Synthesis of fumed nanostructured lithium borate powder

Abstract

A method for making fumed lithium borate, the method comprising: preparing a solution of a lithium precursor, preferably a lithium carboxylate containing 5 to 20 carbon atoms, and a boron source, preferably an organic boron compound, feeding the solution to a flame burning in a flame reaction zone to produce a fumed product comprising fumed lithium borate particles; and obtaining the fumed product.

Description

[0001] Synthesis of fumed nanostructured lithium borate powder

[0002] Field of the Invention

[0003] The invention relates to a process for producing lithium borate, lithium borate obtainable by this process, and use thereof in secondary batteries.

[0004] Background of the Invention

[0005] Secondary batteries such as lithium-ion batteries are one of the most important battery types currently used. Secondary lithium-ion batteries typically comprise an anode made of a carbon material or a lithium-metal alloy, a cathode made of a lithium-metal oxide (lithium-mixed oxide), an electrolyte in which a lithium salt is dissolved in an organic solvent and a separator providing passage of lithium-ions between the positive and the negative electrodes during charging and discharging of the battery.

[0006] A limitation with existing cathode active materials is loss of performance during repetitive cycling. This aging phenomenon is especially pronounced for high nickel-NMC (Nickel, Manganese, Cobalt) batteries. During cycling the positive electrode material may suffer from several electrochemical degradation mechanisms, resulting in a decrease of capacity, performance, and cycle life.

[0007] Surface coating of the cathode active material is known for addressing this aging phenomenon by preventing direct contact between the active material and the liquid electrolyte.

[0008] Also, in recent developments, use of solid electrolytes instead of liquid electrolytes has further improved the intrinsic safety and energy density of secondary batteries. Among such batteries, secondary lithium batteries with electrodes made of lithium metal or lithium metal alloys provide high energy density and are particularly suitable for advanced more demanding applications. Such all-solid-state secondary lithium-ion batteries require good ion conductivity at an interface between an electrode active material and an electrolyte in order to have the required load characteristics. This high ion conductivity can be achieved by coating the surface of an active electrode material with some lithium-comprising compounds, LiTi2(PO4)3 such as described in JP 4982866 B2.

[0009] US 9450239 B1 describes forming amorphous solid-state lithium boride electrolyte directly onto a negative electrode by flame spray pyrolysis. Journal publication by Zhang, et al., describe in Powder Technology Volume 394, December 2021 , Pages 448-458, surface coating with tri-lithium borate (IJ3BO3) for enhancing the electrochemical performance and safety properties of Ni-rich LiNio sbCoo ceMno 10O2 by a wet chemical processing. International application W02022056039A1 entitled “cathode coating" to Yu et al. describes coating a cathode active material with solutions containing different metals including solutions that include lithium and optionally boron.

[0010] Powder Technology 394 (2021) 448-458 discloses preparation of IJ3BO3 protection layer on surface of Ni-rich LiNio ssCoo ceMno 10O2 cathode material by wet chemical process. Journal of The Electrochemical Society, 2020 167 130516 discloses dry processed with boric acid that reacts with surface impurities of LiOH and IJ2CO3 on LiNiosCoo iMno 1O2 (NCM811).

[0011] US 2022 / 149368 discloses a process of dry mixing a transition metal oxide and a pyrogenically produced lithium titanate or lithium aluminate.

[0012] In “Electrochemical Properties of Boron-Doped LiMn2O4 Nanoparticles Covered with Glass Material Prepared by High-Temperature Flame Spray Pyrolysis”, Int. J. Electrochem. Sci. International Journal, vol. 8, 1 January 2013 (2013-01-01), pages 1146-1162, Seung Ho Choi et. al describe the doping of LiMn2O4 nanoparticles with lithium boron oxide.

[0013] Seung Ho Choi describes in “Preparation and electrochemical properties of glass-modified LiCoO2 cathode powders”, Journal of Power Sources, vol. 244, 1 December 2013 (2013-12-01), pages 129-135, LiCoO2 powders coated with lithium boron oxide.

[0014] Meng Zhang discloses in “Surface coating with IJ3BO3 protection layer to enhance the electrochemical performance and safety properties of Ni-rich LiNiossCoOo ceMno 10O2 cathode material”, Powder Technology, vol. 394, 1 December 2021 (2021 -12-01), pages 448-458, the preparation of IJ3BO3 coated LiNiossCoOo osMno 10O2 cathode materials.

[0015] In spite the above-mentioned efforts for coating lithium borate on electrode materials of secondary batteries, further improvements are needed.

[0016] Summary of the Invention

[0017] It has been surprisingly found that fumed lithium borate, i.e., lithium borate prepared by a flame spray pyrolysis method has improved particle properties that are particularly suitable for coating cathode active materials used in secondary batteries and in particular lithium-ion batteries.

[0018] Moreover, using a special combination of metal and boride precursors and the solvents in the inventive process has turned out to be of critical importance for obtaining a lithium borate powder with desired properties according to the invention.

[0019] The present invention provides a method for making a fumed lithium borate coating material, a cathode active material employing the fumed lithium borate coating and a secondary battery employing the cathode active material as defined in the independent claims. Various embodiments of the present invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

[0020] The secondary battery may be used in any electrical or electronic device including, for example, mobile phones, computers (lap top computers, desk top computers, computer pads), electronic watches, key fabs, electric appliances, power tools, vacuum cleaners, electric lawn mowers and electric vehicles to mention just a few of the many uses of the lithium-ion batteries. A method for making a fumed product comprising fumed lithium borate, comprises: preparing a solution comprising a lithium precursor, preferably a lithium carboxylate containing 5 to 20 carbon atoms, and a boron source, preferably an organic boron compound, feeding the solution to a flame burning in a flame reaction zone to produce a fumed product comprising fumed lithium borate particles; and obtaining the fumed product.

[0021] The fumed product comprising the fumed lithium borate particles may also be referred to as the fumed, nanostructured lithium borate powder, or simply the fumed lithium borate powder. The fumed product may also comprise lithium carbonate to less than 50%, or less than 40%, or less than 30%, or less than 20%, or less than 10 % by weight.

[0022] The method may further comprise, before the feeding step of the solution to the flame, atomizing the solution in a form of fine droplets and feeding the droplets into the flame zone. The flame may be formed by ignition of a fuel gas and an oxygen containing gas.

[0023] The organic boron compound may be selected from the group consisting of trimethyl borate (C3H9BO3), triethyl borate (C6H15BO3), and tripropyl borate (C9H21BO3).

[0024] The solution may comprise an organic solvent containing less than 10 % by weight water, preferably less than 5 % by weight water, more preferably less than less than 3 % by weight water, even more preferably less than 2 % by weight water, and still more preferably less than 1 % by weight water.

[0025] The solution may be atomized in fine droplets preferably of 1 to 120 mm, more preferably of 30 to 100 mm, by mixing the solution with an atomizer gas, such as nitrogen, air, and / or other gases. The lithium carboxylate may be a linear, branched, or cyclic lithium pentanoate (C5), lithium hexanoate (C6), lithium heptanoate (C7), lithium octanoate (C8), lithium nonanoate (C9), lithium decanoate (D10), lithium undecanoate (C11), lithium dodecanoate (C12), lithium tridecanoate (C13), lithium tetradecanoate (C14), lithium pentadecanoate (C15), lithium hexadecanoate (C16), lithium heptadecanoate (C17), lithium octadecanoate (C18), lithium nonadecanoate (C19), lithium icosanoate (C20) of lithium, and mixtures thereof.

[0026] The lithium borate particles obtained by the process may be one or more of the compounds having a formula IJ3BO3, IJ2B4O7, IJBO2, or IJ4B2O5.

[0027] The amount of the lithium carboxylate, and the boron compound may be 1 to 100 %, by weight, preferably 80 to 100 % by weight, and more preferably 90 to100 % by weight based on the total weight of the solution.

[0028] The Lambda value, defined as the ratio of oxygen provided to the flame to the oxygen used during combustion of the fuel gas oxygen is 1 .0 to 6.0. A mean residence time of the reaction mixture in the flame zone may be 0.25 to 2.5 seconds and an average velocity in the flame zone is 1 - 20 m / s.

[0029] The method may further comprise thermally treating the fumed lithium borate powder to obtain crystalline lithium borate particles as measured by XRD analysis. The lithium borate powder obtained from the FSP process may comprise lithium borate particles which are generally amorphous and become crystalline only after a thermal treatment of the fumed lithium borate powder which follows the FSP process. More specifically, the lithium borate particles obtained from the FSP process are: before thermal treatment 50-70% amorphous, 30-50% crystalline phase while after thermal treatment 20-40% amorphous, 60-80% crystalline phase.

[0030] The fumed, nanostructured lithium borate powder obtained by the above method is characterized in that it has: a small aggregate size d50 of 50 nm to 1000 nm, preferably of 100 nm to 900 nm, more preferably 150 nm to 800 nm, a high BET surface area of 1 m2 / g to 100 m2 / g preferably of 5 m2 / g to 70 m2 / g, more preferably 10 m2 / g to 50 m2 / g, and a low tamped density of 10 g / L to 500 g / L, preferably of 30 g / L to 300 g / L, more preferably 50 g / L to 200 g / L.

[0031] The fumed, nanostructured lithium borate powder is used as a coating for a cathode active material of a secondary battery. The cathode active material may be a mixed metal oxide, preferably of at least two of Ni, Co, Mn, and Li. The cathode active material is in the form of particles. The fumed nanostructured lithium borate powder may be dried coated on the cathode active material particles to form a layer having a thickness of 20 nm to 200 nm.

[0032] A method of coating a cathode active material of a secondary battery with the fumed, nanostructured, lithium borate powder comprises: adding a fumed, nanostructured, lithium borate powder and a cathode active material which is in the form of particles of a mixed metal oxide of at least two of Li, Co, Ni, and Mn inside a mixer, performing a first mixing at low intensity to homogenize the mixture, and performing a second mixing at high intensity to dry coat the cathode active material particles with a layer of the fumed, nanostructured lithium borate.

[0033] A cathode active material for a secondary battery may comprise mixed metal oxide particles coated with a layer of the above described fumed, nanostructured, lithium borate having a thickness of 20 nm to 200 nm. The mixed metal oxide particles of the cathode active material may contain, for example, two or more of Li, Ni, Co, and Mn.

[0034] A secondary battery and an apparatus comprising the secondary battery may use the above described cathode active material. The apparatus may include, for example, an electric or electronic device including a mobile phone, an electronic watch, a key fab, a laptop computer, a desktop computer, a computer pad, a power tool, a vacuum cleaner, an electric lawn mower, an electric appliance, and an electric vehicle.

[0035] These and other features and advantages of the present invention will become apparent to the skilled person in this art from the following figures and detailed description.

[0036] Brief Description of the Drawings

[0037] Figure 1 is a simplified flow chart of a method of making fumed lithium borate powder, according to an embodiment of the present invention

[0038] Figure 2 is a simplified flow chart of a method of coating the fumed lithium borate powder on a mixed metal oxide cathode active material according to an embodiment of the present invention. Figure 3 is a simplified diagram of a secondary battery employing the coated cathode active material of figure 3 and an electronic device including the secondary battery.

[0039] Figure 4 shows XRD analysis of fumed lithium borate powder as described in example 1.

[0040] Figure 5 shows XRD analysis of fumed lithium borate powder as described in example 2.

[0041] Figure 6 is a TEM image of fumed lithium borate powder as described in example 1.

[0042] Figure 7 is a SEM image of commercially available lithium borate powder purchased from Toshima MFG as described in comparative example 1 .

[0043] Figure 8 is a SEM image of LBO (lithium borate as described in example 1) dry coated LCO showing that the LBO nanoparticles were well dispersed on the LCO particles.

[0044] Figure 9 shows the cycling performance of LCO dry coated with fumed lithium borate particles by the inventive process in all-solid-state battery using LGPS (LiioGeP2Si2) as solid electrolyte.

[0045] Figure 10 shows the cycling performance of LCO dry coated with fumed lithium borate particles by the inventive process with thermal treatment at 300 °C in all-solid-state battery using LGPS as solid electrolyte.

[0046] Figure 11 shows the cycling performance of LCO dry coated with fumed lithium borate particles by the inventive process with thermal treatment at 500 °C in all-solid-state battery using LGPS as solid electrolyte.

[0047] Figure 12 shows the cycling performance of LCO dry coated with commercial lithium borate particles with thermal treatment at 300 °C in all-solid-state battery using LGPS as solid electrolyte. Figure 13 shows the cycling performance of uncoated LCO in all-solid-state battery using LGPS as solid electrolyte.

[0048] Figure 14 shows the cycling performance of LCO dry coated with fumed lithium titanate particles in all-solid-state battery using LGPS as solid electrolyte.

[0049] Figure 15 shows an SEM-image of NMC dry coated by fumed lithium borate (LBO). LBO nanoparticles were well dispersed on surface of NMC particles.

[0050] Figure 16 shows the influence of the received lithium borate coating layer on the cycling performance in liquid lithium-ion batteries. The performance of NMC coated by fumed lithium borate is compared against the uncoated NMC. Detailed Description of the Invention

[0051] The process for producing lithium borate particles

[0052] In some embodiments a process is provided for producing lithium borate in the form of particles formed by a flame spray pyrolysis. The lithium borate particles may be aggregates of primary nanoparticles. The fumed lithium borate is particularly suitable for dry coating a cathode active material of a secondary battery, such as a lithium-ion secondary battery.

[0053] Referring to Figure 1 , the method comprises preparing a solution in step 102 of at least one metal precursor and at least one boron source, subjecting in step 104 the solution to a flame inside a pyrolysis reactor to produce lithium borate, and obtaining in step 106 the lithium borate.

[0054] The solution of the at least one metal precursor and the at least one boron source may comprise a lithium carboxylate (Li+-RCOO ) containing 5 to 20 carbon atoms, a boron source such as an organic borate, and a solvent containing less than 10% by weight water.

[0055] The lithium carboxylate used in the process according to the invention may be a linear, branched, or cyclic lithium pentanoate (C5), lithium hexanoate (C6), lithium heptanoate (C7), lithium octanoate (C8), lithium nonanoate (C9), lithium decanoate (D10), lithium undecanoate (C11), lithium dodecanoate (C12), lithium tridecanoate (C13), lithium tetradecanoate (C14), lithium pentadecanoate (C15), lithium hexadecanoate (C16), lithium heptadecanoate (C17), lithium octadecanoate (C18), lithium nonadecanoate (C19), lithium icosanoate (C20) of lithium, and the mixtures thereof. Even more preferably lithium neodecanoate (C10) may be used.

[0056] The boron source may be an inorganic compound such as borane, diborane (B2H6), diboron tetrachloride (B2CI4) or an organic borate such as trimethyl borate (C3H9BO3), triethyl borate (C6H15BO3), and tripropyl borate (C9H21BO3). In some embodiments the boron source may be an organic borate such as a trimethyl borate.

[0057] The reaction initially forms highly dispersed approximately spherical primary particles, which in the further course of the reaction coalesce to form aggregates. The aggregates may then accumulate into agglomerates. In contrast to the agglomerates, which may be separated into the aggregates relatively easily by introduction of energy, the aggregates are broken down further, if at all, only by intensive introduction of energy. The formed aggregates may have a median particle size (d50) of 50 nm to 1000 nm, preferably of 100 to 900 nm, and, more preferably of 150 to 800 nm. The primary particles may range from 50 nm to 2 |_im measured by DLS (dynamic light scattering) with a median particle size d50 of 615 nm. The produced aggregated lithium borate is referred to also as “fumed” or “pyrogenically produced” lithium borate.

[0058] The d50 value results from the cumulative volume distribution curve of the volume-averaged large distribution. This is determined in ethanol dispersion, by dynamic light scattering (DLS).

[0059] Preferably, the pyrolysis may be a flame spray pyrolysis. An example of a flame spray pyrolysis process is described in WO2015173114 A1 entitled “method for producing mixed oxide powder comprising lithium, lanthanum, and zirconium” to Katusic et al., also, in US 2022 / 0306485 A1 entitled “preparation of nanostructured mixed lithium zirconium oxides by means of spray pyrolysis” to Schafer et al. and elsewhere.

[0060] The flame spray pyrolysis preferably comprises the following steps: at least one solution of metal precursors is atomized to afford an aerosol by means of an atomizer gas, the aerosol is brought to reaction in the reaction space of the reactor with a flame obtained by ignition of a mixture of fuel gas and an oxygen-containing gas to obtain a reaction stream, the reaction stream is cooled and the solid metal oxide is subsequently removed from the reaction stream.

[0061] In a flame spray pyrolysis, the solution of the at least one metal precursor and the at least one boron source is atomized in the form of fine droplets which are then introduced into a flame burning inside a reaction space (or flame zone) of a pyrolysis reactor.

[0062] In some embodiments two different solutions may be formed, one containing the at least one metal precursor and another solution containing the at least one boron source, the two solutions may then be atomized into fine droplets, mixed in a mixing chamber, and fed into the flame zone of the pyrolysis reactor where they react to produce lithium borate primary particles, aggregates of the primary particles and agglomerates of the aggregates. A reaction stream exiting the flame zone is cooled and then the solid lithium borate particles are removed from the reaction stream in the form of aggregated nanostructured (or nanosized) particles. The aggregated nanostructured particles may also be referred to as hollow nanoparticles having an empty interior or cavity surrounded by a solid shell. Such hollow nanoparticles are lightweight and have a high surface area.

[0063] For obtaining the aerosol of fine droplets, the solution may be vaporized and mixed with an atomizer gas, such as nitrogen, air, and / or other gases. The resulting fine droplets of the aerosol preferably may have an average droplet size of 1 -120 pm, particularly preferably of 30-100 pm. The droplets may be produced using single- or multi-material nozzles. To increase the solubility of the metal precursor and to attain a suitable viscosity for atomization of the solution, the solution may be heated.

[0064] Other than the lithium metal carboxylate precursors other suitable metal precursors may also be used optionally such as inorganic lithium compounds like nitrates, carbonates, chlorides, bromides, or other organic lithium compounds, such as alkoxides, e.g., ethoxides, n-propoxides, isopropoxides, n-butoxides and / or tert-butoxides.

[0065] A suitable solvent for the solution may be an organic solvent. The solvent may preferably be selected from the group consisting of water, C 5 - C 20 alkanes, C 1 - C 6 alkane carboxylic acids and / or C 1 -C 6 alkanols or combinations thereof. An organic solvent mixture may be used, preferably one or more alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol or tert-butanol, diols such as ethanediol, pentanediol, 2-methyl-2,4-pentanediol, C1 -C12-carboxylic acids such as acetic acid, propionic acid, butanoic acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, octanoic acid, 2-ethylhexanoic acid, valeric acid, capric acid, lauric acid may be used. Furthermore, benzene, toluene, naphtha and / or gasoline may be used.

[0066] The solvent mixture may contain less than 10 % by weight water, preferably less than 5 % by weight water, more preferably less than less than 3 % by weight water, even more preferably less than 2 % by weight water, still more preferably less than 1 % by weight water.

[0067] In some embodiments, the solvent mixture may optionally contain a chelating agent, i.e., a compound capable of forming two or more coordination bonds with metal ions. The examples of such chelating agents may be, for example, diamines like ethylenediamine, ethylenediaminetetraacetic acid (EDTA) and 1 ,3 dicarbonyl compounds such as acetyl acetone and alkyl acetyl acetates. Even more preferably, acetyl acetone is used as such a chelating agent. The chelating agent may be used preferably in an amount of from 10.0 to 0.001 % by weight, more preferably 5.0 to 0.01 % by weight and even more preferably 2.0 to 0.1 % by weight based on the total weight of the solution.

[0068] As fuel gases that form water in the reaction with oxygen, hydrogen, methane, ethane, propane, butane, and mixtures thereof may be used. In some embodiments, preference is given to using hydrogen.

[0069] The oxygen-containing gas may be air or oxygen-enriched air. An oxygen-containing gas is particularly beneficial for obtaining a high BET surface area of the lithium borate to be produced is desired. The total amount of oxygen is generally chosen such that, it is sufficient at least for complete conversion of the fuel gas and the metal precursors.

[0070] The flame-forming, oxygen-containing gas is usually air.

[0071] The amount of oxygen is to be selected in the inventive method so that it is sufficient at least for complete conversion of the fuel gas and all metal compounds. It is usually advantageous to use an excess of oxygen. This excess is conveniently expressed as the ratio of existing Oxygen / combustion of the fuel gas necessary oxygen and referred to as Lambda. The Lambda value is preferably 1 .0 to 6.0, particularly preferably 1 .0 to 3.0. Also, additional oxygen-containing gas may be introduced into the reaction space.

[0072] The solution is preferably introduced by means of a nebulizer gas into the reaction space. For example, nitrogen or air are suitable as nebulizer gases. If air is used, it will not be taken into account when calculating lambda. Furthermore, the average residence time of the reaction mixture in the reaction space may preferably be 0.5-2.5 seconds (“s”), more preferably 0.5-1 seconds.

[0073] The average velocity in the reaction space may preferably be 1 -20 Nm / s, more preferably 3-10 Nm / s. The speed information is a standardized speed obtained by dividing the volume flow Nm3 / h within a unit cross-sectional area.

[0074] The use of the special combination of the lithium metal precursor, the boron precursor and the solvent in the inventive process allows ensuring good solubility of the precursors and achieving the desired particle properties of the resulting lithium borate including small aggregate size d50 of 50 nm to 1000 nm, preferably of 100 nm to 900 nm, more preferably 150 nm to 800 nm, a high BET surface area of 1 m2 / g to 100 m2 / g preferably of 5 m2 / g to 70 m2 / g, more preferably 10 m2 / g to 50 m2 / g, and low tamped density of 10 g / L to 500 g / L, preferably of 30 g / L to 300 g / L, more preferably 50 g / L to 200 g / L. This type of fumed lithium borate particles is referred to here also as a fumed, nanostructured, lithium borate.

[0075] The d50 was determined in a suitable dispersion, e.g., in an aqueous dispersion, by dynamic light scattering (DLS) method.

[0076] The BET surface area can be determined according to DIN 9277: 2014 by nitrogen adsorption according to Brunauer-Emmett-Teller (BET) procedure. Tamped density was determined according to DIN ISO 787-11 :1995 "General methods of test for pigments and extenders-Part 11 : Determination of tamped volume and apparent density after tamping". This involves measuring the apparent density of a bed after agitation and tamping.

[0077] The inventive process may further comprise a thermal treatment of the lithium borate produced by the flame spray pyrolysis.

[0078] The thermal treatment may preferably be carried out at a temperature of 100 °C - 700 °C, more preferably at 150 °C - 650 °C, even more preferably at 200 °C - 600 °C, still more preferably at 250 °C - 550 °C.

[0079] The thermal treatment according to the inventive process allows obtaining a thermally treated lithium borate with desirable properties, especially the desired crystalline structure.

[0080] The inventive process may comprise a further sieving and shifting treatment of the thermally treated lithium borate to remove the larger agglomerates. The sieving and shifting process may be performed in an air jet mill.

[0081] Referring to figure 2 a method for coating lithium-mixed oxide particles includes adding fumed lithium borate powder and the mixed metal oxide particles to be coated inside a high intensity mixer in step 103, mixing first at low intensity to homogenize the mixture in step 105 and secondly at high intensity in step 107 to dry coat the mixed metal oxide particles with a layer (or coating) of the fumed lithium borate. The mixed metal oxide particles maybe a cathode active material such as an LCO (Li-Cobalt Oxide) powder or an NMC (Nickel, Manganese, Cobalt) powder and the like.

[0082] The underlying mixed metal oxide particles may be coated with a layer of the fumed lithium borate of a thickness ranging from 10 nm to 1 pm, preferably from 20 nm to 800nm, more preferably 30 nm to 600 nm and even more preferably from 40 nm to 400 nm.

[0083] The invention further relates to the fumed lithium borate coated cathode material as well as to a battery cell containing these encapsulated lithium borate encapsulated coated cathode active material particles. Figure 3 illustrates a lithium-ion battery generally designated with numeral 300 including a separator 316, 318, a cathode active material 312 on a cathode plate 310, and an anode active material 322 on an anode plate 320. The cathode active material 312 comprises mixed metal particles coated with the lithium borate as described herein. The cathode active material 312 may preferably be in the form of particles of mixed metal oxide particles such as for example LCO, or NMC particles coated with the fumed lithium borate nanoparticles of the present invention which may form a layer of at least 20 nm and less than about 200 nm in thickness. An electrolyte 324 is placed around the separator and between the anode and cathode active materials 322 and 312. The separator 316, 318 may, for example, comprise a polymeric membrane 316 covered on both sides thereof with a ceramic coating 318. The lithium-ion battery 300 may be used in electronic and electrical apparatuses 400 including, for example, mobile phones, computers (lap top computers, desk top computers, computer pads), electronic watches, key fabs, electric appliances, power tools, vacuum cleaners, electric lawn mowers and electric vehicles to mention just a few of the many uses of the lithium ion battery.

[0084] Examples

[0085] LCO is a Lithium Cobalt Oxide (CELLSEED®, LiCoO2, type C-5H with D50 of particle size distribution is 7.2 pm) purchased from Nippon Chemical Industrial.

[0086] Commercial lithium borate (LBO) is non-fumed tri-lithium borate (LisBOs) purchased from Toshima MFG Co., Ltd

[0087] Fumed LTO: Nanostructured fumed lithium titanium particles produced by flame spray pyrolysis as described in US2022149368 (A1) with BET surface area of 47 m2 / g.

[0088] Example 1 :

[0089] 11 .17 kg of a solution containing 10150 g of a commercial solution (Borchers® Deca Lithium2), containing 2 wt.-% lithium in the form of lithium neodecanoate, 1018.5 g of a commercial solution (Sigma Aldrich), containing 10.4 wt.-% B (boron) in the form of trimethyl borate (B(OCH3)3) were mixed, resulting in a clear solution. This solution corresponds to a composition of U3BO3.

[0090] An aerosol of 2.5 kg / h of this solution and 15 Nm3 / h of air was formed via a two-component nozzle and sprayed into a tubular pyrolysis reactor with a burning flame. The burning gases of the flame consisted of 10.7 Nm3 / h hydrogen and 55 Nm3 / h of air. Additionally, 40 Nm3 / h secondary air was used. After the reactor, the reaction gases were cooled down and filtered to collect the formed fumed lithium boron oxide powder.

[0091] The particle properties were measured and are shown in table 1 . The BET surface area was determined according to DIN ISO 9277. The XRD analysis (Figure 4) showed, that the major phases of the product were U2CO3 and Li4B2O5. Example 2 :

[0092] The lithium boron oxide precursor powder obtained in example 1 was calcined at 500 °C for 6 hours in a furnace. The XRD analysis (Figure 5) showed, that the major phases of the product were monoclinic U3BO3, IJ2CO3 and IJ4B2O5. The amount of IJ2CO3 in the product after calcination was less than 20 % by weight.

[0093] Comparative example 1 :

[0094] Commercial non-fumed LBO purchased from Toshima MFG.

[0095] TABLE 1 : Physicochemical properties of the powders obtained in the examples.

[0096] Synthesis of solid electrolytes

[0097] For preparation of the LGPS (LiioGeP2Si2) solid electrolyte, the raw materials U2S (lithium sulfide from Mitsuwa, 99.9%), P2S5 (phosphorus pentasulfide from Aldrich, 98%), and GeS2 (germanium disulfide from Kojundo Chemicals, 99.9%) were mixed in an appropriate molar ratio in an argon- filled glove box. The resulting mixture was placed in a ZrO2 (zirconium dioxide) pot together with ZrO2 balls (with a diameter <p10 mm) and mechanically milled by planetary ball milling at 380 rpm for 40 h, prior to placing in a quartz tube and heating at 550 °C for 8 h.

[0098] Coating of the transition metal oxide (tests in solid electrolyte)

[0099] Lithium-Cobalt Oxide powder LCO (CELLSEED®, LiCoO2, type C-5H) commercially available from Nippon Chemical Industrial (Japan) having a BET surface area of 0.46 m2 / g and a diameter d50 = 7.2 ± 2 pm was used as the transition metal oxide in the following Examples.

[0100] The LCO powder was mixed with the respective amount (1 .0 wt.-%) of the powders obtained in Example 1 in a high intensity laboratory mixer (SOMAKON mixer MP-GL with 0.5 L mixing unit) at first for 1 min at 500 rpm to homogeneously mix the two powders. Afterwards, the mixing intensity was increased to 2000 rpm for 5 min to achieve the dry coating of the LCO powder by the respective powders obtained in Example 1.

[0101] Thermal treatment of the LBO coated LCO

[0102] The LBO-coated LCO powder was thermally treated at respective designated temperatures under air atmosphere. The LBO-coated and pristine LCO were dried at 120 °C under vacuum before mixed with solid electrolyte for preparation of composite cathode.

[0103] Preparation of the composite cathode and all-solid-state battery

[0104] All preparation processes were conducted under an argon atmosphere inside a glove box. The cathode of the all-solid-state cell consisted of LBO dry coated LiCoO2 powder and solid electrolyte powder. Before preparing the cell, large solid electrolyte particles were removed using a sieve of 10 pm mesh. The LBO dry coated LiCoO2 and solid electrolyte (LiioGeP2Si2) were mixed in a 70:30 wt.-% ratio for 10 min using a pot mill rotator.

[0105] The solid electrolyte powders were used as the separator during the preparation process, and the cathode / separator / anode (In-Li) layers were compressed to form a disc-shaped pellet. The all- solid-state cells were prepared by connecting the cathode and anode to stainless-steel current collectors. The diameter of the all-solid-state cell was 10 mm (0.79 cm2).

[0106] Example 1a: fumed LBO coated LCO

[0107] 1 wt.-% of fumed LBO as described in Example 1 was dry coated on LCO and used as cathode active material in all-solid-state battery.

[0108] Example 1 b: fumed LBO coated LCO + additional thermal treatment at 300°C

[0109] 1 wt.-% of fumed LBO as described in Example 1 was dry coated on LCO and then annealed in a furnace at 300°C for 1 hour. After that, LBO coated LCO was used as cathode active material in all-solid-state battery.

[0110] Example 1c: fumed LBO coated LCO + additional thermal treatment at 500°C

[0111] 1 wt.-% of fumed LBO as described in Example 1 was dry coated on LCO and then calcined in a furnace at 500°C for 1 hour. After that, LBO coated LCO was used as cathode active material in all-solid-state battery.

[0112] Comparative example 1a: LBO (Toshima) coated LCO + additional thermal treatment at 300°C

[0113] 1 wt.-% of commercially available LBO as described in Comparative example 1 was dry coated on LCO and then annealed in a furnace at 300°C for 1 hour. This LBO coated LCO was used as cathode active material in all-solid-state battery.

[0114] Comparative example 2: pristine LCO (without coating)

[0115] Commercially available LCO was used as cathode active material in all-solid-state battery.

[0116] Comparative example 3: Fumed LTO coated LCO

[0117] The procedure is identical as described as Comparative example 1 a except Fumed LTO was used instead of commercially available LBO.

[0118] Electrochemical tests of lithium-ion batteries with solid electrolyte

[0119] The LiioGeP2Si2 electrolyte (80 mg) was prepared as a pellet with a 10 mm diameter. An aluminum foil and mesh were used as current collectors for the cathode. The cathode powder (8 mg) was pressed onto the LhoGeP2Si2 electrolyte pellet under 555 MPa. The negative electrode was consisted of Li foil (<|>5 mm, t0.1 mm) and In foil (<|)10 mm, t0.1 mm) on a copper mesh current collector. Finally, the three-layers of the cathode / electrolyte / anode were pressed together at 220 MPa to fabricate the all-solid-state batteries. A pressure of 100 MPa was applied on the battery during the charge-discharge operation. All the processes for the solid-state batteries were performed in a dry Ar-filled glovebox (DBO-1 .5-T1000, Miwa). Charge and discharge experiments of the all-solid-state cells with Li / ln were conducted between 1 .9 and 3.6 V at 25 °C. The cells were charged in the constant current charging mode (0.2 C, 1 .9 to 3.6 V) and constant voltage charging mode (the cell voltage held constant until the charging current reached 0.02C. After charging at 3.6 V, the cells were discharged at a constant current at 0.2 C. Charging at 0.2 C means supplying a current of 0.2 times the capacity of the battery. The electrochemical properties of the cells were determined using a charge-discharge unit (VSP-300, Bio-Logic). The specific capacities (mAh / g) of the charge-discharge curves were calculated on the basis of the mass of LiCoO2.

[0120] Figure 9, 10, 11 , 12, 13 and 14 show the electrochemical performance of 1 wt.-% fumed LBO coated LCO (Example 1 a, 1 b and 1c) samples, 1 wt.-% commercial LBO coated LCO (Comparative example 1a), uncoated LCO (Comparative example 2) and fumed LTO coated LCO (Comparative example 3) in LGPS-LCO || LGPS || Li-ln ASSLIBs compared with the electrochemical performance of uncoated LCO (Comparative example 2) as a reference. The best performance was obtained with 1 wt.-% fumed LBO coated LCO that was further thermally treated at 300°C (Example 1 b). The improvement of cell performance due to thermal treatment may be attributed to the phase transition of the surface coated LBO, since XRD data showed more than 50% amorphous phase particles partially turned into the crystalline phase upon thermal treatment..

[0121] Example 3: Test of fumed lithium borate as additive in liquid lithium-ion batteries

[0122] Dry coating of fumed lithium borate on cathode active material (CAM)

[0123] The commercial NMC 7 1 .5 1 .5 - powder (Linyi Gelon LIB Co., Type PLB-H7) with a BET surface area of 0.30-0.60 m2 / g, medium diameter d50 = 10,6 ± 2 pm (via laser scattering), was mixed with the respective amount (1.0 wt.-%) of lithium borate-powder (fumed LBO) in a high intensity laboratory mixer (Somakon mixer MP-GL with 0.5 L mixing unit) at first for 1 min at 500 rpm to homogeneously mix the two powders. Afterwards the mixing intensity was increased to 2000 rpm for 5 min to achieve the dry coating of the NMC particles by LBO.

[0124] Coated NMC particles are obtained with an LBO-coating layer thickness of 20-200 nm.

[0125] Figure 15 shows an SEM-image of NMC dry coated by fumed lithium borate (LBO). The high- resolution SEM image shows that the LBO nanoparticles were well dispersed on the surface of NMC particles.

[0126] The obtained LBO-coated NMC particles are used as cathode active material in liquid lithium-ion batteries without additional thermal treatment, with additional thermal treatment at 300°C for 3 hours in oxygen atmosphere and with additional thermal treatment at 500°C for 6 hours in oxygen atmosphere.

[0127] Electrochemical tests of lithium-ion batteries with liquid electrolyte

[0128] Electrodes for electrochemical measurements were prepared by blending 90 wt.-% NMC with

[0129] 5 wt.-% PVDF (Solef PVDF 5130) as a binder and 5 wt.-% Super C65 (Imerys) as a conductive additive under inert gas atmosphere. N-Methyl-2-pyrrolidone (NMP) was used as the solvent. The slurry was casted on aluminum foil and dried for 20 min on 120 °C heating plate in air. Afterward, the electrode sheet was dried in a vacuum furnace at 120 °C for 2 h. The area-related cathode loading is adjusted to 2,0 ± 0,1 mAh cm-2. Circular electrodes with a diameter of 12 mm were punched out, calendered to achieve an electrode density of 3.0 g / cm3, and dried again in a vacuum furnace at 120 °C for 12 h to remove any residual water and NMP. For the cycling tests the cells were assembled as CR2032 type coin cells (MTI Corporation) in an argon-filled glovebox (Glovebox Systemtechnik GmbH). Lithium metal (Rockwood Lithium GmbH) was used as the anode material. Celgard 2500 was used as the separator. 35 mL of a solution of 1 molar LiPF6 in ethylene carbonate and ethyl methyl carbonate (50:50 wt / wt; Sigma-Aldrich) was used as electrolyte. The cells were locked with a crimper (MTI).

[0130] For electrochemical evaluations galvanostatic cycling was performed between 3.0 and 4.3 V vs Li+ / Li at 25 °C. For the calculation of the capacities and the specific currents, only the mass of the active material was considered and a theoretical capacity of 180 mAh / g of NMC 7 1 .5 1 .5 was supposed. For the coin half-cells during cycling, the C-rate was increased every four cycles, starting from 0.1 / 0.1 (Charge / Discharge) to 0.2 / 0.2, 0.5 / 0.5, 1.0 / 1.0 and 1.0 / 2.0 C. Afterward, the cell was cycled at 1 .0 / 1 .0 C for long term stability test.

[0131] Figure 16 shows the influence of the received lithium borate coating layer on the cycling performance in liquid lithium-ion batteries. The performance of NMC coated by fumed lithium borate is compared against the uncoated NMC. From the graph data, it can be intuitively concluded that the fumed lithium borate coating improves the performance and cycle life of NMC significantly. The NMC coated with the fumed lithium borate without and with additional thermal treatment showed an improved rate capability and long-term cycling stability compared to the uncoated NMC. The highest rate performance and long-term cycling stability was achieved with LBO-coated NMC additionally annealed at 300°C for 3 hours. The rate performance and long-term cycling stability of LBO-coated NMC with additional thermal treatment at 500°C for 6 hours is superior compared to the LBO-coated NMC without additional thermal treatment.

[0132] Although the invention has been described in reference to only specific examples, it should be understood that the invention is not limited only to the described specific examples. The skilled person after reading the present disclosure would be able to envisage a number of variations of the described examples and other examples that fall within the scope of the invention as defined in the following claims. For example, an element described as employed either alone or in combination with other features in an example may also be used with another combination of features in another example without departing from the scope of the disclosed and claimed invention.

[0133] Also, for example, although the invention has been described in reference primarily to lithium-ion batteries, it should be understood that the fumed lithium borate and cathode active materials coated with the fumed lithium borate may also be used for active materials of other secondary batteries. List of Reference Numerals

[0134] 102, 103, 104, 105, 106, 107 process steps 400 Electronic device

[0135] 300 battery

[0136] 310 cathode plate

[0137] 312 cathode active material coated with fumed lithium borate

[0138] 324 electrolyte 316 separator

[0139] 318 separator ceramic coating

[0140] 322 active anode material

[0141] 320 anode plate

Claims

Claims1 . A method for making fumed lithium borate by flame spray pyrolysis, the method comprising: preparing a solution (102) comprising- a lithium precursor, preferably a lithium carboxylate containing 5 to 20 carbon atoms, and- a boron source, preferably an organic boron compound, feeding the solution to a flame burning in a flame reaction zone to produce a fumed product comprising fumed lithium borate particles (104); and obtaining the fumed product (106).

2. The method of claim 1 , further comprising, before the feeding step of the solution to the flame, atomizing the solution in a form of fine droplets and feeding the droplets into the flame zone, and wherein the flame is formed by ignition of a fuel gas and an oxygen containing gas.

3. The method of claims 1 or 2, wherein the organic boron compound is selected from the group consisting of trimethyl borate (C3H9BO3), triethyl borate (C6H15BO3), and tripropyl borate (C9H21BO3).

4. The method of any of the claims 1 to 3, wherein the solution is comprising an organic solvent containing less than 10 % by weight water, preferably less than 5 % by weight water, more preferably less than 3 % by weight water, even more preferably less than 2 % by weight water, and still more preferably less than 1 % by weight water.

5. The method of any of the preceding claims wherein the solution is atomized in fine droplets preferably of 1 to 120 mm, more preferably of 30 to 100 mm, by mixing the solution with an atomizer gas, such as nitrogen, air, and / or other gases.

6. The method of any of the preceding claims wherein the lithium carboxylate is linear, branched, or cyclic lithium pentanoate (C5), lithium hexanoate (C6), lithium heptanoate (C7), lithium octanoate (C8), lithium nonanoate (C9), lithium decanoate (D10), lithium undecanoate (C1 1), lithium dodecanoate (C12), lithium tridecanoate (C13), lithium tetradecanoate (C14), lithium pentadecanoate (C15), lithium hexadecanoate (C16), lithium heptadecanoate (C17), lithium octadecanoate (C18), lithium nonadecanoate (C19), lithium icosanoate (C20) of lithium, and mixtures thereof.

7. The method of any of the preceding claims, wherein the lithium borate particles are one or more of the compounds having a formula U3BO3, IJ2B4O7, UBO2, IJ4B2O5, and IJ6B4O9.

8. The method of any of the preceding claims, wherein the amount of the lithium carboxylate, and the boron compound is 1 to 100 %, by weight, preferably 80 to 100 %by weight, and more preferably 90 to100 % by weight based on the total weight of the solution, or wherein a Lambda value, defined as the ratio of oxygen provided to the flame to the oxygen used during combustion of the fuel gas oxygen is 1.0 to 6.0, or wherein a mean residence time of the reaction mixture in the flame zone is 0.25 to 2.5 seconds and an average velocity of the gases in the flame zone is 1 - 20 m / s.

9. The method according to any of the preceding claims, further comprising thermally treating the fumed lithium borate particles (106) which are, before the thermal treatment, 50-70% amorphous and 30-50% crystalline to obtain lithium borate particles which are 20-40% amorphous and 60-80% crystalline, after the thermal treatment, as measured by XRD analysis.

10. A fumed, nanostructured lithium borate powder obtained by the method of any of the preceding claims characterized in that it has: an aggregate size d50 of 50 nm to 1000 nm, preferably of 100 nm to 900 nm, more preferably 150 nm to 800 nm, as determined by dynamic light scattering (DLS) method, a BET surface area of 1 m2 / g to 100 m2 / g preferably of 5 m2 / g to 70 m2 / g, more preferably 10 m2 / g to 50 m2 / g, as determined according to DIN 9277: 2014 by nitrogen adsorption according to Brunauer-Emmett-Teller (BET) procedure a tamped density of 10 g / L to 500 g / L, preferably of 30 g / L to 300 g / L, more preferably 50 g / L to 200 g / L, as determined according to DIN ISO 787-11 :1995.11 . Use of the fumed, nanostructured lithium borate powder of claim 10 as a coating for a cathode active material of a secondary battery, wherein the cathode active material is a mixed metal oxide, preferably of Ni, at least two of Ni, Co, Mn, and Li, wherein the cathode active material is in the form of particles and the fumed nanostructured lithium borate is dried coated on the cathode active material particles forming a layer having a thickness of 20 nm to 200 nm.

12. A method of coating a cathode active material of a secondary battery with a fumed, nanostructured lithium borate powder, the method comprising: adding a fumed, nanostructured lithium borate powder and a cathode active material which is in the form of particles of a mixed metal oxide of at least two of Li, Co, Ni, and Mn inside a mixer (103), performing a first mixing at low intensity to homogenize the mixture (105), and performing a second mixing at high intensity to dry coat the cathode active material particles with a layer of the fumed, nanostructured lithium borate (107).

13. A cathode active material for a secondary battery comprising: mixed metal oxide particles coated with a layer of fumed, nanostructured, lithium borate powder (312), wherein the fumed, nanostructured lithium borate powder is according to claim 10, wherein the mixed metal oxide particles of the cathode active material contain two or more of Li, Ni, Co, and Mn, and wherein the layer of the fumed,nanostructured lithium borate has a thickness of 20 nm to 200 nm.

14. A secondary battery (300) comprising the cathode active material of claim 13.

15. An apparatus (400) comprising the secondary battery (300) of claim 14, the apparatus comprising an electric or electronic device including a mobile phone, an electronic watch, a key fab, a laptop computer, a desktop computer, a computer pad, a power tool, a vacuum cleaner, an electric lawn mower, an electric appliance, and an electric vehicle.

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