Process for making a coated cathode active material, and coated cathode active material

Abstract

Process for making a coated cathode active material for lithium-ion batteries wherein said cath- ode active material comprises lithium, nickel and at least one of cobalt and manganese with at least 50 mol-% being nickel, referring to metals other than lithium, wherein said process com- prises the steps of: (a) providing an aqueous solution of chlorides of nickel and of at least one of cobalt and man- ganese in the targeted ratio, (b) performing a pyrolysis of the aqueous solution of step (a) in a flame fed by natural gas, methane, or hydrogen, thereby obtaining a precursor of a cathode active material, (c) adding a source of lithium and, optionally, at least one dopant selected from oxides and (oxy)hydroxides of Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, W, Ce or Mo to the precursor from step (b), (d) performing a thermal treatment at a temperature in the range of from 700 to 1100°C, (e) performing a coating on the material resulting from step (d) with at least one oxide or (oxy)hydroxide of Mn, Co, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, B, W or Ce, followed by another thermal treatment at a temperature in the range of from 200°C to 800°C.

Description

[0001] Process for making a coated cathode active material, and coated cathode active material

[0002] The present invention is directed towards a process for making a coated cathode active material for lithium-ion batteries wherein said cathode active material comprises lithium, nickel and at least one of cobalt and manganese with at least 50 mol-% being nickel, referring to metals other than lithium, wherein said process comprises the steps of:

[0003] (a) providing an aqueous solution of chlorides of nickel and of at least one of cobalt and manganese in the targeted ratio, with or without water of crystallization,

[0004] (b) performing a pyrolysis of the aqueous solution of step (a) in a flame fed by natural gas, methane, or hydrogen, thereby obtaining a precursor of a cathode active material,

[0005] (c) adding a source of lithium and, optionally, at least one dopant selected from oxides and (oxy)hydroxides of Mg, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, W, Ce or Mo and combinations of at least two of the aforementioned to the precursor from step (b),

[0006] (d) performing a thermal treatment at a temperature in the range of from 700 to 1100°C,

[0007] (e) performing a coating on the material resulting from step (d) with at least one oxide or (oxy)hydroxide of Mn, Co, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, B, W or Ce and combinations of at least two of the aforementioned, followed by another thermal treatment at a temperature in the range of from 200°C to 800°C.

[0008] Lithium-ion secondary batteries are modern devices for storing energy. Many application fields have been and are contemplated, from small devices such as mobile phones and laptop computers through car batteries and other batteries for e-mobility. Various components of the batteries have a decisive role with respect to the performance of the battery such as the electrolyte, the electrode materials, and the separator. Particular attention has been paid to the cathode materials. Several materials have been suggested, such as lithium iron phosphates, lithium cobalt oxides, and lithium nickel cobalt manganese oxides.

[0009] The cathode material is of crucial importance for the properties of a lithium-ion battery. Lithium- containing mixed transition metal oxides have gained particular significance, for example spinels and mixed oxides of layered structure, especially lithium-containing mixed oxides of nickel, manganese and cobalt; see, for example, EP 1 189 296. Such lithium-containing mixed oxides of nickel, manganese and cobalt are generally prepared in a two-stage process. In a first stage, a sparingly soluble salt of the transition metal(s) is prepared by precipitating it from a solution, for example a carbonate or a hydroxide. This sparingly soluble compound is in many cases also referred to as a precursor. In a second stage, the precursor is mixed with a lithium compound, for example U2CO3, LiOH or U2O2, and calcined at high temperatures, for example at 600 to 1100°C. In the precursor manufacturing process, when performed by (co-)precipitation, usually the sulfates of transition metals such as nickel, cobalt and manganese are used as starting materials. However, this leads to the formation of stoichiometric amounts of alkali metal sulfate. The stoichiometric amounts of sulfate, e.g., Na2SC>4, are undesired by-products that need to be disposed of.

[0010] In WO 2019 / 191837, a process is disclosed wherein cathode active materials are made from precursors that are made by oxidation of metals and simultaneous precipitation. The process, however, leads to disadvantages when manganese is present because under the prevailing alkaline conditions, manganese may be precipitated as MnO2 that is not incorporated well into the precursor. In addition, the magnetic separation as suggested for the removal of unreacted metals does not work for many materials such as, but not limited to aluminum and manganese. In addition, it is disadvantageous to first reduce an ore to a metal and to then re-oxidize the metal because many of the reduction methods available have a high energy demand.

[0011] It was an objective of the present invention to provide a process to make cathode active materials for lithium-ion batteries without generating stoichiometric amounts of alkali sulfates, and it was an objective to provide cathode active materials with good electrochemical properties such as low capacity fade upon cycling that were made in a process that allows to make cathode active materials without the generation of stoichiometric amounts of alkali sulfate and without a highly energy demanding step of reducing a metal oxide to a metal followed by a re-oxidation.

[0012] Accordingly, the process as defined at the outset was found, hereinafter also referred to as inventive process. Accordingly, the process as defined at the outset was found, hereinafter also defined as inventive process. The inventive process comprises step (a), step (b), step (c), step (d) and step (e), hereinafter in brief also referred to as (a), (b), (c), (d), and (e). Further - optional - steps are possible. The steps (a) to (e) are described in more detail below.

[0013] The inventive process is a process for making a coated cathode active material for lithium-ion batteries wherein said cathode active material comprises lithium, nickel and at least one of cobalt and manganese with at least 50 mol-% being nickel, referring to metals other than lithium, preferably at least 60 mol-% and more preferably at least 80 mol-%. A suitable upper limit for nickel is 99 mol-%, preferably 95 mol-%. Elements in the coating are neglected in this context.

[0014] The cathode active material made in the course of the inventive process is a coated cathode active material. It thus contains a core and a shell, with the shell being the coating. The coating may be continuous, thus, a complete layer on the core, or it may be discontinuous, for example as a Swiss cheese with “holes” or voids in the coating, or it may even display an island struc- ture, thus, only some isolated parts of the outer surface of the core being coated and the rest being non-coated.

[0015] Said coating may have a thickness in the range of from 1 nm to 0.1 pm, preferably 10 nm to 100 nm and more preferably 20 nm to 50 nm. The thickness is to be considered an average thickness. With respect to the overall particle diameter, the coating is negligible.

[0016] In one embodiment of the present invention, the core of cathode active material as manufactured according to the inventive process has a core according to general formula Lii+xTMi-xO2 with x being in the range of from -0.05 to +0.05 and TM being a combination of metals of which at least 90 mol-% are transition metals, preferably at least 98 mol-%, and TM comprises nickel and at least one metal selected from cobalt and manganese, and at least 50 mol-% of TM is nickel, preferably at least 60 mol-% and more preferably at least 80 mol-%. A suitable upper limit for nickel is 99 mol-%, preferably 95 mol-%, referring to TM.

[0017] In one embodiment of the present invention, TM is a combination of metals according to general formula (I)

[0018] (NiaCobMnc)i-dMd(I) wherein a is in the range of from 0.6 to 0.95, preferably from 0.8 to 0.94, b is in the range of from 0.025 to 0.2, preferably from 0.025 to 0.15, c is in the range of from zero to 0.2 or up to 0.3, preferably from zero to 0.15, and d is in the range of from zero to 0.1, preferably from 0.02 to 0.1,

[0019] M is selected from Ti, Zr, Mo, W, Al, Mg, Nb, Y, Sr, Ba, Ce and Ta and combinations of at least two of the aforementioned, preferably selected from Al, Zr, Sr, Ba, Y and Ce and combinations of at least two of the aforementioned, more preferably a combination of Sr and Al or a combination of Al, Sr and Ba or a combination of Ba and Al. a + b + c = 1 , and b + c > zero. In another embodiment of the present invention, TM corresponds to general formula (II)

[0020] (NiaCobMnc)i-dMd(II) with a being in the range of from 0.25 to 0.4, b being in the range of from zero to 0.2, c being in the range of from 0.6 to 0.75, and d being in the range of from 0.02 to 0.1,

[0021] M is selected from Ti, Zr, Mo, W, Al, Mg, Nb, Y, Sr, Ba, Ce and Ta and combinations of at least two of the aforementioned, preferably selected from Al, Mg, Nb, W, Ti, and Zr. a + b + c = 1.

[0022] In each case, TM may contain traces of further metal ions other than the above, for example traces of ubiquitous metals such as sodium, iron, or zinc, as impurities but such traces will not be taken into account in the description of the present invention. Traces in this context will mean amounts of 0.05 mol-% or less, referring to the total metal content of TM.

[0023] Precursors as used herein are particulate materials. In one embodiment of the present invention, precursors have an average particle diameter (D50) in the range of from 0.5 to 10 pm, preferably from 1 to 8 pm, more preferably from 3 to 5 pm. The average particle diameter may be determined, e. g., by light scattering or LASER diffraction or electroacoustic spectroscopy. In one embodiment, particles of precursors are composed of primary particles, in particular they are agglomerates of primary particles, and the above particle diameter refers to the secondary particle diameter.

[0024] In a preferred embodiment, cathode active materials obtained by the inventive process are in the form of monolithic particles. No secondary particles may be detected. In an even more preferred embodiment, the majority of the cathode active materials obtained by the inventive process is in the form of monolithic particles.

[0025] Although (D50) is - strictly speaking - the median value rather than an average diameter both expressions are used interchangeably in the context of the present invention.

[0026] In one embodiment of the present invention, the span of the particle diameter distribution of precursors is in the range of from 0.2 to 4.0, preferably from 1.0 to 3.0 and more preferred from 1.1 to 2.5. The span is defined as [(d90) - (d10)] / (d50), with the values of (d90), (d50) and (d10) being determined by dynamic light scattering. The values (d90) and (d10) refer to the respective percentiles.

[0027] Preferably, the particle diameter distribution and especially its span of the precursors strongly influences or even translates into the particle size distribution and especially its span of the respective cathode active material.

[0028] Said particles of precursors may have an irregular shape but in a preferred embodiment, said particulate material has a regular shape, for example spheroidal, or even cubic or almost cubic. In this context, almost cubic shall include those particles in which one axis, for example the x- axis, is ± 5% longer or shorter as the other two.

[0029] In step (a), an aqueous solution of chlorides of nickel and of at least one of cobalt and manganese or preferably both is provided in the targeted ratio. The targeted ratio refers to the molar ratio of nickel and the at least one of cobalt and manganese in the core of the respective cathode active material. Examples of suitable chlorides are NiCh, anhydrous or especially NiCh'6 H2O, C0CI2, anhydrous or especially C0CI26 H2O, MnCh or especially MnCh'4 H2O. Further, optional, chlorides to be provided in step (a) are TiCh or TiCU, especially a-TiCh, AICI3, especially AICI36 H2O. In a preferred embodiment, in step (a) no elements other than nickel, cobalt and manganese are provided as chlorides.

[0030] In step (b), a pyrolysis of the aqueous solution of step (a) is performed in a flame fed by natural gas, methane, or hydrogen, thereby obtaining a precursor of a cathode active material. One or more of such flames is / are located in a reaction vessel. Said precursor is an oxide of nickel and at least one of cobalt and manganese but contains chloride, for example in the range of from 10 to 10,000 ppm. A flame fed by hydrogen is an oxyhydrogen based flame.

[0031] Preferably, pyrolysis is performed by spraying the aqueous solution of step (a) through a flame fed by natural gas, methane, or hydrogen. Through spraying, for example with the help of a nozzle, the aqueous solution of step (a) is converted into droplets, for example with a diameter of from 3 to 500 pm. Spraying is preferred because the conversion is more complete.

[0032] In one embodiment of the present invention, the flame may be vertical or horizontal, horizontal being preferred, thereby creating a swirl gas flow pattern in the reactor vessel.

[0033] In one embodiment of the present invention, the aqueous solution of step (a) is blown through a flame fed by natural gas, methane, or hydrogen. In one embodiment of the present invention, step (b) is performed with a residence time in the flame is in the range of from 1 to 60 seconds, preferably 2 to 10 seconds.

[0034] A precursor is obtained from step (b). Precursor may be collected from the bottom of the reaction vessel where it accumulates through gravity, or through transport by gas flow.

[0035] In one embodiment of the present invention, the resultant precursor is comprised of secondary particles that are agglomerates of primary particles.

[0036] In one embodiment of the present invention the specific surface area (BET) of the resultant precursor is in the range of from 2 to 70 m2 / g, determined by nitrogen adsorption, for example in accordance with to DIN-ISO 9277:2003-05. The outgassing temperature is 120°C.

[0037] Precursor obtained from step (b) is an oxide of TM wherein TM comprises Ni and at least one metal selected from Co and Mn, and, optionally, at least one further metal selected from Ti, Al, Zr, and Mg.

[0038] Precursor obtained from step (b) usually contains chloride, for example in the range of from 10 to 10,000 ppm, determined by heating an aliquot of such precursor in oxygen with nitrogen as carrier gas. The resulting off-gasses are adsorbed in acetic acid. The resulting solution is then titrated with silver nitrate solution.

[0039] Step (c) includes adding a source of lithium and, optionally, at least one dopant selected from oxides and (oxy)hydroxides of Ti, Zr, Nb, Ta, Mg, Al, Y, Sr, Ba, W, Ce and Mo to precursor from step (b).

[0040] Source of lithium may be selected from inorganic compounds of lithium, such as LiOH or U2O2 or U2CO3, without or with water of crystallization. Preferred sources of lithium are IJ2CO3, LiOH and LiOH y H2O with y being in the range of from 0.5 to 2.5.

[0041] The molar ratio of lithium / metals in the mixture of source of lithium / precursor is in the range of from 0.99 : 1 .0 to 1.3 : 1.0, preferably 1.03 : 1.0 to 1 .09 : 1 .01 .

[0042] Preferably, at least one dopant is added to the precursor from step (b) and the source of lithium, wherein the dopant selected from oxides and (oxy) hydroxi des of Mg, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, W, Ce and Mo and combinations of at least two of the aforementioned. Examples are TiC>2, TiO2aq, TiO(OH)2, Ti(OH)4, ZrO2, ZrO2aq, ZrO(OH)2, Zr(OH)4, Nb2O5, Nb2O5aq, Ta2O5, AI2O3, AIOOH, AI(OH)3, AI2O3aq, Y2O3, YOOH, Y(OH)3, Y2O3aq, SrO, Sr(OH)2, MgO, Mg(OH)2, BaO, Ba(OH)2, WO3, CeO2, Ce2O3, and MoO3. Preferred examples are TiO2, ZrO2, Zr(OH)4, Nb2Os, Ta2C>5, AI2O3, AI(OH)3, Y2O3, SrO, Sr(OH)2, BaO, Ba(OH)2, WO3, CeO2, and combinations of at least two of the aforementioned compounds.

[0043] In embodiments wherein no manganese is present in the respective precursor, a manganese containing dopant may be added in step (c), e.g., Mn3O4 or Mn2O3.

[0044] In embodiments wherein no cobalt is present in the respective precursor, a cobalt containing dopant may be added in step (c), e.g., Co2O3, Co3O4, CoO, CoOOH, or Co(OH)2.

[0045] In embodiments wherein at least one dopant is used, the molar amount of source of lithium is preferably lithium / sum of metals in precursor plus metals from dopants is in the range of from 0.99 : 1 .0 to 1.3 : 1.0, preferably 1.03 : 1.0 to 1.09 : 1.0.

[0046] In step (c), precursor and source of lithium and, if applicable, dopant(s) are mixed thoroughly, for example in a mixer, for example a tumbler mixer, a ball mill or a high-speed mixer. In laboratory experiments with a scale of 10 g or less, a mortar with pestle is feasible as well.

[0047] In one embodiment of the present invention, the mixing has a duration in the range of from 5 minutes to one hour, preferably from 10 to 30 minutes.

[0048] Step (d) includes performing a thermal treatment at a temperature in the range of from 700 to 1100°C, for example calcining said mixture in a pusher kiln or roller hearth kiln or rotary kiln at a temperature in the range of from 700 to 1100°C.

[0049] In one embodiment of the present invention, the mixture of precursor and source of lithium and, optionally, dopant(s), is heated to 700 to 1000 °C with a heating rate of 0.1 to 10 °C / min.

[0050] In one embodiment of the present invention, the temperature in step (d) is ramped up before reaching the desired temperature of from 700 to 1100°C, preferably 750 to 900°C. For example, first the mixture of precursor and source of lithium and, optionally, dopant(s) is heated to a temperature from 350 to 550°C and then held constant for a time of 10 min to 4 hours, and then it is raised to 700°C up to 1100°C.

[0051] In one embodiment of the present invention, step (d) is performed in an oxygen-containing atmosphere, for example in a nitrogen-air mixture, in a rare gas-oxygen mixture, in air, in oxygen or in oxygen-enriched air. In a preferred embodiment, the atmosphere in step (d) is selected from air, oxygen and oxygen-enriched air. Oxygen-enriched air may be, for example, a 50:50 by volume mix of air and oxygen. Other options are 1 :2 by volume mixtures of air and oxygen, 1 :3 by volume mixtures of air and oxygen, 2:1 by volume mixtures of air and oxygen, and 3:1 by volume mixtures of air and oxygen.

[0052] In one embodiment of the present invention, step (d) is performed under a stream of gas, for example air, oxygen and oxygen-enriched air. Such stream of gas may be termed a forced gas flow. Such stream of gas may have a specific flow rate in the range of from 0.5 to 15 m3 / h kg material according to general formula Lii+xTMi-xO2. The volume is determined under normal conditions: 298 Kelvin and 1 atmosphere. Said stream of gas is useful for removal of gaseous cleavage products such as water and carbon dioxide.

[0053] The inventive process may include further steps such as, but not limited, additional calcination steps at a temperature in the range of from 500 to 1000°C subsequently to step (d).

[0054] In one embodiment of the present invention, step (d) has a duration in the range of from one hour to 30 hours. Preferred are 5 to 12 hours. In step (d), the duration of cooling and before reaching the maximum temperature is neglected.

[0055] In one embodiment of the present invention, step (d) is performed in a roller hearth kiln, a pusher kiln or a rotary kiln or a combination of at least two of the foregoing. Rotary kilns have the advantage of a very good homogenization of the material made therein. In roller hearth kilns and in pusher kilns, different reaction conditions with respect to different steps may be set quite easily.

[0056] In one embodiment of the present invention, step (d) is performed in a pusher kiln or in a roller hearth kiln, in each case after compaction of the mixture of Li source and precursor. Mixture from step (c) is then shaped and pressed to form bricks or tiles and then perform a thermal treatment as outlined above. After the thermal treatment and cooling to ambient temperature, the resultant brick or tile shaped material is crushed to form a powdery base cathode active material.

[0057] A base cathode active material results from step (d).

[0058] Step (e) includes a coating step. At least one additive selected from oxides and (oxy)hydroxides of Mn, Co, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, B, W or Ce is added to base cathode active material from step (d) followed by performing a thermal treatment in the range of from 200°C to 800°C, preferably 600 to 750°C. The duration of the thermal treatment in step (e) may be in the range of from 30 minutes to 6 hours, preferably one to 3 hours. The duration is the time at the maximum temperature, neglecting the time used for heating to the maximum temperature and for cooling.

[0059] In one embodiment of the present invention, the thermal treatment in step (e) is performed in a rotary kiln, roller hearth kiln, in a pusher kiln, preferably in a roller hearth kiln.

[0060] The thermal treatment in step (e) may be performed under an atmosphere of air but oxygen- enriched air such as an oxygen : air volumetric ratio of from 1 :1 to 10:1 is preferred. Pure oxygen atmosphere is preferred as well.

[0061] The respective oxides and (oxy)hydroxides may be selected from the list of compounds that is suitable as dopants as indicated above, but with no restriction with respect to cobalt compounds and cobalt content of the respective base cathode active material, and without restriction with respect to manganese compounds and manganese content of the respective base cathode active material.

[0062] In step (e), usually no lithium compound is added deliberately. However, lithium compounds may be present as impurity, e.g., from the equipment used.

[0063] In one embodiment of the present invention, the coating has a thickness in the range of from 1 nm to 0.1 pm, preferably 10 nm to 100 nm and more preferably 20 nm to 50 nm.

[0064] In one embodiment of the present invention, the coating is a continuous coating. In other embodiments, the coating has a Swiss cheese like appearance with holes or an island structure.

[0065] In one embodiment of the present invention, the inventive process comprises an additional step to remove chloride, before step (c) or after step (d), e.g., performed as a heating or a washing step. A washing is preferably performed with water, for example by stirring the precursor or the base cathode active material in water. After washing, a solid-liquid separation step is performed, e.g., a filtration, followed by drying the solid residue.

[0066] Drying may be performed in vacuo, under air or under an inert gas such as nitrogen. Oxygen- depleted air is possible as well. CO2 is not a suitable atmosphere.

[0067] In one embodiment, after washing, a solid-liquid separation step is performed, e.g., a filtration, but a drying step is omitted, and step (e) is performed with the filter cake. In one embodiment of the present invention, a heating step, hereinafter step (b*), is performed. Said step (b*) is preferably performed by heating the precursor obtained from step (b) to 300 to 700°C in the absence of a lithium compound, for example for 3 to 10 hours. Step (b*) is preferably performed in a stream of CCh-free air or oxygen, with CCh-free air being preferred. Such CC>2-free air or oxygen may contain humidity or be dry.

[0068] In a preferred embodiment of the present invention, a de-agglomeration step is performed after step (d). Said de-agglomeration may be performed in one or more sub-steps, for example a jaw breaker or roller crusher followed by a milling in a jet-mill, ball-mill, planetary ball-mill, or air classifying mill.

[0069] By performing the inventive process, a coated cathode active material is obtained that meets the objectives discussed at the outset, and no stoichiometric amounts of alkali sulfate are generated.

[0070] A further aspect of the present invention is related to coated cathode active materials. They have a core and a coating and are referred to as “inventive coated cathode active materials” in the context of the present invention. Specifically, inventive cathode active material has a core according to general formula Lh+xTMi-xCh with x being in the range of from -0.05 to +0.05 and TM being a combination of metals of which at least 90 mol-% being transition metals and comprising nickel and at least one metal selected from cobalt and manganese, comprising a coating selected from lithiated and non-lithiated oxides of a least one of Mn, Co, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, W, B and Ce, and a core, wherein the chloride content of the core is in the range of from 10 to 10,000 ppm, preferably from 50 to 1 ,000 ppm.

[0071] The chloride content may be determined by heating a sample and absorbing the off-gas in acetic acid, followed by titration with silver nitrate solution. The method is related to the Wickbold method, see Angew. Chem. 1957, 69, 530.

[0072] In one embodiment of the present invention, the coating has a thickness in the range of from 1 nm to 0.1 pm, preferably 10 to 100 nm, more preferably from 20 to 50 nm.

[0073] In one embodiment of the present invention, the coating is a continuous coating. In other embodiments, the coating has a Swiss-cheese like appearance or an island structure. In one embodiment of the present invention, inventive cathode active materials have an average particle diameter (D50) from 0.5 to 10 pm, preferably from 1 to 8 pm, more preferably from 3 to 5 pm, determined by dynamic light scattering.

[0074] In one embodiment of the present invention, inventive coated cathode active materials have a particle size distribution with a span [(d90) - (d10)] / (d50) in the range of from 0.2 to 2.5, preferably from 1.0 to 2.0. The diameters (D10), (D50) and (D90) may be determined by dynamic light scattering.

[0075] In one embodiment of the present invention, TM in inventive coated cathode active materials is a combination of metals according to general formula (I)

[0076] (NiaCobMnc)i-dMd(I) with a being in the range of from 0.6 to 0.95, preferably from 0.8 to 0.94, b being in the range of from 0.025 to 0.2, c being in the range of from zero to 0.2 or up to 0.3, and d being in the range of from zero to 0.1 ,

[0077] M is selected from Ti, Zr, Mo, W, Al, Mg, Nb, and Ta and combinations of at least two of the aforementioned, a + b + c = 1.

[0078] Inventive coated cathode active materials may favorably be made according to the inventive process.

[0079] In one embodiment of the present invention, the coating is selected from oxides of Al, Zr, Sr, Ba, Y and Ce and combinations of at least two of the aforementioned.

[0080] A further aspect of the present invention is directed to oxides of TM, hereinafter also referred to as inventive precursors. Inventive precursors may be made according to steps (a) and (b) and step (b*) of the inventive process.

[0081] Specifically, inventive precursors are particulate oxides of TM with TM being a combination of metals of which at least 90 mol-% are transition metals and comprise nickel and at least one metal selected from cobalt and manganese, wherein at 50 mol-% of TM is nickel, wherein said oxide has chloride content in the range of from 10 to 10,000 ppm, preferably 15 to 5,000 ppm and more preferably 20 to 1 ,000 ppm, and wherein at least 50% of the particles have a cubic shape, for example with a length of edges in the range of from 100 nm to 20 pm, preferably at least 60%. Some irregular particles may be contained, for example at least 1%, preferably at least 5%. The shape may be determined by SEM image analysis of at least of three samples of at least 50 randomly selected particles.

[0082] Inventive precursors may advantageously be made according to steps (a) and (b) of the inventive process, followed by an additional chloride removal step (b*). Said step (b*) is preferably performed by heating the precursor obtained from step (b) to 300 to 700°C in the absence of a lithium compound, for example for 3 to 10 hours. Step (b*) is preferably performed in a stream of oxygen or air, especially CCh-free air. Said stream of air may contain humidity. Step (b*) may be performed in a rotary kiln.

[0083] A total or almost total removal of chloride from precursor would be tedious and require a lot of steps or energy. Thus, a partial removal of chloride is preferred.

[0084] A further aspect of the present invention refers to electrodes and specifically to cathodes, hereinafter also referred to as inventive cathodes. Inventive cathodes comprise

[0085] (A) at least one inventive coated cathode active material,

[0086] (B) carbon in electrically conductive form,

[0087] (C) at least one binder.

[0088] In a preferred embodiment of the present invention, inventive cathodes contain

[0089] (A) 80 to 99 % by weight inventive coated cathode active material,

[0090] (B) 0.5 to 19.5 % by weight of carbon,

[0091] (C) 0.5 to 9.5 % by weight of binder polymer, percentages referring to the sum of (A), (B) and (C).

[0092] Cathodes according to the present invention contain carbon in electrically conductive modification, in brief also referred to as carbon (B). Carbon (B) can be selected from soot, active carbon, carbon nanotubes, graphene, and graphite. Carbon (B) can be added as such during preparation of electrode materials according to the invention.

[0093] Electrodes according to the present invention can comprise further components. They can comprise a current collector (D), such as, but not limited to, an aluminum foil. They further comprise a binder polymer (C), hereinafter also referred to as binder (C). Current collector (D) is not further described here. Suitable binders (C) are preferably selected from organic (co)polymers. Suitable (co)polymers, i.e., homopolymers or copolymers, can be selected, for example, from (co)polymers obtainable by anionic, catalytic or free-radical (co) polymerization, especially from polyethylene, polyacrylonitrile, polybutadiene, polystyrene, and copolymers of at least two comonomers selected from ethylene, propylene, styrene, (meth)acrylonitrile and 1 ,3-butadiene. Polypropylene is also suitable. Polyisoprene and polyacrylates are additionally suitable. Particular preference is given to polyacrylonitrile.

[0094] In the context of the present invention, polyacrylonitrile is understood to mean not only polyacrylonitrile homopolymers but also copolymers of acrylonitrile with 1 ,3-butadiene or styrene. Preference is given to polyacrylonitrile homopolymers.

[0095] In the context of the present invention, polyethylene is not only understood to mean homopolyethylene, but also copolymers of ethylene which comprise at least 50 mol% of copolymerized ethylene and up to 50 mol% of at least one further comonomer, for example a-olefins such as propylene, butylene (1 -butene), 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene, 1 -pentene, and also isobutene, vinylaromatics, for example styrene, and also (meth)acrylic acid, vinyl acetate, vinyl propionate, Ci-C -alkyl esters of (meth)acrylic acid, especially methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, and also maleic acid, maleic anhydride and itaconic anhydride. Polyethylene may be HDPE or LDPE.

[0096] In the context of the present invention, polypropylene is not only understood to mean homopolypropylene, but also copolymers of propylene which comprise at least 50 mol% of copolymerized propylene and up to 50 mol% of at least one further comonomer, for example ethylene and a- olefins such as butylene, 1 -hexene, 1 -octene, 1 -decene, 1 -dodecene and 1 -pentene. Polypropylene is preferably isotactic or essentially isotactic polypropylene.

[0097] In the context of the present invention, polystyrene is not only understood to mean homopolymers of styrene, but also copolymers with acrylonitrile, 1 ,3-butadiene, (meth)acrylic acid, Ci- Cw-alkyl esters of (meth)acrylic acid, divinylbenzene, especially 1 ,3-divinylbenzene, 1 ,2- diphenylethylene and a-methylstyrene.

[0098] Another preferred binder (C) is polybutadiene.

[0099] Other suitable binders (C) are selected from polyethylene oxide (PEO), cellulose, carboxymethylcellulose, polyimides and polyvinyl alcohol. In one embodiment of the present invention, binder (C) is selected from those (co)polymers which have an average molecular weight Mwin the range from 50,000 to 1 ,000,000 g / mol, preferably to 500,000 g / mol.

[0100] Binder (C) may be cross-linked or non-cross-linked (co)polymers.

[0101] In a particularly preferred embodiment of the present invention, binder (C) is selected from halogenated (co)polymers, especially from fluorinated (co)polymers. Halogenated or fluorinated (co)polymers are understood to mean those (co)polymers which comprise at least one (co)polymerized (co)monomer which has at least one halogen atom or at least one fluorine atom per molecule, more preferably at least two halogen atoms or at least two fluorine atoms per molecule. Examples are polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyvinylidene fluoride (PVdF), tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-hexafluoropropylene copolymers (PVdF-HFP), vinylidene fluoride-tetrafluoroethylene copolymers, perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers and ethylene-chlorofluoroethylene copolymers.

[0102] Suitable binders (C) are especially polyvinyl alcohol and halogenated (co)polymers, for example polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers such as polyvinyl fluoride and especially polyvinylidene fluoride and polytetrafluoroethylene.

[0103] A further aspect of the present invention is an electrochemical cell, containing

[0104] (A) a cathode comprising inventive coated cathode active material (A), carbon (B), and binder (C),

[0105] (B) an anode, and

[0106] (C) at least one electrolyte.

[0107] Embodiments of cathode (1) have been described above in detail.

[0108] Anode (2) may contain at least one anode active material, such as carbon (graphite), TiC>2, lithium titanium oxide, silicon or tin. Anode (2) may additionally contain a current collector, for example a metal foil such as a copper foil.

[0109] Electrolyte (3) may comprise at least one non-aqueous solvent, at least one electrolyte salt and, optionally, additives. Non-aqueous solvents for electrolyte (3) can be liquid or solid at room temperature and is preferably selected from among polymers, cyclic or acyclic ethers, cyclic and acyclic acetals and cyclic or acyclic organic carbonates.

[0110] Examples of suitable polymers are, in particular, polyalkylene glycols, preferably poly-Ci-C4- alkylene glycols and in particular polyethylene glycols. Polyethylene glycols can here comprise up to 20 mol% of one or more Ci-C4-alkylene glycols. Polyalkylene glycols are preferably polyalkylene glycols having two methyl or ethyl end caps.

[0111] The molecular weight Mwof suitable polyalkylene glycols and in particular suitable polyethylene glycols can be at least 400 g / mol.

[0112] The molecular weight Mwof suitable polyalkylene glycols and in particular suitable polyethylene glycols can be up to 5,000,000 g / mol, preferably up to 2,000,000 g / mol.

[0113] Examples of suitable acyclic ethers are, for example, diisopropyl ether, di-n-butyl ether, 1 ,2-dimethoxyethane, 1,2-diethoxyethane, with preference being given to 1,2-dimethoxyethane.

[0114] Examples of suitable cyclic ethers are tetrahydrofuran and 1,4-dioxane.

[0115] Examples of suitable acyclic acetals are, for example, dimethoxymethane, diethoxymethane, 1 ,1 -dimethoxyethane and 1,1 -diethoxyethane.

[0116] Examples of suitable cyclic acetals are 1,3-dioxane and, in particular, 1,3-dioxolane.

[0117] Examples of suitable acyclic organic carbonates are dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0118] Examples of suitable cyclic organic carbonates are compounds of the general formulae (II) and (HI) where R1, R2and R3can be identical or different and are selected from among hydrogen and Ci-C4-alkyl, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tertbutyl, with R2and R3preferably not both being tert-butyl.

[0119] In particularly preferred embodiments, R1is methyl and R2and R3are each hydrogen, or R1, R2and R3are each hydrogen.

[0120] Another preferred cyclic organic carbonate is vinylene carbonate, formula (IV).

[0121] The solvent or solvents is / are preferably used in the water-free state, i.e. with a water content in the range from 1 ppm to 0.1 % by weight, which can be determined, for example, by Karl-Fischer titration.

[0122] Electrolyte (3) further comprises at least one electrolyte salt. Suitable electrolyte salts are, in particular, lithium salts. Examples of suitable lithium salts are LiPFe, UBF4, l_iCIC>4, LiAsFe, UCF3SO3, LiC(CnF2n+iSO2)3, lithium imides such as LiN(CnF2n+iSO2)2, where n is an integer in the range from 1 to 20, LiN(SC>2F)2, Li2SiFe, LiSbFe, LiAICL and salts of the general formula (CnF2n+iSO2)tYLi, where m is defined as follows: t = 1 , when Y is selected from among oxygen and sulfur, t = 2, when Y is selected from among nitrogen and phosphorus, and t = 3, when Y is selected from among carbon and silicon.

[0123] Preferred electrolyte salts are selected from among LiC(CF3SO2)3, LiN(CF3SC>2)2, LiPFe, UBF4, LiCICL, with particular preference being given to LiPFe and LiN(CF3SC>2)2. In a preferred embodiment of the present invention, electrolyte (3) contains at least one flame retardant. Useful flame retardants may be selected from trialkyl phosphates, said alkyl being different or identical, triaryl phosphates, alkyl dialkyl phosphonates, and halogenated trialkyl phosphates. Preferred are tri-Ci-C4-alkyl phosphates, said Ci-C4-alkyls being different or identical, tribenzyl phosphate, triphenyl phosphate, Ci-C4-alkyl di- Ci-C4-alkyl phosphonates, and fluorinated tri-Ci-C4-alkyl phosphates,

[0124] In a preferred embodiment, electrolyte (3) comprises at least one flame retardant selected from trimethyl phosphate, CH3- (O)(OCH3)2, triphenylphosphate, and tris-(2,2,2-trifluoroethyl)- phosphate.

[0125] Electrolyte (3) may contain 1 to 10% by weight of flame retardant, based on the total amount of electrolyte.

[0126] In an embodiment of the present invention, batteries according to the invention comprise one or more separators (4) by means of which the electrodes are mechanically separated. Suitable separators (4) are polymer films, in particular porous polymer films, which are unreactive toward metallic lithium. Particularly suitable materials for separators (4) are polyolefins, in particular film-forming porous polyethylene and film-forming porous polypropylene.

[0127] Separators (4) composed of polyolefin, in particular polyethylene or polypropylene, can have a porosity in the range from 35 to 50%. Suitable pore diameters are, for example, in the range from 30 to 500 nm.

[0128] In another embodiment of the present invention, separators (4) can be selected from among PET nonwovens filled with inorganic particles. Such separators can have a porosity in the range from 40 to 55%. Suitable pore diameters are, for example, in the range from 80 to 750 nm.

[0129] Batteries according to the invention can further comprise a housing which can have any shape, for example cuboidal or the shape of a cylindrical disk. In one variant, a metal foil configured as a pouch is used as housing.

[0130] Batteries according to the invention provide a very good discharge and cycling behavior, in particular at high temperatures (45 °C or higher, for example up to 60°C) in particular with respect to the capacity loss. Batteries according to the invention can comprise two or more electrochemical cells that combined with one another, for example can be connected in series or connected in parallel. Connection in series is preferred. In batteries according to the present invention, at least one of the electrochemical cells contains at least one electrode according to the invention. Preferably, in electrochemical cells according to the present invention, the majority of the electrochemical cells contain an electrode according to the present invention. Even more preferably, in batteries according to the present invention all the electrochemical cells contain electrodes according to the present invention.

[0131] The present invention further provides for the use of batteries according to the invention in appliances, in particular in mobile appliances. Examples of mobile appliances are vehicles, for example automobiles, bicycles, aircraft or water vehicles such as boats or ships. Other examples of mobile appliances are those which move manually, for example computers, especially laptops, telephones or electric hand tools, for example in the building sector, especially drills, battery-powered screwdrivers or battery-powered staplers.

[0132] The invention is further illustrated by working examples.

[0133] The chloride content was determined as follows: An aliquot of a sample (ca. 1 to 10 mg) was heated in oxygen with nitrogen as carrier gas (oven temperature ca. 1050 °C). The resulting offgas gas was adsorbed in 75% (v / v) acetic acid. The resulting solution was titrated with silver nitrate solution with potentiometric end-point detection.

[0134] Step (a.1):

[0135] NiCh © H2O, C0CI2 6 H2O, and MnCh'4 H2O were dissolved in de-ionized water in a molar ratio (referring to the metals) of 93.5 : 4.5 : 2.0. A clear aqueous solution was obtained. The total concentration of transition metals was 100 g / l.

[0136] Step (b.1): An amount of 2 liters of the solution was transferred to a beaker. A constant volume flow of 30 ml / min was pumped from the beaker into a one-component nozzle with the help of a membrane pump. The solution was sprayed through the nozzle into a tube-shaped reactor that was heated by two natural gas burners attached to the reactor’s side walls, creating a reactor temperature of 800°C. While passing the tube reactor from top to bottom, the solution droplets were first dried. Subsequently, the beam of the chloride mixture was blown through the flame and thus pyrolyzed to form a composite oxide as particulate material. The resulting particulate material was collected at the bottom of the reactor through gravity, while the chlorine leaves the reactor together with the off-gas as HCI and is treated in an absorption column filled with NaOH / H2O solution.

[0137] Step (b*.1): The particulate material from step (b.1) is removed from the reactor and treated in a lab furnace by an additional high temperature step at 650°C for 5 hours to further reduce the amount of chloride impurities. A particulate metal oxide is obtained from step (b*.1), inventive P- CAM.1. The chloride content of P-CAM.1 is 1 ,000 ppm, determined by heating in a pipe in a stream of oxygen. SEM images revealed that more than 50% of the particles of three randomly selected samples have a cubic shape, the others have a random shape. The traces of Mg, Al, Ti, Zr, Mo, W, Nb, Sr, Ba, Y, Ce, and Ta in P-CAM.1 are below detection level.

[0138] Step (c.1): P-CAM.1 is mixed with LiOH H2O in a molar ratio Li / TM as 1.05 : 1.00. A mixture is obtained. No dopant is added.

[0139] Step (d.1): The mixture obtained from step (c.1) is heated in a lab furnace to 500°C for three hours. The heating rate is 3°C / min. Then, the mixture is calcined at 830°C for 12 hours in a stream of oxygen and then cooled naturally. A base cathode active material is obtained.

[0140] Step (e.1): The base cathode active material is mixed with 2 mol-% Co(OH)2, referring to Co in CO(OH)2 and to the sum of Ni, Co and Mn in P-CAM.1 , and heated to 700°C with a temperature hold of 3 hours in a lab furnace before natural cooling to perform a Co coating. Inventive cathode active material CAM.1 is obtained. The chloride content is in the range of from 100 to 1 ,000 ppm.

[0141] Step (c.2): P-CAM.1 is mixed with LiOH H2O and with AI(OH)3 in a molar ratio Li / TM / AI as 1.05 : 1.00 : 0.003. A mixture is obtained.

[0142] Step (d.2): mixture obtained from step (c.2) is heated in a lab furnace to 500°C for three hours. The heating rate is 3°C / min. Then, the mixture is calcined at 830°C for 12 hours in a stream of oxygen and then cooled naturally. A base cathode active material is obtained.

[0143] Step (e.2): The base cathode active material is mixed with 2 mol-% Co(OH)2, referring to Co in CO(OH)2 and to the sum of Ni, Co and Mn in P-CAM.1 , and heated to 700°C with a temperature hold of 3 hours in a lab furnace before natural cooling to perform a Co coating. Inventive cathode active material CAM.2 is obtained. The chloride content is in the range of from 100 to 1 ,000 ppm.

Claims

Patent Claims1 . Process for making a coated cathode active material for lithium-ion batteries wherein said cathode active material comprises lithium, nickel and at least one of cobalt and manganese with at least 50 mol-% being nickel, referring to metals other than lithium, wherein said process comprises the steps of:(a) providing an aqueous solution of chlorides of nickel and of at least one of cobalt and manganese in the targeted ratio,(b) performing a pyrolysis of the aqueous solution of step (a) in a flame fed by natural gas, methane, or hydrogen, thereby obtaining a precursor of a cathode active material,(c) adding a source of lithium and, optionally, at least one dopant selected from oxides and (oxy)hydroxides of Mg, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, W, Ce or Mo and combinations of at least two of the aforementioned to the precursor from step (b),(d) performing a thermal treatment at a temperature in the range of from 700 to 1100°C, and(e) performing a coating on the material resulting from step (d) with at least one oxide or (oxy)hydroxide of Mn, Co, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, B, W or Ce, followed by another thermal treatment at a temperature in the range of from 200°C to 800°C.

2. Process according to claim 1 wherein step (b) is performed with a residence time in the flame in the range of one to ten seconds.

3. Process according to claim 1 or 2 wherein the source of lithium is selected from IJ2CO3, LiOH and LiOH y H2O with y being in the range of from 0.5 to 2.5.

4. Process according to any of the preceding claims wherein said cathode active material has a core according to general formula Lii+xTMi-xO2 with x being in the range of from - 0.05 to +0.05 and TM being a combination of metals of which at least 90 mol-% are transition metals and comprise nickel and at least one metal selected from cobalt and manganese, and at least 50 mol-% of TM is nickel.

5. Process according to claim 4 wherein TM is a combination of metals according to formula (I)(NiaCobMnc)i-dMd(I) witha being in the range of from 0.6 to 0.95, b being in the range of from 0.025 to 0.2, c being in the range of from zero to 0.2 or up to 0.3, and d being in the range of from zero to 0.1 ,M is selected from Mg, Al, Ti, Zr, Mo, W, Nb, Sr, Ba, Y, Ce, and Ta and combinations of at least two of the aforementioned, a + b + c = 1.

6. Process according to any of the preceding claims wherein in step (a) and in the coated cathode active material, both cobalt and manganese are present.

7. Process according to any of the preceding claims wherein M is selected from Al, Sr, Ba, Y, Zr and Ce and combinations of at least two of the aforementioned.

8. Process according to any of the preceding claims wherein said process comprises an additional step to remove chloride, before or after step (c).

9. Process according to any of the preceding claims wherein cathode active material obtained from step (e) has an average particle diameter (D50) in the range of from 1 to 8 pm.

10. Process according to any of the preceding claims wherein the cathode active material obtained is in the form of monolithic particles.11 . Coated cathode active material in particulate form according to general formula Lii+xTMi-xO2 with x being in the range of from -0.05 to +0.05 and TM being a combination of metals of which at least 90 mol-% being transition metals and comprising nickel and at least one metal selected from cobalt and manganese, comprising a coating selected from lithiated and non-lithiated oxides of a least one of Mn, Co, Ti, Zr, Nb, Ta, Al, Y, Sr, Ba, B, W and Ce and combinations of at least two of the aforementioned, and a core, and wherein at least 50 mol-% of TM is nickel, and wherein the core has a chloride content in the range of from 10 to 1 ,000 ppm.

12. Coated cathode active material according to claim 11 wherein the coating is selected from lithiated and non-lithiated oxides of a least one of Al, Sr, Ba, Y, Co, B and Ce and combinations of at least two of the aforementioned.

13. Particulate oxide of TM with TM being a combination of metals of which at least 90 mol-% being transition metals and comprising nickel and at least one metal selected from cobalt and manganese, wherein at least 50 mol-% of TM is nickel, wherein said oxide has a chloride content in the range of from 10 to 10,000 ppm, and wherein at least 50% of the particles have a cubic shape.

14. Use of a particulate oxide according to claim 13 for the manufacture of a cathode active material in accordance with claim 11.

15. Cathode containing(A) at least one electrode active material according to any of claims 11 or 12,(B) carbon in electrically conductive form,(C) a binder material.

16. Cathode according to claim 14 containing(A) 80 to 99 % by weight coated cathode active material,(B) 0.5 to 19.5 % by weight of carbon,(C) 1 to 17 % by weight of carbon, percentages referring to the sum of (A), (B) and (C).

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