System and method for coating cathode active material

Abstract

A method for coating cathode active material particles is provided. The method comprises preparing a lithium niobate precursor solution, wherein the molar ratio of lithium to niobium in the lithium niobate precursor solution is determined by the surface composition of the cathode active material particles; mixing the cathode active material particles with the lithium niobate precursor solution; hydrolyzing the mixture, and then heating the mixture to obtain cathode active material particles coated with amorphous lithium niobate.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to U.S. Provisional Application No. 63 / 581,951, filed on 11 September 2023, entitled “SYSTEMS AND METHODS FOR COATING CATHODE ACTIVE MATERIAL.” The entire contents of the above-mentioned application(s) are incorporated herein by reference for any purpose.

[0002] This specification generally relates to lithium metal oxide coatings on battery cathode particles. [Background technology]

[0003] All-solid-state lithium-ion batteries, which include a solid electrolyte, are desirable, in part, for the improved safety achieved by replacing the highly flammable conventional liquid electrolyte with a less reactive solid electrolyte. However, replacing the electrolyte may introduce additional undesirable side reactions that can degrade battery performance unless addressed. One example of such a side reaction is the decomposition of sulfide-based solid electrolytes at the interface with the cathode active material, forming byproducts that are both electronically and ionically insulating. Thus, the deposition of byproducts on the surface of the cathode active material increases cell impedance over time, degrading battery performance. [Overview of the project] [Problems that the invention aims to solve]

[0004] To prevent undesirable side reactions between the sulfide-based solid electrolyte and the cathode active material, the cathode active material particles have been coated with a buffer layer to prevent direct contact between the sulfide-based solid electrolyte and the cathode active material. The buffer layer is configured to be ionically conductive and electrically insulating so as to allow the transport of lithium ions to and from the cathode active material while still preventing undesirable side reactions. LiNbO3, Li3BO3, Li3PO4, Li4SiO4, LiAlO2, Al2O3, ZrO2, Li4Ti5O 12 , LiTaO3, and LiNb x Ta 1-x Lithium metal oxides and metal oxides containing O3 have been identified as coating materials with desired properties. However, current systems and methods for coating cathode active materials with LiNbO3 and other lithium metal oxides may rely on methods that result in undesirable carbon residues or require heating to excessively high temperatures to remove carbon. In addition, systems may not adequately consider the surface stoichiometry of the cathode active material, and methods may not be optimized to achieve thin, uniform coatings with desired physical and electrical properties. [Means for solving the problem]

[0005] The inventors of this specification have identified the above problems and determined solutions to at least partially solve them. In one example, a method for coating a cathode active material includes preparing a lithium niobate precursor solution, wherein the molar ratio of lithium to niobium in the lithium niobate precursor solution is determined by the surface composition of the cathode active material particles; mixing the cathode active material particles with the lithium niobate precursor solution; hydrolyzing the mixture of the lithium niobate precursor solution and the cathode active material particles; and heating the hydrolyzed mixture to obtain cathode active material particles coated with amorphous lithium niobate. An alkoxide hydrolysis pathway, including calcination over a specified temperature range, may be a cost-effective and reproducible method for forming an amorphous LiNbO3 coating. By adjusting the molar ratio of lithium to niobium in the lithium niobate precursor solution according to the surface composition of the cathode active material particles, the desired 1:1 ratio of lithium to niobium in the coating is maintained. Furthermore, controlling the rate of water addition may be an effective process control for achieving a thin and uniform LiNbO3 coating.

[0006] It should be understood that the above summary is provided in a simplified form to introduce selected concepts that will be further explained in the detailed description. It is not intended to identify any important or essential features of the claimed subject matter, whose scope is uniquely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to any implementation that solves any defects described above or in any part of this disclosure. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram of an all-solid-state lithium-ion battery, including a coated cathode material, is shown. [Figure 2] A flowchart illustrating an example of a method for synthesizing amorphous LiNbO3 is shown. [Figure 3] This graph shows the X-ray diffraction of LiNbO3 powder. [Figure 4] A flowchart illustrating an example of a method for coating cathode active material powder with amorphous LiNbO3 is shown. [Figure 5] A schematic diagram of NCM particles with a LiNbO3 coating is shown. [Figure 6] The first transmission electron microscope (TEM) image of NCM811 particles coated with LiNbO3 is shown. [Figure 7] The second TEM image of NCM811 particles coated with LiNbO3 is shown. [Figure 8] The graph shows the electrochemical impedance spectra (EIS) of coated and uncoated NCM cathode powders. [Figure 9] This graph shows the retention rate as a function of cycle count for all-solid-state lithium-ion batteries (SS-LIBs) containing single-crystal NMC811 (SC-NMC) material coated with LiNbO3, and for SS-LIBs containing polycrystalline NMC811 (PC-NMC) material coated with LiNbO3. [Figure 10] This graph shows the current density as a function of cycle number for SS-LIBs containing SC-NMC and SS-LIBs containing PC-NMC materials. [Figure 11] This graph shows the EIS spectra of SS-LIBs containing SC-NMC material and SS-LIBs containing PC-NMC material. [Figure 12] The graph shows the voltage as a function of specific capacitance for SS-LIBs containing SC-NMC material and SS-LIBs containing PC-NMC material. [Modes for carrying out the invention]

[0008] The following description relates to a system and method for coating cathode active materials for all-solid-state lithium-ion batteries. An example of an all-solid-state lithium-ion battery is shown in Figure 1. All-solid-state lithium-ion batteries may contain a solid electrolyte, such as a sulfide-based electrolyte, and the cathode of an all-solid-state lithium-ion battery may contain lithium nickel cobalt manganese oxide (NCM) particles. To minimize undesirable side reactions and improve the performance of all-solid-state lithium-ion batteries, NCM cathode particles may be coated with LiNbO3. Physical properties of LiNbO3, such as carbon content and crystallinity, can affect the desired electrical properties. To understand the physical properties of LiNbO3, LiNbO3 may be synthesized separately from the cathode active material particles. A flowchart of an example of a method for synthesizing LiNbO3 powder is shown in Figure 2. Using the method shown in Figure 2, the effect of firing temperature on crystallinity can be determined, as shown by the X-ray diffraction (XRD) spectrum of the LiNbO3 powder in Figure 3. The method in Figure 2 can be adapted to form a LiNbO3 coating on cathode active material particles such as NCM811 particles. A flowchart of an example method for coating cathode active material with LiNbO3 is shown in Figure 4. Coated NCM811 particles are schematically shown in Figure 5, and TEM images showing a thin, uniform coating of LiNbO3 on NCM811 are shown in Figures 6-7. NCM811 particles coated with LiNbO3 according to the method in Figure 4 can be incorporated into all-solid-state lithium-ion batteries that can exhibit improved electrical properties compared to all-solid-state lithium-ion batteries containing uncoated NCM particles, as demonstrated by the graph in Figure 8. NCM811 particles for the cathode can be either single-crystal or polycrystalline particles. The LiNbO3 coating can be applied to both single-crystal and polycrystalline NCM811. All-solid-state lithium-ion batteries incorporating monocrystalline NCM811 coated with LiNbO3 can offer unexpectedly improved performance compared to those incorporating polycrystalline NCM811 coated with LiNbO3, as illustrated in the graphs shown in Figures 9-12.

[0009] Referring here to Figure 1, an illustration of a non-limiting embodiment of an all-solid-state lithium-ion battery cell subassembly (e.g., a battery cell) 100 is shown. In order, the battery cell 100 may include an anode current collector 101, an anode material coating 102, an anode separator interface coating 106, a separator coating 103, a cathode separator interface coating 107, a cathode material coating 104, and a cathode current collector 105. Thus, the separator coating 103 can function as a battery separator. In some examples of the all-solid-state lithium-ion battery cell subassembly 100, the anode separator interface coating 106 and / or the cathode separator interface coating 107 may be omitted. In further examples, multiple cathode separator interface coatings and / or anode separator interface coatings may be included.

[0010] One or more of the anode material coating 102 and the anode separator interface coating 106 may contain an anode active material containing lithium. One or more of the cathode material coating 104 and the cathode separator interface coating 107 may contain a cathode active material containing lithium. For example, the cathode active material may be cathode active material particles coated with LiNbO3. Furthermore, in some examples, the coated cathode active material particles may be NCM or other cathode active material species. In the example where the coated cathode active material is NCM, the NCM may be a high-nickel NCM having a nickel content of more than 60 mol% (e.g., NCM811 LiNi 0.8 Co 0.1 Mn 0.1 O2). One or more of the anode material coating 102, anode separator interface coating 106, separator coating 103, cathode separator interface coating 107, and cathode material coating 104 may include a sulfide-based electrolyte and a polymer binder. The polymer binder may be electrically and ionically insulating. The sulfide-based electrolyte is Li6PS5Cl, Li7P3S11 It may be one or more of Li5PS4ClBr and Li3PS4, but is not limited to these.

[0011] In some examples, an adhesive interface can be defined between the separator coating 103 and the electrode structure. The adhesive interface can be a three-dimensional interface between the separator coating 103 and the electrode structure such that the separator coating 103 can conform to the surface of the electrode structure and penetrate into it. In a first example, the electrode structure may be an anode material coating 102 deposited on an anode current collector 101, with an anode separator interface coating 106 optionally deposited thereon. In a second example, the electrode structure may be a cathode material coating 104 deposited on a cathode current collector 105, with a cathode separator interface coating 107 optionally deposited thereon.

[0012] Referring here to Figure 2, an example of method 200 for synthesizing LiNbO3 powder is shown. LiNbO3 powder does not necessarily have to be directly incorporated into all-solid-state lithium-ion batteries. Instead, method 200 for synthesizing LiNbO3 powder may be useful in providing information for coating methods discussed further below and in understanding the physical properties of LiNbO3, such as crystallinity, which may not be readily measured in the presence of the cathode active material.

[0013] Method 200 may be classified as an alkoxide hydrolysis method. The alkoxide hydrolysis method may be desirable because it produces a product with no or minimal residual carbon. Residual carbon on the surfaces of cathode material particles increases electrical conductivity, which can lead to undesirable electrochemical interactions on the particle surfaces. Therefore, reducing the amount of residual carbon can improve the electrical properties of the coating. Accordingly, LiNbO₃ coatings synthesized using an alkoxide method such as method 200 are more insulating and less prone to electrochemical interactions than LiNbO₃ coatings formed using other methods that result in more residual carbon. At 202, method 200 includes preparing a lithium niobate precursor solution. The lithium niobate precursor solution may comprise a mixture of lithium alkoxide and niobium alkoxide in a non-aqueous solvent that is miscible with water. In one example, the lithium alkoxide may be lithium ethoxide, and the niobium alkoxide may be niobium ethoxide. Further, lithium ethoxide may be provided by dissolving solid lithium metal in ethanol, or alternatively, lithium ethoxide may be supplied as a solid salt dissolved in ethanol. The precursor solution may be prepared with a molar ratio of lithium to niobium of 1:1.

[0014] At 204, method 200 includes hydrolyzing the lithium niobate precursor solution to form a lithium niobate gel precursor by adding water at a rate not exceeding a threshold rate. Adding water at a rate not exceeding the threshold rate can ensure that water completely reacts with the lithium niobate precursors (e.g., lithium alkoxide and niobium alkoxide) in the hydrolysis reaction before condensation occurs. If water is added at a rate exceeding the threshold rate, immediate condensation can be favored over hydrolysis. Immediate condensation instead of hydrolysis can result in an undesirable heterogeneous gel precursor.

[0015] In one example, forming the precursor gel may comprise adding water in a molar ratio relative to the number of moles of lithium / niobium. In one example, 4 to 12 moles of water may be added per 1 mole of lithium / niobium. In an alternative example, 5 to 10 moles of water may be added per 1 mole of lithium / niobium. As a further example, the threshold rate of water addition may be based on adding water at a rate of 5 mL or less per minute as a solution in a non-aqueous solvent. The solution may comprise water in an amount ranging from 2.5 to 10% by volume. In an alternative example, water may be added at a rate not faster than 0.01 mL per minute. Adding water below the threshold rate may be assisted by first diluting water in ethanol and adding water as an aqueous solution in the solvent of the precursor solution. Adding water slowly may favor the desired hydrolysis product of the reaction between water and the alkoxide precursor over undesired condensation products. The precursor gel may be formed after stirring for a certain period of time at room temperature. In one example, this certain period of time may be as short as 5 minutes.

[0016] At 206, method 200 comprises heating the precursor gel in a temperature range favorable for forming amorphous LiNbO₃ powder. The heating temperature range may determine the crystallinity of the LiNbO₃ powder. Amorphous LiNbO₃ may be a desired material for coating NCM particles in all-solid-state lithium ion batteries. Although physically more fragile than crystalline LiNbO₃, amorphous LiNbO₃ may have lower ionic insulation than crystalline LiNbO₃ (for example, the conductivity of amorphous LiNbO₃ is 10 -5 of the order of magnitude, and the conductivity of crystalline LiNbO₃ is 10 -10which is ordered according to [the above]), thereby reducing resistance to lithium movement when coated on a cathode active material. In one example, heating the precursor gel may comprise heating in oxygen. In such examples, oxygen gas may be flowed over the precursor gel at a flow rate of 2 to 2.5 standard cubic feet per hour (SCFH) during heating. A temperature range favorable for forming amorphous LiNbO₃ may be 250°C to 275°C. Heating above 275°C can result in undesirable crystalline LiNbO₃. Furthermore, insufficient heating can cause residual organic materials to remain as carbon interspersed in the LiNbO₃ powder. Carbon may be undesirable because it is electrically conductive. Method 200 may be desirable based on relatively low or no residual carbon remaining after heating. In other methods, high temperatures are required to achieve low / no residual carbon, which causes these methods to produce crystalline LiNbO₃ coatings rather than amorphous ones. Method 200 provides low / no residual carbon achieved after heating in a temperature range low enough to produce an amorphous LiNbO₃ coating. Method 200 ends.

[0017] By separately preparing LiNbO₃ powder (e.g., not as a coating on a cathode material), the physical properties of LiNbO₃ can be more easily measured and observed. FIG. 3 shows an example 300 of an XRD spectrum of LiNbO₃ obtained by method 200, depicting intensity as a function of diffraction angle (2θ). Plots 302, 304, and 306 correspond to LiNbO₃ powder heated at different temperatures in step 206 of method 200. Plot 302 corresponds to LiNbO₃ powder heated at 300°C, plot 304 corresponds to LiNbO₃ powder heated at 275°C, and plot 306 corresponds to LiNbO₃ powder heated at 250°C. Plots 302, 304, and 306 share a common x-axis 301 corresponding to diffraction angle. Y-axis 303 corresponds to intensity in arbitrary units. Plots 302, 304, and 306 are offset with respect to y-axis 303 for clarity.

[0018] Plot 302, corresponding to heating at 300°C, shows clear diffraction peaks indicating a periodic crystalline structure that constructively diffracts X-rays. Line 308 corresponds to the positions of some of the strongest peaks in plot 302. Looking at the position of line 308 relative to plot 304, although the XRD intensity along the y-axis is lower than in plot 302, some peaks may still be present. Thus, plot 304 indicates that heating at 275°C can produce a powder with some localized crystalline regions, although the majority of the powder may be amorphous. Looking at the position of line 308 as a guide, plot 306 shows no diffraction peaks, indicating that heating at 250°C produces amorphous LiNbO3 powder. For this reason, 250°C may be a preferred heating temperature for synthesizing a LiNbO3 coating on a cathode active material, and the amorphous material results in increased ionic conductivity.

[0019] Based on an understanding of the method and processing parameters for obtaining the desired LiNbO3 powder, this method and processing parameters can be applied to a method for coating cathode active material particles. A flowchart of an example of method 400 for coating cathode active material with LiNbO3 via the alkoxide hydrolysis pathway is shown in Figure 4.

[0020] In step 402, method 400 includes preparing a lithium niobate precursor solution. The lithium niobate precursor solution may be a solution of lithium alkoxide and niobalkoxide in a non-aqueous, water-miscible solvent. In one example, the weight percentage of lithium niobate precursor in the lithium niobate precursor solution may be 2% to 3%. Step 402 may be the same as step 202 of method 200. For example, preparing the lithium niobate precursor may include preparing a solution of lithium metal (or lithium ethoxide) and niobethoxide in ethanol. The relative molar ratio of lithium to niobium in the lithium niobate precursor solution may be adjusted according to the surface chemistry of the cathode active material. For example, the surface of the cathode active material may be lithium-rich or lithium-deficient, based on the material and manufacturing method. As an example, the molar ratio of lithium to niobium may be in the range of 0.9 to 1.25:1. In this way, a lithium niobate coating can be formed with a desired 1:1 ratio of lithium to niobium. In some cases, the molar ratio of lithium to niobium may be 1.1:1.

[0021] In 404, method 400 comprises mixing cathode active material particles with a lithium niobate precursor solution. The mixing may involve mixing the cathode active material particles and the lithium niobate precursor solution at room temperature for a certain period of time. For example, this period may be in the range of 1 to 10 minutes. The mixing rate may be in the range of 150 rpm to 2000 rpm. In this way, the lithium niobate precursor adheres to the surface of the cathode active material particles. The weight percentage of LiNbO3 in the coated particles can determine the thickness of the LiNbO3 coating formed by method 400. If the coating is too thin, it may not completely cover the cathode active material particles and may not prevent side reactions between the cathode active material and the electrolyte. If the coating is too thick, lithium ions or electrons may not be able to effectively move through the coating when the battery containing the cathode active material particles is being charged and / or discharged. In one example, the weight percentage of LiNbO3 in the coated particles is 0.1% to 3%. In alternative examples, the weight percentage of LiNbO3 in the coated particles is 0.5% to 3%. In yet another example, the weight percentage of LiNbO3 in the coated particles is 1%.

[0022] In one example of Method 400, the cathode active material particles may be NCM particles. In some examples, the cathode active material particles may be NCM811 particles. Furthermore, the NCM811 particles may be single-crystal or polycrystalline particles. Additional types of cathode active material particles have also been investigated, in particular, including lithium cobalt oxide (LCO), lithium iron phosphate (LFP), and lithium manganese nickel oxide (LMNO), as well as lithium nickel cobalt aluminum oxide (NCA).

[0023] In 406, method 400 includes hydrolyzing a mixture of lithium niobate precursors attached to cathode active material particles by adding water at a rate below a threshold rate. The threshold rate may be similar to or the same as the threshold rate for adding water in step 204 of method 200. In one example, hydrolysis may be completed by adding 4 to 12 moles of water per mole of niobium in the mixture. In an alternative example, hydrolysis may be completed by adding 5 to 10 moles of water per mole of niobium in the mixture. Adding water faster than the threshold rate may result in an undesirable turbid solution. Turbidity may occur because the presence of excess water promotes the condensation of alkoxide precursors instead of the desired hydrolysis reaction. If condensation occurs before hydrolysis, the hydrolysis may be incomplete, and the resulting coating may not be molecularly homogeneous. For this reason, hydrolysis of a mixture of lithium niobate precursors attached to cathode active material includes adding water at a rate below the threshold rate. Adding water at a rate below the threshold rate may be more favorable to the hydrolysis of the lithium niobate precursor than to its condensation. In one example, the threshold rate may be 5 mL / min or less, added as a 2-10 vol% aqueous solution in a non-aqueous solvent. In some examples, the solution may be a 5 vol% aqueous solution in a non-aqueous solvent. Additionally or alternatively, the threshold rate may be 0.1 ml of water per minute. By slowly adding water, complete hydrolysis of the lithium niobate precursor can be ensured, ultimately forming a uniform coating of lithium niobate. After adding the total amount of water, the mixture may be stirred at room temperature for 5 minutes or less. After 5 minutes, the hydrolysis of the lithium niobate precursor may be complete.

[0024] In 408, method 400 includes heating the hydrolyzed mixture in a temperature range favorable to amorphous LiNbO3. As described above with respect to Figures 2-3, heating may include heating in an O2 atmosphere in a temperature range of 250°C to 275°C. In some examples, heating may include first removing the solvent under vacuum at a lower temperature (e.g., via a rotary evaporator at 65°C) before heating the dry particles in an O2 atmosphere. In this way, not only is the degree of crystallinity of the LiNbO3 coating minimized, but the amount of residual carbon is also minimized, and the electrical properties of the LiNbO3 coating for the cathode active material may be improved (e.g., increased ionic conductivity and decreased electrical conductivity). After heating, the cathode active material particles may contain a uniform amorphous lithium niobate coating.

[0025] In 410, method 400 includes deaggregating the coated particles. The particle size distribution of the cathode active material particles may not change significantly after coating (e.g., no change by more than 5%). However, mechanically inflexible aggregates may form after heating. In one example, deaggregation may include sieving the coated particles through a 40 μm mesh. In an alternative example, air jet milling or other deaggregation techniques may be used.

[0026] In 412, method 400 includes coating deaggregated particles onto a cathode current collector and assembling a battery. In one example, coating the deaggregated particles may include dispersing the coated cathode active material particles in a slurry containing a solid electrolyte. The slurry may further include one or more of the following components, among other known components of all-solid-state lithium-ion battery slurry: solvents, binders, and carbon additives. By coating the sieved particles, a cathode material coating, such as the cathode material coating 104 in Figure 1, can be formed. The solid electrolyte used for coating may be a sulfide-based solid electrolyte. The cathode material coating may be further assembled into a battery, such as the all-solid-state lithium-ion battery cell 100 in Figure 1.

[0027] Referring here to Figure 5, an illustration 500 of a cross-section of cathode active material particles 502 coated with an amorphous LiNbO3 layer 504 according to method 400 is shown. In one example, the cathode active material particles 502 are NCM. In addition, the cathode active material particles 502 may be NCM 811. In one example, the cathode active material particles may be formed by the aggregation of many primary particles to form spherical secondary particles. Such an example is shown in Figure 5 and may include protrusions such as projections 507 and depressions such as depressions 506 formed by the aggregation of primary particles. A desirable coating is conformable to the surface of the cathode active material particles, including uniformly coating the surface of the cathode active material particles 502 and conforming to both the projections 507 and depressions 506. In some examples, the LiNbO3 layer 504 may partially penetrate into the depressions, resulting in LiNbO3 boundaries 508 that may not be in surface-sharing contact with the cathode active material particles 502. The LiNbO3 layer 504 may have a thickness of 510. The average thickness 510 may be in the range of 5 nm to 60 nm. In some examples, the average thickness 510 may be in the range of 10 nm to 50 nm. In alternative examples, the average thickness 510 may be in the range of 5 nm to 30 nm. In further examples, the average thickness 510 may be in the range of 20 nm to 40 nm.

[0028] Referring now to Figure 6, a first transmission electron microscope (TEM) image 600 of NCM811 particles coated with LiNbO3 according to Method 400 is shown. As described above with respect to Figure 5, the NCM811 particles include a plurality of primary particles 602. Image 600 shows a LiNbO3 coating layer 604 formed as a substantially (e.g., ±5%) uniform coating with a thickness 606. In one example, the thickness 606 may be 30 nm to 60 nm. Figure 7 shows a second TEM image 700 of NCM811 particles coated with LiNbO3 according to Method 400. The magnification of the second TEM image 700 is lower than that of image 600. Image 700 shows a LiNbO3 coating layer 604 fitting into a protrusion 702. The protrusion 702 may be similar to the protrusion 507 in Figure 5. In addition, image 700 shows a LiNbO3 coating layer 604 fitting into a depression 704. The recess 704 may be the same as the recess 506 in Figure 5.

[0029] Cathode active material particles such as NCM811 can be coated with LiNbO3 and incorporated into all-solid-state lithium-ion battery cells, such as battery cell 100 in Figure 1. In one example, a sulfide-based solid electrolyte may be included in the all-solid-state lithium-ion battery. Electrical characterization of a fully assembled all-solid-state lithium-ion battery can be performed using electrochemical impedance spectroscopy (EIS). Figure 8 shows graph 800 comparing the electrochemical impedance spectrum (plot 804) collected from an all-solid-state lithium-ion battery (SS-LIB) containing uncoated NCM811 with the electrochemical impedance spectrum (plot 802) collected from an SS-LIB containing NCM811 coated with LiNbO3 according to Method 400. Each SS-LIB was charged at a voltage of 4.3V for 10 hours before impedance measurement. The SS-LIBs containing uncoated NCM811 and the SS-LIBs containing coated NCM811 were fabricated using the same coating formulation and battery assembly method.

[0030] The width 806 of the semicircle formed by plot 802 and the width 808 of the semicircle formed by plot 804 may be proportional to the amount of resistance to lithium ion charge transfer to and from the cathode active material, respectively. The width 806 of plot 802 is smaller than the width 808 of plot 804. Thus, the EIS shows that coating NCM811 with LiNbO3 according to method 400 can effectively reduce the resistance to lithium ion charge transfer in SS-LIBs and maintain low resistance to lithium ion charge transfer after 10 hours of operation. Furthermore, this result shows that SS-LIBs containing LiNbO3-coated cathode active material particles may have reduced charge transfer resistance compared to SS-LIBs containing uncoated cathode active material particles.

[0031] NCM811 can be obtained as single-crystal or polycrystalline particles. In one example, single-crystal particles of NCM811 with other cathode active material particles may have a D50 in the range of 3 μm to 5 μm. In an alternative example, the single-crystal particles may have a D50 in the range of 3 μm to 4 μm. In a further example, the single-crystal particles may have a D50 of 3 μm. Polycrystalline particles can be sized to have a D50 of 10 μm. In conventional liquid electrolyte lithium-ion batteries, polycrystalline NCM811 with larger particle sizes (e.g., 10 μm) may be preferred. However, the performance of SS-LIBs with LiNbO3-coated NCM811 requires experimental comparison and experimentation to determine the most desirable cathode active material particle properties.

[0032] Single-crystal NCM811 (SC-NMC) and polycrystalline NCM811 (PC-NMC) can be coated with LiNbO3, respectively, according to Method 400. Each of SC-NMC and PC-NMC can be coated with an equivalent weight percent of LiNbO3. Thus, the coating thickness on SC-NMC can be thinner than the coating thickness on PC-NMC, based on the smaller D50 of SC-NMC and therefore on the larger surface area-to-volume ratio. SS-LIBs containing LiNbO3-coated SC-NMC and SS-LIBs containing LiNbO3-coated PC-NMC are constructed using substantially the same formulations and methods for comparison between batteries containing coated SC-NMC and batteries containing PC-NMC.

[0033] Referring now to Figure 9, graph 900 shows the retention rate as a function of the number of cycles. Plot 902 corresponds to an SS-LIB containing LiNbO3-coated SC-NMC, and plot 904 corresponds to an SS-LIB containing LiNbO3-coated PC-NMC. A cycle is a complete charge and discharge of the SS-LIB (e.g., from a 0% state of charge [SOC] to 100% SOC). The retention rate corresponds to the relative amount of the available capacity of the SS-LIB. Plot 902 decreases at a slower rate than plot 904 as the number of cycles increases. After 10 cycles, the retention rate of the SS-LIB containing SC-NMC is greater than that of the SS-LIB containing PC-NMC. The retention rate of the SS-LIB containing SC-NMC indicates that coated SC-NMC decomposes at a slower rate than coated PC-NMC.

[0034] Referring to Figure 10, a graph 1000 of the specific capacity in mAh / g as a function of the number of cycles is shown. Plot 1002 corresponds to an SS-LIB containing SC-NMC, and plot 1004 corresponds to an SS-LIB containing PC-NMC. Even after just one cycle, the specific capacity of plot 1002 starts at a higher amount than plot 1004. In addition, plot 1002 decreases at a slower rate than plot 1004 as the number of cycles increases. After 10 cycles, the specific capacity of the SS-LIB containing SC-NMC is greater than that of the SS-LIB containing PC-NMC. The larger specific capacity of the SS-LIB containing SC-NMC further indicates that batteries containing coated SC-NMC are more robust and perform better than batteries containing coated PC-NMC.

[0035] Referring here to Figure 11, Graph 1100, the EIS of SS-LIBs containing LiNbO3-coated SC-NMC and SS-LIBs containing LiNbO3-coated PC-NMC are shown. Each SS-LIB was held at a charging voltage of 4.3V for 10 hours before impedance measurement. Plot 1102 corresponds to the SS-LIB containing LiNbO3-coated SC-NMC, and plot 1104 corresponds to the SS-LIB containing LiNbO3-coated PC-NMC. The semicircle formed by plot 1102 has a width of 1106, and the semicircle formed by plot 1104 has a width of 1108. The fact that width 1106 is smaller than width 1108 indicates that the SS-LIB containing LiNbO3-coated SC-NMC has lower resistance to lithium ion migration from the cathode than the SS-LIB containing LiNbO3-coated PC-NMC.

[0036] Referring to Figure 12, we see voltage vs. Li / Li as a function of specific capacity, including both charge and discharge profiles for SS-LIBs containing LiNbO3-coated SC-NMC and SS-LIBs containing LiNbO3-coated PC-NMC. +Graph 1200 is shown. Plot 1202 corresponds to charging of SS-LIBs containing LiNbO3-coated SC-NMC, and plot 1208 corresponds to discharging of SS-LIBs containing LiNbO3-coated SC-NMC. Plot 1204 corresponds to charging of SS-LIBs containing LiNbO3-coated PC-NMC, and plot 1206 corresponds to discharging of SS-LIBs containing LiNbO3-coated PC-NMC. Comparing plots 1206 and 1208, SS-LIBs containing LiNbO3-coated SC-NMC show a desirable increase in maximum discharge capacity compared to SS-LIBs containing LiNbO3-coated PC-NMC. In addition, SS-LIBs containing LiNbO3-coated SC-NMC show lower overpotential at the start of the charge / discharge cycle than SS-LIBs containing LiNbO3-coated PC-NMC.

[0037] As demonstrated in Figures 9–12, SS-LIBs containing SC-NMC coated with LiNbO3 exhibit remarkably high performance in terms of capacity retention, robustness over multiple cycles, and improved charge transfer. The combination of amorphous LiNbO3 coating on small single-crystal NMC particles is remarkably robust, with no evidence of adverse effects caused by the amorphous / single-crystal interface. Thus, this disclosure provides support for a cathode active material comprising core particles formed from lithium nickel manganese cobalt oxide (NMC) and a coating surrounding the core particles, where the NMC is single-crystal and the coating is formed from amorphous LiNbO3. In the first example of the cathode active material, the diameter of the NMC core is in the range of 3 μm–5 μm. In the second example of the cathode active material, the coating is homogeneous.

[0038] The technical effect of Method 400 is to provide a LiNbO3 coating on cathode active material particles. The molar ratio of lithium to niobium in the lithium niobate precursor solution may be selected based on the surface chemistry of the cathode active material particles selected to maintain a 1:1 Li:Nb ratio in the coating. Furthermore, the method may include hydrolyzing the precursor solution by slowly adding water so that hydrolysis is preferred over condensation, thereby promoting a uniform and even coating of LiNbO3 on the cathode active material particles. A uniform and even coating, when used in SS-LIBs containing sulfide-based electrolytes, can result in slowing the decomposition of the cathode active material over time. In addition, the heating temperature may be selected so that an amorphous LiNbO3 coating is formed, thereby reducing the ionic resistance of the coating and improving the performance of the SS-LIB.

[0039] This disclosure also provides support for a method for coating cathode active material particles, the method comprising: preparing a lithium niobate precursor solution, wherein the molar ratio of lithium to niobium in the lithium niobate precursor solution is determined by the surface composition of the cathode active material particles; mixing the cathode active material particles with the lithium niobate precursor solution; hydrolyzing the mixture of the lithium niobate precursor solution and the cathode active material particles; and heating the hydrolyzed mixture to obtain cathode active material particles coated with amorphous lithium niobate. In a first example of the method, the cathode active material particles are NCM811 particles, and the molar ratio of lithium to niobium in the lithium niobate precursor solution is greater than 1. In a second example of the method, optionally including the first example, the cathode active material particles are NCM811 particles, and the molar ratio of lithium to niobium in the lithium niobate precursor solution is 0.9 to 1.25:1. In the third example of this method, either or both of the first and second examples are optionally included, and the solid weight percentage of the lithium niobate precursor in the mixture of lithium niobate precursor solution and cathode active material particles is 0.1% to 3%. In the fourth example of this method, one or more of the first to third examples are optionally included, and heating the hydrolyzed mixture includes heating at 250°C to 275°C in an O2 atmosphere. In the fifth example of this method, one or more of the first to fourth examples are optionally included, and hydrolysis of the mixture of lithium niobate precursor solution and cathode active material particles includes adding water at room temperature and mixing for 5 minutes or less. In the sixth example of this method, one or more of the first to fifth examples are optionally included, and the lithium niobate precursor is attached to the surface of the cathode active material particles by mixing the cathode active material particles with the lithium niobate precursor solution.

[0040] This disclosure also provides evidence for a method comprising: mixing cathode active material particles with a lithium niobate precursor solution; adding water to the mixture of lithium niobate precursor solution and cathode active material particles at a rate favorable to the hydrolysis of the lithium niobate precursor rather than the condensation of the lithium niobate precursor; and heating the hydrolyzed mixture to obtain an amorphous lithium niobate coating on the cathode active material particles. In the first example of this method, the rate favorable to the hydrolysis of the lithium niobate precursor solution rather than the condensation of the lithium niobate precursor is the addition of 5 mL / min or less of a 5 vol% aqueous solution in a non-aqueous solvent. In the second example of this method, optionally comprising the first example, the addition of water includes adding water as an aqueous solution in ethanol. In the third example of this method, optionally comprising either or both of the first and second examples, the thickness of the amorphous lithium niobate coating is 5 nm to 60 nm. In the fourth example of this method, optionally comprising one or more of the first to third examples, the amorphous lithium niobate coating conforms to the protrusions and depressions on the surface of the cathode active material particles. In the fifth example of this method, optionally comprising one or more of the first to fourth examples, the amorphous lithium niobate coating is molecularly homogeneous.

[0041] The disclosure also provides a basis for an all-solid-state lithium-ion battery comprising an anode current collector, an anode material coating, a separator coating, and a cathode material coating, wherein the cathode material coating includes cathode active material particles coated with LiNbO3, which are formed by preparing a lithium niobate precursor solution, wherein the molar ratio of lithium to niobium in the lithium niobate precursor solution is determined by the surface composition of the cathode active material particles; mixing the cathode active material particles with the lithium niobate precursor solution; hydrolyzing the mixture of the lithium niobate precursor solution and the cathode active material particles; and heating the hydrolyzed mixture to obtain cathode active material particles coated with amorphous lithium niobate. In a first example of the system, the separator coating is formed from a sulfur-based solid electrolyte.

[0042] In alternative embodiments, the Disclosure also provides evidence for a method comprising: mixing lithium alkoxide, niobalkoxide, and lithium nickel manganese cobalt oxide (NCM) particles in a non-aqueous solvent, wherein the molar ratio of lithium alkoxide to niobalkoxide is greater than 1; hydrolyzing the mixture of lithium alkoxide, niobalkoxide, and NCM particles by adding water at a rate of 0.1 mL / min or less; and heating the hydrolyzed mixture in an O2 atmosphere at a temperature range of 250°C to 275°C to form NCM particles coated with amorphous lithium niobate (LiNbO3). In the first example of the Method, the NCM particles are single-crystal particles. In the second example of the Method, optionally including the first example, the D50 of the NCM particles is in the range of 3 μm to 5 μm. In a third example of this method, optionally comprising one or both of the first and second examples, the method further comprises constructing an all-solid-state lithium-ion battery in which NCM particles coated with amorphous LiNbO3 are used for the cathode material coating of the all-solid-state lithium-ion battery. In a fourth example of this method, optionally comprising one or more of the first to third examples, or each of them, the all-solid-state lithium-ion battery comprises a sulfide-based solid electrolyte. In a fifth example of this method, optionally comprising one or more of the first to fourth examples, or each of them, the NCM particles coated with amorphous LiNbO3 reduce the resistance to charge transfer of the all-solid-state lithium-ion battery compared to an all-solid-state lithium-ion battery containing uncoated NCM particles. In a sixth example of this method, optionally comprising one or more of the first to fifth examples, or each of them, the molar ratio of lithium alkoxide to niobalkoxide is 0.9 to 1.25:1.

[0043] In addition to those shown and described herein, various modifications of the invention will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. The foregoing description illustrates certain embodiments of the invention, but does not mean to be a limitation on its practice. The foregoing discussion should be understood as illustrative and should not be considered limiting in any sense. While the invention is specifically shown and described with reference to its preferred embodiments, it should be understood to those skilled in the art that various modifications in form and detail can be made within the spirit and scope of the invention without departing from the spirit and scope of the invention as defined by the claims. The corresponding structures, materials, actions, and equivalents of all means-plus-function or step-plus-function elements in the following claims are intended to include any structures, materials, or actions for performing their function in combination with other specifically claimed elements.

[0044] Finally, it will be understood that the articles, systems, and methods described above are embodiments of the present disclosure and are non-limiting examples, with numerous variations and extensions similarly intended. Accordingly, the present disclosure includes all novel and non-trivial combinations and partial combinations of the articles, systems, and methods disclosed herein, as well as any and all equivalents thereof.

[0045] The following claims specifically point to certain combinations and partial combinations that are considered novel and non-obvious. These claims may refer to a “single” element or a “first” element or its equivalent. Such claims should be understood to include the incorporation of one or more such elements, and not to require or exclude two or more such elements. Other combinations and partial combinations of the disclosed features, functions, elements, and / or properties may be claimed through modifications to these claims or through the presentation of new claims in this application or related applications. Such claims, whether broader, narrower, equal to or different from the original claims, are also considered to be included within the subject matter of this disclosure.

Claims

1. A method for coating cathode active material particles, The preparation of a lithium niobate precursor solution, wherein the molar ratio of lithium to niobium in the lithium niobate precursor solution is determined by the surface composition of the cathode active material particles. Mixing the cathode active material particles with the lithium niobate precursor solution, Hydrolysis of a mixture of lithium niobate precursor solution and cathode active material particles, A method comprising heating the hydrolyzed mixture to obtain cathode active material particles coated with amorphous lithium niobate.

2. The method according to claim 1, wherein the cathode active material particles are NCM811 particles, and the molar ratio of lithium to niobium in the lithium niobate precursor solution is greater than 1.

3. The method according to claim 1, wherein the cathode active material particles are NCM811 particles, and the molar ratio of lithium to niobium in the lithium niobate precursor solution is 0.9 to 1.25:

1.

4. The method according to claim 1, wherein the solid weight percentage of the lithium niobate precursor in the mixture of the lithium niobate precursor solution and cathode active material particles is 0.1% to 3%.

5. Heating the hydrolyzed mixture is ２ The method according to claim 1, comprising heating at 250°C to 275°C under atmospheric conditions.

6. The method according to claim 1, wherein hydrolysis of the mixture of lithium niobate precursor solution and cathode active material particles is performed by adding water and mixing at room temperature for 5 minutes or less.

7. The method according to claim 1, wherein the lithium niobate precursor is attached to the surface of the cathode active material particles by mixing the cathode active material particles with the lithium niobate precursor solution.

8. A method for coating cathode active material particles, Mixing cathode active material particles with lithium niobate precursor solution, Water is added to a mixture of lithium niobate precursor solution and cathode active material particles at a rate more favorable to the hydrolysis of the lithium niobate precursor than to the condensation of the lithium niobate precursor. A method comprising heating a hydrolyzed mixture to obtain an amorphous lithium niobate coating on the cathode active material particles.

9. The method according to claim 8, wherein the rate that is more favorable to the hydrolysis of the lithium niobate precursor solution than to the condensation of the lithium niobate precursor is the addition of 5 mL / min or less of a 5 vol% aqueous solution in a non-aqueous solvent.

10. The method according to claim 8, wherein the addition of water includes adding water as an aqueous solution in ethanol.

11. The method according to claim 8, wherein the thickness of the amorphous lithium niobate coating is 5 nm to 60 nm.

12. The method according to claim 8, wherein the amorphous lithium niobate coating conforms to the protrusions and depressions on the surface of the cathode active material particles.

13. The method according to claim 8, wherein the amorphous lithium niobate coating is molecularly homogeneous.

14. All-solid-state lithium-ion battery, The anode current collector includes an anode material coating, a separator coating, and a cathode material coating, wherein the cathode material coating is The preparation of a lithium niobate precursor solution, wherein the molar ratio of lithium to niobium in the lithium niobate precursor solution is determined by the surface composition of the cathode active material particles. Mixing the cathode active material particles with the lithium niobate precursor solution, Hydrolysis of a mixture of lithium niobate precursor solution and cathode active material particles, The hydrolyzed mixture is heated to obtain cathode active material particles coated with amorphous lithium niobate, and LiNbO is formed by this process. ３ All-solid-state lithium-ion battery containing cathode active material particles coated with [a specific material].

15. The all-solid-state lithium-ion battery according to claim 14, wherein the separator coating is formed from a sulfide-based solid electrolyte.

16. The all-solid-state lithium-ion battery according to claim 14, wherein the cathode active material particles are NCM811 particles.

17. The all-solid-state lithium-ion battery according to claim 16, wherein the NCM811 particles are single-crystal particles.

18. The all-solid-state lithium-ion battery according to claim 14, wherein the D50 of the cathode active material particles is in the range of 3 μm to 5 μm.

19. The LiNb ３ LiNbO2 coated cathode active material particles ３ The all-solid-state lithium-ion battery according to claim 14, wherein the coating is homogeneous and amorphous.

20. The all-solid-state lithium-ion battery according to claim 14, wherein the charge transfer resistance of the all-solid-state lithium-ion battery is reduced compared to the charge transfer resistance of an all-solid-state lithium-ion battery containing uncoated cathode active material particles.

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