Pu, Xiong (2014-08). High Energy Density Cathode for Lithium Batteries: From LiCoO_(2) to Sulfur. Doctoral Dissertation. Thesis uri icon

abstract

  • Lithium batteries are receiving increasing interest worldwide due to the urgent demand for higher energy density, longer cycling life, cheaper price, and better safety, so that long-distance electric vehicles and stationary energy storages can be viable. This dissertation, motivated with these aims, investigated both Li-ion batteries and Li-S batteries. LiCoO_(2), though it has been commercialized in Li-ion batteries, still has the potential to achieve higher energy density, since its practical capacity is limited to half of its theoretical capacity due to the overcharge problem. Surface coatings of lithium vanadate (Li_(3)VO_(4)) on LiCoO_(2) nanoparticles were employed to overcome this issue. With 3.4-wt.% and 5.5-wt.% Li_(3)VO_(4) coatings, both the cyclability and high-rate capability of LiCoO_(2) cells were greatly improved when overcharged to voltages as high as 4.5 V and 4.7 V. The improvement was attributed to the structurally protective and Li-ion conductive Li_(3)VO_(4) coating, which can suppress the side reaction and structure damage of LiCoO_(2) nanoparticles, as indicated by TEM images after the cycling test. Li-S batteries, promising due to the high energy density and low price, face two challenges that have not been well addressed, i.e. the safety hazard resulted from the Li dendrite formation on the Li metal anode and the poor cyclability arising from the polysulfides shuttle. Firstly, to overcome the safety issue, this dissertation reported a lithiated Si-S (LSS) battery that replaced the Li metal with a pre-lithiated Si anode. Due to the high theoretical capacity of Si, no sacrifice of the energy density was made. Stable cycling performances with capacity retention up to 80% were achieved in the organic electrolyte. The better safety of the LSS battery in terms of external and internal short-circuits was also demonstrated. Secondly, to suppress the polysulfides shuttle, a novel semi-liquid Li-S battery was designed with carbon nanotubes (CNT) sponges soaked by liquid polysuflides as the cathode. Stable cycling performances were achieved over 300 cycles. Due to the absence of the polymer binder and metal current collector in this design, the energy density of the total electrode was improved significantly.
  • Lithium batteries are receiving increasing interest worldwide due to the urgent demand for higher energy density, longer cycling life, cheaper price, and better safety, so that long-distance electric vehicles and stationary energy storages can be viable. This dissertation, motivated with these aims, investigated both Li-ion batteries and Li-S batteries.

    LiCoO_(2), though it has been commercialized in Li-ion batteries, still has the potential to achieve higher energy density, since its practical capacity is limited to half of its theoretical capacity due to the overcharge problem. Surface coatings of lithium vanadate (Li_(3)VO_(4)) on LiCoO_(2) nanoparticles were employed to overcome this issue. With 3.4-wt.% and 5.5-wt.% Li_(3)VO_(4) coatings, both the cyclability and high-rate capability of LiCoO_(2) cells were greatly improved when overcharged to voltages as high as 4.5 V and 4.7 V. The improvement was attributed to the structurally protective and Li-ion conductive Li_(3)VO_(4) coating, which can suppress the side reaction and structure damage of LiCoO_(2) nanoparticles, as indicated by TEM images after the cycling test.

    Li-S batteries, promising due to the high energy density and low price, face two challenges that have not been well addressed, i.e. the safety hazard resulted from the Li dendrite formation on the Li metal anode and the poor cyclability arising from the polysulfides shuttle. Firstly, to overcome the safety issue, this dissertation reported a lithiated Si-S (LSS) battery that replaced the Li metal with a pre-lithiated Si anode. Due to the high theoretical capacity of Si, no sacrifice of the energy density was made. Stable cycling performances with capacity retention up to 80% were achieved in the organic electrolyte. The better safety of the LSS battery in terms of external and internal short-circuits was also demonstrated. Secondly, to suppress the polysulfides shuttle, a novel semi-liquid Li-S battery was designed with carbon nanotubes (CNT) sponges soaked by liquid polysuflides as the cathode. Stable cycling performances were achieved over 300 cycles. Due to the absence of the polymer binder and metal current collector in this design, the energy density of the total electrode was improved significantly.

publication date

  • August 2014