Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention is concerned with a family of novel cathode materials and a unique processing method for the materials synthesis for Li-ion batteries.
• LiFePO 4 materials suitable for lithium ion battery applications require the synthesis utilizing high temperature heat treatment (>600°C) under an inert atmosphere.
• electrically conductive carbon is usually used for enhancing the conductivity and therefore the electrochemical properties of the synthesized material.
• the use of the inert atmosphere is a key factor that assures the good quality of the materials because of its importance in relation to
• olivine structured material it is known to use olivine structured material to be the active material for a battery cathode, such as in U.S. Patent No. 5,910,382.
• U. S. Patents US 6,723,470, US 6,730,281, US 6,815,122, US 6,884,544, and US 6,913,855, in general, teach methods and precursors utilized for the formation of stoichiometric LiFePO 4 , or the substitution of cations for Fe.
• the above publications only show how stoichiometric olivine structured materials having different cation substitutions are synthesized. None of the prior art teaches how to synthesize phosphate materials having a defective crystalline structure, in air, which have consistent good electrochemical properties for use as an active material in a cathode of a Li-ion battery.
• defects in the crystalline structure of a material can affect the electrochemical property of the synthesized material drastically.
• a classical example is the synthesis of stoichiometric LiNiO 2 .
• a deficiency of lithium would lead to Ni mispositioned on the Li sites therefore retarding the diffusivity of Li drastically and causing the loss in capacity at certain rates.
• the influence of electrochemical properties caused by misposition of Ni on Li sites has been studied by Chang et al. (Solid State Ionics, 112 (1998) 329-344), which is hereby incorporated herein by reference.
• the concentration of the defects can be affected by different processing precursors and processing protocols. For example, a solution processed precursor would in general possess higher reaction kinetics compared to conventional solid state processes and therefore exhibit lower defect concentration.
• a family of defective lithium transition metal phosphate material that can be synthesized at low temperature in air atmosphere possessing excellent rate and cycling capability is created.
• the formation of defects is caused by incorporating various lithiated transition metal oxides with distinct stoichiometry.
• the present invention is focused on the development of a family of defective lithium transition metal phosphate that can be easily synthesized in air atmosphere at low temperature meanwhile possessing excellent consistency, rate capability and cyclability.
• the method includes, a) providing a crystalline lithium transition metal oxide (layer structured or spinel structured), b) providing an intermediate as-synthesized material consisting starting chemicals of Li: Fe: P: C in molar ratios of 1: 1: 1: 2, c), combining and milling the above materials so as to form a mixture of the materials in particulate form, and d) heating the material of step c) to form
• a cathode material of defective lithium transition metal phosphate crystalline The heating is carried out in a vessel in air and surfaces of the material facing the air are covered by a layer of inert blanket which is porous to air and escaping gases caused by the heating.
• Fig. 1 is a cross-sectional view of a furnace reaction vessel and an inert blanket for use in synthesizing the material of the invention
• Fig. 2 is an x-ray diffraction (XRD) pattern for conventional LiFePO 4 cathode material of Example 1;
• Figs 3(a) and 3(b) are graphs for showing the cycling behavior of a test battery fabricated from the cathode material of Example 1;
• Fig. 4 is an XRD pattern for the LiNi ( 0 . 92 ) Mg ( 0 . 08) O 2 cathode material of Example 2;
• Fig. 5 is an XRD pattern for the defective crystalline lithium transition metal phosphate cathode material of Example 3;
• Figs. 6(a) and 6(b) are graphs for showing the cycling behavior of a test battery fabricated from the cathode material of Example 3;
• Figs. 7(a) and 7(b) are XRD patterns for defective crystalline lithium transition metal phosphate having 10wt% and 20 wt %, respectively, of LiNi ⁇ 0. 9 2) Mg (o.os) O 2 as shown in Example 5;
• Figs 8(a) and 8(b) are graphs for showing the cycling behavior of a test battery fabricated from the cathode material of Example 5 having 10 wt% of Li Ni (o. 92 ) Mg (o.os) O 2 ;
• Figs 8(c) and 8(d) are graphs for showing the cycling behavior of a test battery fabricated from the cathode material of Example 5 having 20 wt% of Li Ni (o. 92 > Mg (o.os) O 2 ;
• Figs. 9 (a) and 9(b) are stacks of XRD patterns for comparing peak intensity for various cathode materials found in examples described herein;
• Fig. 10 is an XRD pattern for defective crystalline lithium transition metal phosphate
• Figs. 11 (a) and l l(b) are graphs for showing the cycling behavior of a test battery fabricated from the cathode material of Example 8.
• Fig. 1 shows the design of a furnace and a heat treatment environment for the synthesis of the materials presently disclosed.
• Fig. 1 shows reaction vessel 1, which is open to air in furnace 2.
• the furnace is open to the atmosphere at 3a and 3b so as to maintain substantially atmospheric pressure in the furnace.
• Flow of gases into or out of the furnace is dependent on heating and cooling cycles of the furnace and chemical reactions taking place with materials in the furnace.
• Air is free to enter the furnace, and air and/or products of a chemical reaction of materials 4 in the reaction vessel 1 are free to exit the furnace.
• Materials 4 in vessel 1 react chemically during heating steps to form cathode materials of the invention.
• Materials 4 in vessel 1 react chemically during heating steps to form cathode materials of the invention.
• Fe 2 O 3 , Li 2 CO 3 , and H 3 PO 4 are particularly chosen as the starting materials for the synthesis of lithium transition metal phosphate.
• Reasons for the choice include a relatively low cost of the starting material and a chemical reaction that releases CO 2 and H 2 O,
• Stoichiometric LiFePO 4 is conventionally known as the "active material" in a cathode for use in a Li-ion battery.
• the electrical conductivity of stoichiometric LiFePO 4 is not good and the performance of the battery can be improved with the presence of a material having good electrical conductivity along with the LiFePO 4 .
• Carbon is known to be a good material for improving the electrical conductivity of the cathode. It is known to provide an amount of C in the starting material of the above-reaction, which is greater than the stoichiometric amount, so as to provide a residual amount of C with the produced
• a method for making defective lithium transition metal phosphates having a defective crystalline structure that does not require high temperature heat treatment as well as inert atmosphere condition is provided.
• the way to create the defective structure is to dissolve other lithiated materials with different stoichiometry into a LiFePO 4 structure.
• the chemistry is proposed as follows:
• the target is not to synthesize stoichiometric LiFePO 4 .
• low temperature heat treatment is utilized for the synthesis.
• the meaning of low temperature implies just enough temperature for the formation of desirable material.
• the temperature is chosen to be between 550 to 65O 0 C, preferably at 600 0 C. Too high of a temperature not only increases energy consumption, but also increases the difficulties in maintaining the consistency of the synthesized material.
• Features of the present invention include:
• low temperature heat treatment can minimize the possibility of decomposition of the desirable defective material.
• lower temperature heat treatment lower than the decomposition temperature of carbon black at ⁇ 600°C
• low temperature heat treatment is still recommended for minimizing unnecessary variations.
• the purpose of adding layer structured or spinel structured materials during synthesis is to create a defective crystalline structure of the resultant material.
• the importance of the creation of defective crystalline structure is to promote the occurrence of the change of band structure and thus the electrical conductivity of the resultant material.
• a new family of defective crystalline structure lithium metal phosphate materials that can be obtained using an air environment heat treatment, is provided. Excellent electrochemical properties are exhibited. The high rate capability has been demonstrated to be more than 2OC.
• cathode materials both prior art materials and cathode materials of the invention.
• Heat treatment for synthesis was conducted in a sealed metallic box with the flow of nitrogen gas.
• the materials were heat treated at 65O 0 C for 10 hours under the nitrogen gas flow.
• XRD data is shown in Fig. 2. It is observed that phase pure material can be obtained using the described conventional heat treatment protocol.
• Battery data (obtained using a three electrode design test battery and lithium as the reference electrode) is shown in Figs. 3. From Fig. 3(a) it can be seen that the capacity is high during the first charge-discharge cycle ( ⁇ C/5 rate, 0.23mA/cm 2 ). The cycles following the first cycle were tested using ⁇ 2C test conditions (2.3mA/cm 2 in constant current charge and discharge, with constant voltage charge to current ⁇
• the Mg cations are substituting at the transition metal sites.
• EXAMPLE 3 Synthesis of defective lithium transition metal phosphate obtained by incorporating 3 wt%of LiNio.9 2 Mgo. 08 ⁇ 2 and heat treating in an air environment
• Fe 2 O 3 , Li 2 CO 3 and Super P (carbon black), molar ratio of (1:1:2) were mixed together with the addition of a suitable amount of water to produce a slurry. After mixing thoroughly, a stoichiometric amount of phosphoric acid was added to the mixture and extended mixing was
• Synthesis of the material was carried out by heat treatment at 600 0 C for 10 hours in the furnace shown in Fig. 1, under air atmosphere.
• XRD data is shown in Fig. 5.
• the phase pure nature of the material synthesized is verified by comparing the present XRD data with the XRD data shown in Fig. 2. It is clear that a
• the slurry was coated on an aluminum foil using a comma coater.
• the coated film was dried at 14O 0 C for approximately 10 minutes in a convective furnace.
• the other side of the aluminum foil was coated with the same material. After drying, the coated foil was subjected to rolling.
• the resulting compressed films and foil had a thickness of 160 ⁇ 5um.
• Anode preparation 8wt% of PVDF and 92 wt% of natural graphite material were mixed thoroughly using NMP as a solvent. After stirring and mixing for about 12 hours a homogeneous slurry was obtained. The slurry had a viscosity of ⁇ 15,000 cp prior to coating. The slurry was coated on a copper foil using a comma coater. The coated film was dried at 14O 0 C for approximately 10 minutes in a convective furnace. Similarly, the other side of the copper foil was coated with the same material. After drying, the coated foil was subjected to coating with a polymer solution as disclosed in the Applicant's earlier U.S. Patent No. U.S. 6,727, ,017. The as-coated anode was subjected to rolling to a thickness of 210 ⁇ 5um.
• a battery was made using 28 pairs of cathodes (4cm x 5cm) and anodes (4cm x 5cm). The electrodes were placed in an alternating sequence, as in ABABAB fashion. After soaking with an electrolyte (EC/DMC 1:1) for about 12 hours, the battery was subjected to cycling.
• EC/DMC 1:1 electrolyte
• Table 1 shows the cycling behavior of the resultant battery.
• the battery shows a capacity of -1200 mAh at a charge/discharge current of 1.5 A.
• the average voltage of the battery during charge/discharge is also shown in Table 1.
• the battery was subjected to a high rate capability test at > 2OC as follows: Test setup and configuration: 7 light bulbs (12V, 5OW for each bulb) were connected in series with one voltage meter and one ampere meter for monitoring the voltage and current. Four of the batteries of Example 4 were also connected in series and a total voltage of 13.2V was obtained (prior to closing the circuit). On closing the circuit an initial ampere meter reading of >30 Amp and a voltage reading of 10.5V (a total of 315W) was observed. After 10 seconds, the reading of the ampere meter dropped to 28A and the voltage reading dropped to 10.2V (a total of 286W). Thereafter, the readings remained stable for the next 20 seconds.
• EXAMPLE 5 Additional example showing the synthesis of defective lithium transition metal phosphate obtained by incorporating 10 wt% and 20 wt% of LiNiQ. 9 2Mgo. 0 8O 2 and heat treating in an air environment
• XRD data is shown in Figs. 7(a) and 7(b). Stronger impurity phase patterns are observed for the 10 wt% and 20 wt% LiNio. 92 Mgo.osO 2 added samples compared to the XRD data shown for pure LiFePO 4 and 3 wt% LiNio. 92 Mgo. 08 O 2 incorporated material (Figs. 2 and 5, respectively). This suggests that the existence of LiNio. 92 Mgo.osO 2 during synthesis could result in some impurity phases including un-reacted LiNio. 92 Mgo. 08 O 2 and partially dissolved material.
• Electrochemical data is shown in Figs. 8(a) - 8(d). From Figs. 8 it can be seen that the cycling behavior is as good as the 3 wt% LiNio. 92 Mgo.osO 2 incorporated material, although the capacity decreased from 75mAh/g to 50 ⁇ 60mAh/g range. It can be concluded that with the addition of more LiNio. 9 2Mgo.osO 2 material, although good electrical conductivity of the material is ensured, owing to the presence of the defective crystalline structure, with too much
• LiNio. 92 Mgo. 08 O 2 the proper amount of LiNio. 92 Mgo. 08 O 2 should be added for achieving the best electrical conductivity and capacity of the material.
• the amount of LiNio. 92 Mgo.osO 2 addition during synthesis is thus very important for obtaining the best electrochemical performance in a battery.
• Fig. 9(a) shows a stack of XRD patterns of the conventionally synthesized LiFePO 4 (prepared as shown in EXAMPLE 1), defective, lithium transition metal phosphate having 3 wt%
• LiNio. 92 Mgo. 08 O 2 prepared as shown in EXAMPLE 3
• defective lithium transition metal phosphate having 10 wt% and 20 wt% LiNio. 9 2Mgo.osO 2 (prepared as shown in EXAMPLE 5).
• Fig. 9b shows a stack of XRD patterns of 0 " wt%, 3 wt%, 10 wt%, and 20 wt%
• LiNio. 9 2Mgo. 08 O2 simply mechanically added and mixed with conventional stoichiometric LiFePO 4 . From Fig. 9(b) it can be seen that with a slight LiNio. 92 Mgo.osO 2 addition (3 wt%), distinct LiNio.92Mgo.osO 2 peaks can be observed (-18.6° for (003) and 44.4° for (104)). This result suggests that the phase pure nature of the 3 wt% LiNio. 92 Mgo.osO 2 reacted sample (Example 3) is the result of total dissolution of LiNio. 92 Mgo.osO 2 into the LiFePO 4 structure, therefore
• EXAMPLE 7 Chemical analyses for conventional LiFePO 4 (material made in EXAMPLE 1) and defective lithium transition metal phosphate synthesized by incorporating 3 wt% LiNio.92Mgo.08O2 (material made in EXAMPLE 3)
• the Li, Fe, P, Ni, and Mg were analyzed using ICP-OES
• the C was analyzed using ASTM D5373
• the oxygen content can not be determined directly owing to the relatively high concentrations of metals.
• EXAMPLE 8 Synthesis of defective lithium transition metal phosphate incorporated with spinel structured Lii. 07 Mni. 93 O 4 (3 wt%) in air environment
• FeaOs, Li 2 CO 3 and Super P (carbon black), molar ratio of (1:1:2) were mixed together with the addition of a suitable amount of water. After mixing thoroughly, a stoichiometric amount of phosphoric acid was added to the solution and extended mixing was utilized. Finally, the slurry was dried in air at 15O 0 C for 10 hours followed by further heat treatment at 400 0 C for 5 hours until chunks of materials were obtained.
• Li 1 . 07 Mn 1 . 93 O 4 was synthesized using Li 2 CO 3 , and Mn 3 O 4 with a stoichiometric ratio of Li:Mn of 1.1: 2 in the precursor.
• the starting materials Li 2 CO 3 and Mn 3 O 4 were first mixed using a ball mill for 8 hours, followed by heat treating the material to 800 0 C for 24 hours in air. The material obtained was then subjected to grinding and sieving.
• the materials prepared above were then subjected to grinding and ball milling for about 12 hours with the amount of Li 1 . 07 Mn L93 O 4 being 3 wt%. Further heat treatment at 600 0 C for 10 hours in the furnace shown in Fig. 1 under air atmosphere was conducted on the materials.
• the XRD data is shown in Fig. 10. Slightly more impurity phases are observed compared to the XRD data shown for pure LiFePO 4 and 3 wt% LiNio. 92 Mgo.os ⁇ 2 incorporated material.
• Electrochemical data is shown in Figs. 1 l(a) and 1 l(b). From Fig. 1 l(a) it can be seen

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