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, in which residual lithium impurities are reduced and water-washing damage is recovered by performing a primary surface treatment on a primary calcined and water-washed lithium transition metal oxide by using Co(OH)2, and then performing a secondary surface treatment on the lithium transition metal oxide by using LZO(Li2ZrO3) or LNO(LiNbO3); and a method of 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 the cathode active material is surface-treated primarily with Co(OH)2 on a lithium transition metal oxide that has been first calcined and washed, and then surface-treated secondary with LZO(Li2ZrO3) or LNO(LiNbO3), thereby reducing residual lithium impurities and restoring washing damage.

[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 positive electrode materials using a rinsing solution to reduce residual lithium impurities, a major cause of cathode material deterioration. While distilled water is generally effective in reducing residual lithium, it is difficult to prevent damage to the surface of the positive electrode material due to rinsing. A representative example is that lithium ions are easily eluted from the surface of the NCM positive electrode material during rinsing, which reduces the structural stability of the positive electrode material, tends to reduce lifespan and capacity, and increases resistance.

[0006] If the residual lithium impurities on the surface of the cathode active material are not removed by washing, no washing damage occurs, but there is a problem that the C-rate characteristics are lowered due to the resistance caused by the residual lithium layer.

[0007] Accordingly, there is a need for a cathode active material and a method for manufacturing the same that can improve structural stability by reducing surface water damage and reduce residual lithium impurities that cause increased resistance.

[0008]

[0009] The technical problem to be solved by the present invention is to provide a cathode active material for an all-solid-state battery, characterized in that, instead of going through a washing step after the first calcination, the surface is first treated by mixing Co(OH)2 with a lithium transition metal oxide and then heat-treating at a temperature range of 600°C to 700°C, and then the surface is secondarily coated using LZO (Li2ZrO3) or LNO (LiNbO3).

[0010] 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.

[0011]

[0012] 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; a first coating layer containing a cobalt material positioned on a surface of the core; and a second coating layer positioned on the first coating layer and containing at least one selected from LZO (Li2ZrO3) or LNO (LiNbO3); 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 selected from metallic cobalt and a cobalt compound.

[0013] According to another embodiment of the present invention, a method for manufacturing a cathode active material for an all-solid-state battery includes the steps of: preparing a lithium transition metal oxide; mixing the lithium transition metal oxide with Co(OH)2 powder and dry milling the mixture to form a first coating layer; performing a second heat treatment on the dry-milled mixture; and adding an interface protection coating material to the second heat-treated mixture and then forming a second coating layer using a wet coating process; wherein the interface protection coating material may include at least one selected from LZO (Li2ZrO3) or LNO (LiNbO3).

[0014]

[0015] According to one embodiment of the present invention, a cathode active material for an all-solid-state battery can improve the phenomenon of reduced output performance of a cathode active material without causing damage from washing by performing a first surface treatment using Co(OH)2 on a lithium transition metal oxide that has not undergone a first calcination and washing step and then performing a second surface treatment using LZO(Li2ZrO3) or LNO(LiNbO3).

[0016] 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.

[0017]

[0018] Figure 1 is a schematic diagram showing a method for manufacturing a cathode active material for an all-solid-state battery according to one embodiment of the present invention.

[0019] Figure 2 is a flow chart illustrating a method for manufacturing a cathode active material for an all-solid-state battery according to one embodiment of the present invention.

[0020] Figure 3 shows the discharge capacity according to the cycle of the examples and comparative examples of the present invention.

[0021]

[0022] 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 solely 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0027] Hereinafter, a cathode active material for an all-solid-state battery according to one embodiment of the present invention will be described.

[0028] 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; a first coating layer containing a cobalt material positioned on a surface of the core; and a second coating layer positioned on the first coating layer and containing at least one selected from LZO (Li2ZrO3) or LNO (LiNbO3); 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 selected from metallic cobalt and a cobalt compound.

[0029] 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.

[0030] In a cathode active material for an all-solid-state battery according to one embodiment, the content of the first coating layer may be in the range of 1 mol% to 3 mol% based on the total mole number of Ni, Co, and Mn elements constituting the cathode active material.

[0031] When the content of the first coating layer is within the above-mentioned range, safety and life characteristics can be improved. However, when the content of the first coating layer is below the lower limit of the above-mentioned range, the Co(OH)2 component that should participate in the reaction with residual lithium such as LiOH and Li2CO3 present on the positive electrode surface is insufficient, so the output characteristics may not be sufficiently improved. In addition, when the content of the first coating layer exceeds the upper limit of the above-mentioned range, although there is an advantage of improved stability due to the introduction of a large amount of expensive Co into the positive electrode active material, there is a problem of the price of the positive electrode active material rapidly increasing, so it may not be suitable for commercialization.

[0032] In a cathode active material for an all-solid-state battery according to one embodiment, the first coating layer may include cobalt and lithium compounds distributed in an island shape.

[0033] The above first coating layer may have a shape in which metallic cobalt or a cobalt compound is discontinuously distributed.

[0034] In one embodiment, the weight of the second coating layer in the positive electrode active material for an all-solid-state battery may be in the range of 0.3 wt% to 3 wt% based on the total weight of the positive electrode active material.

[0035] When the weight of the second coating layer is within the aforementioned range, stability and life characteristics can be improved. However, when the weight of the second coating layer is below the lower limit of the aforementioned range, the interfacial reaction prevention effect is minimal, so side reactions easily occur, which may lower the life characteristics. In addition, when the weight of the second coating layer exceeds the upper limit of the aforementioned range, although the interfacial reaction prevention effect is excellent, the coating layer may act as a resistance layer that hinders the insertion and de-insertion of lithium, which may reduce the charge / discharge capacity.

[0036] In one embodiment, the thickness of the second coating layer in the positive electrode active material for an all-solid-state battery may be in the range of 5 nm to 20 nm.

[0037] When the thickness of the second coating layer is within the aforementioned range, side reactions that may occur at the interface between the positive electrode material and the solid electrolyte can be prevented, thereby improving the life characteristics of the positive electrode active material. When the thickness of the second coating layer is less than the lower limit of the aforementioned range, the surface of the positive electrode active material that has not been covered directly comes into contact with the solid electrolyte, causing a side reaction with the solid electrolyte, thereby causing deterioration of the interface between the NCM positive electrode material and the solid electrolyte, thereby continuously reducing the life of the positive electrode active material. When the thickness of the second coating layer exceeds the upper limit of the aforementioned range, the coating layer becomes excessively thick, making it difficult for lithium ions to be inserted and deintercalated smoothly, and thus making it difficult for the capacity to be sufficiently expressed.

[0038]

[0039] 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.

[0040] Figure 1 is a schematic diagram showing a method for manufacturing a cathode active material for an all-solid-state battery according to one embodiment of the present invention.

[0041] Figure 2 is a flow chart illustrating a method for manufacturing a cathode active material for an all-solid-state battery according to one embodiment of the present invention.

[0042] Referring to FIGS. 1 and 2, a method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment includes the steps of: preparing a lithium transition metal oxide; mixing the lithium transition metal oxide and Co(OH)2 powder and dry milling the mixture to form a first coating layer; performing a second heat treatment on the dry-milled mixture; and adding an interface protection coating material to the second heat-treated mixture and then forming a second coating layer using a wet coating process; wherein the interface protection coating material may include at least one selected from LZO (Li2ZrO3) or LNO (LiNbO3).

[0043] In the first coating layer forming step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the molar ratio of Co(OH)2 to the total number of moles of transition metals constituting the lithium transition metal oxide mixed may be 1 mol% to 3 mol%.

[0044] When the total mole number of transition metals constituting the lithium transition metal oxide and the mole ratio of Co(OH)2 powder satisfy 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 washing can also be maximized. However, when the total mole number of transition metals constituting the lithium transition metal oxide and the mole ratio of Co(OH)2 powder are not within the above-mentioned range, the Co(OH)2 element that can participate in the reaction with the residual lithium may be insufficient, so the output improvement phenomenon may not appear. In particular, when the amount of Co introduced is excessively large, not only does the cost of manufacturing the cathode material increase, but the contact between the cathode material surface and the solid electrolyte may be hindered, which may actually reduce the capacity.

[0045] In another embodiment, the dry milling time in the first coating layer forming step of the method for manufacturing a cathode active material for an all-solid-state battery may be 10 to 30 minutes.

[0046] When the dry milling time falls 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 dry milling time does not fall 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 cathode active material, thereby drastically reducing the life characteristics of the cell.

[0047] In the second heat treatment step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the heat treatment temperature may be 600 to 700°C.

[0048] In the second coating layer forming step of the method for manufacturing a cathode active material for an all-solid-state battery according to another embodiment, the weight of the interface protection coating material may be in the range of 0.3 wt% to 3 wt% based on the total weight of the second heat-treated mixture.

[0049]

[0050] 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.

[0051] <Example 1>

[0052] (1) Primary plasticity stage

[0053] Ni with an average particle size of 4㎛ 0.88 Co 0.095 Mn 0.025 (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 700°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 process, and the average particle diameter (D 50 ) is a first lithium transition metal oxide Ni with a diameter of 4 to 5 μm 0.88 Co 0.095 Mn 0.025 O2 was formed.

[0054]

[0055] (2) First coating layer formation step

[0056] Ni is the first lithium transition metal oxide manufactured in the primary calcination 0.88 Co 0.095 Mn 0.025 Co(OH)2 powder corresponding to 2 mol% of the total moles of transition metal constituents of O2 was mixed by a dry mixing process. Afterwards, it was heat-treated at 650℃ for 5 hours in an oxygen atmosphere to obtain the first lithium transition metal oxide, Ni. 0.88 Co 0.095Mn 0.0.025 The first coating layer was formed by reacting the residual lithium layer on the O2 surface with Co(OH)2.

[0057]

[0058] (3) Interfacial protection coating layer (second coating layer) formation step

[0059] 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.

[0060] 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 m 3 / h), rotation speed (400 rpm), and coating solution spraying speed (10 mL / min) were used 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 forming a Li2ZrO3 amorphous coating layer as an interface protection coating layer on the surface of the lithium transition metal oxide, thereby manufacturing a positive electrode active material.

[0061] <Comparative Example 1>

[0062] A positive electrode active material was manufactured under the same conditions as Example 1, except that the first coating layer formation step was performed immediately after the primary firing, excluding the first coating layer formation step.

[0063]

[0064] Experimental Example 1 - Electrochemical Characteristics Evaluation

[0065] (1) Manufacturing of all-solid-state batteries for evaluation

[0066] 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.

[0067] (2) Evaluation of charge and discharge characteristics of all-solid-state batteries for evaluation

[0068] The manufactured solid-state battery cell for evaluation was mounted on a charger and discharger, and the charge-discharge characteristics were evaluated at 30 degrees. 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.

[0069] The discharge capacity was determined as the average of three times for each C-rate from 0.1C, 0.2C, 0.33C, 0.5C, 1.0C, and 2.0C. From 0.1C to 0.5C, the charge and discharge current densities were set to be the same in the constant current section, and the charge current density was set to 0.5C at 1.0C and 2.0C. Since constant current-constant voltage charging was performed, the charge end current was set to 0.02C at 0.1C, and under other conditions, the charge end current was set to 20% of the current during constant current charging. The initial capacity was 0.1C for the first cycle, and the output characteristics were applied as the average value of the discharge capacity of three times for each C-rate. The pause time between charge and discharge of each cycle was set to 20 minutes.

[0070] Figure 3 shows the discharge capacity according to the cycle of the examples and comparative examples of the present invention.

[0071] As shown in Table 1 below and FIG. 3 above, since the positive electrode base material and the interface protective coating layer are the same, the initial characteristics are almost similar, but in the high-power range of 0.5C to 2.0C, it can be confirmed that the positive electrode material for an all-solid-state battery manufactured according to the example has a high over-discharge capacity due to the effect of lithium carbonate and lithium hydroxide remaining on the surface of the positive electrode material after the primary firing reacting with Co(OH)2, thereby reducing the content and resistance.

[0072] Classification 0.1C Initial charge capacity (mAh / g) 0.1C Initial discharge capacity (mAh / g) 0.1C Initial coulombic efficiency (mAh / g) 0.1C Average discharge capacity (mAh / g) 0.1C Average discharge capacity (mAh / g) 0.1C Average discharge capacity (mAh / g) 0.1C Average discharge capacity (mAh / g) 0.1C Average discharge capacity (mAh / g) 0.1C Average discharge capacity (mAh / g) Comparative example 1228.2218.995.9218.6214.1207.5197.3178.5145.0 Exemplary example 1227.2218.296.0217.9213.4207.5199.6181.6150.0

Claims

1. A core comprising a lithium transition metal oxide of the NCM series; A first coating layer containing a cobalt material positioned on the core surface; and A second coating layer positioned on the first coating layer and containing at least one selected from LZO (Li2ZrO3) or LNO (LiNbO3); 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 first coating layer is in the range of 1 mol% to 3 mol% based on the total mole number of Ni, Co, and Mn elements constituting the cathode active material. Cathode active material for all-solid-state batteries.

3. In paragraph 1, The first coating layer comprises cobalt and lithium compounds distributed in an island shape. Cathode active material for all-solid-state batteries.

4. In paragraph 1, The weight of the second coating layer is in the range of 0.3 wt% to 3 wt% based on the total weight of the positive electrode active material. Cathode active material for all-solid-state batteries.

5. In paragraph 1, The thickness of the second coating layer is in the range of 5 nm to 20 nm. Cathode active material for all-solid-state batteries.

6. Step of preparing lithium transition metal oxide; A step of forming a first coating layer by mixing the lithium transition metal oxide and Co(OH)2 powder and then dry milling them; A step of second heat treating the above dry milled mixture; and A step of forming a second coating layer by using a wet coating process after adding an interface protection coating material to the second heat-treated mixture; The above-mentioned interface protective coating material comprises at least one selected from LZO (Li2ZrO3) or LNO (LiNbO3). Method for manufacturing a cathode active material for an all-solid-state battery.

7. In paragraph 6, In the step of forming the first coating layer, the molar ratio of Co(OH)2 to the total molar number of transition metals forming the lithium transition metal oxide mixed is in the range of 1 mol% to 3 mol%. Method for manufacturing a cathode active material for an all-solid-state battery.

8. In paragraph 6, In the above first coating layer forming step, the dry milling time is 10 to 30 minutes. Method for manufacturing a cathode active material for an all-solid-state battery.

9. In paragraph 6, In the second heat treatment step, the heat treatment temperature is 600 to 700°C. Method for manufacturing a cathode active material for an all-solid-state battery.

10. In paragraph 6, In the second coating layer forming step, the weight of the interface protection coating material is in the range of 0.3 wt% to 3 wt% based on the total weight of the second heat-treated mixture. Method for manufacturing a cathode active material for an all-solid-state battery.

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