CN115458736A - Method for determining thermal safety of high-nickel ternary cathode material - Google Patents

Abstract

The application discloses a method for determining the thermal safety of a high-nickel ternary cathode material, which is used for prejudging the thermal safety of the high-nickel ternary cathode material, so that the efficiency of determining the performance of the high-nickel ternary cathode material is improved. The method comprises the following steps: acquiring a section of the high-nickel ternary cathode material; wherein the high-nickel ternary cathode material is secondary particles formed by primary particles; determining the number parameter beta of the primary particles on any line segment passing through the center of the section plane and/or the number parameter alpha of the primary particles on the section plane; wherein the end point of the line segment is located at the profile edge, and β is obtained by: β = N/L, N being the number of primary particles on the line segment, L being the length of the line segment, and α is obtained by: α = M/S, M being the sum of the number of sides of all the primary particles on the cross section, S being the area of the cross section; and determining the thermal safety of the high-nickel ternary cathode material according to beta and/or alpha.

Description

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

technical field

This application relates to the technical field of new energy batteries, in particular to a method for determining the thermal safety of high-nickel ternary cathode materials.

Background technique

At present, ternary cathode materials are gradually being put into the market due to their good lithium ion extraction and insertion performance and stable structure. For the structural stability of the positive electrode material, the positive electrode material is generally tested for structural stability for a set period of time. Then, the cathode material is assembled into a lithium battery, and the stability of the lithium battery is tested to determine the thermal safety of the lithium battery when it is put into the market. However, the above-mentioned stability (ie, thermal safety) test has the problems of long test period, low efficiency and high cost; thus, there is a lack of a method for pre-judging the thermal safety of the prepared material.

Contents of the invention

The present application provides a method for determining the thermal safety of high-nickel ternary cathode materials, which is used to predict the thermal safety of high-nickel ternary cathode materials, thereby improving the efficiency of determining the performance of high-nickel ternary cathode materials.

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

Obtaining a profile of a high-nickel ternary positive electrode material; wherein, the high-nickel ternary positive electrode material is a secondary particle composed of primary particles;

Determine the number parameter β of the primary particles on any line segment passing through the center of the section, and/or, the side number parameter α of the primary particles on the section; wherein, the endpoint of the line segment is located at the Section edge, the β is obtained by the following formula: β=N/L, N is the number of the primary particles on the line segment, L is the length of the line segment, and the length unit is micron, and the α is obtained by the following The formula obtains: α=M/S, M is the sum of the number of sides of all the primary particles on the section, S is the area of the section, and the unit of the area is square micron;

The thermal safety of the high-nickel ternary positive electrode material is determined according to β and/or α.

In the embodiment of the present application, the thermal safety of the high-nickel ternary cathode material is judged by determining the intrinsic properties of the high-nickel ternary cathode material: the number of edges and the quantity of the primary particles on the profile of the high-nickel ternary cathode material. The problem of low efficiency caused by performing stability (thermal safety) tests on all high-nickel ternary cathode materials in the prior art is avoided.

In a possible implementation manner, the section is the largest section passing through the center of the high-nickel ternary positive electrode material.

A possible implementation manner, 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 high-nickel ternary positive electrode material has good thermal safety.

A possible implementation manner, 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 high-nickel ternary positive electrode material has good thermal safety.

A possible implementation manner, 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 high-nickel ternary positive electrode material has good thermal safety.

A possible implementation manner, 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 positive electrode material is good.

In a possible embodiment, the molecular formula of the nickel-rich ternary positive electrode material is: Li _x Ni _a Co _b Mn _c Al _d M _1-abcd O ₂ ; wherein, M is Zr, Mo, Ca, Mg, Ba, At least one of 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 -abcd<0.06; and c and d are not 0 at the same time.

In a possible implementation manner, the high-nickel ternary positive electrode material is obtained by the following method:

It is obtained by high-temperature sintering treatment of 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 0 at the same time;

When the high-nickel ternary positive electrode material contains the doping element M, the mixture of the high-nickel ternary precursor, the lithium source and the doping source corresponding to the doping element is sintered at high temperature.

In a second aspect, the present application provides a high-nickel ternary positive electrode material, including:

The high-nickel ternary positive electrode material is a secondary particle composed of primary particles, and the section passing through the midpoint of the high-nickel ternary positive electrode material at least meets the following requirements: α<7, and/or, β<2; wherein,

β is the quantity parameter of the primary particles on any line segment passing through the section, the endpoint of the line segment is located at the edge of the section, and the β is obtained by the following formula: β=N/L, N is the The quantity of the primary particle, L is the length of the line segment, and the length unit is micron; α is obtained by the following formula: α=M/S, M is the number of sides of each primary section on the section The total amount, S is the area of the section, and the unit of the area is square micron.

The embodiment of the present application proposes a high-nickel ternary positive electrode material whose profile satisfies α<7, and/or, β<2. Since the high-nickel ternary positive electrode material is under the aforementioned conditions, one The stress between the particles and the primary particles is effectively relieved, so 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.

A possible implementation manner, α×β<12.

A possible implementation manner, α/β<6.

A possible implementation manner, the molecular formula of the high-nickel ternary positive electrode material is:

Li _x Ni _a Co _b Mn _c Al _d M _1-abcd 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-abcd<0.06; and c and d are not 0 at the same time.

In a possible implementation manner, the critical temperature at which the phase transition of the high-nickel ternary positive electrode material occurs is not less than 212°C, and the phase transition indicates that the transition from layered structure to rock-salt phase structure occurs in the high-nickel ternary positive electrode material Variety.

Description of drawings

Fig. 1 is a schematic flow chart of a method for determining the thermal safety of a high-nickel ternary positive electrode material provided by the embodiment of the present application;

Fig. 2 is a schematic diagram of determining α and β on the section of Example 3-4 provided by the embodiment of the present application.

detailed description

Aiming at the lack of a method for determining the thermal safety of ternary cathode materials in the prior art, this application proposes a method for determining the thermal safety of high-nickel ternary cathode materials: The number of sides of the particles, and/or the number of primary particles on the line segment passing through the center of the cross-section in any direction, determines the thermal safety of the high-nickel ternary cathode material; thereby avoiding all positive electrode materials and lithium batteries where the positive electrode material is located Both conduct thermal stability tests, leading to the problem of low efficiency in determining the performance of cathode materials.

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

Further, the good thermal safety described in the embodiments of the present application means that the corresponding high-nickel ternary positive electrode material reduces safety risks in practical applications; The chemical reaction (mainly oxidation-reduction reaction) inside the high-nickel ternary cathode material leads to high-temperature aggregation inside the material, resulting in a phase transition of the material, causing the internal structure of the high-nickel ternary cathode material to collapse, releasing lattice oxygen, and even Combustion, fire and explosion with electrolyte and its decomposition products.

In order to better understand the above technical solutions, the technical solutions of the present application will be described in detail below through the accompanying drawings and specific examples. It should be understood that the embodiments of the present application and the specific features in the examples are detailed descriptions of the technical solutions of the present application, and It is not a limitation to the technical solutions of the present application, and the embodiments of the present application and the technical features in the embodiments can be combined without conflict.

Please refer to Figure 1. This application proposes a method for determining the thermal safety of high-nickel ternary cathode materials to judge the thermal safety of high-nickel ternary cathode materials. The method specifically includes the following implementation steps:

Step 101: Obtain a profile of a high-nickel ternary positive electrode material.

Wherein, the high-nickel ternary positive electrode material is secondary particles composed of primary particles.

Specifically, the molecular formula of the nickel-rich ternary cathode material is: Li _x Ni _a Co _b Mn _c Al _d M _1-abcd O ₂ ; wherein, M is Zr, Mo, Ca, Mg, Ba, B, Ti, Sr , at least one of 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-abcd<0.06; And c and d are not 0 at the same time.

Further, in one embodiment of the present application, when the high-nickel ternary positive electrode material contains both manganese and aluminum elements, that is, when both c and d are not 0, c+d<0.2, and d<0.06 .

Furthermore, the high-nickel ternary positive electrode material can be obtained by mixing a lithium source with a high-nickel ternary precursor for high-temperature sintering. Moreover, when the high-nickel ternary positive electrode material contains the doping element M, the mixture of the high-nickel ternary precursor, the lithium source and the doping source corresponding to the doping element is sintered at high temperature.

In the embodiment of the present application, the high-nickel ternary precursor and molecule are: Ni _x Co _{y Mnz} Al _P (OH) ₂ , or Ni _x Co _{y Mnz} Al _P CO ₃ .

Wherein, x, y, z, 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 0 at the same time.

In one embodiment of the present application, in the high-nickel ternary precursor Ni _x Co _y Mnz Al _P (OH) ₂ , or Ni _x Co _y Mn _z Al _P CO ₃ , when _z and p are not When 0, z+p<0.2, and p<0.06.

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.

Wherein, the end point of the line segment is located at the edge of the section, the β is obtained by the following formula: β=N/L, N is the number of the primary particles on the line segment, L is the length of the line segment, and the The unit of length is micron, and the α is obtained by the following formula: α=M/S, M is the sum of the number of sides of all the primary particles on the section, S is the area of the section, and the unit of the area is square micron.

The number of sides of the primary particles on the above cross section corresponds to the grain boundaries of the primary particles. That is, the number of sides of the primary particles is the number of sides whose angles on the grain boundaries constituting the primary particles are not zero. On the section, however, for adjacent primary grains with overlapping grain boundaries, only one of the sides of the overlapping grain boundaries is recorded. Based on the above rules, the number of edges of all primary particles in the secondary sphere section can be determined by size measurement software.

Specifically, for secondary particles composed of primary particles, the more fully grown the primary particles are, the better the thermal stability of the secondary particles is, and accordingly, the better the thermal safety is.

Therefore, in the examples of the present application, β is used to determine the growth of the primary particles inside the secondary particles (high-nickel ternary cathode material).

Furthermore, when the high-nickel ternary cathode material is applied to a lithium battery, along with the extraction and insertion of lithium ions, the primary particles show a corresponding volume shrinkage and expansion phenomenon, so the internal defects of the secondary particles, that is, in the primary particle On the premise of not being spherical, the more the number of sides of the primary particle, the less significant the stress concentration phenomenon when the primary particle shrinks and expands. Therefore, the thermal stability of the high-nickel ternary cathode material is better, and accordingly, the thermal safety is also better. the better.

Therefore, in the embodiment of the present application, the stress condition of the primary particle in the secondary particle is determined by determining α.

After determining β and/or α, step 103 can be performed.

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

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

Further, β may be the average number of quantity parameters on multiple line segments on different sides on the same profile.

It is worth noting that the thermal safety described in the examples of the present application is a good indication that the critical temperature for the high-nickel material to change from a layered structure to a rock-salt phase structure at high temperature is high, that is, the phase transition of the high-nickel material causes a structural The critical temperature for collapse is high. The aforementioned critical temperature is at least 212°C.

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, which can effectively determine the high-nickel ternary cathode material. thermal safety. At the same time, high-nickel ternary cathode materials of different preparation batches and/or preparation parameters can be screened and judged to avoid unnecessary stability (thermal safety) tests, thereby effectively improving the performance test efficiency of materials, as well as thermal The efficiency of judging whether the security is good or not.

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

Wherein, β is the number parameter of primary particles on any line segment passing through the section, and the endpoint of the line segment is located at the edge of the section, and the β is obtained by the following formula: β=N/L, N is the The quantity of the primary particles on the line segment, L is the length of the line segment, and the unit of the length is micron.

α is obtained by the following formula: α=M/S, M is the total number of sides of each primary section on the section, S is the area of the section, and the unit of the area is square micron.

In the examples of the present application, the critical temperature for the phase transition of the high-nickel ternary cathode material with good thermal safety is not less than 212°C, and the phase transition indicates that the high-nickel ternary cathode material has a layered structure to a rock-salt phase Structural changes.

In one embodiment of the present application, α×β<12. Preferably, α×β<5.

In one embodiment of the present application, α/β<6. Preferably, α/β<4.

Further illustrate by embodiment 1-10 below:

Embodiment 1-10 all carries out DSC test by following steps, to determine DSC peak temperature, specifically test procedure is:

S1. Disperse the positive electrode material and acetylene black in a mass ratio of 98:2 in an NMP solution containing 5% PVDF and stir for 20 minutes, wherein the concentration of the positive electrode material is 60%.

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

S3, cut the dried pole pieces into discs with a diameter of 15 mm, and in the glove box according to the positive electrode shell, pole piece, electrolyte (EC/DMC/EMC volume ratio 1:1, LiPF6 concentration is 1mol/L), separator ( CelgardPP/PE/PP three-layer composite film), lithium sheet, electrolyte, nickel foam, and negative electrode case are assembled and sealed to obtain a battery.

S4. The obtained battery is charged with a current of 0.1 C after standing for 24 hours.

S5. The charged battery is disassembled in the glove box, and the obtained pole pieces are cleaned and dried by NMP and then subjected to DSC test. The parameters of the DSC test are: in the glove box, take 2-3 mg of the positive electrode piece and place it on 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 The above-mentioned LiPF6 solution is evenly distributed on the surface of the pole piece, and the crucible is sealed in a special mold; the sealed crucible is placed in a differential scanning calorimeter (TADSC25), and nitrogen gas is introduced to carry out the heating at a heating rate of 10°C/min. For the test, the maximum temperature was set at 350°C.

Table 1 shows the DSC measurement peak values obtained based on the above S1-S5, and the corresponding specific values of α and β in Examples 1-10. The above-mentioned DSC measurement peak value corresponds to the critical temperature (°C) at which the high-nickel ternary positive electrode material in the embodiment changes from a layered structure to a rock-salt phase structure. The higher the peak value, that is, the higher the critical temperature, the higher the thermal safety of the corresponding embodiment. it is good.

It should be noted that the sintering temperature for the high-temperature sintering treatment of the precursor, lithium source, and additives in Examples 1-10 is 750°C. Please refer to 1 for the corresponding precursor and high-nickel ternary cathode material.

For the high-nickel ternary positive electrode material (polycrystalline) in embodiment 1-10, utilize Gatan 697 Ilion II ion grinder to cut, make section contain the high nickel ternary positive electrode material (polycrystalline) of embodiment 1-10 center. Further, the α and β parameters are obtained by measuring the side number of primary particles in the secondary sphere profile, the length of any straight line and the number of primary particles passing through the size measurement software. Among them, β is the average value of the number parameter β of primary particles on 10 line segments on the same profile. Please refer to Figure 2 for details.

Table 1

Note: M in the molecular formula of the high-nickel ternary cathode material in Table 1 uniformly represents the doping element, and the subscript of M is the sum of the content of the doping element in the corresponding high-nickel ternary cathode material.

As shown in Table 1, the smaller the value 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 value of α and β, the more sufficient the growth of the primary particles inside the corresponding positive electrode material, and the stress generated between the primary particles is not concentrated, so the secondary particles (ie, the positive electrode material in the embodiment) are more stable and thermally safe. Sex is better. 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.

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 also intends to include these modifications and variations.

Claims (13)

1. A method for determining the thermal safety of a high-nickel ternary cathode material is characterized by comprising the following steps:

acquiring a section of the high-nickel ternary cathode material; the high-nickel ternary cathode material is secondary particles formed by primary particles;

determining the number parameter beta of the primary particles on any line segment passing through the center of the section, and/or the number parameter alpha of the primary particles on the section; wherein the end point of the line segment is located at the profile edge, and β is obtained by: β = N/L, N being the number of primary particles on the line segment, L being the length of the line segment, the length being in microns, and α being obtained by the following equation: α = M/S, M being the sum of the number of sides of all said primary particles on said cross-section, S being the area of said cross-section, said area having units of square microns;

and determining the thermal safety of the high-nickel ternary cathode material according to beta and/or alpha.

2. The method of claim 1, wherein the profile is a maximum profile through a center of the high-nickel ternary positive electrode material.

3. The method of claim 2, wherein determining the thermal safety of the high-nickel ternary positive electrode material from β and/or a comprises:

when the value of beta is less than 2.0, the high-nickel ternary cathode material is determined to have good thermal safety.

4. The method of claim 2, wherein determining the thermal safety of the high-nickel ternary cathode material as a function of β and/or a comprises:

when the value of alpha is less than 7.0, the high-nickel ternary cathode material is determined to have good thermal safety.

5. The method of any one of claims 2-4, wherein determining the thermal safety of the high-nickel ternary positive electrode material from β and/or a comprises:

when the product of alpha and beta is less than 12.0, the thermal safety of the high-nickel ternary cathode material is determined to be good.

6. The method of any one of claims 2-4, wherein determining the thermal safety of the high-nickel ternary positive electrode material from β and/or a comprises:

when the ratio of alpha to beta is less than 6.0, the high-nickel ternary cathode material is determined to have good thermal safety.

7. The method of claim 1, wherein the high nickel ternary positive electrode material has a formula of: li _x Ni _a Co _b Mn _c Al _d M _1-a-b-c-d O ₂ (ii) a 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.

8. The method of claim 7, wherein the high nickel ternary positive electrode material is obtained by:

performing high-temperature sintering treatment on the mixture of the high-nickel ternary precursor and a lithium source to obtain the high-nickel ternary precursor; wherein the molecular formula of the high-nickel ternary precursor is as follows: 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 0 at the same time;

and when the high-nickel ternary cathode material contains a doping element M, carrying out high-temperature sintering treatment on the mixture of the high-nickel ternary precursor, the lithium source and the doping source corresponding to the doping element.

9. A high nickel ternary positive electrode material, comprising:

the high-nickel ternary cathode material is secondary particles formed by primary particles, and a section passing through the midpoint of the high-nickel ternary cathode material at least meets the following requirements: alpha < 7, and/or beta < 2; wherein,

the beta is a quantity parameter of primary particles on any line segment passing through the section, the end point of the line segment is positioned at the edge of the section, and the beta is obtained by the following formula: β = N/L, N being the number of primary particles on the line segment, L being the length of the line segment, the length being in microns; α is obtained by the following formula: α = M/S, M being the total number of sides of each of said primary sections on said section, S being the area of said section, said area having the unit of square microns.

10. The high-nickel ternary positive electrode material of claim 9, wherein α x β < 12.

11. The high nickel ternary positive electrode material of claim 9 or 10, wherein α/β < 6.

12. The high-nickel ternary positive electrode material of claim 9, wherein the high-nickel ternary positive electrode material has a molecular formula of:

Li _x Ni _a Co _b Mn _c Al _d M _1-a-b-c-d O ₂ (ii) a 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.

13. The high-nickel ternary positive electrode material according to claim 9, wherein the high-nickel ternary positive electrode material has a critical temperature at which a phase transition occurs, which indicates that a change from a layered structure to a rock salt phase structure occurs in the high-nickel ternary positive electrode material, of not less than 212 ℃.

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