CN114481322B - A kind of quasi-spherical single crystal cathode material and preparation method thereof - Google Patents

Abstract

The invention provides a spherical-like single crystal positive electrode material, which is a layered lithium transition metal oxide positive electrode material containing Ni and M, wherein primary particles of the single crystal positive electrode material are spherical-like, and the average size is 2.0-2.3 mu M. The preparation method of the single crystal positive electrode material is characterized in that the precursor is subjected to low-temperature pre-oxidation and lithium mixing, and then a three-section primary sintering process is adopted, wherein the precursor is obtained through the first-section low-temperature heat preservation, the second-section short-time high-temperature heat preservation and the third-section long-time low-temperature heat preservation. The spherical single crystal anode material has small particles, higher tap density, difficult particle breakage, low internal resistance and good electrochemical performance.

Description

A kind of quasi-spherical single crystal cathode material and preparation method thereof

technical field

The invention belongs to the technical field of lithium ion battery materials, and relates to a quasi-spherical single crystal positive electrode material and a preparation method thereof.

Background technique

At present, the positive electrode materials that have been applied are divided into two types: secondary particle polycrystalline and primary particle single crystal. Among them, there are a large number of grain boundaries inside the polycrystal, and grain boundary cracking is prone to occur during the cycle, and the secondary particles are broken, resulting in a decline in performance stability. However, there is no grain boundary inside the single crystal, and the ability to resist cracking is strong, which can effectively slow down the accumulation of stress, suppress the generation of microcracks, and have more excellent cycle life and thermal stability.

In the prior art, CN 106910882 B prepares a micron-sized large single crystal layered positive electrode material based on a new method of step-by-step lithium addition to the precursor, which has higher tap density and compaction density, and can significantly increase the volumetric energy density of the layered positive electrode material; CN 106505193 B coats the surface with Li₂ZrO₃, Li₂SnO₃, LiNbO₃, Li₄Ti₅o₁₂with LiAlO₂The isofast ion conductor improves the rate performance and gram capacity of single crystal materials, and further improves the cycle performance of materials; CN 109216688 B mixes precursors, lithium sources, fluxes, etc., sprays and dries them, and then presses them to obtain lumps; sintering produces single crystal ternary materials with large particle size and uniform distribution, which have excellent high-temperature storage performance and high-temperature cycle performance.

The single crystal products developed by the existing technology are produced by adding lithium step by step or adding a co-solvent to produce large-grained single crystals with an average particle size of 3.0-5.0 μm, or secondary sintering after surface modification to improve the capacity and rate performance of the material. However, these methods have the following problems: the size of large-grained single crystals is too large, resulting in reduced gram capacity and rate performance, and increased internal resistance; large-grained single crystals are mostly irregular in shape, with obvious edges and corners, and internal stress is relatively concentrated. Partial fragmentation of particles is more likely to occur during the pole piece rolling process, and cycle performance is reduced; although surface modification can improve the performance of single crystal materials to a certain extent, it increases process complexity and manufacturing costs.

Contents of the invention

The purpose of the present invention is to provide a small-particle spherical single-crystal positive electrode material in order to solve the problems in the prior art. The positive electrode material has a high tap density, is not easily broken, has low internal resistance, and has good electrochemical performance.

Aiming at the technical problems of existing single crystal materials such as large particles, irregular shape, or complex preparation process, the inventors of the present invention found after painstaking research that by using a precursor with a certain particle size, first pre-oxidizing the precursor until a certain specific surface area is obtained, after mixing lithium and additives, performing a three-stage sintering process, first performing low-temperature long-term heat preservation, then high-temperature short-time heat preservation, and finally low-temperature long-term heat preservation, the spherical small particle single crystal layered lithium transition metal oxide cathode material can be obtained. The average size of primary particles of this single crystal positive electrode material is only 2.0-2.3 μm, so it has higher gram capacity, rate performance and lower battery internal resistance; the primary particle of this single crystal positive electrode material is spherical, with less bridging phenomenon between particles, high tap density, and the particles are not easy to break under rolling state.

To achieve the above object, the present invention provides the following technical solutions:

A quasi-spherical single crystal cathode material, the single crystal cathode material is a layered lithium transition metal oxide cathode material containing Ni and M, wherein M is one or more of Mn, Co, Al, Ti, Zr, B, Sr, Mg, Y, W, Si, the primary particles (particles) of the single crystal cathode material are spherical, and the average size of the primary particles (particles) is 2.0-2.3 μm (the average particle size is the actual size of the particles observed under the SEM image, Measurement method: use the length scale in the SEM shooting software, under the magnification of 2 ~ 3K, measure the vertical and horizontal dimensions of the primary particles in the picture respectively, the average value of the vertical and horizontal is the actual size of the particles, usually several particles can be taken, for example, the number of particles measured is 300 ~ 400, and finally the average value of all measured values is taken).

Preferably, the average aspect ratio of the primary particles of the single crystal positive electrode material is 1.0-1.1 (longitudinal is the distance in the long direction of the particle, transverse is the distance in the short direction perpendicular to the longitudinal direction, and the aspect ratio is the ratio of the two). The preferred single crystal positive electrode material with an average particle aspect ratio is conducive to further improving the compaction density of the single crystal positive electrode material, and can further improve the rolling resistance strength, that is, the particles are less likely to be broken under rolling state. The single crystal positive electrode material includes single crystal primary particles and secondary particles agglomerated by the single crystal primary particles, and the particle size D50 of the single crystal positive electrode material is 3.0-5.0 μm.

Preferably, the chemical formula of the single crystal cathode material is Li _x Ni _y M _1-y O ₂ , and 0.9≤x≤1.1, 0.5≤y≤0.95.

As a general inventive concept, the present invention also provides a method for preparing a spherical single crystal positive electrode material, comprising the following steps:

(1) Pre-oxidize the secondary particle precursor Ni _y M _1-y (OH) ₂ with a D50 of 2.0-4.0 μm to obtain a pre-oxidized precursor with a specific surface area of 60-80 m ² /g; where M is one or more than two of Mn, Co, Al, Ti, Zr, B, Sr, Mg, Y, W, and Si;

(2) Mixing the pre-oxidized precursor with a lithium source and an additive containing M'; the M' is one or more of Mn, Co, Al, Ti, Zr, B, Sr, Mg, Y, W, and Si;

(3) The obtained mixture is sintered in an oxidizing atmosphere. The sintering system is as follows: firstly, keep the temperature at 300-600°C for t1, then raise the temperature to 850-1000°C and keep it for t2, then lower the temperature to 300-600°C and keep it for t3, and then cool and pulverize to obtain the desired positive electrode material; wherein t2<t1, t2<t3.

(4) Preferably, in step (3), t1 is 10-15 hours; t2 is 3-6 hours; t3 is 10-15 hours.

Preferably, in step (3), the heating rate is 3-8° C./min. If the heating rate is too fast, the melting and reaction rate of the compound will be accelerated, so that the compounds cannot penetrate effectively, the effective reaction degree will be reduced, and the morphology and electrical properties of the product will be affected to a certain extent. If the heating rate is too slow, the energy consumption will be increased.

Preferably, in step (1), the pre-oxidation condition is: keep warm at 250-450° C. for 3-6 hours. The total metal mass percentage content in the precursor after pre-oxidation is 70-74%.

As a preference, in step (2), the lithium source is lithium hydroxide and/or lithium carbonate;

The M'-containing additive is an oxide or hydroxide containing M'; and M' is different from M;

The molar ratio of the lithium source, the M'-containing additive and the pre-oxidized precursor is 0.9-1.1:0.0-0.1:0.9-1.0.

Preferably, in step (3), before sintering, the mixture is compacted under a pressure of 5-20KN and cut into small pieces, which can further increase the contact area between the granular materials and increase the internal atmosphere of the materials, ensure sufficient contact and reaction between the materials and the materials, and between the materials and the atmosphere, and improve the uniformity and electrical properties of the product.

In step (3), the crushing is carried out by a fluidized bed jet mill, and the material with a D50 of 3.0-5.0 μm is collected after crushing to obtain the desired positive electrode material.

The positive electrode material prepared by the present invention adopts the precursor after low-temperature pre-oxidation with a particle size D50 of 2.0-4.0 μm, and is sintered once under the condition of a three-stage sintering curve to form a spherical single-crystal particle material with a particle size D50 of 3.0-5.0 μm, an average primary particle size of 2.0-2.3 μm, and an average primary particle aspect ratio of 1.0-1.1.

The precursor used in this single crystal cathode material has a specific surface area of 60-80 m ² /g after low-temperature pre-oxidation, which is conducive to the uniform diffusion of lithium salts on the surface of the precursor. When the specific surface area is too high, the product is difficult to mix evenly, and the consistency of the obtained material is poor. When the specific surface area is too low, it is not conducive to the uniform diffusion of lithium salts in the subsequent sintering process, and it is difficult to obtain materials with the required morphology and structure.

After the precursor is pre-oxidized at low temperature and mixed with lithium, this single crystal cathode material adopts a three-stage sintering process. The first long-term low-temperature heat preservation is conducive to the slow penetration of lithium salts in the crystal after decomposition, and can make the reaction more uniform, which is conducive to the formation of subsequent particle morphology and structure; the second short-term high-temperature heat preservation promotes the rapid formation of single-crystal morphology of the particles and reduces manufacturing costs; the third long-term low-temperature heat preservation is conducive to modifying the particle shape and ensuring the final formation of spherical single-crystal particles.

Compared with the prior art, the present invention has the following beneficial effects:

1. The average primary particle size of the single crystal positive electrode material of the present invention is small, and it is a spherical primary particle, so it has higher gram capacity and rate performance and lower battery internal resistance, less bridging phenomenon between particles, and the particles are not easily broken under rolling state. Compared with the existing large-grain single crystal material with an irregular shape and an average primary particle size of 3.0-5.0 μm, the tap density is equivalent, but the cycle performance is better.

2. The present invention pre-oxidizes the precursor with a certain particle size until the pre-oxidized precursor with a certain specific surface area is obtained. After mixing lithium and additives, a three-stage sintering process is performed. First, the low temperature is kept for a long time, and then the high temperature is kept for a long time, and finally the low temperature is kept for a long time, and the spherical small particle single crystal layered lithium transition metal oxide positive electrode material can be obtained.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings used in the description of the embodiments or prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings can also be obtained based on these drawings without creative work.

Fig. 1 is the product SEM figure of embodiment 1, comparative example 1, comparative example 2 and comparative example 3, wherein (a), (b) is the product SEM figure of embodiment 1, (c), (d), (e) is the product SEM figure of comparative example 1, comparative example 2 and comparative example 3 respectively.

Detailed ways

In order to facilitate the understanding of the present invention, the invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Example 1:

(1) Pre-oxidized precursor Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ with a particle size D50 of 3.0 μm was incubated at 300 °C for 5 h under air conditions to obtain a pre-oxidized precursor with a metal content of 72.5 % and a specific surface area of 75 m ² /g.

(2) LiOH·H ₂ O was mixed with the obtained precursor and WO ₃ in a molar ratio of 1.04:0.98:0.02.

(3) After the mixture is put into a bowl, it is compacted with a pressure of 10KN and cut into small pieces. It is sintered once under an oxygen atmosphere with a heating rate of 3°C/min. The sintering curves are 500°C for 12 hours, 930°C for 4 hours, and 500°C for 12 hours, then naturally cool to room temperature to obtain small block materials.

(4) The small block materials were pulverized by a fluidized bed jet mill, and collected to obtain a quasi-spherical single crystal cathode material Li _1.04 Ni _0.6 Co _0.2 Mn _0.18 W _0.02 O ₂ with a particle size D50 of 3.75 μm, an average primary particle size of 2.10 μm, and an average primary particle aspect ratio of 1.05.

Example 2:

(1) Pre-oxidized precursor Ni _0.5 Co _0.2 Mn _0.3 (OH) ₂ with a particle size D50 of 3.4 μm was incubated at 350 °C for 5 hours under air conditions to obtain a pre-oxidized precursor with a metal content of 72.8 % and a specific surface area of 73 m ² /g.

(2) Li ₂ CO ₃ was mixed with the obtained precursor and H ₃ BO ₃ in a molar ratio of 1.04:0.98:0.01.

(3) After the mixture is filled in a bowl, it is compacted with a pressure of 10KN and cut into small pieces. It is sintered once in an air atmosphere with a heating rate of 4°C/min. The sintering curves are 600°C for 12 hours, 950°C for 4 hours, and 600°C for 12 hours, then naturally cool to room temperature to obtain small blocks.

(4) The small block materials were pulverized by a fluidized bed jet mill, and collected to obtain a quasi-spherical single crystal cathode material Li _1.04 Ni _0.5 Co _0.2 Mn _0.29 B _0.01 O ₂ with a particle size D50 of 3.75 μm, an average primary particle size of 2.05 μm, and an average primary particle aspect ratio of 1.05.

Comparative example 1:

(1) LiOH·H ₂ O was mixed with precursors Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ and WO ₃ with a particle size D50 of 3.0 μm in a molar ratio of 1.04:0.98:0.02.

(2) After the mixture is filled in a bowl, it is compacted with a pressure of 10KN and cut into small pieces. It is sintered once under an oxygen atmosphere with a heating rate of 4°C/min. The sintering curves are 500°C for 12 hours, 930°C for 4 hours, and 500°C for 12 hours, then naturally cool to room temperature to obtain small block materials.

(3) The small block materials were pulverized by a fluidized bed jet mill, and the single crystal cathode material Li _1.04 Ni _0.6 Co _0.2 Mn _0.18 W _0.02 O ₂ with a particle size D50 of 3.74 μm and an average primary particle size of 2.02 μm was collected.

Comparative example 2:

(1) Pre-oxidized precursor Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ with a particle size D50 of 3.0 μm was incubated at 350 °C for 5 h under air conditions to obtain a pre-oxidized precursor with a metal content of 72.5 % and a specific surface area of 72 m ² /g.

(2) LiOH·H ₂ O was mixed with the obtained precursor and WO ₃ in a molar ratio of 1.04:0.98:0.02.

(3) After the mixture is placed in a bowl, it is sintered once under an oxygen atmosphere, and the temperature is raised to 930°C at a heating rate of 4°C/min for 12 hours, and then naturally cooled to room temperature to obtain a large block material.

(4) The bulk material was pulverized by a fluidized bed jet mill, and the agglomerated single crystal cathode material Li _1.04 Ni _0.6 Co _0.2 Mn _0.18 W _0.02 O ₂ with a particle size D50 of 3.70 μm and an average primary particle size of 1.30 μm was collected.

Comparative example 3:

(1) LiOH·H ₂ O was mixed with precursors Ni _0.6 Co _0.2 Mn _0.2 (OH) ₂ and WO ₃ with a particle size D50 of 3.0 μm in a molar ratio of 1.04:0.98:0.02.

(2) After the mixture is placed in a bowl, it is sintered once under an oxygen atmosphere, and the temperature is raised to 960°C at a heating rate of 4°C/min for 12 hours, and then naturally cooled to room temperature to obtain a large block material.

(3) The bulk material was pulverized by a fluidized bed jet mill, and the large single crystal cathode material Li _1.04 Ni _0.6 Co _0.2 Mn _0.18 W _0.02 O ₂ with a particle size D50 of 3.85 μm and an average primary particle size of 3.10 μm was collected.

Table 1 Sample physical and chemical properties data table

Table 2 Sample button cell performance data sheet

analyze:

Fig. 1 is the SEM image of the material prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3. As can be seen from the figure, Example 1 is a spherical small single crystal morphology, Comparative Example 1 is an irregular small single crystal morphology, Comparative Example 2 is a small particle agglomerated morphology, and Comparative Example 3 is an irregular large single crystal morphology.

The difference between Example 1 and Comparative Example 1 and Comparative Example 2 is that Comparative Example 1 is sintered by using a precursor that has not undergone low-temperature pre-oxidation treatment. Comparative Example 2 is sintered by using a precursor that has undergone low-temperature pre-oxidation treatment, but the mixture has not been pressure-compacted and cut into small pieces and sintered using a one-stage sintering curve. However, Example 1 is that the low-temperature pre-oxidized precursor is mixed with lithium salt and additives. The mixture is compacted under a pressure of 10KN and cut into small pieces, and sintered under a three-stage sintering curve. Knotted. From the point of view of physicochemical properties and button battery performance, the physical and chemical properties of Example 1 and Comparative Example 1 are at the same level, but Comparative Example 1 has lower button capacity, higher internal resistance, and lower cycle performance; it shows that the porosity of the precursor increases after pre-oxidation, and the super large specific surface area can be more fully and uniformly contacted with lithium salt during the mixing process. More lithium enters the crystal structure after sintering, which is more conducive to the formation of a complete crystal structure and a round spherical shape; The compaction and dicing process, the lithium salt melting time is short, the synthesis reaction is not sufficient and uniform, the primary particles are small, the consistency is poor, and they are in an agglomerated state, resulting in a decrease in tap density, an increase in the amount of residual alkali, and a decrease in internal resistance and cycle performance. It shows that the multi-stage sintering curve and the mixture are compacted and cut into small pieces are conducive to the adequacy and uniformity of the synthesis reaction, and can promote the formation of spherical single crystal morphology.

The difference between Example 1 and Comparative Example 3 is that Comparative Example 3 also adopts the common single crystal material preparation process, and increases the sintering temperature to increase the single crystal particle size, thereby increasing the tap density. From the perspective of physical and chemical properties, although the tap density of Comparative Example 3 is improved, the amount of residual alkali is reduced, and the BET is reduced, but the diffusion path of lithium ions is increased, resulting in a significant decrease in gram capacity and rate performance, and increased internal resistance. increases, the cycle performance decreases.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered as the protection scope of the present invention.

Claims (8)

1. The spherical-like single crystal positive electrode material is characterized in that the single crystal positive electrode material is a layered lithium transition metal oxide positive electrode material containing Ni and M, wherein M is 1 or more than 2 of Mn, co, al, ti, zr, B, sr, mg, Y, W, si, primary particles of the single crystal positive electrode material are spherical-like, and the average size of the primary particles is 2.0-2.3 mu M; the average aspect ratio of primary particles of the single crystal positive electrode material is 1.0-1.1, the single crystal positive electrode material comprises single crystal primary particles and secondary particles agglomerated by the single crystal primary particles, and the granularity D50 of the single crystal positive electrode material is 3.0-5.0 mu m; the chemical formula of the single crystal positive electrode material is Li _x Ni _y M _1-y O ₂ And x is more than or equal to 0.9 and less than or equal to 1.1,0.5, y is more than or equal to 0.95.

2. A method for preparing the spheroid single crystal positive electrode material according to claim 1, comprising the steps of:

(1) The secondary particle precursor Ni with the D50 of 2.0-4.0 mu m is prepared _y M _1-y (OH) ₂ Preoxidation is carried out to obtain the catalyst with specific surface area of 60-80 m ² Pre-oxidized precursor/g; wherein M is 1 or more than 2 of Mn, co, al, ti, zr, B, sr, mg, Y, W, si;

(2) Mixing the pre-oxidized precursor with a lithium source and an additive containing M'; m' is 1 or more than 2 of Mn, co, al, ti, zr, B, sr, mg, Y, W, si;

(3) Sintering the obtained mixture in an oxidizing atmosphere, wherein the sintering is as follows: firstly preserving heat at 300-600 ℃ for t1, then heating to 850-1000 ℃ for t2, then cooling to 300-600 ℃ for t3, and then cooling and crushing to obtain the required anode material; where t2< t1, t2< t3.

3. The method for producing a spheroid single crystal positive electrode material according to claim 2, wherein in the step (3), t1 is 10 to 15 hours; t2 is 3-6 h; t3 is 10-15 h.

4. The method for producing a spheroidic single crystal positive electrode material according to claim 2, wherein in the step (3), the temperature rising rate during sintering is 3 to 8 ℃/min.

5. The method for producing a spheroid single crystal positive electrode material according to claim 2, wherein in the step (1), the pre-oxidation conditions are: preserving heat for 3-6 h at 250-450 ℃.

6. The method for producing a spheroid single crystal positive electrode material according to claim 2, wherein in the step (2), the lithium source is lithium hydroxide and/or lithium carbonate;

the additive containing M 'is an oxide or hydroxide containing M'; and M' is different from M.

7. The method for preparing a spheroid single crystal positive electrode material according to claim 2, wherein the molar ratio of the lithium source, the additive containing M' and the pre-oxidation precursor is 0.9 to 1.1:0.0 to 0.1:0.9 to 1.0.

8. The method for producing a spheroidic single crystal positive electrode material according to claim 2, wherein in the step (3), the step of compacting the mixture is further included before sintering; the compacting comprises the steps of compacting under the pressure of 5-20 KN and cutting into small pieces.