Secondary particles for cathodes of secondary lithium batteries and method for their production

Abstract

The invention relates to secondary particles (6) for cathodes of secondary lithium cells. The secondary particles have a multiplicity of primary particles (8), which each have a layered crystal structure in which layers of transition metal oxide (2) and lithium layers (4) alternate. Here, each primary particle (8) has a spatial extension in the direction of its crystallographic c axis (c) which is greater than in a direction perpendicular to this axis. The invention also relates to a method for producing the secondary particles.

Description

Technical Field

[0001] This invention relates to secondary particles for cathodes used in single-cell lithium-ion batteries. The secondary particles comprise a plurality of primary particles, each having a layered crystal structure in which transition metal oxide layers and lithium layers alternate. The invention also relates to a method for preparing the secondary particles. Background Technology

[0002] A lithium battery cell (Li battery cell), hereinafter also referred to as a battery cell, has at least one anode and at least one cathode.

[0003] Typically, both the anode and cathode comprise a substrate, also known as a current collector, particularly a metal foil, wherein the substrate is coated. This coating contains an active material, and appropriately includes a binder and a conductive agent, such as graphite or conductive carbon black. In particular, graphite, graphene, so-called hard carbon nanotubes, or soft carbon nanotubes are used as the active material for the anode.

[0004] In particular, the (cathode) active material used for the cathode has a large number of secondary particles, which are formed from a large number of aggregated primary particles. Such primary particles may have a layered crystal structure in which transition metal oxide layers and lithium ion layers (lithium layers) alternate.

[0005] A precursor for a nickel-based active material for lithium-ion batteries is known from US 2020 / 0058937 A1. This precursor comprises secondary particles having a large number of particulate structures, each having a porous core segment and a shell segment. A majority of the primary particles forming the shell segments on the surface of the secondary particles are arranged such that their principal extension direction is arranged perpendicular to the surface of the secondary particles. Here, the (110) crystal surface of the primary particles is oriented perpendicular to the principal extension direction.

[0006] An active material having secondary particles is known from EP 3 723 175 A1, said secondary particles comprising aggregated primary particles. Here, the primary particles elongate in a direction from the internal segments of the secondary particles to the surface segments of the secondary particles. Here, the crystallographic a-axis is substantially aligned with this direction. Summary of the Invention

[0007] The object of this invention is to provide particularly suitable secondary particles and a method for preparing the same. Specifically, a diffusion coefficient for lithium ions in the secondary particles should be achieved as large as possible. Furthermore, a cathode having such secondary particles for use in a lithium-ion battery cell, and a secondary lithium-ion battery cell having such a cathode, should be provided.

[0008] Regarding secondary particles, the objective is achieved according to the invention by the features of claim 1. Regarding the cathode and the lithium-ion battery cell, the objective is achieved by the features of claim 6 or 7, respectively. Regarding the method, the objective is achieved by the features of claim 8. Advantageous improvements and developments are preferred subject matter according to the invention. Here, the interpretation relating to secondary particles also applies to the method, as well as to the cathode and the lithium-ion battery cell, and vice versa.

[0009] The secondary particles are intended for use as cathodes in secondary lithium-ion battery cells, particularly lithium-ion battery cells. Specifically, the active material of the cathode is formed based on these secondary particles. These secondary particles are particularly suitable as cathode active materials.

[0010] The secondary particles, in turn, comprise a large number of primary particles. Specifically, the primary particles aggregate to form the secondary particles. Suitablely, each of the primary particles is a single crystal.

[0011] Each primary particle has a layered crystal structure in which transition metal oxide layers and lithium layers, i.e., lithium-ion layers, alternate. In other words, lithium-ion layers and transition metal oxide layers are alternately stacked (or layered). Further, a lithium-ion layer is arranged between each of the two transition metal oxide layers.

[0012] Primary particles are suitably formed from or contain at least the following: lithium transition metal oxides, such as lithium nickel manganese cobalt oxide (Li-NMC), lithium nickel cobalt aluminum oxide (NCA), lithium nickel oxide, and lithium cobalt oxide (LCO).

[0013] The transition metal oxide layers here span the fundamental ab plane of the lattice. Therefore, the transition metal oxide layers are arranged (or arranged) in their respective cases in the plane defined by the crystallographic a-axis and crystallographic b-axis of the unit cell.

[0014] Specifically, the transition metal oxide layer and the lithium layer are also oriented perpendicular to the crystallographic c-axis. Therefore, the transition metal oxide layer and the lithium layer are stacked in the c-axis direction.

[0015] Each primary particle has a larger spatial extent along its crystallographic c-axis than it has in the direction perpendicular to the c-axis. Therefore, the spatial extent of each primary particle along the crystallographic c-axis is greater than its spatial extent in the plane defined by the crystallographic a-axis and the crystallographic b-axis.

[0016] Primary particles thus form in their respective forms by elongation, that is, in a slender manner. The direction in which each primary particle elongates is called the principal extension direction.

[0017] Therefore, the proportion of the principal extension direction along the crystallographic c-axis is always greater than the proportion of the principal extension direction along the direction parallel to the orientation of the ab crystal plane.

[0018] Due to its layered structure, each primary particle exhibits anisotropic diffusion characteristics. Therefore, the volumetric diffusion of lithium ions (Li ions) in the ab crystal plane occurs much faster than along the crystallographic c-axis.

[0019] Compared to the primary particles that elongate within their ab crystal planes, as mentioned earlier, the diffusion path of lithium ions within the primary particles, particularly within the ab crystal planes, is relatively small due to the elongated structure along the crystallographic c-axis. Furthermore, the proportion of the (100) and (010) crystal surfaces, i.e., the proportion of crystal surfaces oriented perpendicular to the ab crystal plane, is relatively large. This increases the area through which lithium ions can penetrate or extract from the primary particles. Grain boundary diffusion of lithium ions proceeds faster than crystal volume diffusion. Specifically, the relatively slow crystal volume diffusion is overcompensated by the relatively short diffusion paths within the corresponding ab crystal planes. Overall, this thus makes faster lithium ion transport in secondary particles particularly advantageous. The diffusion coefficient of lithium ions in secondary particles is therefore advantageously larger.

[0020] Therefore, a single cell with such secondary particles as active material in its cathode or cathode has advantageously higher power and energy density.

[0021] For example, in addition to the secondary particles described above, secondary particles also have other conventional primary particles known from the prior art, which are, for example, spherical or elongated in a direction parallel to the ab crystal plane. To better distinguish them from the primary particles described above, whose elongation dimension in the direction of their crystallographic c-axis is greater than their elongation dimension in the direction perpendicular to that axis, these other conventional primary particles are referred to below as "additional primary particles".

[0022] In other words, the secondary particles do not necessarily contain only the primary particles according to the invention; conventional primary particles, i.e., other primary particles, may also be mixed in and / or included in the secondary particles. The proportion of primary particles according to the invention, i.e., the proportion of particles whose extension dimension along the crystallographic c-axis is greater than their extension dimension in the direction perpendicular to it, is preferably at least 50% of all primary particles.

[0023] According to a suitable design, the spatial extension dimension of the primary particle in the direction of its crystallographic c-axis is, in each case, at least 1.2 times, especially at least 1.2 times, properly at least twice, the extension dimension of the primary particle in the direction perpendicular to that axis. In this way, the proportion of lithium ions that can pass through their insertion into the primary particle or through their extraction from the (100) and (010) crystal surfaces is advantageously larger.

[0024] For example, the crystallographic c-axis is tilted relative to the principal extension direction of each primary particle, provided that the extension dimension in the direction of its crystallographic c-axis is greater than the extension dimension in the direction perpendicular to that direction. However, in a preferred design, the crystallographic c-axis is parallel to the principal extension direction of each primary particle. In this way, the proportion of lithium ions that can pass through their embedded in the primary particle or through their extracted (100) and (010) crystal surfaces from the primary particle is advantageously further increased.

[0025] In principle, primary particles can have different geometries. For example, primary particles may be pyramidal, cylindrical, or prismatic in their respective cases. Furthermore, primary particles may be ellipsoidal or cuboid in their respective cases.

[0026] The transition metal oxide layer appropriately includes nickel, particularly nickel ions, to increase the capacity of a single cell. For example, the nickel content is at least 50 mol%, preferably at least 75 mol%, and particularly preferably at least 90 mol%, based on all transition metal ions in the transition metal oxide layer.

[0027] For example, the orientation of the primary particles within the secondary particles—and therefore the orientation of the corresponding c-axis of the primary particles—is random. However, according to advantageous development, at least the majority of the primary particles, i.e., more than 50%, particularly in the shell region of the secondary particles, i.e., in the peripheral region of the secondary particles, are morphologically radially aligned. "Morphologically radially aligned" (or simply radially aligned hereinafter) should be understood here as meaning that the principal extension direction and / or crystallographic c-axis of the corresponding primary particles are oriented from the core or center of the secondary particle, which is particularly spherical or elliptical in shape, toward the outer edge of the secondary particle. This has the advantage that the grain boundaries of the primary particles extend radially (or radially), allowing lithium ions to diffuse more quickly into the interior of the secondary particles. Alternatively or otherwise, the primary particles are arranged linearly or circumferentially adjacent to each other in the secondary particle, which is particularly spherical or elliptical in shape, wherein the crystallographic c-axis of the primary particles is parallel to each other, along the circumferential direction of the secondary particle, or parallel to the radial orientation of the secondary particle. Alternatively, adjacent primary particles are arranged offset from each other in this radial direction. Here, different arrangements differ, particularly in size and structure, namely in the network, grain boundaries, and consequently, lithium-ion diffusion along the grain boundaries. Depending on the chosen material, the size of the primary particles, or their aspect ratio, the arrangement of the primary particles can be adjusted in such a way that effective lithium-ion diffusion along the grain boundaries can be achieved.

[0028] The alignment can be particularly affected by process parameters such as stirring speed and / or temperature during calcination, or the choice of precursor particle size.

[0029] Depending on the design, the primary particles have a (maximum) spatial extension size between 50 nm and 5 μm, for example between 100 nm and 3 μm, and particularly between 250 nm and 1 μm. Specifically, the spatial extension size of the corresponding primary particles along their main extension direction is between 50 nm and 5 μm.

[0030] These "medium-sized" primary particles have a larger grain boundary network compared to larger primary particles, which is why lithium ions can diffuse into the interior of secondary particles more quickly. However, compared to the smaller primary particles, there is still a larger amount of material (bulk material) available for lithium ion intercalation.

[0031] Another aspect of the invention relates to a cathode for a single secondary lithium-ion battery cell. Here, the cathode has secondary particles, suitably a plurality of secondary particles, formed according to one of the variants described above. The secondary particles, or these secondary particles, are used herein as the cathode active material. In particular, the secondary particles, or these secondary particles, are part of a cathode coating applied to a substrate.

[0032] Another aspect of the invention relates to a secondary lithium-ion battery cell. This secondary lithium-ion battery cell is, for example, a lithium-ion battery cell having a liquid electrolyte suitably containing lithium ions, or further, for example, a so-called solid-state lithium-ion battery cell in which the electrolyte is solid. According to the invention, this includes a cathode designed according to the above variant. Such secondary lithium-ion battery cells are used, for example, in mobile phones, laptops, etc. Alternatively, such lithium-ion battery cells are used as batteries for electrically driven motor vehicles, especially traction batteries. In this case, for example, multiple such battery cells are connected in series and / or in parallel with each other, wherein the traction battery provides current and / or voltage to an electric motor configured to drive the motor vehicle.

[0033] Another aspect of the present invention relates to a method for preparing secondary particles designed according to one of the above variants.

[0034] First, in a first step, an aqueous solution of a transition metal salt is prepared or provided. In a subsequent second step, an alkali is added to the aqueous solution, thereby initiating a precipitation reaction. This precipitation reaction is used here to form crystal nuclei from the corresponding transition metal compound. These crystal nuclei thus form precipitates from the precipitation reaction. Crystal nuclei are understood herein to refer to crystals of the transition metal compound with a diameter of less than 200 nm, preferably 50-150 nm, and particularly preferably 75-125 nm. These crystal nuclei may have a large extension size in their crystallographic ab plane.

[0035] Therefore, the precipitation reaction is interrupted or terminated after a certain time period, for example by adding acid, i.e. by increasing the pH of the aqueous solution.

[0036] According to a first variant of this method, in the third step, the crystal nuclei generated by the precipitation reaction, particularly on their (100) and / or (110) crystal surfaces, are doped with monovalent cations. This doping method is known in the prior art. Hydrogen cations (H...) + ), sodium cation (Na) + ), potassium cation (K) + or ammonium ions (NH4) + It is preferred for doping. Due to this doping, the surface energy of crystal surfaces parallel to the crystallographic c-axis orientation, especially (100) crystal surfaces, (010) crystal surfaces and / or (110) crystal surfaces, is reduced.

[0037] In particular, excess of these cations are appropriately added, in the form of salts, to the aqueous solution containing the crystal nuclei for doping.

[0038] Then, in the fourth step, the precipitation reaction continues or a further precipitation reaction is initiated. For this purpose, if necessary, a base is added to the solution. During this process, the nuclei of the transition metal compound continue to grow, but the growth in the crystallographic c-axis direction is relatively large due to doping, particularly at the (100), (010), and / or (110) crystal surfaces, such that the precursor particles formed in this precipitation reaction are larger in the crystallographic c-axis direction than in the direction perpendicular to that direction.

[0039] According to a second variant of the method, the crystal nucleus is coated in an alternative third step, particularly on its (100) crystal surface, its (010) crystal surface, and / or its (110) crystal surface. Such coating methods are known in the prior art. This coating is formed or produced, for example, using organic compounds, particularly bitumen, polyisoprene, or preferably oxidizable nanoparticles. Alternatively or in addition, inorganic compounds, such as Al2O3, ZrO2, ZnO, and SrCrO4, can be used.

[0040] Similar to the fourth step of the first variant, the precipitation reaction continues or a further precipitation reaction is initiated in the fourth step according to the second variant. Therefore, due to the coating, especially the coating on the (100) crystal surface, the (010) crystal surface and / or the (110) crystal surface, the growth in the crystallographic c-axis direction is greater.

[0041] According to a third alternative variation of the method, the nuclei are uniaxially compressed in the third step. The nuclei are anisotropic due to their crystal structure. In particular, these nuclei have relatively low stiffness, i.e., relatively high deformability, in their crystallographic c-axis direction. For this reason, and if the nuclei have a relatively large extension dimension in their ab crystal plane, the nuclei are preferably aligned under the pressure applied for compression in such a way that their crystallographic c-axis is oriented in the direction of uniaxial pressure / compression. For example, the nuclei are used here in the solution or a solution. Alternatively, the nuclei (or crystallization nuclei) are removed from the solution before compression and appropriately washed and dried.

[0042] In the fourth step according to the third variant, the aligned nuclei are sintered. Specifically, the sintering process is carried out for 8 to 12 hours, particularly 10 hours, at a temperature between 700°C and 1200°C, preferably 1000°C. For example, uniaxial compression is repeatedly performed during the sintering process.

[0043] Preferably, due to the alignment of the crystal nuclei, the nuclei attach to their (001) crystal surface during sintering. Therefore, a precursor particle is formed through this attachment, the precursor particle having a larger extension dimension in its crystallographic c-axis direction, i.e., its extension dimension perpendicular to the (001) crystal surface compared to the nuclei, relative to the precursor particle's extension dimension in its perpendicular direction. If necessary, the third and / or fourth steps can be repeated.

[0044] In the same fifth step as in the first, second, and third variations of the method, the precursor particles are calcined and then sintered as appropriate. The secondary particles obtained here can then be appropriately reduced to a predetermined size or a predetermined size range by grinding. Attached Figure Description

[0045] Exemplary embodiments of the present invention will now be explained in more detail with reference to the accompanying drawings. In the drawings:

[0046] Figure 1 A schematic diagram of the crystal structure of a lithium-transition metal oxide compound is shown, in which transition metal oxide layers and lithium layers alternate, and the crystallographic c-axis is perpendicular to the orientation of these layers.

[0047] Figure 2 A schematic and partial cross-sectional view of a secondary particle with a large number of primary particles is shown, wherein the primary particles are elongated along their crystallographic c-axis, and

[0048] Figure 3 A flowchart illustrating a method for preparing secondary particles is shown. Detailed Implementation

[0049] In all the accompanying drawings, the corresponding parts and sizes are always labeled with the same reference numerals.

[0050] Figure 1 The crystal structure of a lithium transition metal oxide is shown. This crystal structure has a layered structure formed by alternating layers of transition metal oxide (hereinafter referred to as transition metal layer 2) and lithium ion layers (hereinafter referred to as lithium layer 4). In other words, lithium layer 4 and transition metal oxide layers are alternately stacked.

[0051] Furthermore, the orientations of the crystallographic a-axis, crystallographic b-axis, and crystallographic c-axis are shown in... Figure 1 In the figure, these axes are denoted by reference numerals a, b, and c. Here, the crystallographic c-axis is perpendicular to the orientations of layers 2 and 4. The planes defined by the transition metal layer 2 and the lithium layer 4 extend parallel to each other. In other words, the crystallographic c-axis is perpendicular to one of the transition metal oxide layers 2 or one of the lithium layers 4. The transition metal oxide layers 2 are arranged in planes defined by the crystallographic a-axis and crystallographic b-axis of the unit cell, respectively.

[0052] Figure 2 The image shows details of substantially spherical secondary particles 6 formed by a large number of aggregated primary particles 8 of lithium transition metal oxide. These primary particles here have, according to... Figure 1 The crystal structure is shown. Here, for each primary particle 8, the direction of its crystallographic c-axis is indicated by an arrow. The primary particle 8 elongates along its crystallographic c-axis. In other words, the elongation dimension of the primary particle along its crystallographic c-axis is greater than that perpendicular to the axis. In this case, the crystallographic c-axis corresponds to the principal extension direction of the corresponding primary particle, i.e., the longest semi-axis.

[0053] Each primary particle 8 has a spatial extension between 100 nm and 3 μm along its crystallographic c-axis. Here, the spatial extension along the crystallographic c-axis is more than 1.2 times the spatial extension of the primary particle 8 in the direction perpendicular to this axis. Preferably, these have an aspect ratio between 1:1.2 and 1:5 (spatial extension perpendicular to the c-axis: spatial extension in the c-axis direction).

[0054] from Figure 2 As can be seen, these primary particles 8 are radially aligned in morphology. In other words, the primary particles are designed such that their main extension direction or their crystallographic c-axis is oriented from the core of the secondary particle 6 to the outer edge of the secondary particle 6.

[0055] According to a variant of the secondary particle not shown in detail, its primary particle 8 is not designed as an ellipsoid, but rather has a prismatic or cylindrical form. The main extension direction here is the height direction of the prismatic / cylindrical shape.

[0056] Figure 2 The primary particles 8 shown are relatively uniform in size and aspect ratio. However, according to variants not shown in detail, the secondary particles include primary particles whose size and / or aspect ratio are more uniformly distributed in the range of 50 nm to 5 μm and whose aspect ratio is between 1:1.2 and 1:5.

[0057] According to a variant of the secondary particle 6 not shown in detail, its primary particles 8 are not radially aligned (oriented), but are aligned (oriented) in the circumferential direction of the secondary particles 6 or randomly.

[0058] This type of secondary particle is particularly useful as the cathode for single-cell rechargeable lithium batteries.

[0059] Figure 3 The flowchart shown represents a method for preparing such secondary particles 6, and in particular multiple such secondary particles 6.

[0060] First, in step I, an aqueous solution 9 of a transition metal salt is prepared or provided. For example, for preparation, one or more transition metal sulfates, particularly NiSO4·6H2O, MnSO4·H2O, or CoSO4·7H2O, are added to an aqueous solution consisting of ethylene glycol and softened water.

[0061] In the subsequent second step II, to form crystal nuclei 10 with a diameter less than 200 nm, preferably between 50 and 150 nm, and particularly preferably between 75 and 125 nm, a (first) precipitation reaction is carried out by adding an alkali such as NaOH or NH4OH. Here, the pH value is preferably adjusted to between 8 and 13, preferably to 11, and appropriately kept constant. Here, the stirring speed is 500 to 200 rpm at an ambient pressure between 1 and 5 atmospheres (atm), preferably at 1 atmosphere. Depending on the transition salt used and the stoichiometry used, the temperature of the solution is appropriately set between 20°C and 95°C. For example, the temperature is set to 80°C for the preparation of NMC111 and to 40°C for the preparation of NMC811.

[0062] If the crystal nuclei have a predetermined target size (preferably between 50 and 150 nm, particularly preferably between 75 and 125 nm), the precipitation reaction is interrupted. To do this, the pH value is lowered.

[0063] According to a first variant of this method, in the third step III.a, the crystal nuclei 10 generated by the precipitation reaction are doped with monovalent cations 12 on their (100), (010), and / or (110) crystal surfaces. Doping is preferably carried out in an aqueous solution 9. However, if required by the doping process, the crystal nuclei 10 are appropriately removed from the aqueous solution 9 before doping, and preferably cleaned and dried. Furthermore, hydrogen cations (H+) are used for this purpose. + ), sodium cation (Na) + ), potassium cation (K) + or ammonium ions (NH4) + Due to the excess of these ions and / or due to the exposed oxygen sites of the crystal nucleus, it is preferable to dope the (100), (010), or (110) crystal surfaces.

[0064] For this purpose, an excess of these cations 12, appropriately in the form of salts, is added to an aqueous solution containing crystal nuclei.

[0065] Subsequently, in step IV.a, the precipitation reaction continues by adding a base, i.e., by increasing the pH to a range between 8 and 13, or by initiating a further (second) precipitation reaction. Thus, the nucleus of the transition metal compound continues to grow to form precursor particles 14. However, because doping reduces the surface energy on the (100) crystal surface, the (010) crystal surface, and / or the (110) crystal surface, the growth of the corresponding crystals along their crystallographic c-axis is greater than the growth in the direction perpendicular to that direction.

[0066] According to a second alternative variant of the method, the crystal nucleus 10 is coated on its (100) crystal surface, its (010) crystal surface, and / or its (110) crystal surface in a third step III.b. Coating is preferably carried out in an aqueous solution 9. However, if required by the coating process, the crystal nucleus 10 is suitably removed from the aqueous solution 9 prior to coating, and preferably cleaned and dried. Organic compounds, such as bitumen or polyisoprene, can be used for this coating 16. Alternatively, nanoparticles preferably oxidizable are used for this purpose, having a diameter of 1 / 10 to 1 / 3 of the area of ​​the (100), (010), and / or (110) crystal surfaces. Additionally, inorganic compounds such as Al2O3 or ZrO2 can be used alternatively. Further examples of suitable inorganic compounds are ZnO or SrCrO4, wherein for excess Zn or Cr, 0.05 to 0.2, preferably 0.1 mol / mol of transition metal salt is used. Due to excess and / or due to the exposure of oxygen in the crystal nucleus, it is preferable to dope the (100), (010), or (110) crystal surface.

[0067] Step IV.b of the second variant of the method is similar to step IV.a of the first variant. Due to the coating, the surface energy of the (100) crystal surface, the (010) crystal surface and / or the (110) crystal surface is also reduced, thereby enabling relatively rapid crystal growth along the crystallographic c-axis of the corresponding crystal nucleus 10 in the second precipitation reaction or in the continuation of the first precipitation.

[0068] According to an alternative third variant of this method, the crystal nucleus 10 is uniaxially compressed in the third step III.c. For this purpose, the crystal nucleus 10 is suitably removed from the aqueous solution first, preferably cleaned and dried. Subsequently, the crystal nucleus 10 is subjected to uniaxial pressure, i.e., pressure acting in a single direction.

[0069] Due to its anisotropy, the crystal nucleus 10 is preferably aligned in such a way that its crystallographic c-axis is oriented in the uniaxial pressure / compression direction under the pressure applied for compression.

[0070] In step IV.c according to the third variant, the aligned crystal nuclei are sintered. Here, the sintering process is carried out for 8 to 12 hours, particularly 10 hours, at a temperature of 700°C to 1200°C, preferably 1000°C. Uniaxial compression is repeatedly performed during the sintering process.

[0071] Preferably, due to the alignment of the crystal nuclei, these nuclei are joined to their (001) crystal surfaces during sintering. Thus, through this joining, precursor particles 14 are formed, whose extension dimension in the crystallographic c-axis direction, i.e., the extension dimension relative to the crystal nuclei perpendicular to the (001) crystal surface, is greater than its extension dimension in the direction perpendicular to that axis. If necessary, the third and / or fourth steps can be repeated.

[0072] exist Figure 3 In the first variant of the method, the third and fourth steps are provided with reference numerals III.a and IV.a, the second variant of the method is provided with reference numerals III.b and IV.b, and the third variant of the method is provided with reference numerals III.c or IV.c.

[0073] Suitablely, the precursor particles 14 are first washed, filtered, and dried, for example, at a temperature between 100°C and 110°C. Subsequently, in step V., the precursor particles 14 are calcined. For this purpose, the precursor particles 14 are first mixed with a lithium salt, particularly Li₂CO₃ or LiOH. Suitablely, the mixing is carried out under standard conditions (ambient temperature of 25°C and ambient pressure of 1013 mbar) and at a stoichiometric ratio of Li (from the lithium salt) to the transition metal oxide, for example, 1.05:1 to 1.20:1, preferably 1.10:1. Thus, a lithium surplus (or excess) is achieved. The subsequent calcination is carried out, particularly at a temperature between 350°C and 600°C, preferably at 450°C for one hour. Preferably, this is done using an oxygen atmosphere.

[0074] This is followed by the sintering process of the calcined precursor particles (step VI.). The sintering process is carried out at a temperature between 700°C and 1000°C, preferably at 800°C for 10 hours.

[0075] Due to calcination and / or sintering, dopant elements / compounds may be removed, or the coating may be burned or decomposed into carbon, especially if the coating is based on an organic compound. Non-conductive coatings can also be advantageously used in the preparation process due to this decomposition.

[0076] The secondary particles generated during sintering can then be reduced to a predetermined size or a predetermined size range by grinding, for example, using an air jet mill at an air velocity between 200 m / s and 400 m / s.

[0077] This invention is not limited to the exemplary embodiments described above. Instead, those skilled in the art can derive other variations of the invention without departing from its subject matter. In particular, all the individual features described in the exemplary embodiments can be combined with each other in other ways without departing from the subject matter.

[0078] List of reference numerals

[0079] 2 Transition metal oxide layer

[0080] 4 Lithium layer

[0081] 6 Secondary particles

[0082] 8. Primary granules

[0083] 9 Aqueous solutions

[0084] 10 crystal nuclei

[0085] 12 cations

[0086] 14 Precursor Particles

[0087] 16 Coatings

[0088] I. Preparation / Providing aqueous solutions of transition metal salts

[0089] II. Perform the precipitation reaction

[0090] IIIa. Doping

[0091] III.b Coating

[0092] III.c Compression

[0093] IV.a Precipitation reaction

[0094] IV.b Precipitation reaction

[0095] IV.c Sintering

[0096] V. Roasting

[0097] VI. Sintering

[0098] a crystallographic a-axis

[0099] b crystallography b-axis

[0100] c-c axis in crystallography

Claims

1. Secondary particle (6) for a cathode of a secondary lithium battery cell, having - a multiplicity of primary particles (8), wherein each primary particle has a layered crystal structure in which transition metal oxide layers (2) and lithium layers (4) alternate, characterized in that each primary particle (8) has a greater extension in the direction of its crystallographic c-axis (c) than in a direction perpendicular to this axis, wherein the primary particles, each being single crystals, are aggregated to form the secondary particle.

2. Secondary particle (6) according to claim 1, characterized in that the spatial extension of the primary particles (8) in the direction of their crystallographic c-axis (c) is in each case at least 1.2 times the extension of the primary particles (8) in a direction perpendicular to this axis.

3. Secondary particle (6) according to claim 1, characterized in that the spatial extension of the primary particles (8) in the direction of their crystallographic c-axis (c) is in each case at least twice the extension of the primary particles (8) in a direction perpendicular to this axis.

4. Secondary particle (6) according to one of claims 1 to 3, characterized in that the crystallographic c-axis (c) is parallel to the main direction of extension of the respective primary particle (8).

5. Secondary particle (6) according to one of claims 1 to 3, characterized in that the primary particles (8) are morphologically aligned radially.

6. Secondary particle (6) according to claim 5, characterized in that the primary particles (8) in the shell region of the secondary particle are morphologically aligned radially.

7. Secondary particle (6) according to one of claims 1 to 3, characterized in that the primary particles (8) have in each case an extension of between 50 nm and 5 μιη.

8. Cathode for a secondary lithium battery cell, having secondary particles (6) formed according to one of claims 1 to 7.

9. Secondary lithium battery cell having a cathode according to claim 8.

10. Method for producing secondary particles (6) according to one of claims 1 to 7 - wherein an aqueous solution (9) of a transition metal salt is provided, - wherein a precipitation reaction is carried out by adding a base to the aqueous solution (9) to form crystal nuclei (10) from transition metal compounds, - wherein the crystal nuclei (10) resulting from the precipitation reaction are doped with monovalent cations (12), - wherein a further precipitation reaction is carried out, in the course of which precursor particles (14) are formed from the doped crystal nuclei (10), and - wherein the precursor particles (14) are calcined.

11. Method for producing secondary particles (6) according to one of claims 1 to 7 - wherein an aqueous solution (9) of a transition metal salt is provided, - wherein a precipitation reaction is carried out by adding a base to the aqueous solution (9) to form crystal nuclei (10) from transition metal compounds, - wherein the crystal nuclei (10) resulting from the precipitation reaction are coated, - wherein a further precipitation reaction is carried out, in the course of which precursor particles (14) are formed from the coated crystal nuclei (10), and - wherein the precursor particles (14) are calcined. - wherein the precursor particles (14) are calcined.

12. Method for producing the secondary particles (6) according to one of claims 1 to 7 - wherein an aqueous solution (9) of a transition metal salt is provided, - wherein a precipitation reaction is carried out by adding a base to the aqueous solution (9) to form crystal nuclei (10) from the transition metal compound, - wherein the crystal nuclei (10) resulting from the precipitation reaction are compressed uniaxially into mutual alignment and sintered, in the process forming precursor particles (14), - wherein the precursor particles (14) are calcined.

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