Development of Continuous Synthesis Method of Lithium Transition Metal Oxide Fine Particles via Reactive Crystallization in Supercritical Water

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In this study, we use supercritical hydrothermal synthesis method to continuously produce LiCoOィイD22ィエD2 fine crystals that are used as for the cathode materials of rechargeable lithium ion batteries. LiOH and Co(NOィイD23ィエD2)ィイD22ィエD2 were chosen as starting materials. For oxidizing Co(II) to Co(III), O2 was introduced into the reactor after decomposing aqueous HィイD22ィエD2OィイD22ィエD2 solution in a preheating tubing. LiCoOィイD22ィエD2 particles formed in a single phase at supercritical conditions (400℃ and 30 MPa). On the other hand, CoィイD23ィエD2OィイD24ィエD2 phase formed from the same starting solutions under subcritical conditions (300℃, 350℃ and 30 MPa). This results from an enhancement of oxidation of CoィイD12+ィエD1 due to homogeneous supercritical conditions. Scanning electron micrographs showed that the particle size was in the range of 600 to 1,000 nm in diameter. Using the same method, we could produce another cathode material, LiMnィイD22ィエD2OィイD24ィエD2. Particles obtained were hexagonal plate like particle with 100 - 200 nm in diameter. Electrochemical characterization was performed by a constant current discharge and charge test. The electrochemical capacity of particle obtained was as low as 120 mAh/g, but a loss of capacity was below 5 % during 50 charge-discharge cycles. Little decrease in the discharge capacity suggests high stability of the LiCoOィイD22ィエD2 and LiMnィイD22ィエD2OィイD24ィエD2 crystals prepared by this method.