Method and system for dry surface doping of cathode materials

Abstract

Doped cathode materials for lithium-ion batteries are disclosed. Additionally, methods and systems for doping cathode materials for use in lithium-ion batteries are provided. In one example, the doping can be a dry surface doping process. In some examples, dopants can stabilize the crystalline structure of the cathode material and reduce side reactions with the electrolyte compared to undoped cathode materials. Therefore, cycling performance and capacity retention can be improved compared to undoped cathode materials. Furthermore, in some examples, the doped cathode materials produced by the dry surface doping process can improve cycling performance and capacity retention compared to equivalent doped cathode materials produced by wet surface doping processes.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62 / 845,835, entitled "METHOD AND SYSTEM FOR DRY SURFACE DOPING OF CATHODE MATERIALS," filed May 9, 2019. The entire contents of the above-identified application are incorporated herein by reference for all purposes.

[0002] Field This description relates generally to methods and systems for dry surface doping of cathode materials for use in lithium ion batteries.

[0003] Background and Overview Lithium-ion, or Li-ion, or Li + The batteries offer desirable properties such as high energy density, high power, and long cycle life, leading to their widespread use, for example as secondary batteries in portable electronic devices or electric vehicles.

[0004] During charging of a Li-ion battery, the power source can facilitate the movement of Li ions into and out of the crystal structure of the internal nickel-based cathode material. However, during such delithiation / lithiation, or charge / discharge, processes, changes in the lattice parameters of the crystal structure of the cathode material result in corresponding contraction and expansion of the lattice. The resulting cumulative effect of stress and strain leads to the formation and growth of cracks in the cathode material. Furthermore, the migration of Li ions from said cathode material can cause nickel (Ni) ions to assume a highly reactive valence state, disrupting the crystal structure of the cathode material. In such delithiated cathodes, Ni ions are more likely to be in a highly reactive valence state than Li ions in the cathode material due to the similar ionic radii between the two ions (e.g., Ni 2+ The ionic radius of Li is about 0.69 Å. + The ionic radius of Li is about 0.72 Å. +Thus, a spinel or rocksalt phase is formed and during subsequent lithiation, Li + The transport of ions back to their original sites may be blocked. Each of the above problems may result in capacity degradation, increased resistance, and short cycle life.

[0005] Conventional efforts to address the above-mentioned problems include doping of cations or anions (variously referred to herein as dopants, doping agents, or doping elements) into the crystal structure of the cathode material. The ultimate goal is to stabilize the crystal structure of the cathode material, for example, by inhibiting phase transformations during the charge / discharge process. Traditionally, such structure stabilization can be achieved by one of two main bulk doping approaches. First, the wet approach involves adding a dopant (usually a salt) to a precursor solution during the preparation of the cathode material, so that said dopant precipitates therein along with the precursor. Second, the dry approach involves sintering the dopant (usually a salt, oxide, or hydroxide) with the precursor and a lithium source to obtain the final cathode powder.

[0006] However, in each of the above approaches, the doping elements are electrochemically inactive and may reduce the specific capacity of the cathode material as a whole. Since at least a portion of the surface of the cathode material is exposed to the electrolyte in a Li-ion battery and is therefore more vulnerable to lattice volume changes and phase changes than the portion of the cathode material not exposed to the electrolyte, limiting doping to the cathode material surface can minimize capacity sacrifice while achieving structural stabilization. Thus, dopants can be mixed directly with the synthesized cathode material to achieve surface doping. Since such cathode materials have a denser crystal structure than the precursors used in their synthesis, dopants may be more concentrated at the surface, thus maximizing the surface stabilization effect and minimizing capacity sacrifice.

[0007] In contrast to the bulk doping approaches discussed above, surface doping processes can substantially confine the dopant to the surface of the cathode material. Conventional surface doping processes utilize a wet approach, for example, mixing the cathode material with the dopant in an aqueous or non-aqueous solution, then evaporating the solvent and sintering. However, the effectiveness of such wet surface doping processes can be limited by at least three issues. First, if the solvent used is water, the structure and composition of the cathode material can be negatively affected. Specifically, Li ions can be leached by water, resulting in Li deficiency at the cathode material surface, which can be accompanied by a concomitant phase change. Second, very high costs can be incurred during the manufacturing process if the solvent used is instead an organic solvent, which is often expensive. Third, manufacturing process costs can be further increased due to the evaporation step required to remove the solvent (whether water or an organic solvent is utilized) or to remove it from the waste management process.

[0008] One possible alternative to the wet surface doping process is a dry approach, which can solve at least some of the problems mentioned above. The dry surface doping process can include a mixing step, in which the cathode material is mixed with a dopant, and then a calcination / sintering step, in which the resulting mixture is calcine / sintered. If a salt is utilized as a dopant in such a surface doping process, the efficiency of the process can be limited in at least two ways. First, the melting / evaporation temperature of the dopant salt can be lower than or close to the doping reaction temperature, which can lead to inaccurate dosage due to evaporation of the dopant salt. Second, the solid-state reaction between the dopant salt and the cathode material can be limited by the size of the dopant salt, which is usually tens of microns or more and is not uniformly distributed.

[0009] The present inventors have recognized the above problems resulting from the surface doping process using dopant salts. To that end, a dry surface doping process using metal oxides as dopants is provided to overcome at least some of the difficulties presented herein. Specifically, the metal oxide dopant can be dry mixed with the cathode material and then calcined in dry air or oxygen. Such a dry surface doping process has at least four advantages. First, contact between the cathode material surface and the solvent can be eliminated, preventing structural damage caused by the solvent or phase change therefrom. Second, one or more evaporation steps can be eliminated, as well as waste management steps. Third, the metal oxide dopant can have a higher melting temperature compared to the melting / evaporation temperature of a given dopant salt. Thus, accurate dosage can be guaranteed since there is no melting / evaporation of the metal oxide dopant during the dry surface doping process. Fourth, the metal oxide dopant can be produced in a properly tailored, smaller particle size with a uniform size distribution for a given dopant salt. Therefore, a solid state reaction between the metal oxide dopant and the cathode material is more favorable.

[0010] Cathode configurations are further provided as detailed herein. In one example, a lithium nickel manganese cobalt oxide compound (NMC) can be dry surface doped with one or more metal dopants including metal ions with an ionic radius greater than 0.50 Å. In one example, the metal dopant can be Nd (Nd 3+has a relatively large ionic radius of 0.98 Å). Thus, Nd can act as a "pillar" to support and hold the crystal structure of the cathode material during delithiation / lithiation. Nd doped into the crystal structure of the cathode material (doped Nd) can help suppress the volume change and phase change of the lattice and suppress the formation and growth of cracks. The suppression of crack formation / growth can reduce the generation of new cathode material surface exposed to electrolyte in the battery due to cracking. Therefore, fewer side reactions occur between the electrolyte and the cathode material, thereby limiting the capacity fade. Furthermore, the improved stability of the crystal structure of the cathode material can improve the capacity retention during cycling of the battery.

[0011] It should be understood that the above Summary is provided to introduce in a simplified form a selection of concepts that are further described in the Detailed Description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the Detailed Description. Moreover, the claimed subject matter is not limited to implementations that solve the disadvantages noted above or in any part of this disclosure. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 illustrates a method for a dry surface doping process.

[0013] [Diagram 2] FIG. 2 shows a schematic diagram of the dry surface doping process and its products.

[0014] [Diagram 3] FIG. 3 shows the thermogravimetric analysis (TGA) plots of lithium nickel manganese cobalt oxide (NMC) and mixtures of NMC with Nd2O3.

[0015] [Figure 4]FIG. 4 shows scanning electron microscope (SEM) images of NMC particles mixed with Nd2O3 particles before and after calcination.

[0016] [Diagram 5] Figure 5 shows the X-ray diffraction (XRD) patterns of NMC, Nd-doped NMC, Nd2NiO4, and Nd2O3.

[0017] [Figure 6] FIG. 6 shows the first charge capacity (FCC) and first discharge capacity (FDC) in half coin cells for NMC, Nd-doped NMC manufactured by the wet surface doping process, or wet Nd-doped NMC, and Nd-doped NMC manufactured by the dry surface doping process, or dry Nd-doped NMC.

[0018] [Figure 7] FIG. 7 shows the rate capabilities in half coin cells for NMC, wet Nd-doped NMC, and dry Nd-doped NMC.

[0019] [Figure 8] FIG. 8 shows the capacity retention and specific capacity during cycling in half coin cells for NMC, wet Nd-doped NMC, and dry Nd-doped NMC.

[0020] [Figure 9] FIG. 9 shows the FCC and FDC in single layer pouch (SLP) cells for NMC, wet Nd-doped NMC, and dry Nd-doped NMC.

[0021] [Figure 10] FIG. 10 shows the capacity retention and specific discharge capacity during cycling in SLP cells for NMC, wet Nd-doped NMC, and dry Nd-doped NMC.

[0022] [Figure 11] FIG. 11 shows the direct current resistance (DCR) growth during cycling in SLP cells for NMC, wet Nd-doped NMC, and dry Nd-doped NMC.

[0023] [Figure 12] Figure 12 shows cross-sectional SEM images of cracks formed in NMC and dry Nd-doped NMC after cycling in an SLP cell.

[0024] [Figure 13] Figure 13 shows the evolution of the c-lattice parameters during initial charge and discharge in half-coin cells for NMC and dry Nd-doped NMC.

[0025] [Figure 14] FIG. 14 shows the capacity retention during cycling in half-coin cells for NMC and dry Nd-doped NMC at various molar ratios of Nd to NMC.

[0026] [Figure 15] FIG. 15 shows the specific capacity during cycling in half-coin cells for NMC and dry Nd-doped NMC, where two sizes of dopant precursor particles were used in the dry surface doping process.

[0027] Detailed Description The following description relates to a system and method for dry surface doping of a cathode material with a dopant, such as a metal dopant. The cathode material can be a lithiated compound, such as lithium nickel manganese cobalt oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium rich metal oxide, lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium iron phosphate (LFP), or a combination thereof. In some examples, the dry surface doping can be applied to an anode material, such as lithium titanate oxide (LTO). The metal dopant can be a metal ion with an ionic radius of greater than about 0.50 Å, such as neodymium (Nd). As used herein, "about" in referring to a numerical value can include a deviation of 5% or less.

[0028] In some examples, the volume of the cathode material may be divided into a core or core region and a surface or surface region. Thus, dry surface doping may include doping a metal dopant into the surface of the cathode material. Dry surface doping of the cathode material with a metal dopant may produce a doped cathode material with improved cycling performance and capacity retention compared to an undoped cathode material. In some examples, the doped cathode material produced by the dry surface doping method or the dry doped cathode material may have improved cycling performance and capacity retention compared to a comparable doped cathode material produced by the wet surface doping method or the wet doped cathode material.

[0029] Figures 1 and 2 illustrate a dry surface doping process for doping a cathode material with a dopant (e.g., a metal dopant). Figure 1 illustrates the dry surface doping process as a flow chart. Figure 2 illustrates the dry surface doping process and its product (i.e., the doped cathode material) as a schematic diagram.

[0030] Figure 3 shows the results of undoped NMC and NMC with Nd 2 O 3 Figure 4 shows the TGA plots of the mixture of Nd and NdO before and after calcination in the dry surface doping process. From the TGA plots, the appropriate calcination temperature for the dry surface doping process can be determined. 2 O 3 The SEM images of NMC particles mixed with Nd 2 O 3 The particles are no longer visible after firing. Figure 5 shows the results of the NMC, Nd-doped NMC, and Nd 2 NiO 4 and Nd 2 O 3 As shown, the XRD patterns of Nd 2 O 3 is not detected in Nd-doped NMC.

[0031] Figures 6-8 show examples of the electrochemical performance of half-coin cells containing NMC, Nd-doped NMC fabricated by a wet surface doping process (wet Nd-doped NMC), or Nd-doped NMC fabricated by a dry surface doping process (dry Nd-doped NMC). Figure 6 shows FCC and FDC, Figure 7 shows rate capability, and Figure 8 shows capacity retention and specific capacity during cycling. In each example, the dry doped NMC maintains or improves the electrochemical performance of the NMC and wet Nd-doped NMC.

[0032] Figures 9-11 show examples of electrochemical performance of SLP cells containing NMC, wet Nd-doped NMC, or dry Nd-doped NMC. Figure 9 shows FCC and FDC, Figure 10 shows capacity retention and specific discharge capacity during cycling, and Figure 11 shows DCR growth during cycling. In each example, the dry doped NMC maintains or improves the electrochemical performance of NMC and wet Nd-doped NMC.

[0033] FIG. 12 shows cross-sectional images of cracks formed in NMC and dry Nd-doped NMC after cycling in SLP cells. As shown, dry Nd-doped NMC has fewer and smaller cracks formed compared to undoped NMC. FIG. 13 shows the change in c-lattice parameter during initial charge and discharge in half coin cells for NMC and dry Nd-doped NMC. The smaller change in c-lattice parameter of dry Nd-doped NMC compared to undoped NMC indicates less expansion and contraction of the lattice structure of each sample. FIG. 14 shows the capacity retention during cycling in half coin cells for NMC and dry Nd-doped NMC with various molar ratios of Nd to NMC, showing the optimum value of the molar ratio. FIG. 15 shows the specific capacity during cycling in half coin cells for NMC and dry Nd-doped NMC where two sizes of dopant precursor particles were used in the dry surface doping process. As shown, each size of dopant precursor particle used resulted in dry Nd-doped NMC samples with substantially similar specific capacitance over cycling.

[0034] Referring now to FIG. 1, there is shown a method 100 for producing a doped cathode material by a dry surface doping process, including obtaining a cathode material and a dopant precursor particle, mixing the cathode material and the dopant precursor particle to obtain a mixture, and calcining the mixture in a dry air or dry oxygen atmosphere to obtain a doped cathode material.

[0035] At 102, the cathode material and dopant precursor particles can be obtained. The cathode material can be NMC, NCA, lithium rich metal oxide, LMO, LMNO, LiMPO 4 , or a combination thereof. In one example, the cathode material can be NMC, where NMC is LiNi 0.64 Mn 0.2 Co 0.16 O 2 and the dopant precursor particles can be Nd2 O 3 In some instances, dry surface doping can alternatively be applied to the anode material, such as LTO.

[0036] In one example, the cathode material can include NMC. NMC is LiNi x Mn y Co 1-x-y O 2 (0≦x≦1, 0≦y≦1, 0≦x+y≦1). Exemplary compositions of NMC include LiNi 0.333 Mn 0.333 Co 0.333 O 2 (NMC111), LiNi 0.5 Mn 0.2 Co 0.3 O 2 (NMC523), LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), and / or LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811). In one example, the NMC can include LiNi 0.64 Mn 0.2 Co 0.16 O 2 In another example, the cathode material can include an NCA. The NCA can be LiNi x Co y Al 1-x-y O 2 (0≦x≦1, 0≦y≦1, 0≦x+y≦1). In another example, the cathode material can include a lithium-rich metal oxide having the formula: xLi 2 MnO 3 (1-x)LiNi y Mn z Co 1-y-z O 2(0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦y+z≦1). In another example, the cathode material can include LMO. In one example, the LMO is LiMn 2 O 4 In another example, the cathode material can include LNMO. LNMO can be LiNi x Mn 2-x O 4 (0≦x≦2). In another example, the cathode material can have a structural formula of LiMPO 4 where M can include Fe, Ni, Co, or Mn, i.e., the cathode material can include LiFePO 4 , LiNiPO 4 , LiCoPO 4 Or LiMnPO 4 In some examples, the anode material can be used in place of the cathode material. In one example, the anode material can include LTO. In one example, LTO is Li 4 Ti 5 O 12 The compound may have the structural formula:

[0037] In some examples, the cathode material can be in the form of particles. In one example, the particles can be microscale particles. In some examples, the size of the cathode material particles can be greater than about 0.5 μm and less than about 20 μm.

[0038] In some examples, the dopant precursor particles can be composed of a dopant precursor, such as a metal oxide precursor or a metal hydroxide precursor. In additional or alternative examples, the dopant precursor can include one or more compounds, including, for example, one or more of the following: dopant oxide, dopant acetate, dopant nitride, dopant sulfate, dopant fluoride, dopant nitrate, dopant phosphide, dopant sulfide, dopant iodide, dopant phosphate, dopant carbonate, dopant oxalate, dopant acetylacetonate, and combinations thereof. As a further example, the dopant precursor can include one or more compounds, such as neodymium oxide, neodymium acetate, neodymium nitride, neodymium sulfate, neodymium fluoride, neodymium nitrate, neodymium phosphide, neodymium sulfide, neodymium iodide, neodymium phosphate, neodymium carbonate, neodymium oxalate, neodymium acetylacetonate, and combinations thereof. In some examples, the metal oxide precursor comprises one or more metal oxides. In some examples, the metal hydroxide precursor comprises one or more metal hydroxides. The one or more metal oxides can include any metal oxide that can react with the cathode material at a temperature less than 950° C. The one or more metal hydroxides can include any metal hydroxide that can react with the cathode material at a temperature less than 950° C. By way of example, the dopant precursor can include one or more alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides, alkaline earth metal hydroxides, rare earth oxides, rare earth hydroxides, transition metal oxides, and transition metal hydroxides. In some examples, the one or more metal oxides can include one or more Na 2 O,Na 2 O 2 ,SiO 2 ,K.O. 2 ,K 2 O 2 ,CaO,RuO 2 ,Ta 2 O 5 ,WO 3 ,CoO,Co 3O 4 ,Ga 2 O 3 ,Al 2 O 3 ,ZrO 2 ,MgO,Sc 2 O 3 ,FeO,Fe 2 O 3 ,V 2 O 5 ,NbO,NbO 2 , Nb 2 O 5 ,Cu 2 O, CuO, ZnO, Rh 2 O 3 ,RhO 2 ,TiO 2 ,MoO 2 ,MoO 3 ,CrO,Cr 2 O 3 ,CrO 2 ,CrO 3 ,MnO,Mn 3 O 4 ,Mn 2 O 3 ,GeO,Rb 2 O,SrO,Y 2 O 3 ,In 2 O 3 ,La 2 O 3 ,CeO 2 ,Pr 2 O 3 ,Nd 2 O 3 , Sm 2 O 3 ,EU 2 O 3 ,Tb 2 O 3 , and Tb 4 O 7 In one example, the one or more metal oxides may include Nd 2 O 3 In some examples, the one or more metal hydroxides can include one or more of NaOH, Si(OH), 4 ,KOH,Ca(OH) 2 ,Ru(OH) 3 ,Ru(OH) 4, Ta(OH) 5 , W(OH) 6 , Co(OH) 2 , Co(OH) 3 , Ga(OH) 3 , Al(OH) 3 , Zr(OH) 4 , Mg(OH) 2 , Sc(OH) 3 , Fe(OH) 2 , Fe(OH) 3 , V(OH) 5 , Nb(OH) 2 , Nb(OH) 5 , CuOH, Cu(OH) 2 , Zn(OH) 2 , Rh(OH) 3 , Ti(OH) 4 , Mo(OH) 4 , Mn(OH) 6 , Cr(OH) 2 , Cr(OH) 3 , Cr(OH) 4 , Mn(OH) 2 , Mn(OH) 3 , Ge(OH) 2 , RbOH, Sr(OH) 2 , Y(OH) 3 , In(OH) 3 , La(OH) 3 , Ce(OH) 4 , Pr(OH) 3 , Nd(OH) 3 , Sm(OH) 3 , Eu(OH) 3 , and Tb(OH) 3In some examples, the one or more metal oxides and the one or more metal hydroxides can each include a metal ion having an ionic radius of greater than about 0.50 Å. In some examples, the one or more metal oxides and the one or more metal hydroxides can each include a metal ion having an ionic radius of greater than about 0.60 Å. In some examples, the one or more metal oxides and the one or more metal hydroxides can each include a metal ion having an ionic radius of greater than about 0.70 Å. In some examples, the one or more metal oxides and the one or more metal hydroxides can each include a metal ion having an ionic radius of greater than about 0.80 Å. In some examples, the one or more metal oxides and the one or more metal hydroxides can each include a metal ion having an ionic radius of greater than about 0.90 Å.

[0039] In some examples, the size of the dopant precursor particles may be greater than about 1 nm and less than about 10 μm. In some examples, the size of the dopant precursor particles may be greater than about 5 nm and less than about 5 μm. In some examples, the size of the dopant precursor particles may be greater than about 80 nm and less than about 720 nm. In some examples, the size of the dopant precursor particles may be greater than about 80 nm and less than about 400 nm. In some examples, the size of the dopant precursor particles may be greater than about 80 nm and less than about 300 nm. In some examples, the size of the dopant precursor particles may be greater than about 80 nm and less than about 200 nm. In some examples, the size of the dopant precursor particles may be greater than about 80 nm and less than about 140 nm. In some examples, the size of the dopant precursor particles may be greater than about 400 nm and less than about 720 nm. In some examples, the size of the dopant precursor particles may be greater than about 500 nm and less than about 720 nm. In some examples, the size of the dopant precursor particles may be greater than about 600 nm and less than about 720 nm. In some examples, the size of the dopant precursor particles may be greater than about 660 nm and less than about 720 nm.

[0040] The dopant precursor particles can be ground to a predetermined average size. In some examples, the dopant precursor particles can be ground via a ball or attrition milling process for a period of time selected depending on the desired size. In one example, the dopant precursor particles can be ground to a finer powder having an average size of less than 1 μm. In one example, a volume can be half-filled with inert media, such as YTZ® grinding media, and dopant precursor particles of size <5 mm. The volume can be ground to produce a finer powder having an average size of less than 1 μm.

[0041] At 104, the cathode material and the dopant precursor particles can be dry mixed or dry blended (i.e., mixed or blended substantially free of solvent) to obtain a mixture, dry mixture, or pre-fired mixture. In some examples, the dry mixing can include mixing in a roller mill mixer to achieve a uniform dispersion or distribution of the dopant precursor particles on the surface or surface region of the cathode material. Further, in some examples, following mixing, the dopant precursor particles can protrude from the cathode material surface or can be embedded in the cathode material surface. In some examples, following mixing, the dopant precursor particles can protrude from the cathode material surface by a distance of 0 to 10 μm (e.g., up to 10 μm).

[0042] As used herein, "uniform" may be used to describe a substantially similar density of dopant precursor particles or dopants therefrom at any threshold portion (e.g., a total surface area less than the total surface area) of the surface of the cathode material.

[0043] At 106, the mixture can be fired in a dry firing atmosphere, such as a dry air or dry oxygen atmosphere, to obtain a doped cathode material. Specifically, the dry firing atmosphere can include at least oxygen or air, i.e., the firing is not performed in a vacuum or near-vacuum condition. In some examples, the mixture can be fired at a temperature less than 950°C. In some examples, the firing temperature can be less than 900°C. In some examples, the firing temperature can be less than 800°C. In some examples, the firing temperature can be about 750°C. In one example, the mixture can be fired in a dry oxygen atmosphere at a temperature of 750°C for 4 hours with a temperature ramp rate of 5°C / min. The firing temperature can be selected to avoid degradation / melting / evaporation of one or both of the cathode material and the dopant precursor particles. Thus, the firing temperature can be adjusted based on the composition of one or both of the cathode material and the dopant precursor particles. Furthermore, during firing, reactions between the dopant precursor particles and the cathode material can occur. Thus, the calcination temperature can be selected to allow the reaction to proceed in a controlled manner. The calcination temperature can be determined based on a TGA plot (e.g., the TGA plot described below with reference to FIG. 3).

[0044] The selection of polycrystalline materials such as NMC as cathode materials may affect the kinetics of firing compared to monocrystalline materials such as lithium cobalt oxide due to the presence of grain boundaries. That is, a single secondary particle of a polycrystalline material is composed of multiple single crystal or primary particles, each primary particle corresponding to an additional grain boundary. Those skilled in the art will understand that dry surface doping of polycrystalline materials requires a fundamentally different procedure than dry surface doping of monocrystalline materials.

[0045] After calcination, the resulting doped cathode material can be characterized by SEM and XRD to determine the morphology and crystal structure, respectively (e.g., the SEM images and XRD patterns described below with reference to Figures 4 and 5, respectively). In some examples, after calcination, the dopant precursor particles are absent or substantially absent after calcination.

[0046] During calcination, oxygen may be released from the dopant precursor particles due to the reaction between the cathode material and the dopant precursor particles. Thus, in some examples, after calcination, the dopant precursor particles are absent or substantially absent, and the doped cathode material may include one or more dopants uniformly doped on its surface, where the dopants include one or more of B, N, F, Na, Si, Cl, K, Ca, Ga, Ru, Ta, W, Co, Al, Zr, Mg, Sc, Fe, V, Nb, Cu, Zn, Rh, Y, Ti, Mo, Cr, Mn, Ce, Sm, Nd, Pr, La, Ge, Rb, Sr, In, Eu, and Tb. In some examples, the doped cathode material may include one or more metal ions from the dopant precursor particles. In one example, the doped cathode material may include Nd, or Nd 3+ may include.

[0047] In some examples, in the doped cathode material, the weight ratio of one or more dopants to the cathode material can be less than about 15 wt%. In some examples, the weight ratio may be less than about 1 wt%. In some examples, the weight ratio may be about 1 wt%. In some examples, the weight ratio may be greater than about 0.01 wt% and less than about 15 wt%. In some examples, the weight ratio may be greater than about 0.25 wt% and less than about 8 wt%. In some examples, the weight ratio may be greater than about 0.25 wt% and less than about 6 wt%. In some examples, the weight ratio may be greater than about 0.25 wt% and less than about 4 wt%. In some examples, the weight ratio may be greater than about 0.25 wt% and less than about 2 wt%. In some examples, the weight ratio may be greater than about 0.25 wt% and less than about 1 wt%. In some examples, the weight ratio may be greater than about 0.25 wt% and less than about 0.5 wt%. In some examples, the weight ratio may be about 0.5% by weight. In some examples, the weight ratio may be about 0.4% by weight. In some examples, the weight ratio may be about 0.3% by weight. In some examples, the weight ratio may be about 0.25% by weight.

[0048] In some examples, in the doped cathode material, the molar ratio of one or more dopants to the cathode material may be less than about 15 mol%. In some examples, the molar ratio may be greater than about 0.01 mol%. In some examples, the molar ratio may be about 0.68 mol%. In some examples, the molar ratio may be greater than about 0.01 mol% and less than about 0.68 mol%. In some examples, the molar ratio may be greater than about 0.15 mol% and less than about 0.4 mol%. In some examples, the molar ratio may be greater than about 0.15 mol% and less than about 0.25 mol%. In some examples, the molar ratio may be greater than about 0.25 mol% and less than about 0.4 mol%. In some examples, the molar ratio may be about 0.25 mol%. In some examples, the weight ratio or molar ratio can be selected to achieve balanced cycling performance, specific capacity, DCR, and mechanical strength of a cathode incorporating the doped cathode material in a battery.

[0049] In some examples, at least a portion of the dopants in the doped cathode material may be exposed to the ambient environment. In some examples, the ambient environment may be the electrolyte in the battery. Thus, in some examples, the doped cathode material may be combined with a conductive additive and a binder to produce a positive electrode or cathode. Additionally, the battery may be produced to include a cathode as described above, a negative electrode or anode, a separator disposed between the cathode and the anode, and an electrolyte. In some examples, the negative electrode may include lithium metal, silicon, graphite, a silicon-graphite composite, LTO, or a combination thereof. In some examples, the battery may be a lithium ion battery, such as a secondary lithium ion battery. In further examples, the battery may be one of a plurality of batteries in a battery pack, each of the plurality of batteries being identical to the battery.

[0050] Referring now to Figure 2, there is shown a schematic diagram 200 of a dry surface doping process, such as the dry surface doping process described above with reference to Figure 1. However, it will be understood that the elements / features described with reference to Figure 2, while substantially similar to one or more elements / features described above with reference to Figure 1, are merely exemplary and thus not limited to the description given above with reference to Figure 1.

[0051] A first exemplary diagram 210 illustrates a plurality of dopant precursor particles 201, such as the dopant precursor particles described above with reference to FIG. 1. Thus, in some examples, the dopant precursor particles can include one or more metal oxides. In some examples, the dopant precursor particles can include Nd 2 O 3 may include.

[0052] In some examples, the average size of the dopant precursor particles 201 may be greater than 1 nm and less than 10 μm. In some examples, the average size of the dopant precursor particles 201 may be greater than 5 nm and less than 5 μm. In some examples, the average size of the dopant precursor particles 201 may be greater than 80 nm and less than 720 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 80 nm and less than 400 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 80 nm and less than 300 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 80 nm and less than 200 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 80 nm and less than 140 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 400 nm and less than 720 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 500 nm and less than 720 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 600 nm and less than 720 nm. In some examples, the average size of the dopant precursor particles 201 may be greater than 660 nm and less than 720 nm. In some examples, a relationship between the dopant precursor particles 201 can be formed such that each dopant precursor particle 201 can have a similar size. In some examples, the particle size distribution of the dopant precursor can be a normal distribution.

[0053] The first exemplary diagram 210 further illustrates a cathode material 202, such as the cathode materials described above with reference to FIG. 1. Thus, in some examples, the cathode material 202 may be NMC. In one example, the NMC is LiNi 0.64 Mn 0.2 Co 0.16 O 2The cathode material 202 may include a core 203, or core region 203, and a surface 204, or volume defined by the surface region 204. In some examples, the core region 203 may include a larger volume than the surface region 204. In some examples, the surface region 204 may extend to a threshold depth 205 toward the center of the cathode material 202. That is, the threshold depth 205 may be the maximum possible extent or depth of the surface region 204 in a direction toward the center of the cathode material 202. In some examples, the depth of at least a portion of the surface region 204 may vary from the depth of other portions of at least a portion of the surface region 204.

[0054] In some examples, the threshold depth 205 can be equal to a radius of the cathode material 202. In some examples, the cathode material 202 can be free or substantially free of a core region 203. In some examples, the threshold depth 205 can be 10 μm. In some examples, the threshold depth 205 can be 5 μm. In some examples, the threshold depth 205 can be 2 μm. In some examples, the threshold depth 205 can be 1 μm. In some examples, the threshold depth 205 can be 500 nm. In some examples, the threshold depth 205 can be 100 nm.

[0055] In some examples, the cathode material 202 can be in the form of particles. In some examples, the average particle size of the cathode material 202 can be at least 0.5 μm and at most 20 μm. In some examples, the relationship between the particles of the cathode material 202 can be formed such that each particle can have a similar size. In some examples, the particle size distribution of the cathode material can be a normal distribution. In some examples, the particles of the cathode material 202 can be larger secondary particles made up of smaller primary particles.

[0056] In some examples, the cathode material 202 can include one or more surface structures 206 disposed on the exterior of the cathode material 202. Such surface structures 206 can be openings or cracks in the surface region 204 of the cathode material 202. The size and depth of the surface structures 206 can vary, respectively. In some examples, the surface structures 206 can be irregular such that the surface structures 206 can have different shapes and sizes. The surface structures 206 can increase the surface area of ​​the cathode material 202.

[0057] The dopant precursor particles 201 and the cathode material 202 can be dry mixed by dry mixing 215, such as the dry mixing described above with reference to Figure 1. The result of the dry mixing 215 is shown in a second exemplary diagram 220.

[0058] Specifically, the second exemplary diagram 220 shows dopant precursor particles 201 uniformly dispersed or distributed within a surface region 204 of a cathode material 202. In some examples, the dopant precursor particles 201 may protrude from the surface region 204 via a surface structure 206 or may be embedded within the surface region 204. Specifically, in some examples, the dopant precursor particles 201 may protrude from the surface region 204 at a distance of 0 to 10 μm (e.g., up to 10 μm). Thus, the dopant precursor particles 201 may not extend into the core region 203.

[0059] In some examples, the dopant precursor particles 201 may be attached to or within the surface structures 206 via one or both of van der Waals intermolecular forces and mechanical forces. Thus, the size of each of the dopant precursor particles 201 may be complementary to the size of the mutual surface structures 206 such that the dopant precursor particles 201 may be partially or completely immobilized therein. In some examples, the dopant precursor particles 201 may be ground to a preselected average size. The preselected average size of the dopant precursor particles 201 may result in the particles being held on and partially within the complementary sized surface structures 206 outside the cathode material 202. In other examples, the dopant precursor particles 201 may have substantially different sizes such that the dopant precursor particles 201 may be held within the matching-sized mutual surface structures 206.

[0060] The dopant precursor particles 201 and cathode material 202 may be calcined 225, such as the calcination described above with reference to Figure 1. The result of calcination 225 is illustrated by a third exemplary diagram 230.

[0061] Specifically, the third exemplary diagram 230 illustrates a doped cathode material 207, such as the doped cathode material described above with reference to FIG. 1. The doped cathode material 207 may include a volume divided into a core region 203 and a doped surface 208 or doped surface region 208. Following the calcination 225, the core region 203 may not undergo or may not undergo substantially any chemical or physical changes. In some examples, the core region 203 may include a larger volume than the doped surface region 208. In some examples, the doped surface region 208 may extend to a threshold depth 209 toward the center of the doped cathode material 207. That is, the threshold depth 209 may be the maximum possible extent or depth of the doped surface region 208 in a direction toward the center of the doped cathode material 207. Thus, in some examples, the dopant from the dopant precursor particles 201 may be dispersed throughout the doped cathode material 207 following the calcination 225. In some examples, the threshold depth 209 of the doped surface region 208 can be approximately equal to the threshold depth 205 of the surface region 204. In some examples, the depth of at least a portion of the doped surface region 208 may vary from the depth of at least a portion of another portion of the doped surface region 208. The threshold depth 209 of the doped surface region 208 may depend on one or more of the size of the dopant precursor particles 201, the size of the cathode material 202, the duration of the calcination 225 (i.e., the duration of the reaction between the dopant precursor particles 201 and the cathode material 202), and the temperature of the calcination 225.

[0062] In some examples, the threshold depth 209 can be equal to a radius of the doped cathode material 207. In some examples, the doped cathode material 207 can be free of, or substantially free of, a core region 203. In some examples, the threshold depth 209 can be 10 μm. In some examples, the threshold depth 209 can be 5 μm. In some examples, the threshold depth 209 can be 2 μm. In some examples, the threshold depth 209 can be 1 μm. In some examples, the threshold depth 209 can be 500 nm. In some examples, the threshold depth 209 can be 100 nm.

[0063] During calcination 225, reaction of the dopant precursor particles 201 with the cathode material 202 may release oxygen from the dopant precursor particles 201. Thus, in some examples, following calcination 225, the dopant precursor particles 201 are absent or substantially absent from the doped cathode material 207. Thus, the doped surface region 208 of the doped cathode material 207 may include one or more dopants uniformly doped. In some examples, the doped cathode material 207 may include one or more metal ions from the dopant precursor particles 201. In one example, the doped surface region 208 of the doped cathode material 207 may include Nd, or Nd 3+ may include:

[0064] In some examples, prior to firing 225, each of the core region 203 and the surface region 204 may be comprised of the cathode material 202. In some examples, following firing 225, the core region 203 may be comprised of the cathode material 202 and the doped surface region 208 may be comprised of the cathode material 202 and one or more dopants.

[0065] Referring now to FIG. 3, a TGA plot 300 shows the thermal behavior of pure or undoped NMC particles, as well as NMC particles and Nd 2 O 3The TGA plot 300 shows the weight change of a mixture with particles. The TGA plot 300 can be utilized to determine the appropriate firing temperature for a dry surface doping process, such as the dry surface doping process described above with reference to Figures 1 and 2. As an example, a higher than normal dosage of Nd 2 O 3 Particles, e.g., Nd for NMC particles 2 O 3 A weight ratio of 33% by weight of the particles can be selected to mix with the NMC particles and clearly observe the respective weight changes.

[0066] As shown by curve 303, slight weight loss in pure NMC particles may occur at temperatures above 500° C. due to slight oxygen release. However, as temperatures exceed 900° C., the oxygen loss becomes more severe. Thus, since degradation of NMC may occur at temperatures above 900° C., an upper threshold of 900° C. can be selected for the sintering temperature based on this severe oxygen loss.

[0067] As shown by curve 301, in the temperature range of about 676.2°C to about 711.8°C, the NMC particles and Nd 2 O 3 There may be a significant weight loss in the mixture of NMC particles and Nd 2 O 3 It can be seen that a reaction with particles is occurring, i.e. Nd 2 O 3 Oxygen release from the particles can occur as a result of reactions with NMC particles in the temperature range of about 676.2 °C to about 711.8 °C. Therefore, Nd 2 O 3 A suitable temperature for calcination of NMC according to the method may be about 750°C.

[0068] Referring now to FIG. 4, SEM images 400 and 450 show, respectively, Nd 2 O 4 before and after firing in a dry surface doping process, such as the dry surface doping process described above with reference to FIGS. 1 and 2. 2 O 3Thus, the SEM image 400 shows a mixture of Nd SiO 2 particles and NMC particles before sintering. 2 O 3 The morphology of the mixture of particles 401 and NMC particles 402 is shown. As shown, Nd 2 O 3 The particles 401 are uniformly distributed on the surface of the NMC particle 402. Furthermore, the SEM image 450 shows the morphology of the Nd-doped NMC particle 451 after sintering. As shown, the Nd 2 O 3 The particles 401 are no longer visible after firing, and Nd 2 O 3 It is shown that particle 401 has reacted completely or substantially completely with NMC particle 402, thereby doping Nd into the lattice of NMC particle 402.

[0069] Referring to FIG. 5, a plot 500 shows the results of the measurements of undoped NMC, Nd-doped NMC, and Nd 2 NiO 4 , and Nd 2 O 3 5 shows XRD patterns of Nd doped NMCs (as shown by curves 501, 503, 504 and 505, respectively). In some examples, the Nd doped NMCs can be produced by a dry surface doping process, such as the dry surface doping process described above with reference to FIGs. 1 and 2. As shown by comparing curve 505 with curve 503, in the Nd doped NMCs, Nd 2 O 3 is not detected or is substantially not detected. 2 O 3 The lack of Nd 2 O 3 This may indicate that the doped cathode material (e.g., LiCo) with the precursor present after the heating step is completely or substantially completely reacted with the NMC during the dry surface doping process. y O z ·tMO xHowever, as shown by comparing curve 504 with curve 503, a small amount of impurity phase appears. That is, the peak position in curve 503 is closer to that of Nd 2 NiO 4 This may correspond well to compounds consisting of Nd, Ni, and O such as:

[0070] Inset 525 shows an enlarged region of plot 550. Plot 550 shows a peak shift 551 between curves 501 and 503. The peak shifting 551 to the left is due to the Nd 3+ It has been shown that due to the relatively large ionic radius of Nd, Nd is doped into the NMC lattice in Nd-doped NMC, leading to an expansion of the c-lattice parameter.

[0071] 6-11, to provide a comparison with the dry surface doping process, a wet surface doping process can be used to fabricate Nd-doped NMCs. In one example, the wet surface doping process is carried out by doping Nd(NO 3 ) 3 6H 2 The process involves dissolving O salt in deionized (DI) water to form a solution, mixing NMC powder into this solution, and then stirring to achieve homogenization. After that, the DI water can be evaporated in a rotary evaporator at 75 °C to obtain a dry mixture. The dried mixture can then be calcined in an oxygen atmosphere at a temperature of 750 °C for 4 h with a temperature increase rate of 5 °C / min. After natural cooling, Nd-doped NMC can be obtained. The results in Figures 6 to 11 are extendable to commercial lithium-ion batteries, such as 42 Ah or 65 Ah batteries.

[0072] 6-8, various aspects of the electrochemical performance of half coin cells containing NMC, wet Nd-doped NMC (i.e., Nd-doped NMC fabricated by a wet surface doping process such as the wet surface doping process described above), or dry Nd-doped NMC (i.e., Nd-doped NMC fabricated by a dry surface doping process such as the dry surface doping process described above with reference to FIGS. 1 and 2) are characterized. To prepare the cathode for half coin cell testing, 93 wt% undoped NMC, wet Nd-doped NMC, or dry Nd-doped NMC, 4 wt% carbon conductive additive (Denka), and 3 wt% polyvinylidene fluoride (PVDF) binder (5% Kynar® HSV 900 PVDF in N-methyl-2-pyrrolidone solution) can be mixed three times for 5 minutes at 2000 RPM in a Thinky mixer. The resulting slurry was cast onto aluminum foil with a doctor blade to give an active mass loading of 7 mg / cm. 2 The cast cathode was vacuum dried at 80°C for 6 hours, and then the cast electrode was adjusted to 3.2 g / cm 3 The final cathode can then be calendered to a density of 1000 nm to obtain a final cathode. A Type 2025 half coin cell can then be assembled with the final cathode, a lithium disk anode, a Celgard® 2500 membrane separator, and an electrolyte. The electrolyte is 1M LiPF in a mixture of ethylene carbonate and ethyl methyl carbonate solvents. 6 and the volume to volume ratio of the solvent is 1:2. The half coin cells can then be tested over a voltage range of at least 2.8 to 4.3 V.

[0073] 6, plots 600 and 650 show the FCC and FDC at a 0.1 C (C=180 mA / g) rate, respectively, for half coin cells containing dry Nd-doped NMC, wet Nd-doped NMC, or undoped NMC samples. As shown in plot 600, the FCC of the dry Nd-doped NMC sample is 203.5 mAh / g, the FCC of the wet Nd-doped NMC sample is 191.5 mAh / g, and the FCC of the undoped NMC sample is 199.1 mAh / g (as shown by plots 601, 602, and 603, respectively). As shown in plot 650, the FDC of the dry Nd-doped NMC sample is 179.5 mAh / g, the FDC of the wet Nd-doped NMC sample is 170.6 mAh / g, and the FDC of the undoped NMC sample is 179.4 mAh / g (as shown by plots 651, 652, and 653, respectively). Thus, the half coin cells containing the dry Nd-doped NMC sample versus the undoped NMC sample show similar FCC and FDC. Thus, capacity retention can be maintained by the dry Nd-doped NMC in the half coin cells. However, the half coin cells containing the wet Nd-doped NMC sample show a decrease in FCC and FDC compared to the half coin cells containing the dry Nd-doped NMC sample and the undoped NMC sample.

[0074] 7, plot 700 shows the rate capability in terms of specific discharge capacity for discharge rates of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, and 5 C in half coin cells containing dry Nd-doped NMC, wet Nd-doped NMC, or undoped NMC samples. As shown in plot 700, at 0.1 C, the specific discharge capacity of the dry Nd-doped NMC sample is 180.3 mAh / g, the specific discharge capacity of the wet Nd-doped NMC sample is 170.4 mAh / g, and the specific discharge capacity of the undoped NMC sample is 180.4 mAh / g (as shown by plots 701, 702, and 703, respectively). Furthermore, at 0.2C, the specific discharge capacity of the dry Nd-doped NMC sample is 178.4 mAh / g, the specific discharge capacity of the wet Nd-doped NMC sample is 168.5 mAh / g, and the specific discharge capacity of the undoped NMC sample is 175.9 mAh / g (as shown by plots 711, 712, and 713, respectively). Furthermore, at 0.5C, the specific discharge capacity of the dry Nd-doped NMC sample is 173.4 mAh / g, the specific discharge capacity of the wet Nd-doped NMC sample is 164.2 mAh / g, and the specific discharge capacity of the undoped NMC sample is 170.4 mAh / g (as shown by plots 721, 722, and 723, respectively). Furthermore, at 1C, the specific discharge capacity of the dry Nd-doped NMC sample is 168.9 mAh / g, the specific discharge capacity of the wet Nd-doped NMC sample is 160.1 mAh / g, and the specific discharge capacity of the undoped NMC sample is 165.5 mAh / g (as shown by plots 731, 732, and 733, respectively). Furthermore, at 2C, the specific discharge capacity of the dry Nd-doped NMC sample is 163.7 mAh / g, the specific discharge capacity of the wet Nd-doped NMC sample is 155.1 mAh / g, and the specific discharge capacity of the undoped NMC sample is 160.1 mAh / g (as shown by plots 741, 742, and 743, respectively). Furthermore, at 5C, the specific discharge capacity of the dry Nd-doped NMC sample is 154.7 mAh / g, the specific discharge capacity of the wet Nd-doped NMC sample is 146.4 mAh / g, and the specific discharge capacity of the undoped NMC sample is 149.5 mAh / g (as shown by plots 751, 752 and 753, respectively).As shown by plot 700, the half coin cells containing the dry Nd-doped NMC samples exhibit higher specific discharge capacity at the trend toward higher discharge rates compared to the half coin cells containing the undoped NMC samples. Such improvement may be attributed to the larger c-lattice parameter in the dry Nd-doped NMC samples, which may facilitate the transport of lithium ions in and out of the layered structure of the NMC. In contrast, at all discharge rates shown in plot 700, the half coin cells containing the wet Nd-doped NMC samples exhibit reduced specific discharge capacity compared to the half coin cells containing the dry Nd-doped NMC samples and the undoped NMC samples.

[0075] Referring now to FIG. 8, plots 800 and 850 show the average capacity retention over cycles and specific capacity, respectively, of three half coin cells at a 0.5C rate, with each set of three half coin cells including a dry Nd-doped NMC, a wet Nd-doped NMC, or an undoped NMC sample. In plot 800, the average capacity retention over cycles of the half coin cells including the dry doped NMC sample, the wet Nd-doped NMC sample, and the undoped NMC sample are shown by curves 801, 802, and 803, respectively. As shown in plot 800, the half coin cell including the dry Nd-doped NMC sample has higher capacity retention after 100 cycles (as shown by curve 801) compared to the half coin cells including the wet Nd-doped NMC sample and the undoped NMC sample (as shown by curves 802 and 803, respectively). Further, in plot 850, the specific capacitance over the average cycles of the half coin cells containing the dry doped NMC sample, the wet Nd doped NMC sample, and the undoped NMC sample are shown by curves 851, 852, and 853, respectively. As shown in plot 850, the half coin cell containing the dry Nd doped NMC sample has a higher specific capacitance after 100 cycles (as shown by curve 851) compared to the half coin cells containing the wet Nd doped NMC sample and the undoped NMC sample (as shown by curves 852 and 853, respectively). Thus, dry surface doping of Nd may improve the cycling performance of NMC in the half coin cells. Notably, the half coin cell containing the wet Nd doped NMC sample has a lower specific capacitance over the course of averaged cycles (as shown by curve 852) compared to the half coin cell containing the undoped NMC sample (as shown by curve 853).

[0076] 9-11, various aspects of the electrochemical performance of SLP cells including NMC, wet Nd-doped NMC (i.e., Nd-doped NMC produced by a wet surface doping process such as the wet surface doping process described above), or dry Nd-doped NMC (i.e., Nd-doped NMC produced by a dry surface doping process such as the dry surface doping process described above with reference to FIGS. 1 and 2) are characterized. The cathode for the SLP cell test can be composed of the following: 94.5 wt% undoped NMC, wet Nd-doped NMC or dry Nd-doped NMC, 2.5 wt% carbon conductive additive (2 wt% Denka and 0.5 wt% Engineering Carbon Products), and 3 wt% PVDF binder (Solvay Solef® 5130). Additionally, the anode for the SLP cell test can be composed of the following: 94.5 wt% graphite, 1 wt% vapor grown carbon fiber, 1.5 wt% carboxymethyl cellulose, and 0.5 wt% styrene-butadiene rubber. The active mass loading of the cathode is 19.80 g / cm. 2 and the active mass loading of the anode is 11 g / cm 2 An SLP cell can then be assembled using the cathode, anode, Celgard® 2500 membrane separator, and electrolyte. The electrolyte can be 1M LiPF in a mixture of ethylene carbonate and ethyl methyl carbonate solvents. 6 and the volume to volume ratio of the solvent is 1:2. The SLP cell can then be tested over a voltage range of at least 2.75-4.2V.

[0077] 9, plots 900 and 950 show the FCC and FDC at a rate of 0.05C (C=180mA / g) in SLP cells containing dry Nd-doped NMC, wet Nd-doped NMC, or undoped NMC samples, respectively. As shown in plot 900, the FCC of the dry Nd-doped NMC sample is 196.8mAh / g, the FCC of the wet Nd-doped NMC sample is 193.9mAh / g, and the FCC of the undoped NMC sample is 199.1mAh / g (as shown by plots 901, 902, and 903, respectively). As shown in plot 950, the FDC of the dry Nd-doped NMC sample is 179.4 mAh / g, the FDC of the wet Nd-doped NMC sample is 176.9 mAh / g, and the FDC of the undoped NMC sample is 182.0 mAh / g (as shown by plots 951, 952, and 953, respectively). Thus, the SLP cells containing the dry Nd-doped NMC sample show a slight drop in FCC and FDC compared to the SLP cells containing the undoped NMC sample. However, the SLP cells containing the wet Nd-doped NMC sample showed a large drop in FCC and FDC compared to the SLP cells containing the undoped NMC sample. Thus, the capacity retention may be better maintained by the dry Nd-doped NMC in the SLP cells.

[0078] 10, plots 1000 and 1050 show the average cycle capacity retention and specific discharge capacity of three SLP cells at 1C rate, respectively, with each set of three SLP cells including dry Nd-doped NMC, wet Nd-doped NMC, or undoped NMC samples. In plot 1000, the average cycle capacity retention of the SLP cells including dry doped NMC, wet Nd-doped NMC, and undoped NMC samples are shown by curves 1001, 1002, and 1003, respectively. As shown in plot 1000, the capacity retention of the SLP cells including dry Nd-doped NMC and undoped NMC samples after 300 cycles is 87.1% and 74.7%, respectively. Furthermore, in plot 1050, the specific capacity over the average cycles of the SLP cells containing the dry doped NMC sample, the wet Nd doped NMC sample, and the undoped NMC sample are shown by curves 1051, 1052, and 1053, respectively. As shown in plot 1050, the specific capacity of the SLP cells containing the dry Nd doped NMC sample and the undoped NMC sample after 300 cycles is 138.3 mAh / g and 118.2 mAh / g, respectively. Thus, dry surface doping of Nd may improve the cycling performance of NMC in SLP cells. Notably, the SLP cells containing the wet Nd doped NMC sample have lower capacity retention over the course of cycling (as shown by curve 1002) compared to the SLP cells containing the dry Nd doped NMC sample (as shown by curve 1001). Furthermore, the SLP cell containing the wet Nd-doped NMC sample has a lower average specific capacity over the course of cycling (as shown by curve 1052) compared to the SLP cell containing the dry Nd-doped NMC sample (as shown by curve 1051).

[0079] 11, plot 1100 shows the DCR growth over an average cycle for three SLP cells, with each set of three SLP cells including a dry Nd-doped NMC, wet Nd-doped NMC, or undoped NMC sample. In plot 1100, the DCR growth over an average cycle for the SLP cells including the dry doped NMC, wet Nd-doped NMC, and undoped NMC samples is shown for every 50 cycles by bars 1101, 1102, and 1103, respectively. As shown in plot 1100, at 50 cycles, the DCR for the dry Nd-doped NMC sample is 1.45Ω, the DCR for the wet Nd-doped NMC sample is 1.40Ω, and the DCR for the undoped NMC sample is 1.43Ω. Furthermore, at 100 cycles, the DCR of the dry Nd-doped NMC sample is 1.35Ω, the DCR of the wet Nd-doped NMC sample is 1.31Ω, and the DCR of the undoped NMC sample is 1.34Ω. Furthermore, at 150 cycles, the DCR of the dry Nd-doped NMC sample is 1.33Ω, the DCR of the wet Nd-doped NMC sample is 1.37Ω, and the DCR of the undoped NMC sample is 1.36Ω. Furthermore, at 200 cycles, the DCR of the dry Nd-doped NMC sample is 1.39Ω, the DCR of the wet Nd-doped NMC sample is 1.43Ω, and the DCR of the undoped NMC sample is 1.48Ω. Furthermore, at 250 cycles, the DCR of the dry Nd-doped NMC sample is 1.43Ω, the DCR of the wet Nd-doped NMC sample is 1.47Ω, and the DCR of the undoped NMC sample is 1.55Ω. Furthermore, at 300 cycles, the DCR of the dry Nd-doped NMC sample is 1.47Ω, the DCR of the wet Nd-doped NMC sample is 1.52Ω, and the DCR of the undoped NMC sample is 1.63Ω. Furthermore, at 350 cycles, the DCR of the dry Nd-doped NMC sample is 1.52Ω, the DCR of the wet Nd-doped NMC sample is 1.55Ω, and the DCR of the undoped NMC sample is 1.68Ω. Thus, the SLP cell containing the dry Nd-doped NMC sample exhibits slower DCR growth over the average cycle (as shown by bar 1101) than the SLP cell containing the undoped NMC sample (as shown by bar 1103).The reduced DCR growth when utilizing the dry Nd-doped NMC sample is consistent with other results showing improved electrochemical performance for the sample, as discussed above with reference to Figures 6-10. In comparison, the SLP cell containing the wet Nd-doped NMC sample shows faster DCR growth over the average cycle (as shown by bar 1102) than the SLP cell containing the dry Nd-doped NMC sample (as shown by bar 1101). The increased DCR growth when utilizing the wet Nd-doped NMC sample is consistent with other results showing poorer electrochemical performance for the sample, as compared to the dry Nd-doped NMC sample, as discussed above with reference to Figures 6-10.

[0080] Referring now to FIG. 12, cross-sectional SEM images 1200, 1210, and 1220 show crack growth in undoped NMC particles after 300 cycles in an SLP cell at 2000×, 5000×, and 10,000× magnifications, respectively. Additionally, cross-sectional SEM images 1230, 1240, and 1250 show crack growth in dry Nd-doped NMC particles after 300 cycles in an SLP cell at 2000×, 5000×, and 10,000× magnifications, respectively. The dry Nd-doped particles show fewer and smaller cracks (as shown most clearly by cross-sectional SEM image 1250) compared to the undoped NMC particles (as shown most clearly by cross-sectional SEM image 1220), indicating increased stability of the crystal structure in the former. Specifically, the fewer and smaller cracks in the dry Nd-doped particles are due to the Nd 3+ This may be due to the suppressed lattice volume change during cycling due to the presence of . Furthermore, fewer and smaller cracks may play an important role in improving the cycling performance and reducing the DCR growth rate in SLP cells due to fewer side reactions occurring between the electrolyte and the cathode therein.

[0081] Referring now to FIG. 13, plots 1300 and 1350 show the change in c-lattice parameter determined by in situ XRD over the initial cycles for half coin cells containing dry Nd-doped and undoped NMC samples. Specifically, curves 1301 and 1303 show the results for half coin cells containing dry Nd-doped and undoped NMC samples, respectively, in terms of voltage during the initial charge and discharge, respectively. In contrast, bars 1351 and 1353 show the results for half coin cells containing dry Nd-doped and undoped NMC samples, respectively, in terms of voltage only. Double-headed arrows 1361 and 1363 show the difference in c-lattice parameter between 3.5 and 4 V of 0.280 Å for the dry Nd-doped NMC sample and 0.304 Å for the undoped NMC sample, respectively. Thus, the change in the c-lattice parameter is shown to be less with the dry Nd-doped NMC sample compared to the undoped NMC sample. The smaller change in the c-lattice parameter can correspond to a smaller expansion / contraction of the cathode lattice, which can contribute to fewer and smaller cracks. Thus, the reduced change in the c-lattice parameter when utilizing the dry Nd-doped NMC sample is consistent with fewer and smaller cracks in the dry Nd-doped NMC particles after cycling in half coin cells, as described above with reference to Figure 12. The results in Figure 13 are extendable to commercial Li-ion batteries, such as 42 Ah or 65 Ah batteries.

[0082] Referring now to FIG. 14, plot 1400 shows the capacity retention over average cycles of three half coin cells at 0.5C rate, with each set of three half coin cells containing undoped NMC or dry Nd-doped NMC samples. The other results discussed above with reference to FIGS. 4-13 are based on 1 wt % Nd doping, which corresponds to 0.68 mol % Nd doping. To show that other Nd dosages are also effective, cycle performance is shown in plot 1400 for various molar ratios of Nd to NMC. Specifically, the results of a half coin cell containing a dry Nd-doped NMC sample with a molar ratio of Nd to NMC of 0.68 mol % are shown in curve 1401. Additionally, the results of a half coin cell containing a dry Nd-doped NMC sample with a molar ratio of Nd to NMC of 0.4 mol % are shown in curve 1402. It will be appreciated that curve 1402 may be substantially overlapped in plot 1400 by curves 1401, 1403, and 1404. Additionally, results for a half coin cell including a dry Nd-doped NMC sample with a molar ratio of Nd to NMC of 0.25 mol% are shown in curve 1403. Additionally, results for a half coin cell including a dry Nd-doped NMC sample with a molar ratio of Nd to NMC of 0.15 mol% are shown in curve 1404. Additionally, results for a half coin cell including an undoped NMC sample are shown by curve 1405. Thus, plot 1400 illustrates that a half coin cell including an NMC sample dry surface doped with 0.25 mol% Nd exhibits higher capacity retention than half coin cells including each of the illustrated undoped NMC sample and the other dry Nd-doped NMC samples (as shown by comparing curve 1403 to curves 1405, 1401, 1402, and 1404). Therefore, it is possible to determine the optimum molar ratio of Nd to NMC for capacity retention (and therefore cycling stability) in a dry surface doping process, such as that described above with reference to Figures 1-2. The results in Figure 14 are extendable to commercial Li-ion batteries, such as 42 Ah or 65 Ah batteries.

[0083] 15, plot 1500 shows the specific capacity over average cycles for three half coin cells at 0.5C rate, where each set of three half coin cells includes an undoped NMC sample or an NMC sample dry surface doped with 0.25 mol % Nd. Other results discussed above with reference to FIGS. 4-14 are based on doping with dopant precursor particles having sizes between 80-140 nm, where the dopant precursor particles are Nd 2 O 3 To show that other sizes of dopant precursor particles may also be effective, the cycling performance of two sizes of dopant precursor particles is shown in plot 1500. Specifically, results for a half coin cell including an NMC sample dry surface doped with dopant precursor particles having a smaller size of 80-140 nm are shown by curve 1551. Additionally, results for a half coin cell including an NMC sample dry surface doped with dopant precursor particles having a larger size of 660-720 nm are shown by curve 1552. Additionally, results for a half coin cell including an undoped NMC sample are shown by curve 1553. Thus, plot 1500 shows that a half coin cell including an NMC sample dry surface doped with dopant precursor particles of a larger size can exhibit a substantially similar specific capacity (and thereby cycling performance) as an NMC sample dry surface doped with dopant precursor particles of a smaller size (as shown by comparing curve 1552 to curve 1551). Furthermore, each of the half coin cells containing the dry Nd-doped NMC samples exhibits a higher specific capacity (and therefore cycling performance) than the half coin cell containing the undoped NMC sample (as shown by comparing curves 1551 and 1552 with curve 1553). The results in Figure 15 are extendable to commercially available Li-ion batteries such as 42 Ah or 65 Ah batteries.

[0084] In this way, the cathode material can be doped with one or more metal dopants having a large ionic radius (e.g., greater than about 0.50 Å) in a dry surface doping process. The dry surface doping process can dope one or more metal dopants into the surface of the cathode material. The technical effect of adopting such a dry surface doping process is that the cathode material avoids contact with the solvent, preventing possible damage to the cathode material surface. In addition, the dry surface doping process can limit the deterioration of cycling performance and capacity retention caused by electrochemically inactive metal dopants. This can stabilize the crystal structure of the cathode material, inhibit the generation / growth of cracks, and reduce the portion of the cathode material surface exposed to the electrolyte in the battery. Therefore, there is less side reaction between the electrolyte and the cathode material, and capacity degradation is limited. In addition, the increased structural stability of the crystal structure of the cathode material can improve the capacity retention during cycling of the battery. As a result, problems such as poor cycling performance, fast DCR growth, and crack formation / growth in commercial lithium-ion batteries can be alleviated.

[0085] In one example, the method includes dry mixing NMC and dopant precursor particles to obtain a pre-calcination mixture, and calcining the pre-calcination mixture in a dry calcination atmosphere to obtain a doped cathode material, the dopant precursor particles including one or more of an alkali metal oxide, an alkali metal hydroxide, an alkaline earth metal oxide, an alkaline earth metal hydroxide, a rare earth oxide, a rare earth hydroxide, a transition metal oxide, and a transition metal hydroxide. The first example of the method further includes that the dry calcination atmosphere is a dry air or dry oxygen atmosphere. The second example of the method optionally includes the first example of the method, further including that following the dry mixing, the dopant precursor particles are uniformly distributed on the surface of the NMC. The third example of the method optionally includes one or more of the first and second examples of the method, further including that following the dry mixing, the dopant precursor particles protrude from the surface of the NMC by a distance of 0 to 10 μm. A fourth example of the method optionally includes one or more of the first through third examples of the method, and further includes that the temperature of the calcination is less than 950° C. A fifth example of the method optionally includes one or more of the first through fourth examples of the method, and further includes that the doped cathode material includes a dopant, and the dopant includes one or more of B, N, F, Na, Si, Cl, K, Ca, Ga, Ru, Ta, W, Co, Al, Zr, Mg, Sc, Fe, V, Nb, Cu, Zn, Rh, Y, Ti, Mo, Cr, Mn, Ce, Sm, Nd, Pr, La, Ge, Rb, Sr, In, Eu, and Tb. A sixth example of the method optionally includes one or more of the first through fifth examples of the method, and further includes that the size of the dopant precursor particles is greater than about 1 nm and less than about 10 μm. A seventh example of the method optionally includes one or more of the first through sixth examples of the method, further including a size of the dopant precursor particles greater than about 5 nm and less than about 5 μm. An eighth example of the method optionally includes one or more of the first through seventh examples of the method, further including a molar ratio of dopant to NMC in the doped cathode material greater than about 0.01 mol % and less than about 15 mol %.A ninth example of the method can optionally include one or more of the first through eighth examples of the method, and further includes the dopant precursor particles comprising one or more compounds selected from neodymium oxide, neodymium acetate, neodymium nitride, neodymium sulfate, neodymium fluoride, neodymium nitrate, neodymium phosphide, neodymium sulfide, neodymium iodide, neodymium phosphate, neodymium carbonate, neodymium oxalate, acetylacetonate, and combinations thereof. A tenth example of the method can optionally include one or more of the first through ninth examples of the method, and further includes the dopant precursor particles comprising one or more compounds selected from neodymium oxide, neodymium acetate, neodymium nitride, neodymium sulfate, neodymium fluoride, neodymium nitrate, neodymium phosphide, neodymium sulfide, neodymium iodide, neodymium phosphate, neodymium carbonate, neodymium oxalate, acetylacetonate, and combinations thereof. 2 O 3 Includes.

[0086] In another example, the doped cathode material includes a core region and a surface region, the surface region being composed of NMC and a metal dopant, the metal dopant being a metal ion having an ionic radius greater than about 0.50 Å. The first example of the doped cathode material further includes a molar ratio of the metal dopant to NMC greater than about 0.01 mol % and less than about 15 mol %. The second example of the doped cathode material optionally includes the first example of the doped cathode material and further includes the surface region extending to a threshold depth of the radius of the doped cathode material.

[0087] In yet another example, the doped cathode material includes NMC and a dopant including one or more of B, N, F, Na, Si, Cl, K, Ca, Ga, Ru, Ta, W, Co, Al, Zr, Mg, Sc, Fe, V, Nb, Cu, Zn, Rh, Y, Ti, Mo, Cr, Mn, Ce, Sm, Nd, Pr, La, Ge, Rb, Sr, In, Eu, and Tb, where the dopant is uniformly doped into a surface region of the NMC in a dry surface doping process, where the dry surface doping process includes a dopant precursor mixed with the NMC and calcined, where the dopant precursor is absent following the dry surface doping process. The first example of the doped cathode material further includes that the weight ratio of the dopant to the NMC is less than about 15% by weight. A second example of a doped cathode material optionally includes the first example of a doped cathode material, further including that the dopant precursor comprises one or more compounds selected from a dopant oxide, a dopant acetate, a dopant nitride, a dopant sulfate, a dopant fluoride, a dopant nitrate, a dopant phosphide, a dopant sulfide, a dopant iodide, a dopant phosphate, a dopant carbonate, a dopant oxalate, a dopant acetylacetonate, and combinations thereof. A third example of a doped cathode material optionally includes one or more of the first and second examples of the doped cathode material, and the dopant precursor includes one or more compounds selected from neodymium oxide, neodymium acetate, neodymium nitride, neodymium sulfate, neodymium fluoride, neodymium nitrate, neodymium phosphide, neodymium sulfide, neodymium iodide, neodymium phosphate, neodymium carbonate, neodymium oxalate, acetylacetonate, and combinations thereof. A fourth example of a doped cathode material optionally includes one or more of the first through third examples of the doped cathode material, and the dopant precursor includes one or more compounds selected from neodymium oxide, neodymium acetate, neodymium nitride, neodymium sulfate, neodymium fluoride, neodymium nitrate, neodymium phosphide, neodymium sulfide, neodymium iodide, neodymium phosphate, neodymium carbonate, neodymium oxalate, acetylacetonate, and combinations thereof. 2 O 3 A fifth example of a doped cathode material optionally includes one or more of the first through fourth examples of a doped cathode material, and further includes that the dopant is a metal ion having an ionic radius greater than about 0.50 Å.

[0088] The following claims specifically point out certain combinations and subcombinations that are deemed novel and unobvious. These claims may refer to "a" element, "first" element, or the like. Such claims should be understood to include the inclusion of one or more such elements, and not to require or exclude two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or properties may be claimed through amendment of the claims or presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope from the original claims, are considered to be within the subject matter of this disclosure.

Claims

1. Methods include: Dry mixing lithium nickel manganese cobalt oxide (NMC) and dopant precursor particles to obtain a pre-fired mixture; and firing the pre-fired mixture in a dry firing atmosphere to obtain a doped cathode material; wherein the dopant precursor particles include one or more of neodymium oxide and neodymium hydroxide.

2. The method of claim 1 , wherein the dry firing atmosphere is a dry air or dry oxygen atmosphere.

3. 3. The method of claim 1 or 2, wherein the dry mixing comprises dry mixing with a roller mill mixer, and following the dry mixing, the dopant precursor particles are uniformly distributed on the surface of the NMC.

4. The method of claim 3, wherein following said dry mixing, said dopant precursor particles protrude from the surface of said NMC by a distance of 0 to 10 μm.

5. The method according to any one of claims 1 to 4, wherein the temperature of the calcination is less than 950°C.

6. 6. The method of any one of claims 1 to 5, wherein the doped cathode material further comprises a dopant, the dopant comprising one or more of B, N, F, Na, Si, Cl, K, Ca, Ga, Ru, Ta, W, Co, Al, Zr, Mg, Sc, Fe, V, Nb, Cu, Zn, Rh, Y, Ti, Mo, Cr, Mn, Ce, Sm, Nd, Pr, La, Ge, Rb, Sr, In, Eu, and Tb.

7. The method according to any one of claims 1 to 6, wherein the size of the dopant precursor particles is greater than 1 nm and less than 10 μm.

8. The method according to any one of claims 1 to 7, wherein the size of the dopant precursor particles is greater than 5 nm and less than 5 μm.

9. 9. The method of claim 1, wherein the molar ratio of dopant to NMC in the doped cathode material is greater than 0.01 mol % and less than 15 mol %.

10. The dopant precursor particles are Nd ２ O ３ The method according to any one of claims 1 to 9, comprising:

11. A doped cathode material obtainable by the method according to any one of claims 1 to 10, comprising A doped cathode material including: A core region composed of lithium nickel manganese cobalt oxide (NMC); and a surface region consisting of the NMC and a metal dopant; Here, the metal dopant is a metal ion having an ionic radius of more than 0.50 Å.

12. 12. The doped cathode material of claim 11 , wherein a molar ratio of the metal dopant to the NMC is greater than 0.01 mol % and less than 15 mol %.

13. 13. A doped cathode material according to claim 11 or 12, wherein the surface region extends to a radial threshold depth of the doped cathode material.

14. A doped cathode material obtainable by the method according to any one of claims 1 to 10, comprising A doped cathode material including: NMC; and Dopants, wherein the dopant is uniformly doped into the surface region of the NMC in a dry surface doping process; The dry surface doping process includes a dopant precursor mixed with the NMC and calcined; the dopant precursor comprises one or more of neodymium oxide and neodymium hydroxide; The dopant precursor is not present after the dry surface doping process.

15. 15. The doped cathode material of claim 14, wherein a weight ratio of the dopant to the NMC is less than 15 wt%.

16. The dopant precursor is Nd ２ O ３ 16. The doped cathode material of claim 14 or 15,

17. The doped cathode material of any one of claims 14 to 16, wherein the dopant is a metal ion having an ionic radius of greater than 0.50 Å.

Images