Method and apparatus for preparation of spherical metal carbonates and lithium metal oxides for lithium rechargeable batteries

[0001] This application is a continuation in part of and claims priority to U.S. patent application Ser. No. 10/699,484, titled “Layered Cathode materials for Lithium Ion Rechargeable Batteries”, filed on Oct. 31, 2003, and incorporated herein by reference in its entirety, which claims priority to U.S. Provisional Patent Application No. 60/423,347, filed Nov. 1, 2002, also incorporated herein by reference in its entirety.

[0002] 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.

[0003] Rechargeable lithium batteries have become widely used in both consumer and industrial applications. Rechargeable lithium batteries have a higher volumetric and gravimetric energy densities than other rechargeable batteries such as nickel metal hydride (NiMH) batteries and Ni—Cd batteries. Furthermore, the rechargeable lithium batteries have no memory effects and do not contain any poisonous metal elements such as mercury, lead, and cadmium. The applications of lithium batteries encompass a wide range of applications including small portable electronics such as notebook computers and personal digital assistants to electric vehicles and satellites.

[0004] Li(Mn_0.5Ni_0.5)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 LiCoO_2. However, Li(Mn_0.5Ni_0.5)O₂ exhibits rather small capacity for high-energy applications and rather high impedance for high-power applications.

[0005] In addition to new types of cathode materials, various changes in the uses of lithium batteries have brought focus upon the energy density and packing density of the batteries. To achieve the high packing density of the cathode composite, spherical cathode particles with a narrow size distribution are desired. Furthermore, since a sphere has the smallest surface area among other morphology with the same volume, it is believed that thermal safety is increased with the use of spherical particles by way of reducing the contact areas between the cathode materials and liquid electrolyte.

[0006] A need therefore remains for an improved layered cathode material for use with lithium ion rechargeable batteries.

[0007] It is therefore an object of the present invention to provide an improved cathode for rechargeable batteries that possesses improved impedance characteristics.

[0008] 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.

[0009] It is another object of the present invention to provide an improved cathode for rechargeable batteries that possesses improved packing density and thermal safety.

[0010] It is still another object of the present invention to provide an improved cathode for rechargeable batteries that possesses improved capacity characteristics.

[0011] In accordance with the above objects, a number of materials with composition Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z (M′=Mg,Zn,Al,Ga,B,Zr,Ti) have been developed for use with rechargeable batteries, wherein x is between 0 and about 0.3, α is between about 0.2 and about 0.6, β is between about 0.2 and about 0.6, γ is between 0 and about 0.3, δ is between 0 and about 0.15, and z is between 0 and about 0.2. Surface-coated Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z (M′=Mg,Zn,Al,Ga,B,Zr,Ti) has also been developed, wherein x is between 0 and about 0.3, α is between about 0.2 and about 0.6, β is between about 0.2 and about 0.6, γ is between 0 and about 0.3, δ is between 0 and about 0.15, and z is between 0 and about 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.

[0012] Further, in accordance with the above objects, a number of spherical metal carbonates have been developed with a narrow size distribution and with a composition of (Ni_aCo_bMn_c)CO₃, where the a is between 0 and about 1, the b between 0 and about 1, and the c between 0 and about 1. Extensive testing was conducted to investigate the effect of various experimental factors—concentration of metal solutions, concentration of precipitating agent solutions, reaction temperature, and aging time—on the size and morphology of the precipitates. Spherical lithium metal oxides were synthesized by using the spherical metal carbonates. The composition of the spherical lithium metal oxides thus synthesized is Li_1+xNi_αCo_βMn_γM′₆₇O_yF_z (M′=Mg,Zn,Al,Ga,B, Zr,Ti), where the x is between 0 and about 0.2, the α between 0 and about 1, the β between 0 and about 1, the γ between 0 and about 2, the δ between 0 and about 0.2, the y is between about 2 and about 4, and the z is between 0 and about 0.5.

[0037] 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. Another aspect of the present invention relates to a method of preparing: 1) spherical mixed nickel-cobalt-manganese carbonates with a narrow size distribution, and 2) spherical lithium nickel cobalt manganese oxide using the spherical carbonate precursors.

[0038] 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 Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z with the value M′=Mg,Zn,Al,Ga,B,Zr,Ti.

[0039] 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] or sodium carbonate (Na₂CO₃). 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 Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z (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˜700° C. for 12-30 hours in air and then at 700-1000° C. for 10-24 hours either in air or in an oxygen-containing atmosphere.

[0040] 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 800-1000° C. for about 10-24 hours either in air or in an oxygen-containing atmosphere.

[0041] 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 800-1000° C. for about 10-24 hours either in air or in an oxygen-containing atmosphere.

[0042] For the surface-coating of the synthesized compound Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z, 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 Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z 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 Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z. Thereafter, the surface-coated Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z powder is dried at temperatures between about 25° C. and 700° C. for approximately 1 to 24 hours.

[0043] 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).

[0044] FIGS. 1(a)-1(c) show the morphology of (Ni_αMn_βCo_γ)-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 FIGS. 1(a), 1(b), and 1(c) are ×500, ×2,000, and ×12,000, respectively.

[0045] FIGS. 2(a)-2(c) show the morphology of Li_1+xNi_αMn_βCo_γO₂ prepared by calcinations of (Ni_αMn_βCo_γ)-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 FIGS. 2(a), 2(b) and 2(c) are ×1,000, ×2,000, and ×12,000, respectively.

[0046] FIGS. 3 and 4 represent X-ray diffraction patterns of Li_1+xNi_αMn_βCo_γM′_δO_2−zF_z compounds. All of the compounds exhibit the ordered rock-salt structure with crystallographic structure of R 3m. For the Li-excess composition such as Li(Li_0.2Ni_0.2+0.5zCo_0.1Mn_0.5−0.5z)O_2−zF_z, extra peaks appear at 20˜25°, as shown in FIG. 4, which are generally attributed to cation ordering in the transition metal layer.

[0047] FIG. 5 shows the first charge/discharge curves of Li/Li(Ni_αMn_βCo_γ)O_2−zF_z cells, and FIG. 6 shows cycling performance of Li/Li(Ni_αMn_βCo_γ)O_2−zF_z cells. FIGS. 5 and 6 clearly show that the discharge capacity increases by more than 10%, and the cycling performance improves by the simultaneous substitution of cations and anions.

[0048] FIG. 7 shows area specific impedance (ASI) of C/Li(Ni_αMn_β)O_2−zF_z cells as a function of state of charge (SOC) measured by 30s-current interruption. FIG. 8 shows the variation of the ASI values at 50% SOC of C/Li(Ni_αMn_β)O_2−zF_z cells. FIGS. 7 and 8 clearly show that fluorine doping lowers impedance and enhances cycling stability.

[0049] FIGS. 9 and 10 show the cycling performance of uncoated Li(Ni_αMn_βCo_γ)O₂, Li(Ni_αMn_βCo_γ)O₂ coated with 0.5 wt % Al-isopropoxide, and Li(Ni_αMn_βCo_γ)O₂ coated with 1.0 wt % Al-isopropoxide at room temperature and 55° C., respectively. The coating solution is prepared by dissolving appropriate amount of Al-isopropoxide in ethanol. Li(Ni_αMn_βCo_γ)O₂ powders are then mixed thoroughly with the coating solution and dried at 100° C. for 12 h. The coated powders are subsequently heat-treated at 300° C. for 3 h in air. For FIG. 9, the data identified under group (a), α=0.4, β=0.4, γ=0.2, with the Li(Ni_αMn_βCo_γ)O₂ uncoated. For the data identified under group (b), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂ is coated with 0.5 wt % Al-isopropoxide. For the data identified under group (c), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂ is coated with 1.0 wt % Al-isopropoxide. In FIG. 10, for the data identified under group (a), α=0.4, β=0.4, γ=0.2, with the Li(Ni_αMn_βCo_γ)O₂ uncoated. For the data identified under group (b), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂ is coated with 0.5 wt % Al-isopropoxide.

[0050] FIG. 11 shows the variation of area specific impedance (ASI) with cycling of C/Li(Ni_αMn_βCo_γ)O₂ measured by a 30s current interruption method with C/Li(Ni_αMn_βCo_γ)O₂ cells. The cells with coated cathode materials exhibit a very limited increase of ASI, whereas the cells with uncoated cathode material show a large impedance increase with cycling.

[0051] FIG. 12 shows the a.c. impedance spectroscopy of C/Li(Ni_αMn_βCo_γ)O₂ cells as a function of cycle number measured with C/Li(Ni_αMn_βCo_γ)O₂ cells. This representation indicates the surface coating significantly improves the stability of the cathode surface/electrolyte interface. In FIGS. 11 and 12, for the data identified under chart (a), α=0.4, β=0.4, γ=0.2, with the Li(Ni_αMn_βCo_γ)O₂ uncoated. For the data identified under chart (b), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂ is coated with 0.5 wt % Al-isopropoxide. For the data identified under chart (c), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂ is coated with 1.0 wt % Al-isopropoxide.

[0052] FIG. 13 presents the impedance variation with a 55° C.-storage time measured with C/Li(Ni_αMn_βCo_γ)O₂ cells. For the data identified under group (a), α=0.4, β=0.4, γ=0.2, with the Li(Ni_αMn_βCo_γ)O₂ uncoated. For the data identified under group (b), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂ is coated with 0.5 wt % Al-isopropoxide. For the data identified under group (c), α=0.4, β=0.4, γ=0.2, and the Li(Ni_αMn_βCo_γ)O₂is coated with 1.0 wt % Al-isopropoxide. FIGS. 9-13 clearly show the surface coating greatly improving the cycle life, as well as calendar life, of the lithium-ion cells.

[0053] FIG. 14 shows the first charge/discharge curves and variation of discharge capacity with cycle number of Li/Li_1+x(Ni_αMn_βCo_γ)O₂ cells. FIG. 15 shows the area specific impedance of C/Li_1+x(Ni_αMn_βCo_γ)O₂ cells as a function of state of charge measured by a 30s current interruption method.

[0054] FIG. 16 shows cycling performance of Li/Li_1+x(Ni_αMn_βCo_γ)O_2−zF_z cells at room temperature and at 55° C. FIG. 17 shows the area specific impedance of Li/Li_1+x(Ni_αMn_βCo_γ)O_2−zF_z cells measured by a 30s current interruption method.

[0055] FIGS. 14-17 clearly show that substitution of oxygen with fluorine significantly improves cycling performance and lowers the impedance of the cathode materials.

[0056] Another aspect of the present invention relates to a method for preparing spherical, mixed nickel-cobalt-manganese carbonates with a narrow size distribution and a method for preparing spherical lithium nickel cobalt manganese oxide using the spherical precursors, a coprecipitation method is used to prepare the spherical precursors, (Ni_aCo_bMn_c)CO₃, where the a is between 0 and 1, the b between 0 and 1, and the c between 0 and 1. Ammonium hydrogen carbonate (NH₄HCO₃) or sodium carbonate (Na₂CO₃) is used for precipitating agents for the coprecipitation. Using the spherical (Ni_αCo_βMn_γ)CO₃, spherical lithium metal oxides with composition Li_1+xNi_αCo_βMn_γM′_δO_yF_z (M′=Mg,Zn,Al,Ga,B,Zr,Ti) are created, where the x is between 0 and about 0.2, the α between 0 and about 1, the β between 0 and about 1, the γ between 0 and about 2, the δ between about 0 and about 0.2, the y is between about 2 and about 4, z is between 0 and about 0.5.

[0057] The spherical (Ni_aCo_bMn_c)CO₃ is prepared by coprecipitation as follows. Appropriate amounts of Ni-acetate (or Ni-nitrate or Ni-sulfate), Co-acetate (or Co-nitrate or Co-sulfate), and Mn-acetate (or Mn-nitrate or Ni-sulfate) are dissolved in distilled water and the metal solution is added to another aqueous solution of ammonium hydrogen carbonate or sodium carbonate. The concentration of metal solutions ([Me]) is varied from about 0.01M to about 2M; the concentrations of ammonium hydrogen carbonate solution ([AHC]) or sodium carbonate ([SC]) is varied from about 0.1M to about 5M. The pH of the ammonium hydrogen carbonate solution or the sodium carbonate solution is varied from about 7 to about 12 using ammonium hydroxide or sodium hydroxide. The reaction temperature is varied from about 20° C. to about 65° C. When the metal solution is added to the ammonium hydrogen carbonate solution, the precipitates form instantly. The precipitates are then aged in the solution at each temperature from about 1 h to about 24 h. All of the precipitation reaction and aging are carried out under constant stirring. After aging, the coprecipitated powders are filtered and dried.

[0058] To prepare a Li_1+xNi_αCo_βMn_γM′_δO_yF_z (M′=Mg,Zn,Al,Ga,B,Zr,Ti) compound, appropriate amounts of lithium hydroxide (or lithium carbonate or lithium nitrate), (Ni_aCo_bMn_c)CO₃, M′-hydroxides (or M′-carbonates or M′-oxides), and LiF (or NH₄F) are mixed. The mixed powers are calcined at about 450° C. to about 700° C. for about 12-30 hours either in air or in oxygen atmospheres and then at about 700° C. to about 1000° C. for about 10-24 hours either in air or in oxygen atmospheres.

[0059] In one exemplary embodiment, the synthesized compound Li_1+xNi_αCo_βMn_γM′₆₇O_yF_z is mixed with a carbon additive and a PVDF binder to form a laminate film on aluminum foil. This laminate is used, for example, in electrochemical testing in the presence of lithium or carbon counter electrode and non-aqueous electrolyte made of LiPF₆/ED:DEC (1:1).

[0060] FIG. 18 shows SEM images of (Ni_1/3Co_1/3Mn_1/3)CO₃ precipitates. The a metal solution and ammonium hydrogen carbonate (AHC) concentrations were 0.1 and 1.0M respectively; the reaction temperature (T_R) and the aging time (t_a) were 65° C. and 17 h, respectively. It can be seen in FIG. 18 that the carbonate precipitates have a spherical morphology with a mean particle size (D50) of about 5-6 μm and a very narrow size distribution of about 1 to 50 microns.

[0061] FIG. 19 shows additional SEM images of (Ni_1/3Co_1/3Mn_1/3)CO₃, prepared by different methods. FIG. 19(a) shows the SEM images of (Ni_1/3Co_1/3Mn_1/3)CO₃ precipitates prepared with a metal solution of about 0.05M, AHC concentration of about 0.5M, T_R=about 65° C., t_a=about 17 h; 19(b) shows the SEM images of (Ni_1/3Co_1/3Mn_1/3)CO₃ precipitates prepared with Me concentration of 0.2M, AHC concentration of 2.0M, T_R=about 65° C., t_a=about 4 h.

[0062] FIGS. 20(a) and 20(b) show the SEM images of (Ni_0.219Co_0.125Mn_0.656)CO₃ precipitates prepared with a metal solution concentration of 0.1M, AHC concentration of about 1.0M, t_a=about 6 h at different temperatures (about 20° C. and about 40° C., respectively).

[0063] FIG. 21 shows an SEM image of MnCO₃ precipitates prepared with a metal solution concentration of about 0.1M, AHC concentration of about 1.0M, T_R=about 55° C., and t_a=about 17 h.

[0064] FIG. 22 shows an SEM image of (Co_0.5Mn_0.5)CO₃ precipitates prepared with a metal solution concentration of about 0.1M, AHC concentration of about 1.0M, T_R=about 50° C., and t_a=about 17 h.

[0065] FIG. 23 represents the x-ray diffraction (XRD) patterns of the (Ni_1/3Co_1/3Mn_1/3)CO₃ and MnCO₃ precipitates shown in FIGS. 18 and 21, respectively, together with the reported XRD patterns of MnCO₃. The XRD patterns of the coprecipitated materials are well matched with the reported XRD patterns of MnCO₃ with rhombohedral structure (space group of R3c).

[0066] FIG. 24 shows the SEM images of Li[Ni_1/3Co_1/3Mn_1/3]O₂ prepared using the (Ni_1/3Co_1/3Mn_1/3)CO₃ shown in FIG. 18. The calcinations were carried out at about 1000° C. for about 10 h in air. It can be seen in FIG. 24 that the Li[Ni_1/3Co_1/3Mn_1/3]O₂ material retained the size and morphology of the (Ni_1/3Co_1/3Mn_1/3)CO₃ precursor.

[0067] FIG. 25 represents the XRD patterns of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ material shown in FIG. 24. The material exhibits the ordered rock-salt structure with crystallographic structure of R3m.

[0068] FIGS. 26(a) and 26(b) show the first charge/discharge curves of the Li/Li[Ni_1/3Co_1/3Mn_1/3]O₂ cells cycled in the voltage range of 2.8-4.6V and the variation of the discharge capacities as a function of cycle number, respectively.

[0069] 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.

[0070] 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.