Patent Application
20140141329
Today, three main types of insertion materials are being studied as lithium ion battery cathodes, the so-called nickel manganese cobalt-based layered oxides, nickel manganese-based spinels, and iron-based olivines. While each class has its own strengths, none are ideal. Nickel manganese cobalt-based layered oxides offer high energy density, but have questionable safety and poor rate capability. Manganese-based spinels, on the other hand, have good rate capability but low specific capacity, low energy density, and poor cycle life at high temperature. Lastly, iron-based olivines are cheap, safe, and show good cycle life, but have low gravimetric and volumetric energy density. Therefore, searching for novel and improved cathode materials is important for the lithium ion battery industry.
The present disclosure describes, among other things, new layered molybdenum oxides for lithium ion battery cathodes from solid solutions of Li2MoO3 and LiCrO2. These materials display high energy density, good rate capability, great safety against oxygen release at charged state due mostly to their low voltage. Therefore, these materials have properties desirable for lithium ion battery cathodes.
The present disclosure encompasses compounds of the formula:
Li(Li(1-x)/3Mo(2-2x)/3Crx)O2,
wherein 0<x≦0.5. In some embodiments, x=0.1, 0.2, 0.3, 0.4. or 0.5. The terms “compound” and “solid solution” are used interchangeably in the present disclosure.
It will be appreciated that in addition to the compositions described herein, the present disclosure encompasses the use of dopants, additives, and/or the presence of impurities in any of the described compositions and uses thereof. In some embodiments, one or more dopants are selected from the group consisting of nickel, cobalt, manganese, iron, titanium, copper, silver, magnesium, calcium, strontium, zinc, aluminum, chromium, gallium, germanium, tin, tantalum, niobium, zirconium, fluorine, sulfur, yttrium, tungsten, silicon, and lead. This is a non-limiting list; other dopants, additives, or impurities are possible. In some embodiments, a dopant, additive, or impurity can be mixed into these compounds to improve properties such as rate, safety, etc, without substantially modifying the chemical nature of the compound.
In addition, during the synthesis of compounds described herein, some loss of lithium may occur, resulting in a substoichiometric amount of lithium relative to the other elements in formula Li(Li(1-x)/3Mo(2-2x)/3Crx)O2. In some embodiments, such compounds deficient in lithium are of formula Li((4-x)/3)-w(Mo(2-2x)/3Crx)O2, wherein 0≦w≦0.2 and w represents a lithium deficiency. The present invention encompasses such lithium deficient compounds, materials comprising such compounds, and uses thereof.
i. Solid Solutions
To prepare Li(Li(1-x)/3Mo(2-2x)/3Crx)O2, Li2CO3, MoO2, and Cr3(OH)2(OOCCH3)7 were used as precursors. A 5% excess of Li2CO3 from the stoichiometric amount needed to synthesize Li(Li(1-x)/3Mo(2-2x)/3Crx)O2 (x=0.1, 0.2, 0.3, 0.4) was used to compensate for possible Li loss during high temperature solid state reaction. The precursors were dispersed into acetone and ball milled for 24 hours and dried overnight to prepare the mixture of precursors. The mixture was fired at 1050° C. for 15 hours under Ar gas, and manually ground to obtain the final products. For the comparison, Li2MoO3 was synthesized using Li2CO3 and MoO2 precursors. Again, a 5% excess of Li2CO3 from the stoichiometric amount was used to compensate for Li loss during the high temperature firing. The mixture of Li2CO3 and MoO2 for Li2MoO3 was prepared by using the same ball milling method and fired at 750° C. for 6 hours under a mixture of H2 (3%) and Ar (97%) gas.
For structure characterization, a Cr-source Rigaku X-ray diffractometer was utilized. For electrochemical tests, Swagelok cells were assembled under Ar atmosphere in a glove box. The cathode was composed of 80 wt % of Li(Li(1-x)/3Mo(2-2x)/3Crx)O2 (x=0, 0.1, 0.2, 0.3, 0.4), 15 wt % of carbon black, and 5 wt % of PTFE. For some samples, instead of hand mixing, planetary ball milling at 500 rpm for 2 hours was adopted to mix the active material and carbon black to decrease the particle size of the active material. 1 M of LiPF6 in 1:1 ratio of EC:DMC solution was used as an electrolyte, and Li metal foil was used as the anode.
ii. Carbon Coating
Sucrose (C12H22O11) was used as a carbon precursor, and it was mixed in a planetary ball mill with Li(Li(1-x)/3Mo(2-2x)/3Crx)O2 (x=0 to 0.3) in weight ratios between 90:10 and 70:30 of active material to sucrose. Then, the mixture was annealed between 400° C. to 800° C. for 2 to 6 hours under Ar gas. The annealed compound was ground manually with a mortar and pestle and mixed with carbon black and PTFE binder for the electrode preparation.
Carbon coating was found to improve the cycling performance of Li(Li0.233Mo0.467Cr0.3)O2, especially when carbon coated Li(Li0.233Mo0.467Cr0.3)O2 was cycled between 1.5-4.3V vs. 1.5-4.0V. Un-coated Li(Li0.233Mo0.467Cr0.3)O2 has shown observable capacity fading while carbon coated Li(Li0.233Mo0.467Cr0.3)O2 shows negligible capacity fading as well as higher discharge capacity upon cycling.
In addition to carbon, other coatings may also be used in accordance with the present invention. For example, by way of nonlimiting example, a coating may be selected from a member consisting of MgO, Al2O3, SiO2, TiO2, ZnO, SnO2, ZrO2, Li2O-2B2O3 glass, phosphates, and combinations thereof.
XRD data
This work was supported by Bosch and Umicore.
The present application claims priority to U.S. provisional patent application No. 61/708,963, filed Oct. 2, 2012, the entire contents of which are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61708963 | Oct 2012 | US |
