Technological improvements in rechargeable solid-state batteries are being driven by an ever-increasing demand for portable electronic devices. Lithium-ion batteries are the systems of choice, offering high energy density, flexible and lightweight design, and longer lifespan than comparable battery technologies. We present a brief historical review of the development of lithium-based rechargeable batteries, highlight ongoing research strategies, and discuss the challenges that remain regarding the synthesis, characterization, electrochemical performance and safety of these systems.

Issues and challenges facing rechargeable lithium batteries

Rechargeable solid-state batteries have long been considered an attractive power source for a wide variety of applications, and in particular, lithium-ion batteries are emerging as the technology of choice for portable electronics. One of the main challenges in the design of these batteries is to ensure that the electrodes maintain their integrity over many discharge-recharge cycles. Although promising electrode systems have recently been proposed, their lifespans are limited by Li-alloying agglomeration or the growth of passivation layers, which prevent the fully reversible insertion of Li ions into the negative electrodes. Here we report that electrodes made of nanoparticles of transition-metal oxides (MO, where M is Co, Ni, Cu or Fe) demonstrate electrochemical capacities of 700 mA h g(-1), with 100% capacity retention for up to 100 cycles and high recharging rates. The mechanism of Li reactivity differs from the classical Li insertion/deinsertion or Li-alloying processes, and involves the formation and decomposition of Li2O, accompanying the reduction and oxidation of metal nanoparticles (in the range 1-5 nanometres) respectively. We expect that the use of transition-metal nanoparticles to enhance surface electrochemical reactivity will lead to further improvements in the performance of lithium-ion batteries.

Nano-sized transition-metal oxides as negative-electrode materials for lithium-ion batteries

Li-ion battery materials: present and future

Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

/pdf/graphene-based-composites-540z2xd3o0.pdf

Graphene-based composites

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

We report our electrochemical and in situ x‐ray diffraction experiments on a variety of tin oxide based compounds; SnO, , , and glass, as cathodes opposite lithium metal in a rechargeable Li‐ion coin cell. These materials demonstrate discharge capacities on the order of 1000 mAh/(g Sn), which is consistent with the alloying capacity limit of 4.4 Li atoms per Sn atom, or 991 mAh/(g Sn). These materials also demonstrate significant irreversible capacities ranging from 200 mAh/(g active) to 700 mAh/(g active). In situ x‐ray diffraction experiments on these materials show that by introducing lithium, lithium oxide and tin form first, which is then followed by the formation of the various Li‐Sn alloy phases. When lithium is removed the original material does not reform. The ending composition is metallic tin, presumably mixed with amorphous lithium oxide. The oxygen from the tin oxide in the starting material bonds irreversibly with lithium to form an amorphous matrix. The Li‐Sn alloying process is quite reversible; perhaps due to the formation of this lithia "matrix" which helps to keep the electrode particles mechanically connected together.

Electrochemical and In Situ X‐Ray Diffraction Studies of the Reaction of Lithium with Tin Oxide Composites

Tin oxide composite glasses represent a new class of material for the anode of Li-ion cells. Using results of experiments on Li/Sn{sub 2}BPO{sub 6} and Li/SnO{sub 2} cells, the authors identify those factors which are responsible for good charge-discharge capacity retention. First, the grains (those regions which diffract coherently) which make up the particles of the material should be as small as possible. Then, regions of tin which form are kept small and two-phase coexistence regions between bulk Li-Sn alloys of different composition do not occur. The Sn{sub 2}BPO{sub 6} glass represents the smallest grains possible. Second, the particles themselves should be small so that they can each be well contacted by carbon black during electrode manufacture. Third, the voltage range of cycling must be selected so that the tin atoms do not aggregate into large regions which grow in size. This aggregation is evidenced by the growth of peaks in the differential capacity vs. voltage as a function of cycle number. The peaks represent the coexistence between bulk Li-Sn alloy phases which have substantially different volumes. The coexistence is thought to cause fracturing and loss of contact between the grains. Therefore, materials with small particles, small grains, and smoothmore » sloping voltage profiles which do not change with cycle number (as indicated by a stable differential capacity) give the best cycling performance. The selection of the voltage limits for cycling strongly influences the stability of the voltage profile (as illustrated here), so this must be done with much care.« less

https://iopscience.iop.org/article/10.1149/1.1837941/pdf

Key Factors Controlling the Reversibility of the Reaction of Lithium with SnO2 and Sn2 BPO 6 Glass

We show that the reaction mechanism in Li/[SnO:(B 2 O 3 ) x :(P 2 O 5 ) y glass (0.1≤x,y≤0.5)], Li/[SnO: B 2 O 3 ) 0.5 :(P 2 O 5 ) 0.5 :(K 2 CO 3 ) 0.04 glass] and Li/SnO cells is common. During the first discharge, the oxygen bonded to tin (as SnO) reacts with lithium to give metallic tin (which can be present as clusters of a few atoms) and lithia. The tin reacts with further lithium to the composition limit of Li 4.4 Sn. During charge the Li is removed from the lithium-tin alloy. The other components of the glass (e.g., B 2 O 3 . P 2 O 5 , Li 2 O, etc, ) are inert with respect to lithium, and we call the atoms which make up these phases spectator atoms, Using X-ray diffraction (XRD) and electrochemical methods, we show that size of the initial tin regions which form is inversely proportional to the spectator:Sn atom ratio. However, during cycling, all of these materials show the subsequent aggregation of the tin atoms into clusters which grow with cycle number until they reach a saturated size. The final cluster size is larger for materials with smaller X:Sn ratio. We propose a speculative model, which predicts the saturated Sn cluster size, as a function of the spectator:Sn ratio.

http://jes.ecsdl.org/content/146/1/59.full.pdf

On the Aggregation of Tin in SnO Composite Glasses Caused by the Reversible Reaction with Lithium

Composites consisting of "active" grains which can alloy with lithium and "inactive" grains which cannot have been made by mechanical alloying of elemental powders. The inactive grains act as a matrix to hold the active grains as they repeatedly alloy with lithium during the operation of a lithium battery. A microscopic mixture of (active) and (inactive) shows a volumetric capacity for which is more than twice that of the graphite materials which are now the anode of choice for the battery. Unlike pure and alloys, the composite retains this capacity for many charge‐discharge cycles suggesting that materials like this will be the anodes of choice for the next generation of compact, high energy, batteries. ©1999 The Electrochemical Society

https://iopscience.iop.org/article/10.1149/1.1390715/pdf

Active/Inactive Nanocomposites as Anodes for Li ‐ Ion Batteries

An ab initio pseudopotential plane-wave method was used to calculate the total energies for several structures (Sn, ${\mathrm{Li}}_{2}{\mathrm{Sn}}_{5},$ LiSn, ${\mathrm{Li}}_{7}{\mathrm{Sn}}_{3},$ ${\mathrm{Li}}_{5}{\mathrm{Sn}}_{2},$ ${\mathrm{Li}}_{13}{\mathrm{Sn}}_{5},$ ${\mathrm{Li}}_{7}{\mathrm{Sn}}_{2},$ and Li) of the lithium-tin phase diagram. This information was used to determine a theoretical electrochemical voltage profile, which compares well with experiment for $xl2.5$ in ${\mathrm{Li}}_{x}\mathrm{Sn}.$ For $xg2.5,$ it was found that the equilibrium structures predicted by the phase diagram were not formed in the room-temperature electrochemical cell, which explains why the calculated results are less good there. Calculations of this type are useful for materials research in lithium-ion batteries.

Ian A. Courtney

Papers

Electrochemical and In Situ X‐Ray Diffraction Studies of the Reaction of Lithium with Tin Oxide Composites

Key Factors Controlling the Reversibility of the Reaction of Lithium with SnO2 and Sn2 BPO 6 Glass

On the Aggregation of Tin in SnO Composite Glasses Caused by the Reversible Reaction with Lithium

Active/Inactive Nanocomposites as Anodes for Li ‐ Ion Batteries

Ab initio calculation of the lithium-tin voltage profile