METHOD OF CONTROLLING AN AMOUNT OF SOLUBLE BASE CONTENT OF MATERIAL COMPRISING LITHIUM CARBONATE AND STRUCTURE, CATHODE, AND BATTERY FORMED USING THE METHOD

Abstract

Methods of controlling an amount of soluble base content of material comprising lithium carbonate and other material. Exemplary methods include using atomic layer deposition, selectively depositing one or more of an oxide, a fluoride, and a nitride to form and/or control the soluble base content.

Claims

1. A method of controlling an amount of soluble base content of a material, the material comprising lithium carbonate, and lithium hydroxide and a lithiated metal oxide, the method comprising the steps of: providing the material within a reaction chamber, the material comprising a surface comprising the lithium carbonate and lithium hydroxide; and using atomic layer deposition, selectively depositing one or more of an oxide, a fluoride, and a nitride on the other material compared to the lithium carbonate, wherein, during the step of using atomic layer deposition, the material is exposed to more than one and less than ten cycles of atomic layer deposition.

2. The method of claim 1, comprising selectively depositing the oxide, wherein the oxide is selected from one or more of the group of transition metal oxides.

3. The method of claim 2, wherein the oxide is selected from the group consisting of Al.sub.2O.sub.3, MgO, SiO.sub.2, TiO.sub.2, ZnO, SnO.sub.2, ZrO.sub.2, NbO.sub.3, and B.sub.2O.sub.3.

4. The method of claim 1, comprising selectively depositing the nitride, wherein the nitride is selected from one or more of the group of metal nitrides and metalloid nitrides.

5. The method of claim 1, wherein the material is exposed to more than one and less than six cycles of atomic layer deposition.

6. The method of claim 1, wherein the material is exposed to more than one and less than four cycles of atomic layer deposition.

7. The method of claim 1, further comprising a step of determining an amount of lithium carbonate in the material by XPS.

8. The method of claim 7, wherein a number of cycles of the atomic layer deposition is determined based on the amount of the lithium carbonate in the material.

9. The method of claim 1, wherein the other material comprises lithium hydroxide.

10. The method of claims 1 and 9, comprising selectively depositing the oxide, wherein the oxide is aluminum oxide, wherein, prior to the step of atomic layer deposition the material comprises lithium hydroxide and lithium carbonate in a first ratio, and after the step of atomic layer deposition the material comprises lithium hydroxide and lithium carbonate in a second ratio, wherein the first ratio is larger than the second ratio.

11. The method of claim 10, wherein after the step of using atomic layer deposition, a surface of the material comprises lithium carbonate and Li—Al-oxide.

12. The method of claim 1, wherein the material comprises nickel-rich lithium manganese cobalt oxide.

13. The method of claim 12, wherein the nickel-rich lithium manganese cobalt oxide comprises greater than 20.2 wt % nickel.

14. The method of claim 1, wherein a number of atomic layer deposition cycles is based on one or more of an amount of nickel in the material, lithium:metal content in the material, a temperature used to form the material, a temperature during the atomic layer deposition, precursor flowrates during the atomic layer deposition, a precursor pulse time, pressure within the reaction chamber during the atomic layer deposition, and the precursors used during the atomic layer deposition.

15. A method of forming cathode material using the method of any of claims 1-14.

16. A cathode formed according to any of the methods of claims 1-15.

17. The cathode of claim 16, wherein the material comprises lithium manganese cobalt oxide.

18. The cathode of claim 17, wherein the material comprises nickel.

19. The cathode of claim 18, wherein the material comprises greater than about 20.2 wt % nickel.

20. A method of forming a battery according to any of claims 1-15.

21. A battery comprising the cathode of any of claims 16-19.

22. The method of any of claims 1-15 wherein the material is in the form of particles and the reaction chamber is a fluidized bed, rotating drum, sequential batch mixer, or vibrating reactor.

23. The method of any of claims 1-6 wherein the material comprises an NCM cathode material and the amount of CO.sub.3 decreases by 50% or less after the step of atomic layer deposition.

24. A method of making a battery comprising the method of claim 23.

25. A battery made by the method of claim 24 wherein the battery comprises the NCM cathode material that has an amount of CO.sub.3 that is no less than 50% that of the material before the step of atomic layer deposition.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0015] A more complete understanding of exemplary embodiments of the present disclosure can be derived by referring to the detailed description and claims when considered in connection with the following illustrative figures.

[0016] FIG. 1 illustrates XPS analysis of NCM materials, including residual LiOH and Li.sub.2CO.sub.3, in accordance with examples of the disclosure.

[0017] FIGS. 2 and 3 illustrate residual CO.sub.3 detected by XPS of NMC cathode material in accordance with examples of the disclosure.

[0018] FIG. 4 illustrates mass spectrometry traces for the first six ALD cycles on LiOH in accordance with examples of the disclosure.

[0019] FIG. 5 illustrates mass spectrometry traces for the first six ALD cycles on Li.sub.2CO.sub.3 in accordance with examples of the disclosure.

[0020] FIG. 6 illustrates calculated TMA breakthrough times in accordance with examples of the disclosure.

[0021] FIG. 7 illustrates ICP results for aluminum content on substrates at various ALD cycles in accordance with examples of the disclosure.

[0022] FIG. 8 illustrates comparative, area-normalized weight percent aluminum deposited on LiOH, Li.sub.2CO.sub.3, and NMC111.

[0023] FIG. 9 illustrates a cathode or structure formed in accordance with examples of the disclosure.

[0024] FIG. 10 illustrates a battery including a cathode formed in accordance with examples of the disclosure.

[0025] It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0026] Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

[0027] The present disclosure generally relates to methods of controlling an amount of soluble base content (SBC) of material—e.g., cathode material of, e.g., lithium-ion electrochemical cells and batteries; to methods of forming cathodes; to methods of forming batteries; and to cathodes and batteries formed using the methods. The SBC to be controlled can be SBC of material comprising lithium carbonate and other material, such as lithium hydroxide, lithium aluminum oxide, lithium fluoride oxide, lithium boron oxide, lithium aluminum fluoride oxide, lithium aluminum boron oxide, or the like.

[0028] Exemplary methods of controlling an amount of SBC material include providing the material within a reaction chamber and, using a cyclical deposition method, such as atomic layer deposition, selectively depositing one or more of an oxide, a fluoride, and a nitride on the other material compared to the lithium carbonate. The other material can be or include lithium hydroxide. After the step of using atomic layer deposition, a surface of the material can include lithium carbonate and/or lithium and one or more of the oxide, the fluoride, the nitride, the boride, a lithium metal (e.g., aluminum) oxide, nitride, boride, or fluoride, a lithium fluoride oxide or nitride, lithium aluminum fluoride oxide or nitride, lithium aluminum boride oxide or nitride, or the like.

[0029] The oxide deposited using ALD can be selected from one or more of the group of transition metal oxides, such as a metal oxide selected from the group consisting of Al.sub.2O.sub.3, MgO, SiO.sub.2, TiO.sub.2, ZnO, SnO.sub.2, ZrO.sub.2, NbO.sub.3, and B.sub.2O.sub.3. The nitride can be selected from one or more of the group of metal nitrides and metalloid nitrides. By way of particular examples, the nitride can include one or more of boron nitride or tungsten nitride. During the step of providing the material within a reaction chamber, a material comprising lithiated metal oxide having a general formula of LiM.sub.xO.sub.y can be provided. The metal represented by “M” in the lithiated metal oxide can be chosen from at least one of Co, Ni, Mn, Fe, Al, and Ti. Non-limiting examples of the lithiated metal can be chosen from at least one of lithium cobalt oxide (LiCo.sub.xO.sub.y), lithium nickel oxide (LiNi.sub.xO.sub.y), lithium manganese oxide (LiMn.sub.xO.sub.y), lithium nickel cobalt manganese oxide, (LiNi.sub.xCo.sub.yMn.sub.zOz.sub.z), lithium nickel cobalt manganese iron oxide (LiNi.sub.xCo.sub.yMn.sub.zFey.sub.yOz.sub.z), lithium iron phosphate (LiFe.sub.xPO.sub.y), lithium nickel cobalt aluminum oxide (LiNi.sub.xCo.sub.yAl.sub.zOz.sub.z), and lithium titanate (LiTi.sub.xO.sub.y). Lithium nickel cobalt manganese oxide (LiNi.sub.xCo.sub.yMn.sub.zOz.sub.z) is also referred to herein as “NMC.” In some cases, the nickel lithium manganese cobalt oxide material can be represented by a general formula of LiNi.sub.xMn.sub.yCo.sub.zO.sub.2, where x+y+z can equal 1. In some cases, the nickel lithium manganese cobalt oxide can be nickel rich. In these cases, the nickel lithium manganese cobalt oxide can include greater than 20.2 wt % nickel or greater than 48.3 wt % nickel. A surface area of the lithiated metal oxide can range from about 0.1 m2/g to about 0.2 m2/g or about 0.5 m2/g to about 5 m2/g.

[0030] The reaction chamber can be or include a suitable particle handling system such as a fluidized bed, rotating drum, sequential batch mixer, or vibrating reactor. These systems can provide a desired environment for the particles to interact with the gases and be coated while not aggregating the particles together.

[0031] During the step of using atomic layer deposition, one or more of an oxide, a fluoride, and a nitride are selectively deposited on the other material compared to the lithium carbonate. During this step, the material can be exposed to more than one and less than ten or to more than one and less than four or to more than one and less than six of atomic layer deposition cycles. In some cases, exemplary methods further include a step of determining an amount of lithium carbonate in the material. In these cases, a number of cycles of the atomic layer deposition can be determined based on the amount of the lithium carbonate in the material. Additionally or alternatively, a number of atomic layer deposition cycles can be based on one or more of an amount of lithium hydroxide in the material, an amount of nickel in the material, lithium:metal content in the material, a temperature used to form the material, a temperature during the atomic layer deposition, precursor flowrates during the atomic layer deposition, a precursor pulse time, pressure within the reaction chamber during the atomic layer deposition, and the precursors used during the atomic layer deposition.

[0032] Atomic layer deposition (ALD) has been identified as a coating methodology to modify cathode surfaces by exploiting the conformal and pinhole-free nature of ALD films deposited using a sufficient number of ALD cycles. ALD is a gas phase deposition method that is generally performed using repeated cycles of alternating exposures of the substrate surface to one or more precursors that are generally followed by purges of unreacted precursor and any ALD byproducts. Typically, each precursor reacts with surface reactive functional groups resulting in a half-reaction of the overall chemistry. Precursors typically do not self-react, but rather only react with the functionalized surface produced by reaction with, e.g., the complementary precursor. Consequently, the deposition produced by each half-reaction can proceed until no remaining active sites on the substrate surface are accessible to the precursor, making the deposition self-limiting. ALD can be carried out under various operating temperatures, pressures, precursor dose times, and reactor configurations.

[0033] In accordance with embodiments of the disclosure, ALD is used to deposit ultra-thin coating technology for modifying NCM and other cathode material surface properties. ALD films are often used to deposit continuous films over the entire surface given sufficient ALD cycle numbers.

[0034] When using ALD to coat materials used in electrochemical cells and batteries (e.g., for use in cathode active material), choice of coating material can be important, because preferred coatings may desirably maintain the bulk capacity of the electrode, be conductive to Li ions and electrons, and be chemically resistant to degradation in the electrolyte environment. In some cases, coating thickness can be sub-2 nm or deposited with less than ˜10 cycles of ALD. Due to the ultrathin and incomplete nature of low cycle number ALD films, the coatings can withstand larger strains and thus be less likely to mechanically fail from the repeated cycle of lattice expansions and contractions caused by lithium intercalation and deintercalation. Oxide, nitride, and fluoride coatings, such as alumina ALD films, have shown improved surface structural stability and chemical durability. And, depositions of less than six ALD cycles are thought to be particularly beneficial. Coated LiCoO.sub.2 powders can exhibit a capacity retention of 89% after a 120 V charge—discharge cycles in the 3.3-4.5 V (vs. Li/Li+) range. In contrast, the bare LiCoO.sub.2 powders retained only 45% of their initial capacity. Initial reversible capacity decreased significantly at six ALD cycles and was negligible (˜20 mAh/g) after the 10.sup.th ALD cycle. The initial capacity loss before battery cycling was attributed to the large overpotential required for LiCoO.sub.2 powders coated with more than six ALD cycles. The electrically insulating nature of alumina resulted in a reduction of the electronic conductivity as the film thickness increased. It was thought that ALD produces ultrathin uniform films that stabilize the metal oxide structure by preventing contact with the electrolyte. Further, it was thought that the ultrathin nature of ALD facilitates diffusion of lithium through the protective films and, because of this, does not result in a significant capacity loss.

[0035] In accordance with examples of the disclosure, precursors and reactants used during the atomic layer deposition step can include one or more of trimethylaluminum(TMA) and water, boron trichloride and ammonia, lithium tert-butoxide (LiOtBut) and hexafluoroacetylacetone (Hfac) or titanium fluoride(TiF.sub.4). A pressure within a reaction chamber during the ALD step can range from about 1 Torr to about 10 torr or about 25 Torr to about 760 Torr. A temperature within a reaction chamber during the ALD step can range from about 33° C. to about 77° C. or about 150° C. to about 300° C.

[0036] As illustrated in more detail below, during the ALD steps, the reactant may react with material (e.g., lithium hydroxide) on a surface relative to other material (e.g., lithium carbonate). The reaction can form lithium metal (e.g., aluminum) oxide, nitride, boride, or fluoride preferentially on the other material. The lithium metal oxide, nitride, boride, or fluoride that thus forms can form part of the SBC.

[0037] The material (e.g., LiOH) may react non-stoichiometrically at first (offset from zero—illustrated in FIG. 7) with substantial reaction product (e.g., Li—Al-oxide), while the transition metals (e.g., Ni, Co, Mn) are coated with the ALD deposited material to protect the transition metals from dissolution. In some cases, 2 to 4 or 6 cycles allows enough Li—Al-oxide to be available for Li diffusion and to protect the transition metals in the cathode material, whereas too many ALD cycles may coat lithium metal oxide (e.g., lithium aluminum oxide) with material and thereby prevent or mitigate lithium diffusion through the SBC—thus insulating the NMC powder with deposited material. After initially reacting to form non-stoichiometric lithium metal oxide, the lithium metal oxide may form stoichiometrically over, for example, LiOH to form, for example, stoichiometric amorphous lithium metal (e.g., aluminum) oxide. It is thought that lithium can diffuse through the amorphous lithium metal (e.g. aluminum) oxide and can be present on the surface, thus enhancing cathode performance.

[0038] In accordance with examples of the disclosure, as illustrated in FIG. 1, XPS analysis of material formed in accordance with the disclosure shows that NCM materials contain residual LiOH and Li.sub.2CO.sub.3. An amount of residual CO.sub.3 detected by XPS decreased by 50% with four ALD cycles as shown in Table 1 and as illustrated in FIGS. 2 and 3.

TABLE-US-00001 TABLE 1 Carbon Chemical States (in % of Total C detected by XPS) Sample C—C, H C—O C═O O—C═O CO.sub.3 Uncoated NMC 67 13 6 6 8 4 cycles Al.sub.2O.sub.3 72 12 4 8 4 ALD on NMC

[0039] Unexpectedly, ALD coating of Al.sub.2O.sub.3 has been found to have growth rates (g Al/g LiOH or g Li.sub.2CO.sub.3) much faster on LiOH than Li.sub.2CO.sub.3. FIG. 8 illustrates Comparative area-normalized wt % Al for LiOH, Li.sub.2CO.sub.3, and NMC111 for

[0040] TMA/H.sub.2O ALD cycling. Aluminum wt % data from ICPMS were normalized by the BET surface area of each uncoated substrate powder. The higher growth rate on LiOH vs Li.sub.2CO.sub.3 indicates that these surfaces behave differently from one another during the Al.sub.2O.sub.3 ALD process, which has implications for the observed Al.sub.2O.sub.3 growth on NMC substrates. It appears that some non-ALD reaction is occurring during the first ˜9 ALD cycles, possibly a reaction forming a Li—Al oxide product, until a typical Al.sub.2O.sub.3 ALD film deposits from 10 to 15 cycles.

[0041] In accordance with further examples of the disclosure, cathode active material or cathode material is formed using material formed using a method described herein. By way of examples, a cathode can be formed using about 70 to about 90 or about 80 wt % active materials, about 5 to about 15 or about 10 wt % carbon black (Alfa Aesar), and about 5 to about 15 or about 10 wt % polyvinylidene fluoride (PVDF, Alfa Aesar) mixed with (e.g., nmethyl-2-pyrrolidone (NMP, Sigma-Aldrich)) solvent. The resulting slurry can be conformally cast on an Al foil by a doctor blade or the like. The wet slurry can be dried in air for ˜10 min at 70-80° C. and then placed in a vacuum oven heated at ˜120° C. overnight to remove residual solvent and moisture. The coated foil can then be punched into round discs or other suitable format and calendared at ˜2 t before assembly. The active cathode can vary according to application. Batteries can be assembled in an argon-filled glovebox using the CR2032 coin cell. Lithium metal can be used as the counter-electrode (anode). Between lithium metal and the cathode, a separator (e.g., Celgard-2320) can be used and a LiPF.sub.6 solution (dissolved in EC:DMC=1:1, Sigma-Aldrich) can be used as an electrolyte and filled on both sides of the separator.

[0042] FIG. 9 illustrates a cathode (or structure) 900, including a current collector 902 and cathode active material 904. Cathode active material 904 can be formed using a method—e.g., a method of controlling an amount of soluble base content of material as set forth herein. Current collector 902 can be formed of any suitable material, such as metal.

[0043] FIG. 10 illustrates a battery 1000 in accordance with additional examples of the disclosure. Battery 1000 includes cathode 900, including current collector 902 and cathode active material 904, a separator 1002, and an anode 1008, including anode active material (e.g., lithium) 1004 and a current collector 1006. Separator 1002 can include a non- conducting material, such as a polymer.

[0044] Specific Examples

[0045] Atomic layer deposition (ALD) of Al.sub.2O.sub.3 was performed on LiOH (Sigma Aldrich, reagent grade >98) and Li.sub.2CO.sub.3 (Sigma Aldrich, ACS reagent grade >99%) substrates in order to compare rates of growth and amount of material deposited on each substrate. In each set of experiments, 7 g of substrate were initially placed in a fluidized bed reactor operating at 120° C. 1 g of substrate was extracted from the reactor at 2, 4, 6, 8, 10, 12, and 15 ALD cycles. The

[0046] ALD process was monitored by in-situ quadrupole mass spectrometry. Following ALD, the materials were analyzed using BET for surface area analysis and ICP-MS to determine elemental content.

[0047] The mass spectrometry traces for the first six ALD cycles on LiOH and Li.sub.2CO.sub.3 are shown in FIGS. 4 and 5. The breakthrough time of the TMA dose in the first half of each of these cycles was calculated in order to qualitatively compare the amount of TMA molecules adsorbing to each surface as the ALD process progressed. The calculated TMA breakthrough times are collected in FIG. 5. Based solely on its longer TMA breakthrough times, LiOH is a more active substrate for Al.sub.2O.sub.3 deposition.

[0048] ICP results for Al content on each substrate at various ALD cycles are shown in FIG.7. The results are expressed both as Al wt % and Al wt % normalized by the BET surface area of the uncoated substrate. In the case of Al wt %, the growth rate of Al.sub.2O.sub.3 was considerably higher on LiOH than it was on Li.sub.2CO.sub.3. When normalized by the initial substrate surface area (3.175 m.sup.2/g for LiOH and 0.7128 m.sup.2/g for Li.sub.2CO.sub.3), the difference in growth rates was not as substantial, indicating that the higher surface area of LiOH may have accounted for some of the enhanced growth; however, area-normalized Al wt % data still showed a slightly higher growth rate on LiOH. Altogether, these data clearly demonstrate that LiOH is innately a more active substrate towards Al.sub.2O.sub.3 ALD than Li.sub.2CO.sub.3.

[0049] Hence, it is possible to functionalize the surface of cathode active materials by coating the particle surface using ALD which can coat transition metals, i.e., Ni, Mn, Co, LiOH, and Li2CO3, while leaving some Li exposed in order to achieve the optimal equilibrium SBC. The surface composition will be almost entirely coating (e.g., Al.sub.2O.sub.3) and Li—Al-oxide.

[0050] The present invention has been described above with reference to a number of exemplary embodiments and examples. It should be appreciated that the particular embodiments shown and described herein are illustrative of the preferred embodiments of the invention and its best mode, and are not intended to limit the scope of the invention.

[0051] Further examples of the disclosure are set forth in the claims. It will be recognized that changes and modifications may be made to the embodiments described herein without departing from the scope of the present invention. These and other changes or modifications are intended to be included within the scope of the present invention.