LixMn2O4-y(C1z) spinal cathode material, method of preparing the same, and rechargeable lithium and li-ion electrochemical systems containing the same

Abstract

A method of preparing a homogeneously dispersed chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel cathode material is provided. Furthermore, a homogeneously dispersed chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel cathode material is provided. In addition, a lithium or lithium ion rechargeable electrochemical cell is provided incorporating a homogeneously dispersed chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel cathode material in a positive electrode.

Claims

1. A method of preparing a homogeneously dispersed Li.sub.xMn.sub.2O.sub.4-yCl.sub.z spinel material, the method comprising: providing a chlorine-containing salt, manganese nitrate, and lithium nitrate in distilled water or deionized water to produce an aqueous solution; and producing the homogeneously dispersed Li.sub.xMn.sub.2O.sub.4-yCl.sub.z spinel cathode material by steps comprising: mixing the aqueous solution with glycine to produce a mixture; heating the mixture to produce an ash; grinding the ash; and calcining the ground ash for a time period no greater than 5 hours at a temperature of at least 350 C., wherein x ranges from 0.05 to 1.9 and y and z range from 0.005 to 0.7, wherein a particle size of the homogeneously dispersed Li.sub.xMn.sub.2O.sub.4-yCl.sub.z spinel cathode material ranges from 2.5 m to less than 10 m, and wherein the heating step comprises: heating the mixture at a temperature ranging from 75 C. to 120 C. to produce a gel; and heating the gel at a temperature ranging from 200 C. to 300 C. to produce an ash.

2. The method according to claim 1, wherein the chlorine-containing salt is a compound selected from a group consisting of lithium chloride and manganese chloride.

3. The method according to claim 1, further comprising mixing the homogeneously dispersed Li.sub.xMn.sub.2O.sub.4-yCl.sub.z spinel cathode material with a conductive carbon and a binder.

4. The method according to claim 3, wherein the conductive carbon is selected from a group consisting of carbon black, graphite, carbon nanofibers, and carbon nanoparticles.

5. The method according to claim 3, wherein the binder is selected from a group consisting of polytetrafluoroethylene, polyvinylidene fluoride, and latex.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide further understanding of the present disclosure, and are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the present disclosure, and together with the description serve to explain the principles of the present disclosure. The present disclosure will now be described further with reference to the accompanying drawings as follows:

(2) FIG. 1 is a flowchart illustrating process steps for preparing a stable lithium manganese-based AB.sub.2O.sub.4 spinel material, according to an exemplary embodiment of the present disclosure.

(3) FIG. 2 is a timeline chart contrasting the required fabrication times for preparing a stable lithium manganese-based AB.sub.2O.sub.4 spinel material, according to the present disclosure, versus required fabrication times for conventional preparation methods.

(4) FIG. 3 is an expanded spinel formation timeline chart showing an exemplary embodiment according to the present disclosure.

(5) FIG. 4 is a graph showing x-ray diffraction data for an exemplary formulation mixture according to the present disclosure.

(6) FIG. 5 is a graph showing x-ray fluorescence data for an exemplary formulation mixture according to the present disclosure.

(7) FIG. 6 is a graph showing thermal analysis data for an exemplary intermediate (pre-calcining) material according to the present disclosure.

(8) FIG. 7 is a graph showing thermal gravimetric data for an exemplary intermediate (pre-calcining) material according to the present disclosure.

(9) FIG. 8 is a graph showing differential scanning calorimetric heating cycle data for an exemplary intermediate (pre-calcining) material according to the present disclosure.

(10) FIG. 9 is a graph showing differential scanning calorimetric cooling cycle data for an exemplary intermediate (pre-calcining) material according to the present disclosure.

(11) FIG. 10 is a graph illustrating representative cycling (charge/discharge) curves for an exemplary chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel material according to the present disclosure.

(12) FIG. 11 is a graph illustrating representative cycling (charge/discharge) curves for an exemplary chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel material according to the present disclosure.

(13) FIG. 12 is a differential capacity graph illustrating the forming cycle traces for a lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to the present disclosure.

(14) FIG. 13 is a differential capacity graph illustrating the forming cycle traces for a lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to the present disclosure.

(15) FIG. 14 is a differential capacity graph illustrating the cycle life traces for a lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to the present disclosure.

(16) FIG. 15 is a differential capacity graph illustrating the cycle life traces for a lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to the present disclosure.

(17) FIG. 16 is a representative hysteresis cycling (charge/discharge) curve illustrating cycle life traces for a lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to the present disclosure.

(18) FIG. 17 is a plot of the charge capacity and delivered discharge capacity per cycle of an exemplary lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to the present disclosure.

DETAILED DESCRIPTION

(19) FIG. 1 is a flowchart illustrating process steps in an exemplary embodiment of the present disclosure. More specifically, FIG. 1 shows exemplary steps according to the present disclosure for the preparation of Li.sub.xMn.sub.2O.sub.4-y(Cl.sub.z) spinel material via a method comprising an initial nitrate glycine flame process followed by a calcining reaction. In step S1, a chlorine-containing salt in a solid state is added to manganese nitrate in a solid state and lithium nitrate in a solid state. The stoichiometric ratio of lithium to manganese to chlorine (Li:Mn:Cl) in the mixture of starting materials ranges from 0.45 to 0.6:1.0:0.005 to 0.35, from 0.45 to 0.6:1.0:0.015 to 0.2, or 0.45 to 0.6:1.0:0.03. to 0.15. Suitable chlorine-containing salts include, but are not limited to, lithium chloride and manganese chloride.

(20) In Step S2, the mixture is then dissolved in distilled or deionized water. Alternatively, the chlorine-containing salt, manganese nitrate, and lithium nitrate may be each dissolved individually in distilled or deionized water, and the aqueous solutions may be then combined. In Step S3, a chelating agent is then dissolved into the aqueous solution. Suitable chelating agents include, but are not limited to, glycine. In Step S4, the solution is heated to a temperature ranging from 75 C. to 120 C. until the water fully evaporates and a gel is formed. In Step S5, the gel is heated further to a temperature ranging from 200 C. to 300 C. until auto ignition occurs and forms an ash. The ash is collected and ground in Step S6. Suitable grinding methods include, but are not limited to, ball milling, high amplitude vibration milling, and mortar and pestle mixing.

(21) In Step S7, the ash is calcined in a furnace at 600 C. for 2 hours. Alternatively, suitable calcination temperatures and times range from 350 C. to 800 C. (for 1 to 4 hours), from 400 C. to 600 C. (for 1.5 to 3 hours), or from 500 C. to 600 C. (for 2 to 2.5 hours). In Step S8, the mixture is cooled at a temperature ranging from 20 C. to 300 C. (for 1 to 24 hours), from 20 C. to 150 C. (for 1 to 4 hours), or from 20 C. to 50 C. (for 1 to 2.5 hours).

(22) The exemplary process described above results in the formulation of a family of chlorine-modified Li.sub.xMn.sub.2O.sub.4 AB.sub.2O.sub.4 spinel materials. The general formula for the lithium electrochemical cell cathode prepared is Li.sub.xMn.sub.2O.sub.4-y(Cl.sub.z), where x1 and proves to be reversible between 5.2 and 2.0 volts. This reversible region for x in a lithium electrochemical cell comprised of the present disclosure ranges from 0.05 to 1.9 and z ranges from 0.005 to 0.70, from 0.015 to 0.4, or from 0.03 to 0.3.

(23) The addition of chlorine in the formulation and fabrication process is evenly distributed throughout the bulk of the chlorine-modified Li.sub.xMn.sub.2O.sub.4 AB.sub.2O.sub.4 spinel material. In the exemplary process described above, the chlorine and metal ions, along with nitrates and glycine, are dissolved in solution and able to interact on a molecular level. As a result of this molecular level interaction the formation of the ash during combustion yields a homogenous mixture of components formed in situ. When chlorine is added using conventional preparation methods, an additional step is required where chlorine must penetrate into the material from the surface, leading to a concentration gradient within each particle with chlorine concentration being the highest at the surface.

(24) FIGS. 2 and 3 illustrate steps and timelines for conventional fabrication methods versus the preparation methods provided in the present disclosure. These conventional solid state and hydrothermal fabrication methods are described in U.S. Pat. No. 5,753,202 and U.S. Pat. No. 5,135,732, respectively (which are incorporated by reference in their entirety). FIG. 3 shows an expanded view of the steps of an exemplary method according to the present disclosure. As shown in FIGS. 2 and 3, the entire fabrication process (including cooling time) takes over 2 or 4 days using conventional solid state and hydrothermal methods, respectively. In contrast, the entire fabrication process (including cooling time) takes approximately 4.5 hours using the present fabrication method.

(25) FIG. 4 shows the X-ray diffraction pattern for the intermediate (pre-calcining) and final Li.sub.xMn.sub.2O.sub.4-yCl.sub.z material according to the present disclosure. FIG. 4 includes standard data for intensity and location from the International Center for Diffraction Data for Mn.sub.2O.sub.3, card file number 24-508 and LiMn.sub.2O.sub.4 spinel, card file number 18-736. FIG. 5 shows the X-ray Fluorescence Pattern for an exemplary formulation mixture of the present disclosure. The data in FIG. 5 shows the X-ray Fluorescence Pattern data of the final Li.sub.xMn.sub.2O.sub.4-yCl.sub.z material as well as intensity and energy level for the system components. These components include the palladium X-ray source and silicon, phosphorus and sulfur from the sample holder.

(26) Optical microscopy using an Olympus metallograph was used to examine the Li.sub.xMn.sub.2O.sub.4-yCl.sub.z material of the present disclosure as well as Li.sub.xMn.sub.2O spinel cathode material made using conventional processing methods. It was found that the Li.sub.xMn.sub.2O.sub.4-yCl.sub.z material of the present disclosure had a typical particle size of about 2.5 m with a maximum particle size of less than 10 m. It was found that Li.sub.xMn.sub.2O spinel cathode material made using conventional processing methods yielded particle sizes of 100 m to 500 m. Further evaluation of the material found that the crystallites within the Li.sub.xMn.sub.2O.sub.4-yCl.sub.z material made using the present preparation method are in the order of 32 nm, and the crystallites within the Li.sub.xMn.sub.2O spinel cathode material made using conventional processing 56.8 nm. The crystallites sizes were determined using the Scherrer equation, a formula that relates the size of sub-micrometer crystallites in a solid to the broadening of a peak in a diffraction pattern.

(27) FIGS. 6-9 show thermal analysis data for the intermediate (pre-calcining) material according to the present disclosure. FIG. 6 shows both the thermal gravimetric data and the differential scanning calorimeter data. In particular, the thermal gravimetric data is displayed in FIG. 7 and the differential scanning calorimeter data, heating trace and cooling trace is displayed in FIGS. 8 and 9 respectively. The data presented in FIG. 7 show the reaction is driven to completion by 600 C. where the weight of the residual material becomes stable. The differential scanning calorimeter data depicted in FIG. 8 shows the phase refinement of the material at 235 C. The featureless differential scanning calorimeter cool down data shown in FIG. 9 shows that the final Li.sub.xMn.sub.2O.sub.4-yCl.sub.z material is stable with no additional phase changes after calcining.

(28) In order to evaluate the electrochemical properties of the present chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel electrochemical system, laboratory coin cells were fabricated using conventional methods described in detail below. Experimental cells may also be fabricated using other methods known in the art, incorporating the chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel material described in the present disclosure. The experimental cells were composed of a lithium anode separated from a Teflon bonded cathode with a nonwoven glass separator. Other suitable anode materials include, but are not limited to, lithium metal, lithium aluminum alloy, lithium silicon alloy, graphite and graphite derivatives, tin oxide, and lithium phosphate. The cathode was fabricated by combining Li.sub.xMn.sub.2O.sub.4-yCl.sub.z, carbon, and Teflon in a 75:15:10 weight percent basis, respectively. Suitable conductive carbon materials include, but are not limited to, conductive carbon black (commercially available from various sources, including Cabot Corporation, under the tradename VULCAN XC72 or VULCAN XC72R), graphite, carbon nanofibers, and carbon nanoparticles (commercially available under the tradename PURE BLACK, manufactured by Superior Graphite Co.). Suitable binders include, but are not limited to, polytetrafluoroethylene (commercially available under the trade name TEFLON, manufactured by DuPont), polyvinylidene fluoride (PVDF), and latex. The cathode may contain by weight 40%-95% of Li.sub.xMn.sub.2O.sub.4-yF.sub.y, 1%-40% of conductive carbon, and 1%-20% binder.

(29) The cathode mix was rolled to 0.06 cm and dried in a vacuum oven. The cathode mass was approximately 0.1 g. The cathode and 0.075 cm thick lithium foil was cut using a 1.58 cm diameter (1.96 cm2) hole punch. A 0.01 cm nonwoven glass separator was used for the separator and as a wick. The electrolyte used was 1 M LiPF6 in proportional mixtures of dimethyl carbonate and ethylene carbonate. Other suitable electrolytes include, but are not limited to, lithium hexafluoroarsenate monohydrate (LiAsF.sub.6), lithium perchlorate (LiClO.sub.4), lithium tetrafluoroborate (LiBF.sub.4), and lithium triflate (LiCF.sub.3SO.sub.3).

(30) The cells were cycled with an ARBIN Model MSTAT4 Battery Test System. The charge profile consisted of a constant current charged at 1.0 mA to 4.75 volts. The cells were discharged at 1.0 mA to 3.5 volts. A rest period of 15 minutes between cycles allowed for the cells to equilibrate. Prior to cycling, cell impedance was recorded with a Solartron, SI1260 Frequency Response Analyzer with a Solartron, SI1287 Electrochemical Interface using Scribner Associates, Inc., ZPlot and ZView software. The data is used as a quality control tool and for comparative use between variant chemistries.

(31) In FIGS. 10-17, the data shows stable chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel material was formulated, fabricated, and characterized as a positive electrode suitable for lithium and lithium ion rechargeable electrochemical cells and batteries. The general formula for the present spinel material is Li.sub.xMn.sub.2O.sub.4-y(Cl.sub.z), where x ranges from 0.05 to 1.9 and y=z ranges from 0.005 to 0.7, from 0.015 to 0.4, or from 0.03 to 0.3. The specific capacity for the chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel cathode material was 87 mAh/g when coupled with lithium and cycled between 3.5 and 4.75 volts. This is comparable to conventional lithium manganese-based AB.sub.2O.sub.4 spinel materials fabricated over a 48 to 72-hour time span. Processing time according to the present disclosure has been dramatically reduced to less than 8 hours.

(32) FIGS. 10 and 11 show galvanostatic (charge/discharge) plots for lithium electrochemical cells fabricated with chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel cathode material, synthesized using the method described in the present disclosure with varying chlorine ratios in the starting material. In FIG. 10, the stoichiometric ratio of chlorine to manganese is 0.012:2.0. In FIG. 11, the stoichiometric ratio of chlorine to manganese is 0.025:2.0.

(33) FIGS. 12 through 15 show the differential capacity data and provides information regarding the underlying thermodynamics and kinetics of an electrochemical cell. The differential capacity data uses galvanostatic control of the electrochemical system being tested, and plots the capacity increase (charge) or decrease (discharge) as a function of potential.

(34) FIGS. 12 and 13 show exemplary forming cycle plots for lithium electrochemical cells fabricated with chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel cathode material, synthesized using the method described in the present disclosure with varying chlorine ratios in the starting material. The charge/discharge data is presented as differential capacity. In FIG. 12, the stoichiometric ratio of chlorine to manganese is 0.012:2.0. In FIG. 13, the stoichiometric ratio of chlorine to manganese is 0.025:2.0.

(35) FIGS. 14 and 15 are differential capacity graphs illustrating exemplary cycle life traces for lithium cells containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to an exemplary embodiment of the present disclosure. The figures show the stable thermodynamic behavior of the chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to an exemplary embodiment of the present disclosure. In FIG. 14, the stoichiometric ratio of chlorine to manganese is 0.012:2.0. In FIG. 15, the stoichiometric ratio of chlorine to manganese is 0.025:2.0.

(36) FIG. 16 is a representative hysteresis cycling (charge/discharge) curve illustrating cycle life traces for a lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to an exemplary embodiment of the present disclosure. FIG. 17 is a plot of the charge capacity and delivered discharge capacity per cycle of an exemplary lithium cell containing a chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel according to an exemplary embodiment of the present disclosure. FIGS. 14-17 show the cycle life achieved with the chlorine-modified lithium manganese-based AB.sub.2O.sub.4 spinel of the present disclosure

(37) The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.