Cathode active material for all-solid-state battery and method of manufacturing same

Abstract

The present invention relates to a cathode active material for an all-solid-state battery and a method of manufacturing same. Specifically, the present invention relates to: a cathode active material for an all-solid-state battery, wherein a lithium metal oxide is washed with a solution containing CoSO4, thus precipitating cobalt on the surface; and a method for manufacturing same.

Description

Cathode active material for all-solid-state batteries and method for producing the same

[0001] The present invention relates to a cathode active material for an all-solid-state battery and a method for producing the same. Specifically, the present invention relates to a cathode active material for an all-solid-state battery and a method for producing the same, wherein cobalt is precipitated on the surface of a lithium metal oxide by washing the material with a solution containing CoSO4.

[0002]

[0003] The electrochemical properties of the cathode active material for an all-solid-state battery that uses solid powder as an electrolyte may vary depending on the surface contact area between the cathode material and the electrolyte, surface reaction characteristics, and whether physical contact is maintained after expansion / contraction during the charge / discharge process, unlike general lithium-ion batteries that use liquid electrolytes.

[0004] In order to manufacture positive electrode materials for all-solid-state batteries with excellent electrochemical properties, attempts have been made to reduce the average particle size of the positive electrode material, and various other studies are being conducted, including single crystal / polycrystal, controlling the sintering temperature, changing the surface coating material, and changing the surface coating method.

[0005] In particular, numerous studies have been conducted on treating the surface of cathode materials using a rinsing solution to reduce residual lithium impurities, a major cause of cathode material deterioration. While distilled water is typically effective in reducing residual lithium, it presents a challenge in preventing surface damage from rinsing. A key issue is the easy dissolution of manganese during rinsing, which reduces the structural stability of the cathode material and, consequently, dramatically reduces its service life.

[0006] Therefore, there is a need for a technology for a cathode active material and a method for manufacturing the same that can improve the life characteristics by effectively reducing residual lithium impurities on the surface of the cathode active material and recovering water damage.

[0007]

[0008] The technical problem to be solved by the present invention is to provide a cathode active material for an all-solid-state battery in which residual lithium is removed by washing lithium metal oxide with an aqueous solution containing CoSO4, and cobalt is precipitated on the surface, thereby recovering surface damage caused by washing.

[0009] Another technical problem to be solved by the present invention is to provide a method for manufacturing a cathode active material for an all-solid-state battery having the aforementioned advantages.

[0010]

[0011] According to one embodiment of the present invention, a cathode active material for an all-solid-state battery comprises: a core including an NCM-based lithium transition metal oxide; and a cobalt material-containing coating layer positioned on a surface of the core; wherein the content of Ni in the NCM-based lithium transition metal oxide is 80 mol% or more based on 100 mol% of the total amount of transition metal, and the cobalt contained in the coating layer may include at least one of metallic cobalt and a cobalt compound.

[0012] According to another embodiment of the present invention, a method for manufacturing a cathode active material for an all-solid-state battery may include: a step of mixing a nickel salt, a cobalt salt, a manganese salt, and a complexing agent to form a transition metal hydroxide by a coprecipitation method; a step of mixing the transition metal hydroxide and a lithium compound to form a lithium transition metal hydroxide; a step of first heat-treating the lithium transition metal hydroxide to form a lithium transition metal oxide; a step of washing the lithium transition metal oxide with a washing solution containing CoSO4; a step of second heat-treating the washed lithium transition metal oxide; and a step of coating the second heat-treated lithium transition metal oxide with a protective coating layer that suppresses an interface reaction with a solid electrolyte.

[0013]

[0014] According to one embodiment of the present invention, a cathode active material for an all-solid-state battery can remove residual lithium and simultaneously precipitate cobalt on the surface by washing lithium metal oxide with a solution containing CoSO4, thereby repairing damage to the surface of the cathode active material for an all-solid-state battery caused by washing.

[0015] A method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment of the present invention can provide a cathode active material having the aforementioned advantages.

[0016]

[0017] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0018] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0019] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0020] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0021] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0022] Hereinafter, a cathode active material for an all-solid-state battery according to one embodiment of the present invention will be described.

[0023] According to one embodiment, a cathode active material for an all-solid-state battery includes: a core including an NCM-based lithium transition metal oxide; and a cobalt material-containing coating layer positioned on a surface of the core; wherein the content of Ni in the NCM-based lithium transition metal oxide is 80 mol% or more based on 100 mol% of the total amount of transition metal, and the cobalt contained in the coating layer may include at least one type of metallic cobalt and a cobalt compound.

[0024] When the content of Ni is within the above-mentioned range, the energy density and capacity of the positive electrode active material can be high.

[0025] In one embodiment, the content of the cobalt material in the coating layer of the positive electrode active material for an all-solid-state battery may be in the range of 0.5 mol% to 2 mol% with respect to the total mole number of transition metals constituting the core including the NCM-based lithium transition metal oxide.

[0026] When the content of the cobalt material falls within the aforementioned range, safety and life characteristics may be improved. However, when the content of the cobalt material falls below the lower limit of the aforementioned range, surface damage to the positive electrode active material may not be sufficiently healed, resulting in reduced life characteristics. Furthermore, when the content of the cobalt material exceeds the upper limit of the aforementioned range, although a large amount of expensive Co is introduced into the positive electrode active material, thereby improving stability, there is the problem of a rapid increase in the price of the positive electrode active material, making it unsuitable for commercialization.

[0027] According to one embodiment, the weight ratio of the coating layer to the total weight of the core of the positive electrode active material for an all-solid-state battery may be in the range of 1:100 to 20:100.

[0028] When the weight ratio of the coating layer is within the above-mentioned range, both the capacity and life characteristics of the positive electrode active material can be evenly improved. However, when the weight ratio of the coating layer is below the lower limit of the above-mentioned range, the amount of the coating layer capable of reacting with the surface of the positive electrode material is not sufficiently formed, so that the water damage on the surface of the positive electrode active material is not healed and is exposed, so that the desorption phenomenon of lithium ions from the positive electrode active material does not proceed smoothly, resulting in a rapid decrease in the charge capacity and discharge capacity.

[0029] In addition, if the weight ratio of the coating layer exceeds the upper limit of the above-mentioned range, the coating layer has the effect of excessively blocking the core, so that the insertion and de-insertion of lithium ions are not smooth, and it may be difficult to sufficiently express the capacity.

[0030]

[0031] Hereinafter, a method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment of the present invention will be described.

[0032] According to another embodiment, a method for manufacturing a cathode active material for an all-solid-state battery may include: a step of mixing a nickel salt, a cobalt salt, a manganese salt, and a complexing agent to form a transition metal hydroxide by a coprecipitation method; a step of mixing the transition metal hydroxide and a lithium compound to form a lithium transition metal hydroxide; a step of first heat-treating the lithium transition metal hydroxide to form a lithium transition metal oxide; a step of washing the lithium transition metal oxide with a washing solution containing CoSO4; a step of second heat-treating the washed lithium transition metal oxide; and a step of coating a protective coating layer that suppresses an interface reaction with a solid electrolyte on the second heat-treated lithium transition metal oxide.

[0033] In the washing step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the solvent included in the washing solution may include at least one selected from water, methanol, and ethanol. Preferably, the solvent may be water.

[0034] In the washing step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the CoSO4 content in the washing solution may be 1 to 30 wt% based on the total weight of the washing solution.

[0035] When the CoSO4 content satisfies the above-mentioned range, lithium impurities remaining on the surface of the lithium transition metal oxide can be effectively removed, and the effect of recovering damage caused by water rinsing can also be maximized. However, when the CoSO4 content is not included in the above-mentioned range, residual lithium impurities may not be removed, or water rinsing damage may not be fully recovered, which may cause side reactions or deterioration in the positive electrode active material, rapidly reducing the life characteristics of the cell.

[0036] In addition, the coating layer using the above CoSO4 solution requires heat treatment, and the heat treatment temperature is 600℃ to 700℃, and the heat treatment time is in the range of 5 hours to 10 hours. If it is below the lower limit of the heat treatment temperature and time range, sufficient recovery from the washing damage is not achieved, and if it exceeds the upper limit, the Co component diffuses into the core particle, reducing the fraction utilized to overcome the washing damage occurring on the surface of the cathode material. In addition, it is effective to separately add a certain amount of LiOH at a level of 2500 to 3500 ppm to the core cathode material particles during the heat treatment process. This is because it directly supplies the insufficient Li component in the area where washing damage has occurred, thereby restoring the layered structure of the cathode material eluted during the washing step. If it is lower than the lower limit, the effect is limited because the lithium supply is limited, and if it is added above the upper limit, the phenomenon of residual lithium increasing again may occur.

[0037] In the washing step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the weight ratio of the lithium transition metal oxide to the washing solution may be in the range of 100:100 to 80:100.

[0038] When the weight ratio of the lithium transition metal oxide is within the aforementioned range, the lithium impurities remaining on the surface of the lithium transition metal oxide can be effectively removed, and the effect of recovering damage caused by water rinsing can also be maximized. However, when the weight ratio of the lithium transition metal oxide is not within the aforementioned range, the residual lithium impurities may not be removed, or the water rinsing damage may not be fully recovered, which may cause side reactions or deterioration in the positive electrode active material, thereby drastically reducing the life characteristics of the cell.

[0039] In the washing step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the time for washing the lithium transition metal oxide may be 5 minutes or more and less than 11 minutes.

[0040] When the above-mentioned rinsing time is within the aforementioned range, lithium impurities remaining on the surface of the lithium transition metal oxide can be effectively removed, and the effect of recovering damage caused by rinsing can also be maximized. However, when the rinsing time is not within the aforementioned range, residual lithium impurities may not be removed, or rinsing damage may not be fully recovered, which may cause side reactions or deterioration in the cathode active material, drastically reducing the life characteristics of the cell.

[0041] The washing step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment may additionally include a stirring process, and the stirring speed may be 100 rpm to 300 rpm.

[0042] When the above stirring process is included and the stirring speed satisfies the above-mentioned range, the washing time of the lithium transition metal oxide can be shortened while the washing effect and damage recovery are maximized, thereby reducing the process cost. On the other hand, when the stirring speed is below the lower limit of the above-mentioned range, it is difficult to effectively shorten the washing time. In addition, when the stirring speed exceeds the upper limit of the above-mentioned range, the energy input may be large compared to the effect of reducing residual lithium impurities and recovering damage, which may increase the process cost.

[0043]

[0044] Hereinafter, examples, comparative examples, and experimental examples of the present invention will be described. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to these examples. Furthermore, various modifications and variations are possible within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and such modifications may also fall within the scope of the present invention.

[0045] <Example 1>

[0046] (1) 1st firing stage

[0047] Ni with an average particle size of 4㎛ 0.83 Co 0.12 Mn0.05 (OH)2 transition metal hydroxide precursor and lithium raw material LiOH H2O were mixed in a molar ratio of 1:1.03 to form a mixture. 1 kg of the mixture was charged into a tube furnace, and the temperature was increased at a rate of 2.5°C / min. The sintering temperature was maintained at 730°C for 10 hours, and then the temperature was lowered at a rate of 2.5°C / min. Pure O2 was supplied so that the O2 concentration could be maintained at 99% or higher during the sintering, so that the first lithium transition metal oxide Ni having an average particle size (D50) of 4 to 5 μm was formed. 0.83 Co 0.12 Mn 0.05 O2 was formed.

[0048] (2) CoSO4 water washing coating and drying step

[0049] The first lithium transition metal oxide manufactured in the first firing is Ni 0.83 Co 0.12 Mn 0.05 After stirring O2600g with 600g of distilled water for 6 minutes, add 2M concentration of CoSO47H2O as a coating solution.

[0050] After reacting for 4 minutes, it was dehydrated for 3 minutes using a filter press and then vacuum dried for 12 hours in a vacuum oven maintained at 140℃.

[0051] (3) Heat treatment stage

[0052] For the powder that had been vacuum-dried, approximately 3000 ppm of LiOH·1H2O was mixed by weight and heat-treated at 650°C for 5 hours in an oxygen atmosphere.

[0053] (3) Interface protection coating layer formation step

[0054] The first coating layer coated on the entire or part of the surface of the second lithium metal oxide was prepared by dissolving the second lithium metal oxide in dehydrated ethanol, adding zirconium(IV) tetrapropoxide (70 wt. % in 1-propanol) in an amount such that the molar ratio of the second lithium metal oxide:zirconium ion = 2:1, and stirring to prepare a coating solution containing lithium ions and zirconium ions. At this time, the concentration of zirconium ions in the coating solution was set to 0.1 mol / L.

[0055] The coating process was performed by spraying 400 mL of the second coating solution onto 1 kg of the second lithium metal oxide formed above using a fluid coating device (MP-01, POWREX). The operating conditions of the fluid coating device were intake gas (nitrogen), intake gas temperature (80°C), intake air volume (0.3 m3 / h), rotation speed (400 rpm), and coating solution spraying speed (10 mL / min), and spraying was performed for a total of 40 minutes. After that, the lithium transition metal oxide sprayed with the second coating solution was loaded into Saggar, and then heat-treated at 300°C while supplying oxygen in a box-type electric furnace, thereby manufacturing a positive electrode active material in which an amorphous coating layer of Li2ZrO3 was formed on the surface of the lithium transition metal oxide as an interface protective coating layer.

[0056] <Comparative Example 1> (2) CoSO4 water-washing coating not implemented

[0057] First lithium transition metal oxide Ni synthesized in the first calcination step 0.83 Co 0.12 Mn 0.05 A cathode active material was manufactured under the same conditions as Example 1, except that the interfacial protective coating layer formation step was performed without washing O2 with CoSO4.

[0058] <Comparative Example 2> (2) CoSO4 water-washed coating and (3) no heat treatment

[0059] First lithium transition metal oxide Ni synthesized in the first calcination step without CoSO4 water-washing coating, LiOH addition, and heat treatment steps 0.83 Co 0.12 Mn 0.05 A cathode active material was manufactured under the same conditions as Example 1, except that the interfacial protective coating layer formation step was performed immediately after washing O2 with pure water.

[0060] <Comparative Example 3> (3) Exclusion of LiOH in the heat treatment step

[0061] A cathode active material was manufactured under the same conditions as Example 1, except that the heat treatment was performed at 650°C for 5 hours in an oxygen atmosphere without adding LiOH in the heat treatment step, and then the interfacial protective coating layer formation step was performed.

[0062]

[0063] Experimental Example 1 - Electrochemical Characteristics Evaluation

[0064] (1) Manufacturing of all-solid-state batteries for evaluation

[0065] 70 wt% of the manufactured positive electrode active material, 29 wt% of the argyrodite solid electrolyte, and 1 wt% of C65 as a conductive material were mixed well to manufacture a mixed powder. The argyrodite solid electrolyte, which functions as a separator, was first quantitatively charged into a jig for evaluating all-solid-state batteries, and pressurized at 300 MPa or more to a thickness of approximately 100 μm. Then, 10 mg of the positive electrode active material mixed powder was added to one side, and a second pressurization was performed to manufacture the positive electrode part. Afterwards, a Li-In alloy was added to the other side, and an appropriate pressure was applied to manufacture a battery for evaluating all-solid-state batteries.

[0066] (2) Evaluation of charge and discharge characteristics of all-solid-state batteries for evaluation

[0067] The manufactured solid-state battery cell for evaluation was mounted on a charger and discharger, and the charge-discharge characteristics were evaluated at 30°C. Charging was performed using the constant current-voltage method, and discharging was performed using the constant current method. The terminal voltage of the charge was set to 3.63 V, and the end voltage of the discharge was set to 1.9 V.

[0068] Constant current-constant voltage charging was performed, and the cut-off voltage in constant voltage mode was set to a current of 0.02 C. The pause time between charge and discharge was set to 20 minutes.

[0069] As summarized in Table 1 below, Comparative Example 2 showed a lower charge / discharge capacity and coulombic efficiency than Comparative Example 1, which was not subjected to water washing treatment, due to a significant decrease in charge / discharge capacity and efficiency caused by water washing damage. In Comparative Example 2, an improvement phenomenon was observed in which lithium hydroxide and lithium carbonate remaining on the surface of the cathode material in the form of residual lithium after dissolution during the water washing process were restored to the surface of the core during the heat treatment process, but the charge / discharge capacity and coulombic efficiency were slightly lower than those of Comparative Example 1, which was not subjected to water washing treatment.

[0070] In Comparative Example 3, LiOH was not added during the heat treatment, and thus the restoration phenomenon of the core surface was confirmed to be somewhat inferior to that of Example 1 in terms of initial charge capacity and initial discharge capacity. However, it was confirmed to have a superior capacity compared to Comparative Example 2, which did not add LiOH during the heat treatment step and did not perform the water-washing coating with CoSO4 solution, confirming that the electrochemical characteristics were improved during the water-washing treatment with CoSO4 solution.

[0071] In Example 1, a process of adding 3000 ppm of LiOH and then heat-treating after water-washing coating with CoSO4 solution was introduced to recover water-washing damage and secure the highest charge-discharge capacity.

[0072] Classification 0.1C Initial charge capacity (mAh / g) 0.1C Initial discharge capacity (mAh / g) 0.1C Initial coulombic efficiency (%) Example 1221.8213.496.2 Comparative example 1217.7207.795.4 Comparative example 2210.2191.991.3 Comparative example 3215.3202.894.2

Claims

1. A core comprising a lithium transition metal oxide of the NCM series; and A cobalt material-containing coating layer positioned on the core surface; The content of Ni in the above NCM-based lithium transition metal oxide is 80 mol% or more based on 100 mol% of the total amount of transition metal, The cobalt contained in the coating layer includes at least one of metallic cobalt and cobalt compounds. Cathode active material for all-solid-state batteries.

2. In paragraph 1, The content of the cobalt material in the above coating layer is in the range of 0.5 mol% to 2 mol% with respect to the total mole number of transition metals constituting the core including the NCM-based lithium transition metal oxide. Cathode active material for all-solid-state batteries.

3. In paragraph 1, The weight ratio of the coating layer to the total weight of the core is in the range of 1:100 to 20:

100. Cathode active material for all-solid-state batteries.

4. A step of forming a transition metal hydroxide by mixing nickel salt, cobalt salt, manganese salt, and a complexing agent through a coprecipitation method; A step of forming a lithium transition metal hydroxide by mixing the above transition metal hydroxide and a lithium compound; A step of forming a lithium transition metal oxide by first heat treating the above lithium transition metal hydroxide; A step of washing the above lithium transition metal oxide with a washing solution containing CoSO4; A step of performing a second heat treatment on the above-mentioned washed lithium transition metal oxide; and A step of coating a protective coating layer that suppresses an interface reaction with a solid electrolyte on the second heat-treated lithium transition metal oxide; comprising; Method for manufacturing a cathode active material for an all-solid-state battery.

5. In paragraph 4, In the above washing step, the solvent included in the washing solution is at least one selected from water, methanol, and ethanol. Method for manufacturing a cathode active material for an all-solid-state battery.

6. In paragraph 4, In the above washing step, the CoSO4 content in the washing solution is 1 to 30 wt% based on the total weight of the washing solution. Method for manufacturing a cathode active material for an all-solid-state battery.

7. In paragraph 4, In the above washing step, the weight ratio of lithium transition metal oxide to the washing solution is in the range of 100:100 to 80:

100. Method for manufacturing a cathode active material for an all-solid-state battery.

8. In paragraph 4, In the above washing step, the time for washing the lithium transition metal oxide is 5 minutes or more and less than 11 minutes. Method for manufacturing a cathode active material for an all-solid-state battery.

9. In paragraph 4, The above washing step may additionally include a stirring process, The above stirring speed is 100 rpm to 300 rpm, Method for manufacturing a cathode active material for an all-solid-state battery.