While little success has been obtained over the past few years in attempts to increase the capacity of Li-ion batteries, significant improvement in the power density has been achieved, opening the route to new applications, from hybrid electric vehicles to high-power electronics and regulation of the intermittency problem of electric energy supply on smart grids. This success has been achieved not only by decreasing the size of the active particles of the electrodes to few tens of nanometers, but also by surface modification and the synthesis of new multi-composite particles. It is the aim of this talk to review the different approaches that have been successful to obtain Li-ion batteries with improved high-rate performance and to discuss how these results prefigure further improvement in the near future.

Currently, it is recognized that the main limiting elements of a Li-ion battery are the positive electrode materials which can be divided into three different families. One is the family of lamellar compounds obtained by the multi-ion substitution of transition-metal ions. The archetype of this family is LiNi_1/3Mn_1/3Co_1/3O₂ (NMC). The second family is the olivine group, the archetype of which is LiFePO₄ (LFP) for which coating the particles with conductive carbon has been a remarkably successful surface modification. The third family consists of compounds with spinel structure such as LiMn_1.5Ni_0.5O₄ (LMN), which is of great interest because it provides access to the Ni(IV)–Ni(II) formal valences at about 4.7 V vs. Li⁺/Li. However, cathode/electrolyte surface reactions lead to degradation in the electrochemical performance.

Recent progress in the reduction in size of the active particles of the electrodes below 100 nm has increased the surface contact with the electrolytes, thus improving the power density of the Li-ion batteries. At the same time, however, the surface-over-volume ratio increases, so that the surface layer, as well as SEI effects, becomes increasingly important. Recent improvements for the positive electrodes have been obtained by well-crystallized surface layer of both lamellar compounds and olivine compounds. The increase of energy density with remarkable thermal stability has been achieved by LiFePO₄-coated particles working at higher operating voltage. The coating is protecting the inner core of the particles from contact and reaction with the electrolyte, which not only prevents the formation of a resistive SEI layer, but also increases the safety of the Li-ion batteries. In particular, the multi-composite particles open the route towards the 5 V operating Li-ion batteries will be presented.