057] It should be noted that the indication of good thermal safety in the embodiment of the present application means that the critical temperature at which the high-nickel material changes from a layered structure to a rock salt phase structure at high temperature is high, that is, the critical temperature at which the high-nickel material undergoes a phase change and causes structural collapse is high. The above critical temperature is at least 212°C.

[0058] The method for determining the thermal stability of the high-nickel ternary cathode material described in steps 101-103 determines the thermal safety of the material through the intrinsic properties of the high-nickel ternary material, and can effectively judge the thermal safety of the high-nickel ternary cathode material. At the same time, it can screen and judge the high-nickel ternary cathode materials with different preparation batches and / or preparation parameters, avoid unnecessary stability (thermal safety) tests, and thus effectively improve the performance test efficiency of the material and the judgment efficiency of whether the thermal safety is good.

[0059] Based on the same inventive concept, the present application proposes a high-nickel ternary cathode material with good thermal safety: the high-nickel ternary cathode material is a secondary particle composed of primary particles. The cross-section passing through the center of the high-nickel ternary cathode material satisfies at least the following requirements: α < 7, and / or, β < 2.

[0060] Among them, β is the quantity parameter of the primary particles on any line segment passing through the cross-section, the endpoints of the line segment are located at the edge of the cross-section, and β is obtained by the following formula: β = N / L, where N is the number of the primary particles on the line segment, and L is the length of the line segment, and the unit of the length is micrometer.

[0061] α is obtained by the following formula: α = M / S, where M is the total number of sides of each primary cross-section on the cross-section, and S is the area of the cross-section, and the unit of the area is square micrometer.

[0062] In the embodiments of the present application, the critical temperature at which the high-nickel ternary cathode material with good thermal safety undergoes a phase change is not less than 212 °C, and the phase change indicates that a change from a layered structure to a rock salt phase structure occurs in the high-nickel ternary cathode material.

[0063] In an embodiment of the present application, α × β < 12. Preferably, α × β < 5.

[0064] In an embodiment of the present application, α / β < 6. Preferably, α / β < 4.

[0065] The following is further illustrated by Examples 1-10:

[0066] Examples 1-10 are all subjected to DSC tests through the following steps to determine the DSC peak temperature. Specifically, the test steps are as follows:

[0067] S1. Disperse the cathode material and acetylene black in an NMP solution dissolved with 5% PVDF by mass ratio of 98:2 and stir for 20 min, where the concentration of the cathode material is 60%.

[0068] S2. Uniformly coat the obtained slurry on the aluminum foil and dry it in a vacuum drying oven at 110 °C for 4 hours.

[0069] S3. Cut the dried electrode sheet into a circular sheet with a diameter of 15 mm, and assemble and seal it in a glove box according to the order of positive electrode shell, electrode sheet, electrolyte (EC / DMC / EMC volume ratio 1:1, LiPF6 concentration is 1 mol / L), separator (Celgard PP / PE / PP three-layer composite membrane), lithium sheet, electrolyte, foam nickel, and negative electrode shell to obtain a battery.

[0070] S4. After the obtained battery is left standing for 24 hours, charge it with a current of 0.1C.

[0071] S5. Disassemble the fully charged battery in the glove box. After the obtained electrode sheets are cleaned and dried with NMP, DSC tests are performed. The parameters of the DSC test are as follows: Take 2 - 3 mg of the positive electrode sheet in the glove box and place it at the bottom of the crucible. Drop 1.7 mg of 1 mol / L LiPF6 solution (the solvent includes EC and DMC with a volume ratio of 1:1) so that the LiPF6 solution is evenly distributed on the surface of the electrode sheet. Seal the crucible in a special mold; put the sealed crucible into a differential scanning calorimeter (TADSC25), introduce nitrogen, and perform the test at a heating rate of 10 °C / min, with the maximum temperature set at 350 °C.

[0072] Table 1 shows the DSC measurement peaks obtained based on the above S1 - S5, as well as the specific values of α and β in Examples 1 - 10. The above DSC measurement peaks correspond to the critical temperature (°C) at which the high - nickel ternary positive electrode material in the example changes from a layered structure to a rock - salt phase structure. The higher the peak, that is, the higher the critical temperature, the better the thermal safety of the corresponding example.

[0073] It should be noted that the sintering temperature for the high - temperature sintering treatment of the precursor, lithium source, and additive in Examples 1 - 10 is 750 °C. For the corresponding precursor and high - nickel ternary positive electrode material, please refer to 1.

[0074] For the high - nickel ternary positive electrode materials (polycrystalline) in Examples 1 - 10, use a Gatan 697 Ilion II ion milling machine to cut, so that the cross - section contains the center of the high - nickel ternary positive electrode materials (polycrystalline) in Examples 1 - 10. Further, the α and β parameters are obtained by measuring the number of sides of the primary particles on the cross - section of the secondary sphere, the length of any straight line, and the number of primary particles passed through using dimension measurement software. Among them, β is the average value of the number parameters β of the primary particles on 10 line segments on the same cross - section. For specific reference, please refer to Figure 2 。

[0075] Table 1

[0076]

[0077]

[0078] Note: In Table 1, M in the molecular formula of the high - nickel ternary positive electrode material uniformly represents the doping element, and the subscript of M is the sum of the doping element contents in the corresponding high - nickel ternary positive electrode material.

[0079] As shown in Table 1, the smaller the values of α and β, the higher the DSC peak temperature of the corresponding cathode material, that is, the better the thermal safety. Obviously, the smaller the values of α and β, the more fully the primary particles inside the corresponding cathode material grow, and the stress generated between the primary particles is not concentrated. Therefore, the secondary particles (i.e., the cathode material in the examples) are more stable and have better thermal safety. Among them, the α and β parameters of Example 3 are the smallest, the corresponding DSC peak temperature is the highest, and the corresponding thermal safety performance is the best.

[0080] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A method for determining the thermal safety of a high-nickel ternary cathode material, characterized in that, it includes: Obtaining a cross-section of the high-nickel ternary cathode material; wherein, the high-nickel ternary cathode material is a secondary particle composed of primary particles; Determining the quantity parameter β of the primary particles on any line segment passing through the center of the cross-section, and / or, the edge number parameter α of the primary particles on the cross-section; wherein, the endpoints of the line segment are located on the edge of the cross-section, and β is obtained by the following formula: β = N / L, N is the number of primary particles on the line segment, L is the length of the line segment, the length unit is micrometer, and α is obtained by the following formula: α = M / S, M is the sum of the edge numbers of all the primary particles on the cross-section, S is the area of the cross-section, and the area unit is square micrometer; Determining the thermal safety of the high-nickel ternary cathode material according to β and / or α; The cross-section is the maximum cross-section passing through the center of the high-nickel ternary cathode material; The determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes: When the value of β is less than 2.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good; The determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes: When the value of α is less than 7.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

2. The method according to claim 1, characterized in that, The determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes: When the product of α and β is less than 12.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

3. The method according to claim 1 or 2, characterized in that, The determining the thermal safety of the high-nickel ternary cathode material according to β and / or α includes: When the ratio of α to β is less than 6.0, it is determined that the thermal safety of the high-nickel ternary cathode material is good.

4. The method according to claim 1, characterized in that, The molecular formula of the high-nickel ternary cathode material is: Li x Ni a Co b Mn c Al d M 1-a-b-c-d O 2 ; where M is at least one of Zr, Mo, Ca, Mg, Ba, B, Ti, Sr, Nb, Y, and W, 1 < x < 1.2, 0.8 ≤ a < 0.95, 0 < b < 0.2, 0 ≤ c < 0.2, 0 ≤ d < 0.2, 0 ≤ 1 - a - b - c - d < 0.06; and c and d are not both 0 at the same time.

5. The method according to claim 4, characterized in that, The high-nickel ternary cathode material is obtained by the following method: Obtained by performing high-temperature sintering treatment on a mixture of a high-nickel ternary precursor and a lithium source; wherein, the molecular formula of the high-nickel ternary precursor is: Ni x Co y Mn z Al P (OH) 2 , or Ni x Co y Mn z Al P CO 3 , 0.8 ≤ x < 0.95, 0 < y < 0.2, 0 ≤ z < 0.2, 0 ≤ p < 0.2, and z and p are not simultaneously 0; When the high-nickel ternary cathode material contains a doping element M, a mixture of the high-nickel ternary precursor, a lithium source, and a doping source corresponding to the doping element is subjected to high-temperature sintering treatment.

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