Patent Application
20230025787
The present disclosure relates to the technical field of lithium-ion batteries, for example, a cobalt-free positive electrode material, a method for preparing the same, a positive electrode of a lithium-ion battery and a lithium battery.
At present, increasingly high requirements are imposed on the safety, range and cost of lithium-ion power batteries in the field of new energy vehicles. Among four main materials of a power battery, the performance of a positive electrode material is critical to the overall performance of the battery and the cost of the positive electrode material accounts for 30-40% of the total cost of the power battery. Therefore, to improve the performance of the battery and reduce the cost of the battery, it is necessary to improve the performance of the positive electrode material and reduce the cost of the positive electrode material.
Cobalt element in lithium nickel manganese cobalt oxides (NCM) positive electrodes widely applied at present is expensive and easy to cause environmental pollution so that the content of cobalt in a ternary positive electrode material needs to be reduced or the material needs to be free of cobalt. However, due to a relatively small primary particle size and a D50 of 2-4 um, a sheet-like cobalt-free single crystal positive electrode material is easy to agglomerate in a dry coating process, resulting in poor coating uniformity. Moreover, the lack of cobalt in a cobalt-free material results in poor conductivity and a bad rate capability.
At present, no solution for improving the sheet-like cobalt-free single crystal positive electrode material has been reported.
Therefore, it is of great significance to study and develop a cobalt-free positive electrode material.
The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.
The present disclosure provides a cobalt-free positive electrode material, a method for preparing the same, a positive electrode of a lithium-ion battery and a lithium battery.
In an embodiment, the present disclosure provides a cobalt-free positive electrode material including a core and a shell coating the core, where the core is a cobalt-free positive electrode material and has a chemical formula of LiNixMnyO2, where 0.55≤x≤0.95 and 0.05≤y≤0.45; and the shell includes a coating agent and carbon.
In an embodiment provided by the present disclosure, the cobalt-free positive electrode material is not easy to agglomerate in a dry coating process and has good coating uniformity so that the conductivity of a cobalt-free single crystal positive electrode material can be improved.
In an embodiment, with reference to a total weight of the core, a content of the shell is 0.1-1.0% by weight, for example, 0.1% by weight, 0.2% by weight, 0.3% by weight, 0.5% by weight, 0.6% by weight, 0.8% by weight, 1.0% by weight or the like.
In an embodiment, the content of the shell is 0.3-1.0% by weight, for example, 0.3% by weight, 0.4% by weight, 0.5% by weight, 0.7% by weight, 0.8% by weight, 0.9% by weight, 1.0% by weight or the like.
In an embodiment, the coating agent is at least one of Al2O3 and ZrO2.
In an embodiment, a content of the coating agent is 0.25-0.3% by weight, for example, 0.25% by weight, 0.28% by weight, 0.29% by weight, 0.30% by weight or the like; and a content of carbon is 0.35-0.45% by weight, for example, 0.35% by weight, 0.36% by weight, 0.38% by weight, 0.40% by weight, 0.41% by weight, 0.43% by weight, 0.45% by weight or the like.
In an embodiment, the positive electrode material is a single crystal material.
In an embodiment, the core is a single crystal material.
The material formed after the surface of the single crystal core is coated with the shell may also be considered as a single crystal material.
In an embodiment, the positive electrode material has an average particle size of 1-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm or the like.
In an embodiment, the positive electrode material has an average particle size of 2-4 μm.
In an embodiment, the present disclosure provides a method for preparing the cobalt-free positive electrode material. The method includes:
(1) mixing a lithium salt and a precursor and performing a reaction to obtain a cobalt-free positive electrode material, where the precursor has a chemical formula of NixMny(OH)2, where 0.55≤x≤0.95 and 0.05≤y≤0.45;
(2) mixing the cobalt-free positive electrode material, a coating agent and a conductive substance and performing calcination; and
(3) crushing the substance after step (2) to obtain the cobalt-free positive electrode material.
In an embodiment provided by the present disclosure, the addition of the conductive substance can improve the dispersibility of particles and a coating effect. Moreover, the preparation method is simple and can be applied on a large scale.
In an embodiment provided by the present disclosure, the method for preparing the cobalt-free positive electrode material can improve dispersibility in a coating process of the cobalt-free positive electrode material and the conductivity of the cobalt-free positive electrode material.
In an embodiment, in step (1), conditions of the reaction include a temperature of 800-1000° C., for example, 800° C., 820° C., 840° C., 850° C., 880° C., 900° C., 925° C., 950° C., 1000° C. or the like, and a duration of 10-20 h, for example, 10 h, 12 h, 14 h, 15 h, 18 h, 19 h, 20 h or the like.
In an embodiment, in step (2), conditions of the calcination include a N2 atmosphere, a temperature of 300-700° C., for example, 300° C., 400° C., 500° C., 550° C., 600° C., 700° C. or the like, and a duration of 5-10 h, for example, 5 h, 6 h, 7 h, 8.5 h, 9 h, 10 h or the like.
In an embodiment, in step (2), with reference to a total weight of the precursor, an amount of the lithium salt is 47-50% by weight, for example, 47% by weight, 48% by weight, 48.5% by weight, 49% by weight, 50% by weight or the like; an amount of the conductive substance is 0.105-0.525% by weight, for example, 0.105% by weight, 0.150% by weight, 0.200% by weight, 0.250% by weight, 0.300% by weight, 0.350% by weight, 0.400% by weight, 0.450% by weight, 0.500% by weight or the like; an amount of the cobalt-free positive electrode material is 105-108% by weight, for example, 105% by weight, 106% by weight, 107% by weight, 108% by weight or the like; and an amount of the coating agent is 0.21-0.525% by weight, for example, 0.21% by weight, 0.23% by weight, 0.30% by weight, 0.35% by weight, 0.40% by weight, 0.45% by weight or the like.
In an embodiment, with reference to the total weight of the precursor, the amount of the lithium salt is 47-48% by weight, for example, 47% by weight, 47.2% by weight, 47.5% by weight, 48% by weight or the like; the amount of the conductive substance is 0.315-0.525% by weight, for example, 0.315% by weight, 0.350% by weight, 0.400% by weight, 0.450% by weight, 0.480% by weight, 0.500% by weight or the like; the amount of the cobalt-free positive electrode material is 105-106% by weight, for example, 105% by weight, 105.2% by weight, 105.5% by weight, 106% by weight or the like; and the amount of the coating agent is 0.21-0.315% by weight, for example, 0.21% by weight, 0.25% by weight, 0.28% by weight, 0.3% by weight or the like.
In an embodiment, the conductive substance is selected from one or more of conductive carbon black, graphite and graphene.
In an embodiment, the conductive substance is conductive carbon black.
In an embodiment, the conductive substance has a specific surface area of 50-200 m2/g, for example, 50 m2/g, 60 m2/g, 80 m2/g, 90 m2/g, 100 m2/g, 120 m2/g, 150 m2/g, 180 m2/g, 200 m2/g or the like, and an average particle size of 50-500 nm, for example, 50 nm, 80 nm, 100 nm, 125 nm, 150 nm, 170 nm, 200 nm, 240 nm, 280 nm, 320 nm, 350 nm, 400 nm, 500 nm or the like.
In an embodiment, the coating agent is selected from at least one of Al2O3 and ZrO2.
In an embodiment, the present disclosure provides a cobalt-free positive electrode material prepared by the method. The conductivity of the cobalt-free positive electrode material prepared by the method can be improved.
In an embodiment, the present disclosure provides a positive electrode of a lithium-ion battery. The positive electrode of a lithium-ion battery contains the cobalt-free positive electrode material.
In an embodiment, the present disclosure provides a lithium-ion battery. The lithium-ion battery includes a positive electrode and a negative electrode, where the positive electrode is the positive electrode of a lithium-ion battery.
The drawings are used to provide a further understanding of technical solutions of the present disclosure, constitute a part of the specification, explain the technical solutions of the present disclosure in conjunction with embodiments of the present application and do not limit the technical solutions of the present disclosure.
Technical solutions of the present disclosure are further described below through specific examples.
In an embodiment, the present disclosure provides a cobalt-free positive electrode material including a core and a shell coating the core, where the core is a cobalt-free positive electrode material and has a chemical formula of LiNixMnyO2, where 0.55≤x≤0.95 and 0.05≤y≤0.45;
and the shell includes a coating agent and carbon.
Inventors of the present disclosure have found through experiments that in the related art, a cobalt-free positive electrode material is easy to agglomerate in a dry coating process due to a relatively small particle size, resulting in poor coating uniformity; and the conductivity of the cobalt-free positive electrode material cannot be improved.
In an embodiment provided by the present disclosure, the inventors mix a cobalt-free positive electrode material, a coating agent and a conductive substance and then perform calcination. The conductive substance having a relatively large specific surface area and a relatively small particle size can improve dispersibility in a coating process. Meanwhile, the conductive substance having good conductivity can improve the conductivity of the cobalt-free positive electrode material.
Additionally, in an embodiment of the present disclosure, the positive electrode material is a cobalt-free positive electrode material, where the cobalt-free positive electrode material is stable in structure, does not depend on a cobalt element, and has a lower cost than a cobalt-containing material.
It is to be noted that in an embodiment provided by the present disclosure, the cobalt-free positive electrode material belongs to a single crystal material, and it can be determined from SEM images that the cobalt-free positive electrode material in the embodiment of the present disclosure is a sheet-like cobalt-free single crystal positive electrode material.
In an embodiment, with reference to a total weight of the core, a content of the shell is 0.1-1.0% by weight.
In an embodiment, with reference to the total weight of the core, the content of the shell is 0.3-1.0% by weight.
In an embodiment provided by the present disclosure, the content of the shell is limited to the preceding range, which can improve the dispersibility in the coating process and the conductivity of the cobalt-free positive electrode material.
In an embodiment, the coating agent is at least one of Al2O3 and ZrO2. This may also be expressed as “the coating agent is Al2O3 and/or ZrO2”.
In an embodiment, a content of the coating agent is 0.25-0.3% by weight and a content of carbon is 0.35-0.45% by weight.
In an embodiment, 0.55≤x≤0.8 and 0.2≤y≤0.45.
In an embodiment, x may be 0.75, 0.55, 0.8 or any value within a range formed by any two of these point values.
In an embodiment, y may be 0.2, 0.25, 0.45 or any value within a range formed by any two of these point values.
In an embodiment, x is 0.75 and y is 0.25.
In an embodiment, x+y=1.
In an embodiment, the positive electrode material is a single crystal material.
In an embodiment, the positive electrode material has an average particle size of 1-10 μm.
In an embodiment, the positive electrode material has an average particle size of 2-4 μm.
In the present disclosure, it is to be noted that the “average particle size” refers to D50 of the positive electrode material.
In an embodiment, the “average particle size” is measured by a laser particle size analyzer.
In an embodiment, the present disclosure provides a method for preparing a cobalt-free positive electrode material. The method includes the steps below.
(1) A lithium salt and a precursor are mixed and a reaction is performed so that a cobalt-free positive electrode material is obtained, where the precursor has a chemical formula of NixMny(OH)2, where 0.55≤x≤0.95 and 0.05≤y≤0.45.
(2) The preceding cobalt-free positive electrode material, a coating agent and a conductive substance are mixed and calcination is performed.
(3) The substance after step (2) is crushed so that the cobalt-free positive electrode material is obtained.
In an embodiment, in step (1), conditions of the reaction include a temperature of 800-1000° C. and a duration of 10-20 h.
In an embodiment, in step (1), the conditions of the reaction include a temperature of 900-1000° C. and a duration of 10-15 h.
In an embodiment, in step (2), conditions of the calcination include a N2 atmosphere, a temperature of 300-700° C. and a duration of 5-10 h.
In an embodiment, in step (2), the conditions of the calcination include a temperature of 300-500° C. and a duration of 5-7 h.
In an embodiment, in steps (1) and (2), mixing is performed in a high-speed mixer.
In an embodiment, steps (1) and (2) are performed at a stirring rate of 800-1000 rpm.
In an embodiment, steps (1) and (2) are performed at a stirring rate of 900-1000 rpm.
In an embodiment, in step (2), with reference to a total weight of the precursor, an amount of the lithium salt is 47-50% by weight, an amount of the conductive substance is 0.105-0.525% by weight, an amount of the cobalt-free positive electrode material is 105-108% by weight, and an amount of the coating agent is 0.21-0.525% by weight.
In an embodiment, in step (2), with reference to the total weight of the precursor, the amount of the lithium salt is 47-48% by weight, the amount of the conductive substance is 0.315-0.525% by weight, the amount of the cobalt-free positive electrode material is 105-106% by weight, and the amount of the coating agent is 0.21-0.315% by weight.
In an embodiment, the conductive substance is selected from one or more of conductive carbon black, graphite and graphene.
In an embodiment, the conductive substance is conductive carbon black.
In an embodiment, the conductive carbon black is selected from one or more of acetylene black, Super P and Super S, where Super P and Super S are models. Specifically, Super P has a specific surface area of 120 m2/g and an average particle size of 55 nm, and Super S has a specific surface area of 80 m2/g and an average particle size of 125 nm.
In an embodiment, the conductive substance has a specific surface area of 50-200 m2/g and an average particle size of 50-500 nm.
In an embodiment, the conductive substance has a specific surface area of 100-200 m2/g.
In an embodiment, the conductive substance has an average particle size of 50-200 nm.
In an embodiment, the coating agent is selected from Al2O3 and/or ZrO2.
In an embodiment, the lithium salt is LiOH and/or Li2CO3.
In an embodiment, in step (3), the material may be crushed through roll crushing and jet milling and then sieved to give the final product.
In an embodiment, the present disclosure provides a cobalt-free positive electrode material prepared by the preceding method.
In an embodiment, the present disclosure provides a positive electrode of a lithium-ion battery. The positive electrode of a lithium-ion battery contains the preceding cobalt-free positive electrode material.
In an embodiment, the present disclosure provides a lithium-ion battery. The lithium-ion battery includes a positive electrode and a negative electrode, where the positive electrode is the preceding positive electrode of a lithium-ion battery.
Typical but non-limiting examples of the present disclosure are described below.
In the following examples and comparative examples:
(1) A content of an element was tested by an ICP that was purchased from PerkinElmer Enterprise Management (Shanghai) Co., Ltd. and whose model was Avio 500.
(2) Surface morphology and dispersibility were tested by a SEM that was purchased from ZEISS in Germany and whose model was SUPRA 55VP.
(3) Initial charge/discharge performance and cycle performance were measured by testing an assembled button cell. The button cell was manufactured as follows:
A positive electrode material, conductive carbon black and a binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 92:4:4, and the mixture was made into a slurry with N-methylpyrrolidone (NMP) as a solvent, coated on an aluminum foil, and vacuum-dried at 90° C. so that a positive electrode sheet was obtained. A negative electrode sheet (lithium sheet), the positive electrode sheet, an electrolyte (LiPF6 of 1 mol/L with ethylene carbonate (EC):ethyl methyl carbonate (EMC)=1:1) and a separator were then assembled into a cell.
(4) Test of initial charge/discharge performance
The resulting cell was subjected to a charge/discharge test in a 25±2° C. environment and at a charge/discharge voltage of 3.0-4.4 V and a current density of 0.1 C/0.1 C. Test of cycle performance after 50 cycles: The resulting cell was subjected to the charge/discharge test in a 25±2° C. environment and at a charge/discharge voltage of 3.0-4.4 V and a current density of 0.1 C/0.1 C (0.5 C for charge and 1 C for discharge).
(5) The lithium salt was purchased from Ganfeng Lithium Co., Ltd.; the precursor was purchased from Jinchi Energy Materials Co., Ltd.; the coating agent was purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.; and the conductive substance was purchased from Tianjin YouMeng Chemical Technology Co., Ltd.
This example provides a cobalt-free positive electrode material prepared by a method described below.
(1) LiOH (48 g) and a precursor NixMny(OH)2 (100 g) (with x being 0.75 and y being 0.25) were mixed in a high-speed mixer at a stirring rate of 950 rpm and then reacted for 10 h at a high temperature of 950° C. so that a cobalt-free positive electrode material was synthesized.
(2) The cobalt-free positive electrode material (105 g), a coating agent (specifically Al2O3) (0.25 g) and conductive carbon black (0.35 g) with a specific surface area of 200 m2/g were mixed in the high-speed mixer at a stirring rate of 1000 rpm, and the mixed materials were heated for 5 h at 400° C. in a N2 atmosphere, where with reference to a total weight of the precursor, an amount of the lithium salt was 48% by weight, an amount of the conductive substance was 0.35% by weight, an amount of the cobalt-free positive electrode material was 105% by weight, and an amount of the coating agent was 0.25% by weight.
(3) The preceding material was crushed through roll crushing and jet milling and sieved by a 300-400 mesh sieve.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as C1—LiNi0.75Mn0.25O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.75Mn0.25O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.6% by weight (where the content of the coating agent Al2O3 was 0.25% by weight and the content of carbon (the conductive carbon black) was 0.35% by weight). The coating layer was uniform.
This example provides a cobalt-free positive electrode material prepared by a method described below.
(1) LiOH (47 g) and a precursor NixMny(OH)2 (100 g) (with x being 0.55 and y being 0.45) were mixed in a high-speed mixer at a stirring rate of 900 rpm and then reacted for 12 h at a high temperature of 980° C. so that a cobalt-free positive electrode material was synthesized.
(2) The cobalt-free positive electrode material (106 g), a coating agent (specifically ZrO2) (0.30 g) and conductive carbon black (0.40 g) with a specific surface area of 120 m2/g were mixed in the high-speed mixer at a stirring rate of 980 rpm, and the mixed materials were heated for 6 h at 500° C. in a N2 atmosphere, where with reference to a total weight of the precursor, an amount of the lithium salt was 47% by weight, an amount of the conductive substance was 0.40% by weight, an amount of the cobalt-free positive electrode material was 106% by weight, and an amount of the coating agent was 0.30% by weight.
(3) The preceding material was crushed through roll crushing and jet milling and sieved by a 300-400 mesh sieve.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as C2—LiNi0.55Mn0.45O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.55Mn0.45O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.7% by weight (where the content of the coating agent ZrO2 was 0.30% by weight and the content of carbon (the conductive carbon black) was 0.40% by weight). The coating layer was uniform.
This example provides a cobalt-free positive electrode material prepared by a method described below.
(1) LiOH (48 g) and a precursor NixMny(OH)2 (100 g) (with x being 0.80 and y being 0.20) were mixed in a high-speed mixer at a stirring rate of 950 rpm and then reacted for 15 h at a high temperature of 900° C. so that a sheet-like cobalt-free single crystal positive electrode material was synthesized.
(2) The sheet-like cobalt-free single crystal positive electrode material (105.5 g), a coating agent (specifically Al2O3) (0.28 g) and conductive carbon black (0.45 g) with a specific surface area of 150 m2/g were mixed in the high-speed mixer at a stirring rate of 1000 rpm, and the mixed materials were heated for 7 h at 500° C. in a N2 atmosphere, where with reference to a total weight of the precursor, an amount of the lithium salt was 48% by weight, an amount of the conductive substance was 0.45% by weight, an amount of the cobalt-free positive electrode material was 105.5% by weight, and an amount of the coating agent was 0.28% by weight.
(3) The preceding material was crushed through roll crushing and jet milling and sieved by a 300-400 mesh sieve.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as C3—LiNi080Mn0.20O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi080Mn0.20O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.73% by weight (where the content of the coating agent Al2O3 was 0.28% by weight and the content of carbon (the conductive carbon black) was 0.45% by weight). A coating layer was uniform.
This example provides a cobalt-free positive electrode material prepared by a method described below.
The cobalt-free positive electrode material was prepared by the same method as that in Example 1 except the differences below.
In step (1), “LiOH” was replaced with “Li2CO3”.
In step (2), “conductive carbon black with a specific surface area of 200 m2/g” was modified to “conductive carbon black with a specific surface area of 80 m2/g” and with reference to the total weight of the precursor, the amount of the lithium salt was 47% by weight, the amount of the conductive substance was 0.35% by weight, the amount of the cobalt-free positive electrode material was 105% by weight, and the amount of the coating agent was 0.25% by weight.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as C4—LiNi0.75Mn0.25O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.75 Mn0.25O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.6% by weight (where the content of the coating agent Al2O3 was 0.25% by weight and the content of carbon (the conductive carbon black) was 0.35% by weight). The coating layer was uniform.
This example provides a cobalt-free positive electrode material prepared by a method described below.
The cobalt-free positive electrode material was prepared by the same method as that in Example 1 except the differences below.
In step (1), “reacted for 10 h at a high temperature of 950° C.” was modified to “reacted for 20 h at a high temperature of 880° C.”.
In step (2), “heated for 5 h at 400° C. in a N2 atmosphere” was modified to “heated for 8 h at 700° C. in a N2 atmosphere”.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as C5—LiNi0.75Mn0.25O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.75Mn0.25O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.6% by weight (where the content of the coating agent Al2O3 was 0.25% by weight and the content of carbon (the conductive carbon black) was 0.35% by weight). The coating layer was uniform.
A cobalt-free positive electrode material was prepared under the same conditions as those in Example 1 except a difference that conductive carbon black was not added in step (2).
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as LiNi0.75Mn0.25O2.
Additionally, in the present disclosure, it is to be noted that in
Therefore, the addition of carbon black in a coating process is conducive to improving the initial charge/discharge efficiency and specific discharge capacity of the material.
A cobalt-free positive electrode material was prepared by the same method as that in Example 1 except the differences below.
In step (2), with reference to the total weight of the precursor, the amount of the lithium salt was 48% by weight, the amount of the conductive substance was 0.08% by weight, the amount of the cobalt-free positive electrode material was 105% by weight, and the amount of the coating agent was 0.25% by weight.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as DC2—LiNi0.75Mn0.25O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.75Mn0.25O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.33% by weight (where the content of the coating agent Al2O3 was 0.25% by weight and the content of carbon (the conductive carbon black) was 0.08% by weight).
A cobalt-free positive electrode material was prepared by the same method as that in Example 1 except the differences below.
In step (1), “reacted for 10 h at a high temperature of 950° C.” was modified to “reacted for 8 h at a high temperature of 1100° C.”.
In step (2), “heated for 5 h at 400° C. in a N2 atmosphere” was modified to “heated for 12 h at 800° C. in a N2 atmosphere”.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as DC3—LiNi0.75Mn0.25O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.75Mn0.25O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.55% by weight (where the content of the coating agent Al2O3 was 0.20% by weight and the content of carbon (the conductive carbon black) was 0.35% by weight).
A cobalt-free positive electrode material was prepared under the same conditions as those in Example 1 except a difference that in step (2), common conductive carbon black, that is, carbon black without a large specific surface area, was added. Specifically, the common conductive carbon black had a specific surface area of 25 m2/g. In addition, in the present disclosure, the common conductive carbon black was purchased from Tianjin Xinglongtai Chemical Products Technology Co., Ltd., and its model was xlt−1.
The final product, which is a cobalt-free positive electrode material, was obtained. The positive electrode material was expressed as LiNi0.75Mn0.25O2. The positive electrode material included a core and a shell coating the core, where the core was a cobalt-free positive electrode material and had a chemical formula of LiNi0.75Mn0.25O2, and the shell included the coating agent and carbon. With reference to a total weight of the core, a content of the shell was 0.6% by weight (where the content of the coating agent Al2O3 was 0.25% by weight and the content of carbon (the conductive carbon black) was 0.35% by weight). However, the coating layer was not uniform.
N samples were prepared by the methods in Comparative Example 1 and Example 1, and three samples were randomly selected therefrom to be tested by an ICP. The results are shown by a comparison of ICP test results in Table 1.
As can be seen from Table 1, the material with carbon black in Example 1 is higher than the material without carbon black in Comparative Example 1 in terms of the uniformity of each of three elements, Ni, Mn and Al (coating agent).
Accordingly, n samples were prepared by the methods in Comparative Examples 2 to 4 and Examples 2 to 5, and three samples were randomly selected therefrom to be tested by the ICP. As a result, the materials with carbon black in Examples 2 to 5 are all higher than the materials without carbon black in Comparative Examples 2 to 4 in terms of the uniformity of each of the three elements, Ni, Mn and Al (coating agent).
The materials prepared in Comparative Examples 1 to 4 and Examples 1 to 5 were tested for rate capabilities. The results are shown in Table 2.
The following can be seen from the results in Table 2:
(1) It can be seen that after the addition of carbon black in the coating process in Example 1, the cobalt-free positive electrode material prepared in Example 1 has a significant improved rate capability at ⅓C to 4 C. For example, the specific discharge capacity of the material with carbon black in Example 1 is increased to 173.1 mAh/g at 1 C rate; and the specific discharge capacity of the material with carbon black in Example 1 reaches 150.9 mAh/g at 4 C rate. On the contrary, the specific discharge capacity of the material without carbon black in Comparative Example 1 is only 164.5 mAh/g at 1 C rate; and the specific discharge capacity of the material without carbon black in Comparative Example 1 is only 138.6 mAh/g at 4 C rate. This proves that the rate capability is improved because carbon black has relatively good electron conductivity and the coating of carbon black can improve the electrochemical activity of the cobalt-free positive electrode material and thus improve the rate capability of the material.
Similarly, the cobalt-free positive electrode material C4—LiNi0.75Mn0.25O2 prepared in Example 4 under the condition that “conductive carbon black with a specific surface area of 200 m2/g” is modified to “conductive carbon black with a specific surface area of 80 m2/g” has a lower capacity and a worse rate capability than that in Example 1.
The cobalt-free positive electrode material C5—LiNi0.75Mn0.25O2 prepared in Example 5 under the conditions that “heated for 5 h at 400° C. in a N2 atmosphere” is modified to “heated for 8 h at 700° C. in a N2 atmosphere” and that with reference to the total weight of the core, the content of the shell is 0.6% by weight has a reduced capacity due to a high temperature in step (2).
The cobalt-free positive electrode material DC2—LiNi0.75Mn0.25O2 prepared in Comparative Example 2 and the cobalt-free positive electrode material prepared in Comparative Example 3 have lower capacities and worse rate capabilities than that in Example 1. Comparative examples show that the capacity increases as X increases and the capacity decreases as X decreases.
The materials prepared in Examples 2 to 5 and Comparative Examples 2 to 4 were subjected to initial charge/discharge tests at 25° C., a voltage of 3.0-4.4 V and 0.1 C/0.1 C. The results are shown in Table 3.
The materials prepared in Examples 2 to 5 and Comparative Examples 2 to 4 were subjected to cycle performance tests at 25° C., a voltage of 3.0-4.4 V and 0.5 C/1 C. The results are shown in Table 3.
The following can be seen from the results in Table 3:
The results of Examples 2 and 3 show that the cycle performance decreases when X is greater than 0.75. The results of Examples 4 and 5 show that a conductive agent with a large specific surface area and suitable reaction conditions (first calcination) and calcination conditions (second calcination) such as the temperature are conducive to improving the cycle performance.
For the material prepared in Comparative Example 3, since the temperatures among the reaction conditions (first calcination) and calcination conditions (second calcination) are too high, part of the coating agent enters the interior of the main material and the content of the shell is reduced. Since conductive carbon black with a relatively small specific surface area is used in Comparative Example 4, the coating layer is not uniform. The results of Comparative Examples 2 to 4 show that too small amount of the conductive agent, too high temperatures among the reaction conditions (first calcination) and calcination conditions (second calcination) and a relatively small conductive agent are not conducive to improving the cycle performance of the cobalt-free material.
In summary, the present disclosure can improve the dispersibility of particles and a coating effect through the addition of the conductive substance. The conductivity of the cobalt-free positive electrode material prepared by the method can be improved. Additionally, the preparation method is simple and can be applied on a large scale.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202010677212.9 | Jul 2020 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2020/134519 | 12/8/2020 | WO |
