成果報告書詳細
管理番号20110000000857
タイトル*平成22年度中間年報 次世代自動車用高性能蓄電システム技術開発 次世代技術開発 高圧合成法による次世代高容量正極材料酸化物の材料設計
公開日2012/6/27
報告書年度2010 - 2010
委託先名学校法人東京理科大学 独立行政法人産業技術総合研究所
プロジェクト番号P07001
部署名スマートコミュニティ部
和文要約1.研究開発の内容及び成果等
<研究目標>
自動車用蓄電池の飛躍的な性能向上に資するため、高圧合成技術を利用することにより、次世代高容量正極材料酸化物の新規材料の設計を行う。本事業終了時点で、パック電池レベルでの重量エネルギー密度500 Wh/kgを見通せる高容量正極材料酸化物の探索を行う。具体的には、リチウム負極との組み合わせで酸化物活物質あたり1,200 Wh/kg以上の重量エネルギー密度を有し、20サイクル後に初期放電容量の70%以上の容量を維持可能な高容量正極材料酸化物を見出す。この目標をクリアーするためには、これまでに検討されてきた層状岩塩型やスピネル型をはじめとする既知の結晶構造の利用では達成が難しく、従来の延長線上にない新しい結晶相を検討する必要がある。そこで、カルシウムフェライト型の結晶構造を有するリチウムマンガン酸化物をはじめとする新結晶相について、構成する遷移金属元素とその化学組成を最適化し、更にリチウム挿入・脱離反応のメカニズムを解明することにより、上記目標を達成する。この材料設計を行う上で、高温高圧条件下での材料合成技術が必要不可欠である。
最終年度(平成23年度終了時)には、リチウム負極との組み合わせで、酸化物重量当たり1,200 Wh/kg以上の初期放電エネルギー密度であり、かつ3 V以上の平均放電電位を有し、100サイクル後に初期放電容量の50%以上の容量を維持可能な新規高容量正極材料酸化物を見出す。上記の目標を達成するために以下の研究開発テーマを設定し実施した。
英文要約To develop next generation electrical vehicles, it is necessary to develop new positive electrode materials with high electrochemical properties. We have improved the properties of calcium ferrite type LiMn2O4 which has excellent electrochemical properties by substituting the Mn sites by other transition metal elements. We found it useful to substitute by Ni and Ti to increase average discharge voltage without deterioration of power density. In this study, we have tried to substitute the Mn sites by V, Fe, Co and Cu so as to improve further. The calcium ferrite type LiMn2O4 samples were obtained by the Na/Li ion exchange reaction of calcium ferrite type NaMn2O4 samples. In the first stage, the sodium manganese samples substituted by transition metal elements were synthesized at 1050-1500 oC under a pressure of 4.5 GPa using cubic anvil type high pressure apparatus. After mixing the products synthesized under high pressure with lithium nitrate, they were annealed for Na/Li ion exchange at 250-420 oC for 3-100 hours. We obtained single phase sodium manganese samples for V, Co and Cu substitutions. However, we do not succeeded in Na/Li ion exchange for these samples so far. We have also tried to substitute the oxygen sites by fluorine, as the enhancement of average discharge voltage can be expected. Single phase sample of calcium-ferrite type LiMn2O3.9F0.1 were successfully obtained by high pressure synthesis of single phase NaMn2O3.9F0.1 and additional Na/Li ion exchange as mentioned above. The charge-discharge measurement of LiMn2O3.9F0.1 was carried out in the voltage range between 1.8 and 4.8 V versus Li. The initial discharge capacity was 221 mAh/g and this value is lower than 299 mAh/g for pristine Li0.81Mn2O4. However, the discharge capacities at high voltage region above 3 V were increased and the cycling stability by 20 cycles was improved. We also revalued the electrochemical properties for LiMn1.8Ti0.2O4 and LiMn1.8Ni0.2O4. We previously reported that the LiMn1.8Ti0.2O4 electrode showed the initial discharge capacity of 310 mAh/g, average discharge potential of 2.93 V, and the energy density of 910 mWh/g in the voltage range between 1.0 and 4.8 V. In this study, we found that the LiMn1.8Ni0.2O4 electrode showed 271 mAh/g, 3.27 V, and 884 mWh/g in the voltage range between 1.8 and 4.8 V, respectively. We also investigated new electrode materials. The titan oxide having new type crystal structure was synthesized when the all Mn site of calcium ferrite type LiMn2O4 were substituted by Ti ion. The crystal structural analysis revealed the material was consisted as the intergrowth structure between ramsdellite type and calcium ferrite type, alternatively. Ramsdellite type titan oxide is reported as the initial lithium intercalation capacity above 300 mAh/g. However, the capacity is decreased to below 200 mAh/g within 10 cycles charge-discharge reactions. On the other hand, the present new material shows the initial lithium intercalation capacity is 219 mAh/g and the corresponding energy density is achieved to be 384 Wh/kg in the voltage range between 3.0 to 1.0 V (vs Li). The capacity is maintained after 20 cycles of lithium charge-discharge reactions. Lithium cupper oxides are expected to have high discharge capacity. However, the coordinate number of cupper site is 4 and the property is obstructed to substrate other metals. In the present study, we found new high-pressure phase of which coordinate number of cupper site was 6. The cupper site consists octahedron and the property should be remove the problem for the substitution. For instance, the Li2(Ni0.25Mn0.25Cu0.5)O2 composition, the ideal charge-discharge capacity is 505 mAh/g. We measured charge-discharge reaction of the sample. The initial discharge capacity was 268 mAh/g in the voltage range between 4.0 to 1.5 V (vs Li), and the discharge capacity was above 244 mAh/g after 10 cycles.
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