Cathode active material coated with lithium tetrafluoroborate doped with boron oxide and sulfide all-solid-state battery comprising same

Abstract

Disclosed herein is CAM at least partially coated with a lithium tetrafluoroborate doped with boron oxide (LBFO), and a preparation method therefor. In some embodiments, the lithium tetrafluoroborate doped with boron oxide (LBFO) has a formula of (LiBF4)1-x—[(Li2O)m(B2O3)1-m]x, wherein 0 < x < 0.33 and 0 ≤ m < 1.0. In some embodiments, the coating has a thickness in a range from 2 nm to 10 nm. Also disclosed is a cathode layer comprising the coated CAM and an all-solid-state battery (ASSB) comprising the cathode layer and a solid electrolyte layer. In some embodiments, the cathode layer and the solid electrolyte layer independently comprise a sulfide-based electrolyte.

Description

Docket No. F103PCT CATHODE ACTIVE MATERIAL COATED WITH LITHIUM TETRAFLUOROBORATE DOPED WITH BORON OXIDE AND SULFIDE ALL- SOLID-STATE BATTERY COMPRISING SAME CROSS-REFERENCE

[0001] The present application claims the priority of US Serial No.63 / 595,378, filed November 2, 2023, the entire content of which is incorporated herein by reference into this application. FIELD

[0002] The present disclosure relates to cathode active material coated with a lithium tetrafluoroborate doped with boron oxide (LBFO) and a sulfide-based all-solid-state battery (ASSB) comprising the same. BACKGROUND

[0003] All-solid-state batteries (ASSBs) are considered as promising candidates for future energy storage devices as they may enable the use of lithium metal as anode material and lead to higher specific energies compared to conventional lithium-ion batteries based on organic liquid electrolytes. Sulfide solid electrolyte (SE) materials comprise element sulfur in the -2 oxidation state (S-2) and have narrow intrinsic electrochemical windows. Thiophosphate-based solid electrolytes (SEs) contain elements phosphorus (P) and sulfur (S) and are particularly promising because of their high ionic conductivities, good mechanical compatibility, and relatively low costs. The passivation of SEs is necessary for the reversible operation of ASSBs. In particular, the adaptation of conventional high-capacity cathode active materials (CAMs) such as lithium metal oxide CAMs (ex. LiNi0.88Co0.09Al0.03O2 -- NCA88) to ASSBs suffer from interfacial resistances. There are two ways to improve the compatibility with high-voltage cathodes: (1) using SEs with high-anodic limit and good interfacial stability and (2) coating protective materials on cathodes. When it comes to sulfide-based ASSBs, the S / O exchange at the CAM / SE interface and the poor ion-conducting properties of the resulting degradation compositions are of major concern. Lithium metal fluoride (LMF) type CAM coatings may offer improved electrochemical stability due to the electronegativity of fluorine and minimization of O / F and S / F atom exchange between the CAM / coating and SE / coating. However, LMF type coatings generally have lower Li ion conductivities compared to their oxide counterparts, which limits high rate capabilities in the cell. Doping small amounts of oxide into the LMF structure may improve Li ion conductivities through the coating while retaining electrochemical stability.SUMMARY

[0004] Disclosed herein is a CAM at least partially coated with a lithium tetrafluoroborate doped with boron oxide (LBFO) with a formula of (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0<x<0.33, 0 ≤ m <1.0, and a preparation method therefor. Also disclosed is a cathode layer comprising the coated CAM and an all-solid-state battery (ASSB) comprising the cathode layer. BRIEF DESCRIPTION OF THE FIGURES

[0005] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure.

[0006] Figure 1 shows a representative structure of a cathode layer comprising CAM particle coated with lithium tetrafluoroborate doped with a boron oxide according to one embodiment of the present disclosure.

[0007] Figure 2 shows a typical structure of an all-solid-state battery (ASSB) according to one embodiment of the present disclosure.

[0008] Figure 3 shows a plot of specific capacity vs. cycle at 45oC of half-cells comprising a Li metal anode, LPSCl (Li6PS5Cl) as SE, and cathode layer comprising particles of NCA88 (LiNi0.88Co0.09Al0.03O2) as CAM, and vapor grown carbon fiber (VGCF) according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0009] In some embodiments, a cathode active material (CAM) is coated with lithium tetrafluoroborate doped with boron oxide (LBFO) having a formula of (LiBF4)1-x–[(Li2O)m(B2O3)1- m]x, wherein 0 < x < 0.33 and 0 ≤ m <1.0. Such a coating can minimize the degradation of a sulfide solid electrolyte at the interface of the solid electrolyte and the coated CAM when the coated CAM is incorporated into a cathode layer for an all-solid-state-battery (ASSB). In some embodiments, minimizing the degradation of the solid electrolyte improves the overall cycle stability and discharge capacity of the ASSB.

[0010] In some embodiments, the cathode active material (CAM) is particulate in form in that it is made of a plurality of individual CAM particles. In some embodiments, each particle of theCAM particulate (or CAM particle) is coated with the lithium tetrafluoroborate doped with boron oxide (LBFO) having a formula of (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0 < x < 0.33 and 0 ≤ m <1.0. In some embodiments, the coated CAM, for example the coated CAM particulate, is incorporated into a cathode layer as shown for example in Figure 1. The cathode layer may have the individual particles of a cathode active material (CAM) (1) coated with LBFO as a CAM coating layer (2), electrically conducting material, such as carbon fibers (3), and a solid electrolyte, such as a sulfur-containing inorganic electrolyte or sulfide based solid electrolyte (4).

[0011] In some embodiments, as shown in Figure 1, a cathode layer comprises a CAM particle (1) coated with lithium tetrafluoroborate doped with a boron oxide (2), an electronically conductive carbon fiber (3), and a sulfide SE (4).

[0012] In some embodiments, the CAM particle coating material is a lithium tetrafluoroborate doped with boron oxide (LBFO), where formula (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0 < x <0.33, and 0≤m<1 expresses the ratio of LiBF4to (Li2O)m(B2O3)1-m(0≤m<1).

[0013] As shown in Table 1 below, it was unexpectedly found incorporating CAM particles coated with LBFO such that 0<x<0.33 into a cathode layer for an ASSB results in the ASSB having improved cycle life retention capacity. Thus, in some embodiments, x has a value less than 0.33, or less than or equal to 0.3, less than or equal to 0.25, or less than or equal to 0.20. In some embodiments, x has a value greater than 0. In some embodiments, x has a value greater than or equal to 0.01, greater than or equal to 0.03, greater than or equal to 0.05, greater than or equal to 0.07, greater than or equal to 0.1, greater than or equal to 0.12, greater than or equal to 0.15, greater than or equal to 0.17 or greater than or equal to 0.20. In some embodiments, 0 < x < 0.33, 0 < x ≤ 0.3, 0 < x ≤ 0.25, 0 < x ≤ 0.20, 0.01 ≤ x < 0.33, 0.01 ≤ x ≤ 0.3, 0.01 ≤ x ≤ 0.25, 0.01 ≤ x ≤ 0.20, 0.02 ≤ x < 0.33, 0.02 ≤ x ≤ 0.3, 0.02 ≤ x ≤ 0.25, 0.02 ≤ x ≤ 0.20, 0.03 ≤ x < 0.33, 0.03 ≤ x ≤ 0.3, 0.03 ≤ x ≤ 0.25, 0.03 ≤ x ≤ 0.20, 0.05 ≤ x < 0.33, 0.05 ≤ x ≤ 0.3, 0.05 ≤ x ≤ 0.25, 0.05 ≤ x ≤ 0.20, 0.07 ≤ x < 0.33, 0.07 ≤ x ≤ 0.3, 0.07 ≤ x ≤ 0.25, 0.07 ≤ x ≤ 0.20, 0.1 ≤ x < 0.33, 0.1 ≤ x ≤ 0.3, 0.1 ≤ x ≤ 0.25, 0.1 ≤ x ≤ 0.20, or all and any ranges and subranges therebetween.

[0014] In some embodiments, boron oxide includes boron trioxide (B2O3), tri-lithium borate (Li3BO3), lithium triborate (LiB3O5), lithium metaborate (LiBO2), lithium tetraborate (Li2B4O7), α-Li4B2O5, β-Li4B2O5, Li6B4O9, Li3B7O12, and Li2B8O13. In some embodiments, the boron oxide is selected from the group consisting of B2O3, Li3BO3, LiBO2, Li2B4O7, α-Li4B2O5, β-Li4B2O5,Li6B4O9, Li3B7O12, Li2B8O13 and mixtures thereof. In some embodiments, the boron oxide is selected from the group consisting of B2O3, LiBO2, Li2B4O7, and mixtures thereof.

[0015] In one embodiment, m has a value of 0. In some embodiments, m has a value greater than zero but less than 1. In some embodiments, m has a value of 0.75, 2 / 3, 0.60, 0.50, 0.40, 1 / 3, 0.30, 0.25, 0.20 or 0.

[0016] In some embodiments, the CAM includes without limitation: LixMn1-yMyA2(Formula 1), LixMn1-yMyO2-zXz(Formula 2), LixMn2O4-zXz(Formula 3), LixMn2-yMyA4(Formula 4), LixCo1-yMyA2 (Formula 5), LixCo1-yMyO2-zXz (Formula 6), LixNi1-yMyA2 (Formula 7), LixNi1-yMyO2-zXz (Formula 8), LixNi1-yCoyO2-zXz(Formula 9), LixNi1-y-zCoyMzAa, (formula 10), LixNi1-y-zCoyMzO2-aXa(Formula 11), LixNi1-y-zMnyMzAa(Formula 12), LixNi1-y-zMnyMzO2-aXa(Formula 13), LixNi1-y-zMnyMzO2 (Formula 14) and combinations thereof wherein 0.95 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 2; M is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, and rare earth elements; A is selected from the group consisting of O, F, S, and P; and X is selected from the group consisting of F, S, and P.

[0017] In some embodiments, the CAM is a particulate in the form of a plurality of individual particles, wherein the particles have an average diameter in a range from about 1 µm to about 15 µm, about 1 µm to about 12 µm, about 1 µm to about 10 µm, about 1 µm to about 7 µm, about 1 µm to about 6 µm , about 3 µm to about 15 µm, about 3 µm to about 12 µm, about 3 µm to about 10 µm, about 3 µm to about 7 µm, about 3 µm to about 6 µm, about 5 µm to about 15 µm, about 5 µm to about 12 µm, about 5 µm to about 10 µm or all ranges and subranges therebetween. In some embodiments, the average diameter is the average particle size of a secondary particle. In some embodiments, the average particle size of a secondary particle of the CAM is measured by a particle size analyzer based on laser-diffraction.

[0018] In some embodiments, the coated CAM may have a weight percentage in a range from about 50 wt% to about 99 wt%, from about 50 wt% to about 95 wt%, from about 50 wt% to about 90 wt%, from about 50 wt% to about 85 wt%, from about 50 wt% to about 80 wt%, from about 55 wt% to about 99 wt%, from about 55 wt% to about 95 wt%, from about 55 wt% to about 90 wt%, from about 55 wt% to about 85 wt%, from about 55 wt% to about 80 wt%, from about 60 wt% to about 99 wt%, from about 60 wt% to about 95 wt%, from about 60 wt% to about 90 wt%, from about 60 wt% to about 85 wt%, from about 60 wt% to about 80 wt%, from about 65 wt% to about 99 wt%, from about 65 wt% to about 95 wt%, from about 65 wt% to about 90 wt%, from about 65wt% to about 85 wt%, from about 65 wt% to about 80 wt%, from about 70 wt% to about 99 wt%, from about 70 wt% to about 95 wt%, from about 70 wt% to about 90 wt%, from about 70 wt% to about 85 wt%, from about 70 wt% to about 80 wt%, or all range and subranges therebetween in the cathode layer. In some embodiments, the CAM particles may be polycrystalline or single crystalline. In some embodiments, the CAM particles may have a unimodal particle size distribution or multi-modal particle size distribution.

[0019] In some embodiments, the LBFO coating may have a thickness in a range from 0.5 to 20 nm, from 0.8 to 20 nm, from 1 to 20 nm, from 2 to 20 nm, from 4 to 20 nm, from 10 to 20 nm, from 0.5 to 10 nm, from 1.0 to 10 nm, from 2 to 10 nm, or from 4 to 10 nm. In some embodiments, the thickness is measured by observing the cross section of a dissected particle using a scanning electron microscope (SEM). In some embodiments, the thickness is measured on a transmission electron microscope (TEM).

[0020] In some embodiments, the CAM particle coated with the LBFO exhibits a core-shell structure. The core is a CAM particle while the shell is the LBFO coating surrounding the CAM particle.

[0021] In some embodiments, the electrically conductive material may be carbon fibers including but not limited to, vapor grown carbon fiber (VGCF), carbon nanotube (CNT), multi-walled carbon nanotubes (MWCNT), carbon nanofiber, and graphite fiber. In some embodiments, the electrically conductive material may have a BET measured specific surface area in a range from 1 to 600 m2 / g and / or an electrical resistance of no more than 0.5 Ω∙cm. In some embodiments, the electrically conductive material may be coated with an oxide material. In some embodiments, the electrically conductive material (coated or uncoated) has a concentration in a range from 0.01 wt% to 5 wt%, from 0.01 wt% to 4 wt%, from 0.01 wt% to 3 wt%, from 0.01 wt% to 2 wt%, from 0.5 wt% to 5 wt%, from 0.5 wt% to 4 wt%, from 0.5 wt% to 3 wt%, from 0.5 wt% to 2 wt%, from 1 wt% to 5 wt%, from 1 wt% to 4 wt%, from 1 wt% to 3 wt%, from 2 wt% to 5 wt%, from 2 wt% to 4 wt%, or any or all ranges and subranges therebetween in the cathode layer.

[0022] In some embodiments, a method for preparing the coated cathode active material particles is disclosed. A coating solution including a solvent, lithium tetrafluoroborate and a boron oxide precursor can be prepared, wherein the amounts of the lithium tetrafluoroborate and boron oxide precursor are calculated based on the formula (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0 < x <0.33, and 0≤m<1. In some embodiments, the solvent is non-aqueous and is selected from the groupconsisting of methanol, ethanol, isopropanol, n-propanol, t-butanol, tetrahydrofuran, and mixtures thereof. The coating solution can be applied to the particles of uncoated cathode active material and then the coating can be annealed, whereby the lithium tetrafluoroborate and the boron oxide precursor form the LBFO coating on the cathode active material. In some embodiments, the annealing occurs in a range from 150oC to 500oC for a duration in a range from 0.5 to 3 hr under an oxygen atmosphere. In some embodiments, the coating solution may be applied by spray coating the coating solution on the uncoated cathode active material particles, referred to herein as a spray coating method. In other embodiments, the coating solution can be applied by mixing the uncoated cathode active material particles with the coating solution to form a mixture. The solvent can then be removed from the mixture to form a gel, referred to herein as a sol-gel method.

[0023] In some embodiments, the solid electrolyte in the cathode may be any sulfide solid electrolyte as long as it contains Li and S and has a desired lithium-ion conductivity. The sulfide solid electrolyte may be any crystalline material, glass ceramic, and glass. In some embodiments, the solid electrolyte is a lithium-phosphate-sulfur (LPS) electrolyte. Examples of the sulfide solid electrolyte include Li2S-P2S5, Li2S-P2S5-LiHa ("Ha" is one or more halogen elements, such as F, Cl, Br and I), Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, Li10GeP2S12, Li3.25Ge0.25P0.75S4, Li7P3S11, Li3.25P0.95S4, and Li7-xPS6-xHax(argyrodite-type solid electrolyte, "Ha" is one or more halogen elements, where 0.2 < x < 1.8). In some embodiments, the sulfide solid electrolyte may have a weight percentage in a range from 1 wt% to 35 wt%, from 1 wt% to 30 wt%, from 1 wt% to 25 wt%, from 1 wt% to 20 wt%, from 1 wt% to 15wt%, from 1 wt% to 10 wt%, from 5 wt% to 35 wt%, from 5 wt% to 30 wt%, from 5 wt% to 25 wt%, from 5 wt% to 20 wt%, from 5 wt% to 15 wt%, from 10 wt% to 35 wt%, from 10 wt% to 30 wt%, from 10 wt% to 25 wt%, from 10 wt % to 20 wt%, from 15 wt% to 35 wt%, from 15 wt% to 30 wt%, from 15 wt% to 25 wt%, from 20 wt% to 30 wt% or any and all ranges and subranges therebetween in the cathode layer.

[0024] In some embodiments, the coated CAM particulate is mixed with other components such as electrically conductive material, solid electrolyte and / or binder, ground, and pressed to form a cathode layer. In some embodiments, a cathode layer is sandwiched between a cathode current collector and the solid electrolyte layer as described herein. In some embodiments, the cathode layer includes a cathode active material (CAM) that requires both lithium ion (Li+) and electron (e-) connectivity with the solid electrolyte layer and current collector, respectively. The Li+ connectivity is mainly provided by small particles of sulfide-based solid electrolyte in the cathodelayer, and the e- connectivity is mainly provided by the electrically conductive material. The sulfide-based solid electrolytes (such as the exemplary sulfide solid electrolyte set forth above) have a high Li+ conductivity. However, they generally degrade at potentials below 1.7 V or above 2.1 V vs. Li / Li+ at the CAM / SE, carbon fiber (CF) / SE, and current collector / SE interface. The degraded byproducts generally have a lower Li+ conductivity, which in return requires a higher percentage of SE in the cathode composite layer, leading to a lower percentage of CAM. Without wishing to be bound by theory, the LBFO coating disclosed herein prolongs the time for degradation, maintains a relatively higher Li+ conductivity, and thus improves the overall battery cell performance.

[0025] The cathode layer disclosed above can be incorporated into an ASSB. As shown for example in Figure 2, an ASSB comprises a cathode layer (5), a cathode current collector (8-2), an anode layer (7), an anode current collector (8-1), and a solid electrolyte layer (6) sandwiched between the anode layer (7) and the cathode layer (5). In some embodiments, the solid electrolyte of the solid electrolyte layer may be the same as or different from the solid electrolyte in the cathode layer. In some embodiments, the solid electrolyte layer is an inorganic solid electrolyte layer, for example a sulfur-containing inorganic electrolyte including, but not limited to Li2S-P2S5, Li2S-P2S5-LiHa (“Ha” is one or more halogen elements such as F, Cl, Br, and I), Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, Li10GeP2S12, Li3.25Ge0.25P0.75S4, Li7P3S11, Li3.25P0.95S4, and Li7-xPS6-xHax(argyrodite-type solid electrolyte, “Ha” is one or more halogen elements, where 0.2 < x < 1.8).

[0026] In some embodiments, the ASSB has an initial discharge specific capacity of at least 190 mAh / g, at least 195 mAh / g, at least 200 mAh / g, at least 203 mAh / g, at least 205 mAh / g, at least 207.5 mAh / g, at least 210 mAh / g, or at least 212.5 mAh / g at a discharge rate of 0.1C at 45oC.

[0027] In some embodiments, the ASSB has an initial discharge specific capacity of at least at least 190 mAh / g, at least 192 mAh / g, at least 195 mAh / g, at least 197 mAh / g, at least 200 mAh / g, or at least 202 mAh / g at a discharge rate of 0.33C at 45oC.

[0028] In some embodiments, the ASSB has an initial discharge specific capacity of at least 180 mAh / g, at least 185 mAh / g, at least 190 mAh / g, at least 192 mAh / g, or at least 195 mAh / g at a discharge rate of 0.5C at 45oC.

[0029] In some embodiments, the ASSB has an initial discharge specific capacity of at least 175 mAh / g, at least 177 mAh / g,at least 180 mAh / g, at least 182 mAh / g, at least 185 mAh / g, or at least 190 mAh / g at a discharge rate of 1C at 45oC.

[0030] In some embodiments, after 20 cycles at 0.5C charge / discharge rate at 45oC, the ASSB has a 20th cycle discharge of at least 180 mAh / g, at least 185 mAh / g, at least 190 mAh / g or at least 190 mAh / g and / or a 20th cycle life retention rate of at least 96%, at least 97 %, at least 97.5 %, at least 98%, at least 98.5 %, or at least 99%. The 20thcycle life retention rate is the ratio of the discharge specific capacity at the 20thcycle to the initial discharge specific capacity at 0.5C at 45oC.

[0031] In some embodiments, the present disclosure provides a coated cathode active material particle (CAM particle) comprising a particle of a cathode active material (CAM) and a coating on the particle of the cathode active material, wherein the coating comprises a lithium tetrafluoroborate doped with boron oxide (LBFO) having a formula of (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0<x<0.33 and 0 ≤ m < 1.0.

[0032] In some embodiments, the coating on the CAM particle has a thickness in a range from 2nm to 10 nm.

[0033] In some embodiments, the formula is (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0<x≤0.25 and 0 ≤ m < 1.0. In some embodiments, m has a value of 0.75, 2 / 3, 0.60, 0.50, 0.40, 1 / 3, 0.30, 0.25 0.20 or 0.

[0034] In some embodiments, the formula is (LiBF4)1-x–(B2O3)x, wherein 0<x≤0.25.

[0035] In some embodiments, the LBFO is selected from the group consisting of (LiBF4)95– (B2O3)5, (LiBF4)90–(B2O3)10, (LiBF4)85–(B2O3)15, (LiBF4)80–(B2O3)20, (LiBF4)75–(B2O3)25, and (LiBF4)67–(B2O3)33.

[0036] In some embodiments, the particle is either polycrystalline or single crystalline and has an average diameter of 1-15µm.

[0037] In some embodiments, the CAM is selected from the group consisting of LixMn1-yMyA2, LixMn1-yMyO2-zXz, LixMn2O4-zXz, LixMn2-yMyA4, LixCo1-yMyA2, LixCo1-yMyO2-zXz, LixNi1-yMyA2, LixNi1-yMyO2-zXz, LixNi1-yCoyO2-zXz, LixNi1-y-zCoyMzAa, LixNi1-y-zCoyMzO2-aXa, LixNi1-y-zMnyMzAa, LixNi1-y-zMnyMzO2-aXa, and mixtures thereof, wherein 0.95 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 2; M is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V,and rare earth elements; A is selected from the group consisting of O, F, S, and P; and X is selected from the group consisting of F, S, and P.

[0038] In some embodiments, the present disclosure provides a method for preparing coated cathode active material particle, comprising: a) preparing a coating solution comprising a solvent, a lithium tetrafluoroborate and a boron oxide precursor, wherein the amounts of the lithium tetrafluoroborate and boron oxide precursor are calculated based on the formula and the surface area of an uncoated cathode active material (CAM) particle; b) applying the coating solution to the uncoated CAM particle; and c) annealing the coating solution on the uncoated CAM particle, wherein the lithium tetrafluoroborate and the boron oxide precursor on a surface of the CAM particle are converted into lithium tetrafluoroborate doped with boron oxide (LBFO) thereby obtaining the coated CAM particle.

[0039] In some embodiments, the solvent for preparing the coating solution is non-aqueous and is selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, t-butanol, tetrahydrofuran, and mixtures thereof and wherein the coating solution on the uncoated CAM particle is annealed in a range from 150 to 500oC for a duration in a range from 0.5 to 3 hr under an oxygen atmosphere.

[0040] In some embodiments, applying the coating solution comprises mixing the uncoated CAM particle with the coating solution or spray coating the coating solution onto the uncoated CAM particle.

[0041] In some embodiments, the present disclosure provides a cathode layer comprising the coated CAM particle as described herein, an electrically conductive material and a sulfur- containing inorganic electrolyte.

[0042] In some embodiments, the coated CAM particle has a weight percentage of at least 65% of the cathode layer.

[0043] In some embodiments, the electrically conductive material is selected from carbon fiber, vapor growth carbon fiber, carbon nanotube, graphite fiber, and mixtures thereof.

[0044] In some embodiments, the sulfur-containing inorganic electrolyte is selected from the group consisting of Li2S-P2S5, Li2S-P2S5-LiHa, Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4,Li4P2S6, Li10GeP2S12, Li3.25Ge0.25P0.75S4, Li7P3S11, Li3.25P0.95S4, Li7-xPS6-xHax, and mixtures thereof wherein “Ha” is one or more halogen elements, and 0.2 < x < 1.

[0045] In some embodiments, the present disclosure provides an ASSB comprising the cathode layer as described herein, an inorganic solid electrolyte layer comprising a sulfur-containing inorganic electrolyte.

[0046] In some embodiments, the ASSB exhibits a 20thcycle life retention rate of at least 98%, wherein the 20thcycle life retention rate is the ratio of the discharge specific capacity at the 20thcycle to the initial discharge specific capacity at 0.5C at 45oC.

[0047] The disclosure will be better understood by reference to the Experimental Details which follow, but those skilled in the art will readily appreciate that the specific experiments detailed are only illustrative, and are not meant to limit the disclosure as described herein, as numerous variations and modifications of these exemplary embodiments are possible without undue experimentation. All such variations and modifications are within the scope of the teachings of this disclosure. It will be appreciated that the foregoing description and following examples, no matter how detailed they may appear in text, the disclosure may be practiced in many ways, and the disclosure should be construed in accordance with the appended claims and equivalents thereof.

[0048] It is to be noted that the transitional term “comprising”, which is synonymous with “including”, “containing” or “characterized by”, is inclusive or open-ended and does not exclude additional, un-recited elements or method steps. EXAMPLE 1

[0049] The stoichiometric amounts of LiBF4 and B2O3 needed to create the LBFO coating are calculated. For a LBFO coating with x=0.10 and m=0, the stoichiometric amounts of a LiBF4and B2O3precursor (such as triisopropyl borate) are dissolved in a dry solvent (such as ethanol or tetrahydrofuran), forming a coating solution comprising LiBF4 and the B2O3 precursor. The coating solution is added to a pre-determined amount of CAMs, calculated to give a desired LBFO coating thickness using the BET surface area of the CAM and an estimated coating density of 0.852g / cm3. The mixture is stirred for 30 minutes followed by solvent removal via vacuum while being sonicated, leading to a gel of CAM coated with LiBF4 and the B2O3 precursor. The gel was then annealed for 1 hour at 300oC under an oxygen flow to form the LBFO coating layer.

[0050] The cathode layers comprising 65wt% CAM (coated or uncoated NCA88), 5wt% carbon fiber (VGCF), and 30wt% lithium phosphorus sulfur chloride (LPSCl) (Li6PS5Cl) were prepared.The cathode layers were electrochemically evaluated in torque-cells (half-cells) using Li metal on copper as the anode and LPSCl (Li6PS5Cl) as the SE. The cells are cycled at 45oC from 2.5V to 4.25V at 0.1C charge / discharge for cycles 1 and 2, 0.33C charge / discharge for cycles 3 and 4, 1.0C charge / discharge for cycle 5, and 0.5C charge / discharge for cycles 6 to 25. Figure 3 shows a plot of specific capacity vs. cycle at 45oC of half-cells comprising a Li metal anode, LPSCl (Li6PS5Cl) as SE, and cathode layer comprising particles of uncoated NCA88 (LiNi0.88Co0.09Al0.03O2) or coated NCA88 as CAM, and vapor grown carbon fiber (VGCF). Cycles 1 & 2 were cycled at 0.1C charge / discharge rate; cycle 3 & 4 were cycled at 0.33C charge / discharge rate, cycle 5 was cycled at 1.0C charge / discharge rate, and cycle 6-25 were cycled at 0.5C charge / discharge rate. The cycle plots compare uncoated NCA88 CAM and NCA88 CAM coated with roughly 3nm of LBFO with x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, and 0.33. Table 1 Initial discharge (dChg.) specific capacities (mAh / g) at 45oC and different C-rates for half- cells using uncoated and LBFO coated CAM for x=0 - 0.33 and m = 0. LBFO Initial Initial Initial Initial 20 Cycle Cycle-life a city bythe initial 0.5C dChg. capacity and multiplying by 100%.

[0051] The specific discharge specific capacities and cycle-life retentions of half-cells comprising various LBFO coating compositions for x = 0 to 0.33 are summarized in Table 1. All coatings showed improvements to cycle-life stability compared to uncoated CAM. However, not all coating can achieve both high cycle-life stability and desirable high-rate capability. The LBFO coating of0 < x ≤ 0.25 decreased the fading of the discharge specific capacity (cycle-life capacity retention) greater than undoped LiBF4 coated CAM, while LBFO coatings of 0.05 ≤ x ≤ 0.20 showed an improvement to both cycle-life capacity retention and rate capabilities (higher discharge specific capacities at 1C) compared to undoped LiBF4 coated CAM (x=0). For example, as shown in Table 1 and Figure 3, the initial discharge capacity is 208.83 mAh / g at 0.1C, 189.84 mAh / g at 1C, and a 20 cycle-life capacity retention of 98.12% for a half-cell comprising undoped LiBF4coated CAM (x=0.00). When x has a value of 0.05, the initial discharge capacity at 0.1C is 205.26 mAh / g, which is comparable to the undoped LiBF4 coated CAM and the 20thcycle capacity retention is 99.87%, which is higher than the uncoated CAM and the undoped LiBF4coated CAM. Doping B2O3into LiBF4(for x = 0.10, 0.15, and 0.20), the initial discharge specific capacities at 0.1C, as well as the discharge capacities at 1C and 20thcycle capacity retention, are higher than that of undoped LiBF4 coated CAM. When x has a value of 0.25, the initial discharge capacity at 0.1C is 207.63mAh / g, which is comparable to the undoped LiBF4coated CAM and the 20thcycle capacity retention is 98.91%, which is higher than the uncoated CAM the undoped LiBF4 coated CAM. When x has a value higher than 0.25 for example when x is 0.33, the cell performance in terms of cycle-life stability and discharge capacities at various C-rates begins to decrease to below undoped LiBF4coated CAM. Aspects

[0052] In a first aspect of the disclosure, a coated cathode active material comprises a cathode active material (CAM) and a coating in contact with the cathode active material, wherein the coating comprises a lithium tetrafluoroborate doped with boron oxide (LBFO) having a formula of (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0<x<0.33 and 0≤m<1.

[0053] In a second aspect according to the first aspect, the coating has a thickness in a range from 2 nm to 10 nm.

[0054] In a third aspect according to any preceding aspect, 0.00 < x ≤ 0.25.

[0055] In a fourth aspect according to any preceding aspect, the cathode active material is in the form of particles and the particles are either polycrystalline or single crystalline and have an average diameter of 1-15µm. In some embodiments, the average diameter of the particle refers to the average diameter of a secondary particle of a CAM. In some embodiments, the average diameter of the CAM particles is measured by a particle size analyzer based on laser diffraction.

[0056] In a fifth aspect according to any preceding aspect, the CAM is at least one selected from the group consisting of LixMn1-yMyA2, LixMn1-yMyO2-zXz, LixMn2O4-zXz, LixMn2-yMyA4, LixCo1-yMyA2, LixCo1-yMyO2-zXz, LixNi1-yMyA2, LixNi1-yMyO2-zXz, LixNi1-yCoyO2-zXz, LixNi1-y-zCoyMzAa, LixNi1-y-zCoyMzO2-aXa, LixNi1-y-zMnyMzAa, LixNi1-y-zMnyMzO2-aXa, and mixtures thereof, wherein 0.95 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 2; M is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, and rare earth elements; A is selected from the group consisting of O, F, S, and P; and X is selected from the group consisting of F, S, and P.

[0057] In a sixth aspect, a method for preparing a coated cathode active material of any preceding aspects, comprises a) preparing a coating solution comprising a solvent, lithium tetrafluoroborate and a boron oxide precursor, wherein the amounts of the lithium tetrafluoroborate and boron oxide precursor are calculated based on the formula and surface area of an uncoated cathode active material (CAM); b) applying the coating solution to the uncoated CAM; and c) annealing the coating solution, wherein the lithium tetrafluoroborate and the boron oxide precursor on a surface of the CAM are converted into lithium tetrafluoroborate doped with boron oxide (LBFO) thereby obtaining the coated CAM.

[0058] In a seventh aspect according to the sixth aspect, the solvent for preparing the coating solution is non-aqueous and is selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, t-butanol, tetrahydrofuran, and mixtures thereof.

[0059] In an eighth aspect according to any of the sixth and seventh aspects, the gel is annealed in a range from 150 to 500oC for a duration in a range from 0.5 to 3 hr under an oxygen atmosphere.

[0060] In a ninth aspect according to any of the sixth through eighth aspects, applying the coating solution to the uncoated CAM comprises mixing the uncoated CAM with the coating solution.

[0061] In a tenth aspect according to any of the sixth through eighth aspects, applying the coating solution comprises spray coating the coating solution onto the uncoated CAM.

[0062] In an eleventh aspect, a cathode layer comprises a coated cathode active material set forth above in any of the first through fifth aspects.

[0063] In a twelfth aspect according to the eleventh aspect, the coated CAM has a weight percentage of at least 65% of the cathode layer.

[0064] In a thirteenth aspect according to the eleventh or twelfth aspect, the cathode layer further comprises an electrically conductive material and a sulfur-containing inorganic electrolyte.

[0065] In a fourteenth aspect according to the thirteenth aspect, the electrically conductive material is selected from carbon fiber, vapor growth carbon fiber, carbon nanotube, graphite fiber, and mixtures thereof.

[0066] In a fifteenth aspect according to the thirteenth or fourteenth aspect, the sulfur-containing inorganic electrolyte is selected from the group consisting of Li2S-P2S5, Li2S-P2S5-LiHa, Li2S- P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, Li10GeP2S12, Li3.25Ge0.25P0.75S4, Li7P3S11, Li3.25P0.95S4, Li7-xPS6-xHax, and mixtures thereof, wherein “Ha” is one or more halogen elements, and 0.2 < x < 1.

[0067] In a sixteenth aspect, an all-solid-state battery (ASSB) comprises a cathode layer set forth above in any of the eleventh through fifteenth aspects.

[0068] In a seventeenth aspect according to the sixteenth aspect, the ASSB further comprises an inorganic solid electrolyte layer.

[0069] In an eighteenth aspect according to the seventeenth aspect, the inorganic solid electrolyte layer comprises a sulfur-containing inorganic electrolyte.

[0070] In a nineteenth aspect according to the eighteenth aspect, the sulfur-containing inorganic electrolyte is selected from the group consisting of Li2S-P2S5, Li2S-P2S5-LiHa, Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, Li10GeP2S12, Li3.25Ge0.25P0.75S4, Li7P3S11, Li3.25P0.95S4, Li7-xPS6-xHax, and mixtures thereof, wherein "Ha" is one or more halogen elements, and 0.2 < x < 1.

[0071] In a twentieth aspect according to any of the sixteenth through nineteenth aspects, the LBFO has a formulation selected from the group consisting of (LiBF4)95–(B2O3)5, (LiBF4)90– (B2O3)10,(LiBF4)85–(B2O3)15,(LiBF4)80–(B2O3)20,(LiBF4)75–(B2O3)25, (LiBF4)67–(B2O3)33.

[0072] In a twenty-first aspect according to any of the sixteenth through twentieth aspects, the ASSB exhibits a 20thcycle life retention rate of at least 98%, wherein the 20thcycle life retention rate is the ratio of the discharge specific capacity at the 20thcycle to the initial discharge specific capacity at 0.5C.

[0073] In a twenty-second aspect according to any of the sixteenth through twenty-first aspects, the ASSB possesses an initial discharge specific capacity of at least 200 mAh / g at 0.1C.

[0074] Various embodiments of the features of this disclosure are described herein. However, it should be understood that such embodiments are provided merely by way of example, andnumerous variations, changes, and substitutions can occur to those skilled in the art without departing from the scope of this disclosure. It should also be understood that various alternatives to the specific embodiments described herein are also within the scope of this disclosure.

Claims

We claim:

1. A coated cathode active material particle comprising: a particle of a cathode active material (CAM); and a coating on the particle of the cathode active material, wherein the coating comprises a lithium tetrafluoroborate doped with boron oxide (LBFO) having a formula of (LiBF4)1-x–[(Li2O)m(B2O3)1-m]x, wherein 0<x<0.33 and 0 ≤ m < 1.

0.

2. The coated cathode active material particle of claim 1, wherein the coating has a thickness in a range from 2 to 10 nm.

3. The coated cathode active material particle of claim 1, wherein 0<x≤0.

25.

4. The coated cathode active material particle of claim 1, wherein the LBFO has a formula selected from the group consisting of (LiBF4)95–(B2O3)5, (LiBF4)90–(B2O3)10, (LiBF4)85–(B2O3)15, (LiBF4)80–(B2O3)20, (LiBF4)75–(B2O3)25, and (LiBF4)67–(B2O3)33.

5. The coated cathode active material of claim 1, wherein the particle is either polycrystalline or single crystalline and has an average diameter of 1-15µm.

6. The coated cathode active material particle of claim 1, wherein the CAM is selected from the group consisting of LixMn1-yMyA2, LixMn1-yMyO2-zXz, LixMn2O4-zXz, LixMn2-yMyA4, LixCo1-yMyA2, LixCo1-yMyO2-zXz, LixNi1-yMyA2, LixNi1-yMyO2-zXz, LixNi1-yCoyO2-zXz, LixNi1-y- zCoyMzAa, LixNi1-y-zCoyMzO2-aXa, LixNi1-y-zMnyMzAa, LixNi1-y-zMnyMzO2-aXa, and mixtures thereof, wherein 0.95 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.5, 0 ≤ a ≤ 2; M is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, and rare earth elements; A is selected from the group consisting of O, F, S, and P; and X is selected from the group consisting of F, S, and P.

7. A method for preparing coated cathode active material particle of claim 1, comprising: a) preparing a coating solution comprising a solvent, a lithium tetrafluoroborate and a boron oxide precursor, wherein the amounts of the lithium tetrafluoroborate and boron oxideprecursor are calculated based on the formula and the surface area of an uncoated cathode active material (CAM) particle; b) applying the coating solution to the uncoated CAM particle; and c) annealing the coating solution on the uncoated CAM particle, wherein the lithium tetrafluoroborate and the boron oxide precursor on a surface of the CAM particle are converted into lithium tetrafluoroborate doped with boron oxide (LBFO) thereby obtaining the coated CAM particle.

8. The method of claim 7, wherein the solvent for preparing the coating solution is non-aqueous and is selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, t- butanol, tetrahydrofuran, and mixtures thereof and wherein the coating solution on the uncoated CAM particle is annealed in a range from 150 to 500oC for a duration in a range from 0.5 to 3 hr under an oxygen atmosphere.

9. The method of claim 7, wherein applying the coating solution comprises mixing the uncoated CAM particle with the coating solution or spray coating the coating solution onto the uncoated CAM particle.

10. A cathode layer comprising the coated CAM particle of claim 1, an electrically conductive material and a sulfur-containing inorganic electrolyte.

11. The cathode layer of claim 10, wherein the coated CAM particle has a weight percentage of at least 65% of the cathode layer.

12. The cathode layer of claim 10, wherein the electrically conductive material is selected from carbon fiber, vapor growth carbon fiber, carbon nanotube, graphite fiber, and mixtures thereof.

13. The cathode layer of claim 10, wherein the sulfur-containing inorganic electrolyte is selected from the group consisting of Li2S-P2S5, Li2S-P2S5-LiHa, Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, Li10GeP2S12, Li3.25Ge0.25P0.75S4, Li7P3S11, Li3.25P0.95S4, Li7-xPS6-xHax, and mixtures thereof wherein “Ha” is one or more halogen elements, and 0.2 < x < 1.

14. An all-solid-state battery (ASSB) comprising the cathode layer of claim 10, an inorganic solid electrolyte layer comprising a sulfur-containing inorganic electrolyte.

15. The ASSB of claim 14, wherein the ASSB exhibits a 20thcycle life retention rate of at least 98%, wherein the 20thcycle life retention rate is the ratio of the discharge specific capacity at the 20thcycle to the initial discharge specific capacity at 0.5C at 45oC.

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