Li(Mn0.5Ni0.5)O2 is a promising cathode material for Li-ion rechargeable batteries due to its lower cost, improved thermal safety performance, and lower toxicity compared with LiNiO2 and LiCoO2 However, Li(Mn0.5Ni0.5)O2 exhibits rather small capacity for high-energy applications and rather high impedance for high-power applications.
A need therefore remains for an improved layered cathode material for use with lithium ion rechargeable batteries.
It is therefore an object of the present invention to provide an improved cathode for rechargeable batteries that possesses improved impedance characteristics.
It is another object of the present invention to provide an improved cathode for rechargeable batteries that possesses improved stability of the layered oxide structure during electrochemical cycling.
It is still another object of the present invention to provide an improved cathode for rechargeable batteries that possesses improved capacity characteristics.
In accordance with the above objects, a number of materials with composition Li1+xNiαMnβCoγM′δO2−zFz (M′=Mg,Zn,Al,Ga,B,Zr,Ti) have been developed for use with rechargeable batteries, wherein x is between about 0 and 0.3, α is between about 0.2 and 0.6, β is between about 0.2 and 0.6, γ is between about 0 and 0.3, δ is between about 0 and 0.15, and z is between about 0 and 0.2. Surface-coated Li1+xNiαMnβCoγM′δO2−zFz (M′=Mg,Zn,Al,Ga,B,Zr,Ti) has also been developed, wherein x is between about 0 and 0.3, α is between about 0.2 and 0.6, β is between about 0.2 and 0.6, γ is between about 0 and 0.3, δ is between about 0 and 0.15, and z is between about 0 and 0.2. Extensive testing has been conducted to investigate the effect of adding the above metal and fluorine dopants and the surface modification on capacity, impedance, and stability of the layered oxide structure during electrochemical cycling.
a)–1(c) show the morphology of (NiαMnβCoγ)-carbonate prepared by a co-precipitation method using ammonium hydrogen carbonate using magnification factors of ×500, ×2,000, and ×12,000, respectively.
a)–2(c) show the morphology of Li1+xNiαMnβCoγO2 prepared by calcinations of (NiαMnβCoγ)-carbonate and lithium carbonate at 1000° C. for 10 h in air, using magnification factors of ×1,000, ×2,000, and ×12,000, respectively;
The present invention presents layered lithium nickel manganese oxide cathode materials for lithium secondary batteries such as: (1) cathode materials doped with fluorine on oxygen sites to reduce impedance and to improve cycling stability at high temperature as well as at room temperature; (2) cathode materials doped with various metal ions on transition metal site to stabilize layered structure, suppress cation mixing and, consequently, improve electrochemical properties; lithium, cobalt, magnesium, zinc, aluminum, gallium, boron, zirconium, and titanium ions were chosen for the latter purposes; and (3) cathode materials surface-coated to improve cycling/power performance and thermal safety, wherein the coating element of the coating material source is at least one element selected from the group consisting of Al, Bi, Ga, Ge, In, Mg, Pb, Si, Sn, Ti, Tl, Zn, Zr. Either a solid-state reaction method or an aqueous solution method or a sol-gel method may be employed for the preparation of the compounds Li1+x NiαMnβCoγM′δO2-zFz with the value M′=Mg,Zn,Al,Ga,B,Zr,Ti Ti and in another embodiment Li1+xNiαMnβCoγM′δO2−zXz (M′=Mg,Zn,Al,Ga,B,Zr,Ti; X=F,S,Cl,I).
For the solid state reaction method, (Ni,Mn,Co)-hydroxides or (Ni, Mn,Co)-carbonates may be prepared by a co-precipitation method. For preparation of (Ni,Mn,Co)-hydroxides, appropriate amount of NiSO4 [or Ni(CH3COO)2.xH2O or Ni(NO3)2.xH2O], MnSO4 [or Mn(CH3COO)2.xH2O or Mn(NO3)2.xH2O], and CoSO4 [or Co(CH3COO)2.xH2O or Co(NO3)2.xH2O] are dissolved in distilled water, and the solution is added to another solution of ammonium hydroxide (NH4OH) and sodium hydroxide (NaOH) with a pH=10˜12. During the co-precipitation process, the pH of the overall solution is kept at 10˜12 using NaOH. For preparation of (Ni,Mn,Co)carbonates, appropriate amount of NiSO4 [or Ni(CH3COO)2.xH2O or Ni(NO3)2.xH2O], MnSO4 [or Mn(CH3COO)2.xH2O or Mn(NO3)2.xH2O], and CoSO4 [or Co(CH3COO)2.xH2O or Co(NO3)2.xH2O] are dissolved in distilled water, and the solution is added to another aqueous solution of ammonium hydrogen carbonate [(NH)4HCO3]. During the co-precipitation process, the temperature of the overall solution is kept at 40–70° C. The co-precipitated powders are filtered and dried. To prepare a Li1+xNiαMnβCoγM′δO2−zFz (M′=Mg,Zn,Al,Ga,B,Zr,Ti) compound, appropriate amounts of lithium hydroxide (or lithium carbonate), lithium fluoride, (Ni,Mn,Co)-hydroxide [or (Ni,Mn,Co)-carbonate], and M′-hydroxides (or M′-oxides) are mixed. The mixed powders are calcined at 450˜550° C. for 12–30 hours in air and then at 900–1000° C. for 10–24 hours either in air or in an oxygen-containing atmosphere.
For the aqueous solution method, appropriate amounts of lithium hydroxide, lithium fluoride, nickel hydroxide, cobalt hydroxide, and M′-hydroxide (or M′-nitrate) are dissolved in distilled water whose pH is adjusted with nitric acid. An aqueous solution of manganese acetate is added to the above solution. The mixed solution is refluxed in a round bottom flask attached with a condenser at 80° C. for about 12–24 hours and evaporated in a rotary vacuum evaporator. Organic contents in the gel precursor are eliminated at 400° C. for 2 hours. Finally, the resulting powder is calcined at 900–1000° C. for about 10–24 hours either in air or in an oxygen-containing atmosphere.
For the sol-gel method, appropriate amounts of lithium acetate, lithium fluoride, nickel acetate, manganese acetate, cobalt acetate, and M′-acetate are dissolved in distilled water and added to a glycolic/tartaric acid solution that is used as a chelating agent. The solution pH is adjusted to around 7 using ammonium hydroxide. The entire process is conducted under continuous stirring and heating on a hot plate. The resulting gel precursor is decomposed at 450° C. for 5 hours in air. The decomposed powders are then fired at about 900–1000° C. for about 10–24 hours either in air or in an oxygen-containing atmosphere.
For the surface-coating of the synthesized compound Li1+xNiαMnβCoγM′δO2−zFz, coating solutions are prepared by dissolving coating material sources in organic solvents or water. The coating material sources include A′-alkoxide, A′-salt or A′-oxide, where A′ includes Al, Bi, Ga, Ge, In, Mg, Pb, Si, Sn, Ti, Tl, Zn, Zr or mixtures thereof. The coating solutions are mixed with the synthesized compound Li1+xNiαMnβCoγM′δO2−zFz by an impregnation method such as dip coating. The amount of coating material sources may be between about 0.05 and 10 weight percent of Li1+xNiαMnβCoγM′δO2−zFz. Thereafter, the surface-coated Li1+xNiαMnβCoγM′67 O2−zFz powder is dried at temperatures between about 25° C. and 700° C. for approximately 1 to 24 hours.
The synthesized compound is mixed with a carbon additive and a PVDF binder to form a laminate film on an aluminum foil. This laminate is used for electrochemical testing in the presence of lithium or carbon counter electrodes and non-aqueous electrolytes made of LiPF6/EC:DEC (1:1).
a)–1(c) show the morphology of (NiαMnβCoγ)-carbonate prepared by the co-precipitation method using ammonium hydrogen carbonate. Spherical shape precursors with homogeneous size distribution are obtained by the co-precipitation. The magnification factors of
a)–2(c) show the morphology of Li1+xNiαMnβCoγO2 prepared by calcinations of (NiαMnβCoγ)-carbonate and lithium carbonate at 1000° C. for 10 h in air. The spherical shape of the precursor is preserved after calcinations. The magnification factors of
The materials described herein can be used as cathodes in lithium-ion rechargeable batteries for products such as electric vehicles, hybrid electric vehicles, portable electronics, and a variety of other products. The materials described herein are less expensive and thermally safer than existing cathode materials such as LiCoO2 and LiNiO2. The materials of the present invention also exhibit improved calendar/cycle life when compared to existing cathode materials.
It should be understood that the above description of the invention and specific examples and embodiments, while indicating the preferred embodiments of the present invention are given by demonstration and not limitation. Many changes and modifications within the scope of the present invention may therefore be made without departing from the spirit thereof and the present invention includes all such changes and modifications.
This application claims the benefit under 35 U.S.C. 119(e) U.S. Provisional Patent Application No. 60/423,347, filed Nov. 1, 2002, incorporated herein by reference in its entirety.
This invention was made with government support under Contract No. W-31-109-ENG-38 awarded to the Department of Energy. The Government has certain rights in this invention.
Number | Name | Date | Kind |
---|---|---|---|
6040090 | Sunagawa et al. | Mar 2000 | A |
6677082 | Thackeray et al. | Jan 2004 | B2 |
6680143 | Thackeray et al. | Jan 2004 | B2 |
20020055042 | Kweon et al. | May 2002 | A1 |
20020119374 | Yang et al. | Aug 2002 | A1 |
Number | Date | Country |
---|---|---|
2000243394 | Sep 2000 | JP |
Number | Date | Country | |
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20040091779 A1 | May 2004 | US |
Number | Date | Country | |
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60423347 | Nov 2002 | US |