Active Cathode Material for Lithium-Ion Cells and Lithium-Ion Cell Having High Energy Density

Abstract

An active cathode material for a lithium-ion cell includes a mixture of particles having particle sizes distributed according to a bimodal particle size distribution which has a first modal value and a second modal value, where the first modal value is greater than the second modal value. The mixture of particles comprises first particles and second particles that intercalate lithium or are configured to intercalate lithium. The first particles have a particle size which is greater than a predefined first particle size range limit. The second particles have a particle size which is less than a predefined second particle size range limit. The second predefined particle size range limit is less than the predefined first particle size range limit. A particle size distribution of each of the first particles and the second particles is unimodal. The second particles have a mechanical strength higher than that of the first particles.

Claims

1-15. (canceled)

16. An active cathode material for a lithium-ion cell, the active cathode material comprising: a mixture of particles having particle sizes distributed according to a bimodal particle size distribution with a first modal value (M1) and a second modal value (M2), the first modal value (M1) being greater than the second modal value (M2), the mixture of particles comprising first particles and second particles which intercalate lithium or are configured to intercalate lithium, wherein the first particles have a particle size greater than a predefined first particle size range limit (G1), the second particles have a particle size smaller than a predefined second particle size range limit (G2), the second predefined particle size range limit (G2) is lower than the predefined first particle size range limit (G1), a particle size distribution of the first particles is unimodal and has a modal value equal to the first modal value (M1), a particle size distribution of the second particles is unimodal and has a modal value equal to the second model value (M2), the second particles have a mechanical strength higher than a mechanical strength of the first particles.

17. The active cathode material according to claim 16, wherein the second particles each have a core coated with a surface layer, and wherein the surface layer gives the second particles the mechanical strength higher than the mechanical strength of the first particles, and the core intercalates lithium or is configured to intercalate lithium.

18. The active cathode material according to claim 17, wherein the mechanical strength of the second particles is achieved through appropriate selection of one of the following or a combination thereof: chemical substance of the surface layer, thickness of the surface layer, porosity of the surface layer.

19. The active cathode material according to claim 16, wherein the second particles are each doped with a dopant which gives the second particles the mechanical strength higher than the mechanical strength of the first particles.

20. The active cathode material according to claim 16, wherein the first particles have a first porosity and the second particles have a second porosity, and the first porosity is greater than the second porosity.

21. The active cathode material according to claim 16, wherein the particle size distribution of the first particles has a first full width at half-maximum (HWB1); the particle size distribution of the second particles has a second full width at half-maximum (HWB2); the predefined first particle size range limit (G1) is equal to a difference between the first modal value (M1) and half the first full width at half-maximum (HWB1); and the predefined second particle size range limit (G2) is equal to a sum total between the second modal value (M2) and half the second full width at half-maximum (HWB2).

22. The active cathode material according to claim 21, wherein the first modal value (M1) is in a range between 7 .Math.m and 14 .Math.m, and the second modal value (M2) is in a range between 1 .Math.m and 6 .Math.m.

23. A process for producing an active cathode material for a lithium-ion cell, the process comprising: providing a first powder comprising first particles having a particle size distributed according to a first particle size distribution, the first particles intercalating lithium or being configured to intercalate lithium, wherein a median value D50 of the first particle size distribution is in a range between 7 .Math.m and 14 .Math.m and a span of the first particle size distribution is less than 1; providing a second powder comprising second particles having a particle size distributed according to a second particle size distribution, the second particles intercalating lithium or being configured to intercalate lithium, wherein a median value D50 of the second particle size distribution is in a range between 1 .Math.m and 6 .Math.m, a span of the second particle size distribution is less than 1, and the second particles have a mechanical strength higher than a mechanical strength of the first particles; and mixing the first powder and the second powder to give a mixture having a bimodal particle distribution.

24. The process according to claim 23, wherein the providing of the second powder further comprises: coating the second particles with a surface layer, whereby the second particles have the mechanical strength higher than the mechanical strength of the first particles.

25. The process according to claim 23, wherein the providing of the second powder further comprises: doping the second particles with a dopant, whereby the second particles have the mechanical strength higher than the mechanical strength of the first particles.

26. The process according to claim 23, wherein the first particles have a first porosity and the second particles have a second porosity, and the first porosity is greater than the second porosity.

27. An active cathode material produced by the process according to claim 23.

28. A lithium-ion cell, comprising: a first electrode; a second electrode; and a separator separating the first electrode and the second electrode, wherein the first electrode has a higher potential than the second electrode, and the first electrode has a binder-bound, pressed active cathode material according to claim 1.

29. A battery comprising a lithium-ion cell according to claim 28.

30. A vehicle comprising a battery according to claim 29.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0085] FIG. 1 shows schematically an active cathode material for a lithium-ion cell according to the present disclosure;

[0086] FIG. 2 shows schematically a bimodal particle size distribution;

[0087] FIG. 3 shows schematically a second (small) particle of an active cathode material according to one embodiment;

[0088] FIG. 4 shows schematically the internal structure of a particle of an active cathode material;

[0089] FIG. 5 shows schematically one process of the disclosure for producing an active cathode material for a lithium-ion cell; and

[0090] FIG. 6 shows schematically another process of the disclosure for producing an active cathode material for a lithium-ion cell.

[0091] The figures consistently use the same reference symbols for the same or mutually corresponding elements.

DETAILED DESCRIPTION OF THE DRAWINGS

[0092] FIG. 1 shows schematically an active cathode material for a lithium-ion cell according to the present disclosure. This material comprises a mixture 100 of particles 101 and 102, whose respective particle sizes are distributed according to a bimodal particle size distribution 200 and which intercalate lithium or are configured to intercalate lithium.

[0093] The bimodal particle size distribution 200 is shown schematically in FIG. 2. It has two peaks with respective modal values M1 and M2. The first modal value M1 represents the particle size at which the first peak (the right-hand peak in FIG. 2) reaches its maximum; and the second modal value M2 represents the particle size at which the second peak (the lefthand peak) reaches its maximum. The first modal value M1 is greater than the second modal value M2; M1 > M2. The width of the first and second peaks may each be indicated by the full width at half-maximum HWB1 and HWB2 respectively. The first full width at half-maximum HWB1 represents the difference between the two particle sizes, for which the frequency of the particle sizes distributed around the first peak has dropped to half of its maximum; and the full width at half-maximum HWB2 represents the difference between the two particle sizes, for which the frequency of the particle sizes distributed around the second peak has dropped to half of its maximum.

[0094] First particles (or large particles) of the mixture 100 are, hereinafter, all particles having a particle size which is greater than a predefined first particle size range G1; and second particles (or small particles) of the mixture 100, hereinafter, are all particles which have a particle size less than a predefined second particle size range limit G2. The second particle size range limit G2 is less than the first particle size range limit G1; G2 < G1. The particle size distribution of the first particles is unimodal and as a modal value has the first modal value M1 of the bimodal distribution 200 and the particle size distribution of the second particles is unimodal and has a modal value of the second modal value M2 of the bimodal distribution 200. Advantageously, as shown in FIG. 2, the first particle size range limit is less than the first modal value; G1 < M1; and the second particle size range limit is greater than the second modal value; G2 > M2. For example, the predefined first particle size range limit may be equal to the difference between the first modal value and half the first full width at half-maximum; G1 = M1-HWB1/2; and the predefined second particle size range limit may be equal to the sum total between the second modal value and half the second full width at half-maximum; G2 = M2+HWB2/2.

[0095] The modal values M1 and M2 and also the full widths at half-maximum HWB1 and HWB2 are advantageously selected such that the second particles find space, and are disposed in, the cavities 105 formed by the first particles. This is the case, for example, when the first modal value M1 is in a range between 7 .Math.m and 14 .Math.m, the first full width at half-maximum HWB1 is in a range between 1 .Math.m and 4 .Math.m, the second modal value M2 is in a range between 1 .Math.m and 6 .Math.m, and the second full width at half-maximum HWB2 is in a range between 1 .Math.m and 4 .Math.m. This allows the density of the active cathode material to be increased.

[0096] In accordance with the disclosure, the second particles are crystalline and each second (small) particle has a mechanical strength which is higher than the mechanical strength of any first (large) particle. As a result, during the calendering (pressing) of a cathode material which is applied to a current collector and which contains the active cathode material 100, the small particles are not crushed by the large particles or by the calender roll; and a lithium-ion cell which contains a cathode comprising the active cathode material 100 is substantially improved.

[0097] A higher mechanical strength can be given to a second particle by a surface layer which overlies the second particle and is configured correspondingly. FIG. 3 shows schematically a second particle 102′, which comprises a core 103 coated with a surface layer 104, where the surface layer 104 surrounds the entire surface of the core 103, the thickness d of the surface layer 104 is substantially constant, and the core 103 intercalates lithium or is configured to intercalate lithium. The surface layer 104 is configured such that it gives the second particle 102′ a higher mechanical strength than that possessed by any first particle 101. This may be achieved through appropriate selection of one or more of the following parameters: chemical substance of the surface layer 104, thickness of the surface layer 104, porosity of the surface layer 104. The surface layer 104 need not cover the entire surface of the core 104 in order to give the respective second particle a higher strength.

[0098] The active cathode material 100 advantageously comprises first particles 101 and second particles 102′; where the core 103 of the second particles 102′ and the first particles 101 each comprise the chemical substance Li.sub.1(Ni.sub.xCo.sub.yMn.sub.zAl.sub.r)O.sub.2 where (y+z+r) = (1-x); the surface layer 104 comprises one of the following chemical substances: LiF, NH.sub.4F, TiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2, ZnO, AlPO.sub.4, Li.sub.2TiO.sub.3, Li.sub.2ZrO.sub.3; and the thickness of the surface layer surrounding the surface of the core 103 is less than 500 nm.

[0099] A higher mechanical strength may also be given to a second particle by a suitable dopant with which the particle is doped. The second particles 102 of the active cathode material 100 may therefore be doped with a dopant which gives each second particle 102 a higher mechanical strength than that possessed by any first particle 101.

[0100] The active cathode material 100 advantageously comprises first particles and second particles, where the first particles and the second particles each comprise the chemical substance Li.sub.1(Ni.sub.xCo.sub.yMn.sub.zAl.sub.r)O.sub.2 where (y+z+r) = (1-x), and the second particles are doped with one of the following dopants: Al, Ti, Si, Mg, Nb, Mo, Fe, Cu, Cr, Zn.

[0101] A higher mechanical strength may also be given to a second particle by a suitably configured porosity of the second particle. FIG. 4 shows schematically a particle 400 of the active cathode material 100. This may be a first or second particle. The particle 400 comprises one or more, usually crystalline subparticles 401 (which are also referred to as primary particles), which are connected to one another and between which there may be cavities 402. As a result, the density (bulk density) of the particle 400 (which is also referred to as secondary particle) can be less than the density (true or crystallographic density) of a primary particle 401. The porosity of a particle, expressed as a percentage below, corresponds to the following formula:

[00001]$\text{Porosity[\%] = [1-(bulk density/true density)]}\times \text{100}$

[0102] In the active cathode material 100, the first particles may have a higher porosity than the second particles. In that case the porosity of the first particles and/or of the second particles is such that each second particle 102 has a higher mechanical strength than any first particle.

[0103] The active cathode material 100 advantageously comprises first particles and second particles, where the first particles 101 and the second particles 102 each comprise the chemical substance Li.sub.1Ni.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2, the porosity of a first particle is in a range between 4% and 40%, and the porosity of a second particle is in a range between 2% and 10%.

[0104] FIG. 5 shows schematically one process of the disclosure for producing an active cathode material for a lithium-ion cell.

[0105] In a step S501 a first powder is provided, comprising first particles whose particle size is distributed according to a first particle size distribution, and which intercalate lithium or are configured to intercalate lithium. The first particle size distribution is preferably unimodal, has a median value D50 which is in a range between 7 .Math.m and 14 .Math.m, and has a span which is less than one. The median value D50 of the first particle size distribution is preferably in a range between 10 .Math.m and 13 .Math.m.

[0106] In a step S502, a second powder is provided, which comprises second particles, yet to be coated, whose particle size is distributed according to a second particle size distribution, and which intercalate lithium or are configured to intercalate lithium. The second particle size distribution is preferably unimodal. The second particles, yet to be coated, may be uncoated particles each formed of only one or of two or more primary particles. The second particles yet to be coated may alternatively be particles which are already surface-coated.

[0107] In a step S503, the second particles yet to be coated are coated with a surface layer which surrounds their surface at least partly, preferably entirely. During coating, the surface layer is configured such that it gives the second particle coated with it a mechanical strength which is higher than that of any particle of the first powder. More particularly, this may be achieved through suitable selection of one or more of the following parameters of the surface layer: chemical substance, thickness, and/or porosity. After coating, the particle size of the second particles (coated with the surface layer) is distributed according to a unimodal distribution corresponding to the second particle size distribution. This distribution has a median value D50 which is in a range between 1 .Math.m and 6 .Math.m and a span which is less than one. The median value D50 is preferably in a range between 2 .Math.m and 4 .Math.m.

[0108] The coating may take place by wet-chemical treatment of the second particles for coating, in a solution which contains the chemical substance of the surface layer to be formed. Coating may also be achieved by mixing the second powder together with a powder which contains the chemical substance of the surface layer to be formed, and then carrying out calcining.

[0109] In a step S504, the first powder is mixed with the second powder surface-coated in step S503.

[0110] Advantageously, the particles of the first powder and the yet-to-be-coated particles of the second powder each comprise Li.sub.1(Ni.sub.xCo.sub.yMn.sub.zAl.sub.r)O.sub.2 where (y+z+r) = (1-x); and, after coating, the second particles each have a surface layer which contains one of the following chemical substances: LiF, NH.sub.4F, TiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2, ZnO, AlPO.sub.4, Li.sub.2TiO.sub.3, Li.sub.2ZrO.sub.3; and the surface layer has a layer thickness of less than 500 nm.

[0111] FIG. 6 shows schematically another process of the disclosure for producing an active cathode material for a lithium-ion cell.

[0112] In a step S601 a first powder is provided, comprising first particles whose particle size is distributed according to a first particle size distribution, and which intercalate lithium or are configured to intercalate lithium. The first particle size distribution is preferably unimodal, has a median value D50 which is in a range between 7 .Math.m and 14 .Math.m, and has a span which is less than one. The median value D50 of the first particle size distribution is preferably in a range between 10 .Math.m and 13 .Math.m.

[0113] In a step S602, a second powder is provided, which comprises second particles, yet to be doped, whose particle size is distributed according to a second particle size distribution, and which intercalate lithium or are configured to intercalate lithium. The second particle size distribution is preferably unimodal, has a median value D50 which is in a range between 1 .Math.m and 6 .Math.m, and has a span which is less than one. The median value D50 of the second particle size distribution is preferably in a range between 2 .Math.m and 4 .Math.m.

[0114] In a step S603, the second particles, still to be doped, are doped with a dopant which gives the second particles doped with the dopant a mechanical strength which is higher than that of any particle of the first powder.

[0115] In a step S604, the first powder is mixed with the second powder doped in step S603.

[0116] Advantageously, the particles of the first powder and the yet-to-be-doped particles of the second powder each comprise Li.sub.1(Ni.sub.xCo.sub.yMn.sub.zAl.sub.r)O.sub.2 where (y+z+r) = (1-x); and the dopant with which the particles of the second powder are doped is one of the following substances: Al, Ti, Si, Mg, Nb, Mo, Fe, Cu, Cr, Zn.

[0117] Whereas the preceding text has described at least one illustrative embodiment, it should be noted that a large number of variations thereon exist. It should also be borne in mind here that the illustrative embodiments described only represent nonlimiting examples, and there is no intention thereby to restrict the scope, the applicability or the configuration of the devices and processes described here. Instead, the description above will give the skilled person instructions regarding the implementation of at least one illustrative embodiment, on the understanding that various changes may be made in the functioning and the arrangement of the elements described in an illustrative embodiment, without departure from the subject matter laid down in each of the appended claims, or from the legal equivalents of that subject matter.

TABLE-US-00001 LIST OF REFERENCE NUMERALS 100 Active cathode material 101 First (large) particles 102, 102′ Second (small) particles 103 Core of a second particle 104 Surface layer of a second particle 105 Cavities 200 Bimodal particle size distribution 400 Particles of an active cathode material (secondary particles) 401 Primary particles 402 Cavities between primary particles