ReviewLithium batteries: Status, prospects and future
Introduction
The present energy economy based on fossil fuels is at a serious risk due to a series of factors, including the continuous increase in the demand for oil, the depletion of non-renewable resources and the dependency on politically unstable oil producing countries. Another worrying aspect of the present fossil fuel energy economy is associated with CO2 emissions, which have increased at a constant rate, with a dramatic jump in the last 30 years, the CO2 level has almost doubled passing from 1970 to 2005, this resulting in a rise in global temperature with associated series of dramatic climate changes.
The urgency for energy renewal requires the use of clean energy sources at a much higher level than that presently in force. The CO2 issue, and the consequent air pollution in large urban areas, may be only solved by replacing internal combustion engine (ICE) cars with ideally, zero emission vehicles, i.e. electric vehicles (EVs) or, at least, by controlled emission vehicles, i.e. full hybrid electric vehicles (HEVs) and/or plug-in electric vehicles (PHEVs).
Accordingly, investments for the exploitation of renewable energy resources are increasing worldwide, with particular attention to wind and solar power energy plants (REPs), which are the most mature technologies. The intermittence of these resources requires high efficiency energy storage systems. Electrochemical systems, such as batteries and super capacitors, that can efficiently store and deliver energy on demand in stand-alone power plants, as well as provide power quality and load levelling of the electrical grid in integrated systems, are playing a crucial role in this field. Indeed, the advantage of the use of electrochemical storage systems has been demonstrated for both wind and photovoltaic REPs [1]. The efficacy of batteries in REPs is directly related to their content in energy efficiency and lifetime. Indeed, in virtue of their high value of energy efficiency, lithium batteries are expected to provide an energy return factor higher than that assured by conventional batteries, e.g. lead-acid batteries [2].
In addition to REPs, lithium ion batteries are also seen as the power sources of choice for sustainable transport because they are considered the best options which can effectively guarantee the progressive diffusion of HEVs, PHEVs, and BEVs at high levels [3]. In HEVs the synergic combination of ICE with an electrochemical battery provides high fuel utilization with proven benefits for fuel economy and therefore, for pollution emission control, as well as favouring driving performances which are similar if not superior to those of pure gasoline cars. Indeed, the production of battery-powered HEVs has very rapidly passed from demonstration prototypes to very successful commercial products, see Fig. 1.
However, problems of various natures still prevent the large-scale diffusions of lithium ion batteries for REP and EV applications. Several countries, including Japan, United States and Europe, are allocating large investments to support R&D programs aimed to solve these problems and thus promote the development of advanced, efficient lithium batteries [4].
The purpose of this review is to report the R&D approaches which are considered to be the most promising for leading to important breakthroughs in the lithium battery technology. We will first report on the present status of this technology, discuss the evolutions which are expected to lead to near-term new batteries and conclude with the illustration of future trends.
Section snippets
Lithium ion batteries
Lithium ion batteries are light, compact and work with a voltage of the order of 4 V with a specific energy ranging between 100 Wh kg−1 and 150 Wh kg−1. In its most conventional structure, a lithium ion battery contains a graphite anode (e.g. mesocarbon microbeads, MCMB), a cathode formed by a lithium metal oxide (LiMO2, e.g. LiCoO2) and an electrolyte consisting of a solution of a lithium salt (e.g. LiPF6) in a mixed organic solvent (e.g. ethylene carbonate–dimethyl carbonate, EC–DMC) imbedded in a
Near-term progress of the lithium ion battery technology
Scaling up the chemistry of common lithium ion batteries in view of their application for sustainable vehicles, or for renewable energy plants, is problematic. Barriers of various natures still prevent this important step. They include safety, cycle life, cost, wide temperature operational range and materials availability. On the other hand, the intrinsic benefit of lithium technology and its use in these key evolving markets, have triggered worldwide efforts to solve these problems in order to
New generation lithium ion batteries
Most of the materials described in the previous section are on their way to be used as alternate electrodes or electrolytes in new lithium ion battery configurations. In most cases, however, the innovation only concerns a single component, either the anode, the cathode or the electrolyte, while the others remain unchanged, reproducing the conventional structure. A current approach, adopted in many emerging commercial batteries, considers innovations which involve the cathode only. Most popular
The lithium batteries of the future
Lithium batteries are one of the great successes of modern electrochemistry. These batteries have an established role in the consumer electronic market with no risk of replacement by any other contender and, by intelligent modification of the electrode and electrolyte components, they will soon also dominate the electric automotive transportation and renewable energy storage markets. The potential of these unique power sources make it possible to foresee an even greater expansion of their area
Conclusion
Lithium battery technology evolves at a pace so rapid that evaluation of its progress may easily become obsolete. With this in mind, we have tried to give some consideration to the type of electrode and electrolyte materials that, based on their related electrochemistry, morphology and engineering design, are expected to influence the progress of these important power sources in terms of energy and cycling performance.
The relevance of the choice of materials is obvious. Crucial battery
Acknowledgement
One of us (J.G.) is grateful to the University of Rome Sapienza for a Visiting Professor Fellowship.
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