Li-ion batteries have reached a dominant position in the consumer electronics, power tools and electromobility sectors. Even stationary storage is looking at lithium-ion as technology of choice. However, the continuous demand for better performance, full safety and lower cost is pushing lithium-ion batteries towards its limits.

Following pioneer work on alkali metal intercalation on Prussian-blue materials by M. Armand and co-workers, the first rechargeable Li-ion battery reported in 1976 by S. Whittingham relied on TiS₂ as positive electrode, lithium metal as negative electrode and a liquid electrolyte based on dimetoxyethane and tetrahydrofuran as organic solvents and LiClO₄ as lithium-ion conductive salt.

However, this cell presented two important problems that prevented commercialisation at the time: 1) low energy density nested on the low cell voltage (<2.5 V), and 2) serious safety hazards originated by lithium dendrite growth that caused internal short circuit.

The investigations led by Goodenough in the 80s solved the energy density problem by developing three families of positive electrode materials: 1) layered oxides, LiCoO₂ delivering a cell voltage ~4 V; 2) spinel oxides, LiMn₂O₄, with cell voltages in the 3 to 4 V range; 3) polyanions, Li_xFe₂(SO₄)₃ which can exceed by one volt the cell voltage of transition metal dichalcogenides.

Even if the energy density problem had been addressed with the three families of positive electrode materials, the lithium dendrite growth problem was still present.

In parallel to the development of new cathode materials, the intercalation of lithium on Li-free anodes such as graphite using propylene carbonate (PC) based electrolytes had been pursued with no success. In 1990, J. Dahn and collaborators obtained reversible lithium intercalation on graphite using ethylene carbonate (EC) as electrolyte co-solvent.

In 1991, inspired by all investigations carried out to date, Sony commercialised the first rechargeable Li-ion battery based on a LiCoO₂ cathode, hard carbon anode and PC-based electrolyte. After this, EC and dimethyl carbonate (DMC) co-solvents, as well as graphite negative electrodes in 1994, were progressively introduced providing stability up to 4 V. Since then, the majority of Li-ion batteries are still based on graphite as negative electrode material.

In contrast, the number positive electrode materials has increased. The need to remove Co, due to environmental and economic reasons, in the first family of layered cathode materials resulted in development of LiNi_1–y–zMn_yCo_zO₂ (NMC) and LiNi_1-y-zCo_yAl_zO₂ (NCA) which, nowadays, are the dominant positive electrode materials owing to their high specific capacity.

As for the other two cathode families, the spinel one evolved through partial Ni-Mn substitutions resulting in the high voltage cathode material LiMn_1.5Ni_0.5O₄ (4.7 V) which, despite the promise of high energy density, still lacks of a stable electrolyte that allows operation at those voltages.

Meanwhile, the exploration of polyanionic materials, third family of positive electrode materials, resulted in olivine LiFePO₄ which despite its low operating voltage ~3.2 V delivers excellent cycling efficiency with long life span and thermal stability. Particularly, after Armand’s idea of coating the iron phosphate with carbon.

The figure below shows a schematic summary of Li-ion battery development in terms of the three positive electrode families that have reached the commercial stage.