Richard Kloepsch

Lithium ion, lithium metal, and alternative rechargeable battery technologies: the odyssey for high energy density

Since their market introduction in 1991, lithium ion batteries (LIBs) have developed evolutionary in terms of their specific energies (Wh/kg) and energy densities (Wh/L). Currently, they do not only dominate the small format battery market for portable electronic devices, but have also been successfully implemented as the technology of choice for electromobility as well as for stationary energy storage. Besides LIBs, a variety of different technologically promising battery concepts exists that, depending on the respective technology, might also be suitable for various application purposes. These systems of the “next generation,” the so-called post-lithium ion batteries (PLIBs), such as metal/sulfur, metal/air or metal/oxygen, or “post-lithium technologies” (systems without Li), which are based on alternative single (Na+, K+) or multivalent ions (Mg2+, Ca2+), are currently being studied intensively. From today’s point of view, it seems quite clear that there will not only be a single technology for all applications (technology monopoly), but different battery systems, which can be especially suitable or combined for a particular application (technology diversity). In this review, we place the lithium ion technology in a historical context and give insights into the battery technology diversity that evolved during the past decades and which will, in turn, influence future research and development.

Morphological Evolution of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Materials for Lithium-Ion Batteries: The Critical Effects of Surface Orientations and Particle Size

An evolution panorama of morphology and surface orientation of high-voltage spinel LiNi(0.5)Mn(1.5)O4 cathode materials synthesized by the combination of the microwave-assisted hydrothermal technique and a postcalcination process is presented. Nanoparticles, octahedral and truncated octahedral particles with different preferential growth of surface orientations are obtained. The structures of different materials are studied by X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption near edge spectroscopy (XANES), and transmission electron microscopy (TEM). The influence of various morphologies (including surface orientations and particle size) on kinetic parameters, such as electronic conductivity and Li(+) diffusion coefficients, are investigated as well. Moreover, electrochemical measurements indicate that the morphological differences result in divergent rate capabilities and cycling performances. They reveal that appropriate surface-tailoring can satisfy simultaneously the compatibility of power capability and long cycle life. The morphology design for optimizing Li(+) transport and interfacial stability is very important for high-voltage spinel material. Overall, the crystal chemistry, kinetics and electrochemical performance of the present study on various morphologies of LiNi(0.5)Mn(1.5)O4 spinel materials have implications for understanding the complex impacts of electrode interface and electrolyte and rational design of rechargeable electrode materials for lithium-ion batteries. The outstanding performance of our truncated octahedral LiNi(0.5)Mn(1.5)O4 materials makes them promising as cathode materials to develop long-life, high energy and high power lithium-ion batteries.

Enhanced electrochemical performance in lithium ion batteries of a hollow spherical lithium-rich cathode material synthesized by a molten salt method

A high voltage layered Li1.2Ni0.16Co0.08Mn0.56O2 cathode material with a hollow spherical structure has been synthesized by molten-salt method in a NaCl flux. Characterization by X-ray diffraction and scanning electron microscopy confirmed its structure and proved that the as-prepared powder is constituted of small, homogenously sized hollow spheres (1–1.5 μm). The material exhibited enhanced rate capability and high first cycle efficiency due to the good dispersion of secondary particles. Galvanostatic cycling at different temperatures (20, 40, and 60 °C) and a current rate of 2 C (500 mA·g−1) showed no significant capacity fade.

Facile Synthesis and Lithium Storage Properties of a Porous NiSi2/Si/Carbon Composite Anode Material for Lithium-Ion Batteries

In this work, a novel, porous structured NiSi2/Si composite material with a core-shell morphology was successfully prepared using a facile ball-milling method. Furthermore, the chemical vapor deposition (CVD) method is deployed to coat the NiSi2/Si phase with a thin carbon layer to further enhance the surface electronic conductivity and to mechanically stabilize the whole composite structure. The morphology and porosity of the composite material was evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption measurements (BJH analysis). The as-prepared composite material consists of NiSi2, silicon, and carbon phases, in which the NiSi2 phase is embedded in a silicon matrix having homogeneously distributed pores, while the surface of this composite is coated with a carbon layer. The electrochemical characterization shows that the porous and core-shell structure of the composite anode material can effectively absorb and buffer the immense volume changes of silicon during the lithiation/delithiation process. The obtained NiSi2/Si/carbon composite anode material displays an outstanding electrochemical performance, which gives a stable capacity of 1272 mAh g(-1) for 200 cycles at a charge/discharge rate of 1C and a good rate capability with a reversible capacity of 740 mAh g(-1) at a rate of 5C.

One-step synthesis of novel mesoporous three-dimensional GeO2 and its lithium storage properties

Novel mesoporous three-dimensional GeO2 was successfully synthesized by a facile one-step synthesis method followed by mixing with graphene using a spray drying process. The well-dispersed mesoporous GeO2 demonstrates a bean-like morphology (b-GeO2) with a particle size of 400 to 500 nm in length and 200 to 300 nm in diameter, in which mesopores with an average size of 3.6 nm are distributed. The b-GeO2 without any additional conductive surface layer shows a high reversible capacity for lithium storage of 845 mAh g−1 after 100 cycles, with nearly no capacity fading. When graphene was employed to be mixed with GeO2via a spray drying method, the electrochemical performance is further significantly improved. The b-GeO2/graphene composite electrode gives a higher de-lithiation capacity of 1021 mAh g−1, and the capacity retention is measured to be as high as 94.3% after 200 charge–discharge cycles for constant current cycling at 0.2 C, as well as an excellent rate performance, even displaying a reversible capacity of 730 mAh g−1 at a rate of 5 C.

O3-type Na[Fe1/3Ni1/3Ti1/3]O2 cathode material for rechargeable sodium ion batteries

A Na[Fe1/3Ni1/3Ti1/3]O2 cathode material for sodium-ion batteries has been synthesized by a solid-state reaction method. The obtained Na[Fe1/3Ni1/3Ti1/3]O2 shows an O3-type structure, and delivers a discharge capacity of 117 mA h g−1 at a current density of 10 mA g−1 in a range of 1.5–4.0 V at 20 °C. Furthermore, the Na[Fe1/3Ni1/3Ti1/3]O2 cathode material shows good rate capability and cycling stability. The working and structural transition mechanisms of the Na[Fe1/3Ni1/3Ti1/3]O2 material are examined by ex situ X-ray absorption spectroscopy (XAS) and in situ X-ray diffraction (XRD) methods. The valence state of Fe ions in the Na[Fe1/3Ni1/3Ti1/3]O2 material is estimated to be 2.67+. The main redox couple is Ni2+/Ni4+, but the Fe2+/Fe3+ contributes a little as well at voltages below 2.0 V. The original O3 phase transforms to a P3 phase during sodium extraction with good reversibility, but a slightly irreversible change of lattice parameters may lead to capacity decay during long-term cycling. Moreover, the gas evolution during the first charge/discharge process is analyzed by using an operando mass spectrometry technique. The obvious release of CO2 gas at the end of the charge process may be the other origin of the capacity decay. Nevertheless, the absence of O2 evolution indicates an improved safety of the Na/Na[Fe1/3Ni1/3Ti1/3]O2 cell.

On the structural integrity and electrochemical activity of a 0.5Li2MnO3·0.5LiCoO2 cathode material for lithium-ion batteries

Structural changes in a 0.5Li2MnO3·0.5LiCoO2 cathode material were investigated by X-ray absorption spectroscopy. It is observed that both Li2MnO3 and LiCoO2 components of the material exist as separate domains, however, with some exchange of transition metal (TM) ions in their slab layers. A large irreversible capacity observed during activation of the material in the 1st cycle can be attributed to an irreversible oxygen release from Li2MnO3 domains during lithium extraction. The average valence state of manganese ions remains unchanged at 4+ during charge and discharge. In the absence of conventional redox processes, lithium extraction/reinsertion from/into Li2MnO3 domains occurs with the participation of oxygen anions in redox reactions and most likely involves the ion-exchange process. In contrast, lithium deintercalation/intercalation from/into LiCoO2 domains occurs topotactically, involving a conventional Co3+/Co4+ redox reaction. The presence of Li2MnO3 domains and their unusual participation in electrochemical processes enable LiCoO2 domains of the material to sustain a higher cut-off voltage without undergoing irreversible structural changes.

Anodic Behavior of the Aluminum Current Collector in Imide-Based Electrolytes: Influence of Solvent, Operating Temperature, and Native Oxide-Layer Thickness

The inability of imide salts to form a sufficiently effective passivation layer on aluminum current collectors is one of the main obstacles that limit their broad application in electrochemical energy-storage systems. However, under certain circumstances, the use of electrolytes with imide electrolyte salts in combination with the aluminum current collector is possible. In this contribution, the stability of the aluminum current collector in electrolytes containing either lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) or lithium fluorosulfonyl-(trifluoromethanesulfonyl) imide (LiFTFSI) as conductive salt was investigated by electrochemical techniques, that is, cyclic voltammetry (CV) and chronocoulometry (CC) in either room-temperature ionic liquids or in ethyl methyl sulfone. In particular, the influence of the solvent, operating temperature, and thickness of the native oxide layer of aluminum on the pit formation at the aluminum current collector surface was studied by means of scanning electron microscopy. In general, a more pronounced aluminum dissolution and pit formation was found at elevated temperatures as well as in solvents with a high dielectric constant. An enhanced thickness of the native aluminum oxide layer increases the oxidative stability versus dissolution. Furthermore, we found a different reaction rate depending on dwell time at the upper cut-off potential for aluminum dissolution in TFSI- and FTFSI-based electrolytes during the CC measurements; the use of LiFTFSI facilitated the dissolution of aluminum compared to LiTFSI. Overall, the mechanism of anodic aluminum dissolution is based on: i) the attack of the Al2 O3 surface by acidic species and ii) the dissolution of bare aluminum into the electrolyte, which, in turn, is influenced by the electrolytes dielectric constant.

In situ X-ray diffraction study on the formation of α-Sn in nanocrystalline Sn-based electrodes for lithium-ion batteries

In situ X-ray diffraction (XRD) was performed to study the formation of the α-Sn structure in nanocrystalline Sn-based electrodes during electrochemical lithium insertion and extraction at room temperature. Therefore, pure β-Sn nanoparticles were synthesised and further processed into electrodes. The lithiation and de-lithiation process of the β-Sn nanoparticles follows the formation of discrete lithium–tin phases which perfectly fits the voltage plateaus in the charge/discharge diagram. However, unlike bulk electrodes, where no α-Sn is formed, we observed the formation of the semiconducting α-modification at 870 mV vs. Li within the first de-lithiation process. This observation explains earlier reports of an increasing internal resistance of such an electrode. Additionally, our study supports earlier suggestions that predominantly small tin crystallites are transformed from the β-Sn phase into the α-Sn phase, while larger crystallites retain their metallic β-Sn structure.