Patent Application
20150180031
This invention relates to electrode materials for electrochemical cells and batteries. Such cells and batteries are used widely to power numerous devices, for example, portable electronic appliances and medical, transportation, aerospace, and defense systems.
State-of-the-art lithium batteries do not provide sufficient energy to power electric vehicles for an acceptable driving range. This limitation arises because the electrodes, both the anode, typically graphite, and the cathode, typically, layered LiMO2 (M=Mn, Co, Ni), spinel LiMn2O4, and olivine LiFePO4, do not offer sufficient capacity or a high enough electrochemical potential to meet the energy demands. Approaches that are currently being adopted to enhance the energy of lithium-ion batteries include the exploitation of recently disclosed cathode materials with composite structures such as ‘layered-layered’ xLi2MnO3.(1−x)LiMO2 (Mn=Mn, Ni, Co) materials and ‘layered-spinel’ xLi2MnO3.(1−x)LiM2O4 (Mn=Mn, Ni, Co) materials, that offer a significantly higher capacity compared to conventional cathode materials, including the high voltage spinel, LiMn1.5Ni0.5O4, that operates at a significantly higher voltage (4.7 V) than the conventional spinel LiMn2O4 (4.1 V). However, these lithium- and manganese-rich high capacity composite cathodes suffer from ‘voltage fade’ on repeated cycling, which reduces the energy output and efficiency of the cell, thereby compromising the management of cell/battery operation. On the other hand, delithiated Li1−xMn1.5Ni0.5O4 electrodes tend to be unstable with respect to organic electrolyte solvents at the high operating potential, compromising the cycle life of the cells.
There is an ongoing need for new electrode materials to ameliorate the problems associated with high-voltage spinel electrode materials. The lithium-rich spinel metal oxides, electrodes, electrochemical cells, and batteries described herein address this need.
The present invention provides a lithium-rich spinel metal oxide electrode material which is useful in lithium battery applications. The lithium-rich spinel metal oxide electrode material has the formula: Li1+dMn2−y−dMyO4; wherein 0<d≦0.2; 0.2<y≦0.6; and M comprises Ni, Co, or a combination thereof. In some embodiments, M further comprises at least one other transition metal in addition to the Ni, Co, or the combination thereof, for example, a first row transition metal other than Ni and Co (e.g., Fe), a second row transition metal (e.g., Zr or Mo), and the like. In addition, or alternatively, M can further comprise one or more metals selected form a first row transition metal, Al and/or Mg, in addition to the Ni and Co. In some embodiments, the relative excess of lithium in the spinel electrode material, represented by “d”, falls within the range of 0<d≦0.1, or 0<d≦0.05. The relative proportion of M in the spinel electrode material, in some embodiments, falls within the range of 0.4<y≦0.6, or 0.45<y≦0.55. In some embodiments, 0<d≦0.1 and 0.4<y≦0.6, particularly when M is Ni, or comprises Ni and Co.
In one preferred embodiment of the lithium-rich spinel material, 2−y−d is greater than or equal to 1.5, M is NiwMaz, Ma comprises at least one metal selected from the group consisting of a first row transition metal, Al, and Mg, w+z=y; and w is less than 0.5. In another preferred embodiment, 2−y−d is less than 1.5, M is NiwMaz, Ma comprises at least one metal selected from the group consisting of a first row transition metal, Al, and Mg; w+z=y; and w is greater than or equal to 0.5. Preferably, in these embodiments, z is 0 or close to 0 (e.g., 0.1 or less); in other words, M is substantially Ni. In another embodiment, the Li, Mn and M ions of the Li1+dMn2−y−dMyO4 spinel structure can be partially disordered in the structure, i.e., the Li, Mn and M ions may partially occupy the tetrahedral and/or octahedral sites of the spinel structure.
Desirably, the lithium rich spinel material can be physically combined with, or integrated with, at least one layered lithium metal oxide. For example, the layered lithium metal oxide component can comprise a material of formula LiMbO2, wherein Mb comprises Mn, Co, Ni, or a combination of two or more thereof. If desired, Mb can also include at least one other metal selected, e.g., from the group consisting of a transition metal, Al, and Mg, in addition to the Mn, Co and Ni. In other embodiments, the layered lithium metal oxide component can comprise a material of formula Li2McO3, wherein Mc comprises Mn, optionally in combination with at least one metal selected from the group consisting of Ti and Zr, and optionally including another transition metal. In some preferred embodiments, the layered lithium metal oxide component comprises an integrated, layered-layered lithium metal oxide of formula: xLi2MdO3.(1−x)LiMfO2; wherein Md comprises Mn, Mf comprises at least one metal selected from Mn, Ni and Co, and 0<x<1. In any of the foregoing embodiments comprising a layered component integrated together with the spinel material, the lithium-rich spinel metal oxide can include alternating layers of metal ions comprising lithium ions and non-lithium metal ions, wherein the lithium ions in the alternating layers constitute greater than 0% and up to about 25% of the total ions in the alternating layers on an atom percentage basis, depending on the formula of the lithium-rich spinel material. The term “integrated” as used herein refers to a material with multiple crystal domains of spinel and layered components sharing a common oxygen lattice; while “physically combined” refers to separately prepared particulate materials that are mixed together, optionally with a binder, to form an electrode material with separate particles of the different materials (e.g., spinel and layered materials) in close proximity or contact with each other. Additionally, the lithium ions and non-lithium metal ions in the spinel and layered components can be partially disordered within the crystal lattice structures thereof (i.e., a partial mixing of some of the ions to form a “hybrid” arrangement that is neither pure spinel or pure layered in form, e.g., boundaries between spinel domains and layered domains in the integrated crystal structure of the material).
In another aspect, the present invention provides a positive electrode for a lithium electrochemical cell comprising a lithium-rich electrode material as described herein (including e.g., a spinel material by itself, or integrated together in a layered-spinel, or a layered-layered-spinel material), optionally formulated with another positive electrode material (e.g., physically mixed with a carbon material, with another metal oxide material, typically held together by a binder). The spinel electrode material can be placed in contact with a current collector, such as a metal foil, or can be coated on the current collector. Such electrodes can be utilized as the positive electrode in a lithium electrochemical cell, in combination with a negative electrode (e.g., a carbon material) in contact with a non-aqueous electrolyte comprising a lithium salt (e.g., LiPF6, LiBF4, or other such materials dissolved in a non-aqueous solvent such as propylene carbonate, ethylene carbonate, or a combination thereof). A lithium battery of the present invention comprises a plurality of such electrochemical cells connected together in series, parallel, or both.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
The electrode materials of the present invention address the limitations of high-voltage spinel electrode materials (e.g., LiMn1.5Ni0.5O4), by a number of means. For example, these limitations can be addressed, first, by stabilizing the electrodes with extra lithium to access additional rechargeable capacity at lower voltage (approximately 3 V); second, by introducing cobalt into the structure to raise the operating voltage of the low-voltage spinel plateau; third, by integrating the spinel with a layered or composite ‘layered-layered’ structure to tune the operating potential of the cell and to enhance the cycling stability over a wide potential range; and fourth, by a combination of two or more of the first, second and third means. As used herein, the term “lithium-rich” as applied to a LiM2O4 spinel, means a material having greater than one lithium for every four oxygen atoms in the spinel formula or, alternatively, having a Li:M ratio (in which M is a metal other than lithium) greater than 1:2 (i.e., 0.5), such as 1.05:1.95 (i.e., 0.538).
The composition of the novel lithium-rich spinel materials of the invention is broadly defined as conforming to the stoichiometric spinel formula of Li1+dMn2−y−dMyO4, in which (a) M comprises one or more metals, such as Ni, Co, Al, Mg, but always including at least some Ni. In some preferred embodiments, M is Ni and Co; or M is Ni. The excess lithium coefficient “d” falls within the range 0<d≦0.2, preferably 0<d≦0.1, and more preferably 0<d≦0.05. The coefficient “y”, which represents the relative proportion of M in the formula, falls within the range 0.2<y≦0.6, preferably 0.4<y≦0.6, and more preferably 0.45<y≦0.55. Preferably, when M is Ni and the Mn coefficient (2−y−d) is greater or equal to 1.5, the Ni coefficient (y) is less than 0.5; and when the 2-y-d is less than 1.5, y is greater than or equal to 0.5. The total number of Li, Mn and M ions in the stoichiometric Li1+dMn2−y−dMyO4 spinel formula is three metal ions per four oxygen ions, recognizing that, when used in an electrochemical cell, the lithium content of the [Mn2−y−dMy]O4 spinel framework will vary during charge (i.e., lithium extraction from the spinel metal oxide to form a lithium-depleted material), and during discharge (i.e., lithium insertion into the lithium-depleted framework). Typically, during charge and discharge, the oxidation state of the manganese ions may vary between 4+ and 3+, whereas the oxidation state of the M cations may vary from 4+ to 2+. Notwithstanding these changes in oxidation state, other redox processes may also occur during the electrochemical redox processes, for example, those that access higher or lower oxidation states of the Mn and/or M cations, and/or redox processes that occur on the oxygen ions. Preferably, the theoretical capacity of the electrode should be greater than 100 mAh/g, more preferably greater than 150 mAh/g, and most preferably greater than 200 mAh/g. The principles of this invention are formulated by way of example in Table 1, which provides examples of lithium-rich spinel formulae, as well as the theoretical metal oxidation states and theoretical capacities of the materials.
The principles of this invention have been reduced to practice. For example, the data in
The relative cycling stabilities of Li1.05Mn1.525Ni0.425O4 and Li1.05Mn1.367Ni0.583O4 electrodes in lithium half cells are shown in
For comparison, the cycling profiles of a standard LiMn1.5Ni0.5O4 spinel electrode, synthesized and tested by the same procedures and conditions as the Li1+δMn2−y−δMyO4 electrodes of this invention, are shown in
It is clear that there are several advantages of the Li1+δMn2−y−δMyO4 electrodes of the invention such as Li1.05Mn1.367Ni0.583O4, described and highlighted in
In a further embodiment, the spinel electrodes of this invention can be integrated into, or blended with, structurally-compatible electrode materials, particularly those with layered-type structures, whether single phase LiMO2 materials, in which M is typically a metal ion, such as LiCoO2 (LCO), LiNi0.8Co0.15AlO2 (NCA), or more complex composite electrode structures containing an Li2MnO3 component as known in the art. These materials have the advantage of providing a voltage profile with both the sloping character of the layered components and the voltage plateaus of the spinel components, thus smoothing the overall voltage profile of high capacity, structurally-integrated, ‘composite’ layered-spinel electrodes of this invention. For example, a physically blended electrode containing 15 wt % Li1.05Mn1.525Ni0.425O4 and 85% 0.5Li2MnO3.(1−x)LiMn0.5Ni0.5O2 shows remarkable stability when cycled between 5.0 and 2.0 V at 15 mA/g. The electrochemical contribution of the spinel component is clearly visible in
The spinel electrode materials of this invention, whether used on their own, physically combined with another metal oxide, or integrated with structurally compatible metal oxides or lithium metal oxides, notably with layered LiMO2 structures, are broad in compositional scope and structure. For example, in an ideal LiM2O4 spinel structure the M cations are distributed in octahedral sites in alternating close-packed oxygen layers in a 3:1 ratio, whereas in an ideal layered structure the M cations occupy all the octahedral sites in alternating layers. Therefore, in the composite layered-spinel structures of this invention, the ratio of M cations in alternating layers of the close-packed oxygen array can vary within the structure from the 3:1 ratio of M (Mn+M) to Li in the transition metal layers of an ideal spinel configuration to the corresponding ratio of the ideal layered configuration (i.e., with no Li in the transition metal layers). Furthermore, the M and Li cations of the spinel and layered electrode materials of this invention can be partially disordered, yielding complex cation arrangements in the spinel and layered components that are not ideally configured in the composite structures.
The compositions and structures of the materials of this invention can be synthesized by various processing methods that are known in the art, for example, by sol-gel or precipitation processing techniques using precursors that decompose during synthesis, such as metal hydroxides, carbonates and oxalates, solid state reactions, or by using a Li2MnO3 template or precursor as described by Croy et al., in Electrochemistry Communications, Volume 13, pages 1063-1066 (2011). In addition, integration or blending of the spinel electrodes with structurally-compatible electrode materials can be performed by several methods including: physical blending; high-energy physical mixing (i.e. ball mill grinding); separate low-temperature (typically 450° C.-650° C.) firing of the metal oxide and other materials followed by physical mixture, and a subsequent annealing step at higher temperature (typically 750-950° C.).
The materials shown in Table 1 were prepared as follows: (NiMnCo)C2O4 (i.e., metal oxalate) precursors were prepared from NiSO4.6H2O, MnSO4.H2O, CoSO4.7H2O, and Na2C2O4 using the required ratios of Ni, Mn and Co for a targeted stoichiometry in the final product. An aqueous solution containing the required stoichiometric amounts of metal sulfates was added under stirring into a solution of the sodium oxalate. The solution was then stirred for about 3 hours at about 70° C. The co-precipitated powder was filtered, washed, and dried in air at about 105° C. The dried powders were thoroughly mixed with stoichiometric amounts of lithium carbonate and annealed at about 450° C. for about 12 hours in air, followed by grinding and an annealing step at about 750° C. for about 12 hours (also in air) to prepare materials with a desired composition. Other annealing conditions included no low temperature intermediate firing step, different annealing times and different annealing temperatures.
Cathodes for the electrochemical tests were prepared by coating Al foil with a slurry containing 82 percent by weight (wt %) of the oxide powder, 8 wt % SUPER P carbon (TIMCAL Ltd.), and 10 wt % polyvinylidene difluoride (PVDF) binder in NMP and assembled in coin cells (size 2032). The cells contained a metallic lithium anode. The electrolyte was a 1.2 M solution of LiPF6 in a 3:7 mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Coin cells were assembled in a glovebox under an inert argon atmosphere.
The invention extends to include lithium metal oxide electrode materials (e.g., lithium-rich spinels, layered oxides, and the like) with surface modification, for example, with metal-oxide, metal-fluoride or metal-phosphate layers or coatings to protect the electrode materials from highly oxidizing potentials in the cells and from other undesirable effects, such as electrolyte oxidation, oxygen loss, and/or dissolution. Such surface protection enhances the surface stability, rate capability and cycling stability of the electrode materials.
In some embodiments, individual particles of a powdered lithium metal oxide composition, a surface of the formed electrode, or both, are coated or treated, e.g., in situ during synthesis, for example, with a metal-oxide, a metal-fluoride, a metal-polyanionic material, or a combination thereof, e.g., at least one material selected from the group consisting of (a) lithium fluoride, (b) aluminum fluoride, (c) a lithium-metal-oxide in which the metal is selected preferably, but not exclusively, from the group consisting of Al and Zr, (d) a lithium-metal-phosphate in which the metal is selected from the group consisting preferably, but not exclusively, of Fe, Mn, Co, and Ni, and (e) a lithium-metal-silicate in which the metal is selected from the group consisting preferably, but not exclusively, of Al and Zr. In a preferred embodiment of the invention, the constituents of the treatment or coating, such as the aluminum and fluoride ions of an AlF3 coating, the lithium and phosphate ions of a lithium phosphate coating, or the lithium, nickel and phosphate ions of a lithium-nickel-phosphate coating can be incorporated in a solution that is contacted with the hydrogen-lithium-manganese-oxide material or the lithium-manganese-oxide precursor when forming the electrodes of this invention. Alternatively, the surface may be treated with fluoride ions, for example, using NH4F, in which case, the fluoride ions may substitute for oxygen at the surface or at least partially within the bulk of the electrode structure.
Preferably, a formed positive electrode comprises at least about 50 percent by weight (wt %) of a powdered lithium metal oxide composition comprising the lithium-rich spinel material, and an electrochemically inert polymeric binder (e.g., polyvinylidene difluoride; PVDF). Optionally, the positive electrode can comprise up to about 40 wt % carbon (e.g., carbon back, graphite, carbon nanotubes, carbon microspheres, carbon nanospheres, or any other form of particulate carbon).
A detailed schematic illustration of a lithium electrochemical cell 10 of the invention is shown in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The terms “consisting of” and “consists of” are to be construed as closed terms, which limit any compositions or methods to the specified components or steps, respectively, that are listed in a given claim or portion of the specification. In addition, and because of its open nature, the term “comprising” broadly encompasses compositions and methods that “consist essentially of” or “consist of” specified components or steps, in addition to compositions and methods that include other components or steps beyond those listed in the given claim or portion of the specification. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All numerical values obtained by measurement (e.g., weight, concentration, physical dimensions, removal rates, flow rates, and the like) are not to be construed as absolutely precise numbers, and should be considered to encompass values within the known limits of the measurement techniques commonly used in the art, regardless of whether or not the term “about” is explicitly stated. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate certain aspects of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/920,276, filed on Dec. 23, 2013, which is incorporated by reference in its entirety.
The United States Government has rights in this invention pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory.
| Number | Date | Country | |
|---|---|---|---|
| 61920276 | Dec 2013 | US |
