Sanghan Lee

Who will drive electric vehicles, olivine or spinel?

Lithium iron phosphate olivine (LFP) and lithium manganese oxide spinel (LMO) are competitive and complementary to each other as cathode materials for lithium ion batteries, especially for use in hybrid electric vehicles and electric vehicles. Interest in these materials, due to their low cost and high safety, has pushed research and development forward and toward high performance in terms of rate capability and capacity retention or cyclability at a high temperature of around 60 °C. From the view point of basic properties, LFP shows a higher gravimetric capacity while LMO has better conductivities, both electrically and ionically. According to our comparison experiments, depending on the material properties and operational potential window, LFP was favored for fast charging while LMO led to better discharge performances. Capacity fading at high temperatures due to metal dissolution was revealed to be the most problematic issue of LFP and LMO-based cells for electric vehicles (EVs), with thicker electrodes, in the case of no additives in the electrolyte and no coating to prevent metal dissolution on cathode materials. Various strategies to enhance the properties of LFP and LMO are ready for the realization of EVs in the near future.

High performance LiMn2O4 cathode materials grown with epitaxial layered nanostructure for Li-ion batteries.

Tremendous research works have been done to develop better cathode materials for a large scale battery to be used for electric vehicles (EVs). Spinel LiMn2O4 has been considered as the most promising cathode among the many candidates due to its advantages of high thermal stability, low cost, abundance, and environmental affinity. However, it still suffers from the surface dissolution of manganese in the electrolyte at elevated temperature, especially above 60 °C, which leads to a severe capacity fading. To overcome this barrier, we here report an imaginative material design; a novel heterostructure LiMn2O4 with epitaxially grown layered (R3̅m) surface phase. No defect was observed at the interface between the host spinel and layered surface phase, which provides an efficient path for the ionic and electronic mobility. In addition, the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at 60 °C. The unique characteristics of the heterostructure LiMn2O4 phase exhibited a discharge capacity of 123 mAh g(-1) and retained 85% of its initial capacity at the elevated temperature (60 °C) after 100 cycles.

Flexible high-energy Li-ion batteries with fast-charging capability

With the development of flexible mobile devices, flexible Li-ion batteries have naturally received much attention. Previously, all reported flexible components have had shortcomings related to power and energy performance. In this research, in order to overcome these problems while maintaining the flexibility, honeycomb-patterned Cu and Al materials were used as current collectors to achieve maximum adhesion in the electrodes. In addition, to increase the energy and power multishelled LiNi0.75Co0.11Mn0.14O2 particles consisting of nanoscale V2O5 and LixV2O5 coating layers and a LiδNi0.75-zCo0.11Mn0.14VzO2 doping layer were used as the cathode-anode composite (denoted as PNG-AES) consisting of amorphous Si nanoparticles (<20 nm) loaded on expanded graphite (10 wt %) and natural graphite (85 wt %). Li-ion cells with these three elements (cathode, anode, and current collector) exhibited excellent power and energy performance along with stable cycling stability up to 200 cycles in an in situ bending test.

Hierarchical Surface Atomic Structure of a Manganese-Based Spinel Cathode for Lithium-Ion Batteries†

The increasing use of lithium-ion batteries (LIBs) in high-power applications requires improvement of their high-temperature electrochemical performance, including their cyclability and rate capability. Spinel lithium manganese oxide (LiMn2O4) is a promising cathode material because of its high stability and abundance. However, it exhibits poor cycling performance at high temperatures owing to Mn dissolution. Herein we show that when stoichiometric lithium manganese oxide is coated with highly doped spinels, the resulting epitaxial coating has a hierarchical atomic structure consisting of cubic-spinel, tetragonal-spinel, and layered structures, and no interfacial phase is formed. In a practical application of the coating to doped spinel, the material retained 90% of its capacity after 800 cycles at 60 °C. Thus, the formation of an epitaxial coating with a hierarchical atomic structure could enhance the electrochemical performance of LIB cathode materials while preventing large losses in capacity.

Enhancing Interfacial Bonding between Anisotropically Oriented Grains using a Glue-Nanofiller for Advanced Li-ion Battery Cathode

Formation of a glue-nanofiller layer between grains, consisting of a middle-temperature spinel-like Lix CoO2 phase, reinforces the strength of the incoherent interfacial binding between anisotropically oriented grains by enhancing the face-to-face adhesion strength. The cathode treated with the glue-layer exhibits steady cycling performance at both room-temperature and 60 °C. These results represent a step forward in advanced lithium-ion batteries via simple cathode coating.

Critical Role of Cations in Lithium Sites on Extended Electrochemical Reversibility of Co-Rich Layered Oxide

Only a very limited amount of the high theoretical energy density of LiCoO2 as a cathode material has been realized, due to its irreversible deterioration when more than 0.6 mol of lithium ions are extracted. In this study, new insights into the origin of such low electrochemical reversibility, namely the structural collapse caused by electrostatic repulsion between oxygen ions during the charge process are suggested. By incorporating the partial cation migration of LiNiO2 , which produces a screen effect of cations in the 3b-Li site, the phase distortion of LiCoO2 is successfully delayed which in turn expands its electrochemical reversibility. This study elucidates the relationship between the structural reversibility and electrochemical behavior of layered cathode materials and enables new design of Co-rich layered materials for cathodes with high energy density.

Spinel LiCo0.7Mn1.3O4 Nanowire Clusters as Electrode Materials

the presence of high-spin Mn 3 + :t2g 3 eg 1 ions—resulting in a huge change of volume and severe fading of the capacity. [7] The power density (rate capability) of these cathode materials with bulk sizes in the micrometer-regime is generally low due to the high level of polarization at high charge–discharge rates (above 2 C). This high polarization is believed to result from slow lithium diffusion or low electrical conductivity in the active material. Therefore, “nanostructuring” was introduced to overcome these shortcomings, through shortening the diffusion paths for mass transport and increasing the surface area for charge transfer. [8–10] In addition, electrode density is considered to be one of the factors that affects the energy density: a higher electrode density leads to a higher energy density. [11] A

Li-Ion Battery Cathodes: Enhancing Interfacial Bonding between Anisotropically Oriented Grains Using a Glue-Nanofiller for Advanced Li-Ion Battery Cathode (Adv. Mater. 23/2016)

The formation of a spinel Lix CoO2 layer in a Ni-rich secondary particle for lithium-ion batteries is reported by S. K. Kwak, J. Cho, and co-workers on page 4705, who find that the spinel-like Lix CoO2 layer, between layered primary particles, can enhance the mechanical strength of secondary particles by enhancing the interfacial binding energy among the grains. Moreover, the layer can effectively protect the unstable surface of the primary particles and offers a fast electron-ion pathway, resulting in overall enhancements of stability and kinetics in battery performance.