Surface Evolution of Lithium Titanate upon Electrochemical Cycling Using a Combination of Surface Specific Characterization Techniques (original) (raw)
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Energies, 2017
Researchers are in search of parameters inside Li-ion batteries that can be utilized to control their external behavior. Physics-based electrochemical model could bridge the gap between Li+ transportation and distribution inside battery and battery performance outside. In this paper, two commercially available Li-ion anode materials: graphite and Lithium titanate (Li 4 Ti 5 O 12 or LTO) were selected and a physics-based electrochemical model was developed based on half-cell assembly and testing. It is found that LTO has a smaller diffusion coefficient (D s) than graphite, which causes a larger overpotential, leading to a smaller capacity utilization and, correspondingly, a shorter duration of constant current charge or discharge. However, in large current applications, LTO performs better than graphite because its effective particle radius decreases with increasing current, leading to enhanced diffusion. In addition, LTO has a higher activation overpotential in its side reactions; its degradation rate is expected to be much smaller than graphite, indicating a longer life span.
Journal of The Electrochemical Society, 1999
Among lithium transition metal oxides used as intercalation electrodes for rechargeable lithium batteries, LiCoO 2 is considered to be the most stable in the ␣-NaFeO 2 structure type. It has previously been believed that cation ordering is unaffected by repeated electrochemical removal and insertion. We have conducted direct observations, at the particle scale, of damage and cation disorder induced in LiCoO 2 cathodes by electrochemical cycling. Using transmission electron microscopy imaging and electron diffraction, it was found that (i) individual LiCoO 2 particles in a cathode cycled from 2.5 to 4.35 V against a Li anode are subject to widely varying degrees of damage; (ii) cycling induces severe strain, high defect densities, and occasional fracture of particles; and (iii) severely strained particles exhibit two types of cation disorder, defects on octahedral site layers (including cation substitutions and vacancies) as well as a partial transformation to spinel tetrahedral site ordering. The damage and cation disorder are localized and have not been detected by conventional bulk characterization techniques such as X-ray or neutron diffraction. Cumulative damage of this nature may be responsible for property degradation during overcharging or in long-term cycling of LiCoO 2 -based rechargeable lithium batteries.
A short review on surface chemical aspects of Li batteries: A key for a good performance
Journal of Power Sources, 2009
We review herein several important aspects of surface chemistry in Li-ion batteries, and discuss the use of ionic liquids (ILs) for rechargeable Li batteries. We explored the suitability of ILs for 5 V cathodes and Li-graphite anodes. Some advantages of the use of ILs to attenuate the thermal behavior of delithiated cathode materials are demonstrated. We also report briefly on a comparative study of the following cathode materials: LiNi 0.5 Mn 0.5 O 2 ; LiNi 0.33 Mn 0.33 Co 0.33 O 2 ; LiNi 0.4 Mn 0.4 Co 0.2 O 2 ; LiNi 0.8 Co 0.15 Al 0.05 O 2 and LiMnPO 4 , in standard electrolyte solutions based on mixtures of alkyl carbonates and LiPF 6 . We also discuss aging, rate capability, cycle life and surface chemistry of these cathode materials. The techniques applied included electrochemical measurements, e.g., XRD, HRTEM, Raman spectroscopy, XPS and FTIR spectroscopy. We found that ILs based on cyclic quaternary alkyl ammonium cations may provide much better electrolyte solutions for 5 V cathodes than standard electrolyte solutions, while being quite suitable for Li-graphite electrodes. All the lithiated transition metal oxides studied (as mentioned above) develop unique surface chemistry during aging and cycling due to the acid-base and nucleophilic reactions of their surface oxygen anions. LiMn 0.33 Ni 0.33 Co 0.33 O 2 has the highest rate capability compared to all the other abovementioned cathode materials. Cathodes comprising nanometric size carbon-coated LiMnPO 4 produced by HPL demonstrate a better rate capability than LiNi 0.5 Mn 0.5 O 2 and LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes. The former material seems to be the least surface reactive with alkyl carbonates/LiPF 6 solutions, among all the cathode materials explored herein.
Surface Characterization of Electrodes from High Power Lithium-Ion Batteries
Journal of The Electrochemical Society, 2002
X-ray photoelectron spectroscopy and scanning electron microscopy were used to study electrode samples obtained from 18650type lithium-ion cells subjected to accelerated calendar-life testing at temperatures ranging from 25 to 70°C and at states-of-charge from 40 to 80%. The cells contained LiNi 0.8 Co 0.2 O 2 -based positive electrodes ͑cathodes͒, graphite-based negative electrodes ͑anodes͒, and a 1 M LiPF 6 ethylene carbonate:diethyl carbonate ͑1:1͒ electrolyte. The results from electrochemically treated samples showed surface film formation on both electrodes. The positive electrode laminate surfaces contained a mixture of organic species that included polycarbonates, and LiF, Li x PF y -type and Li x PF y O z -type compounds. The same surface compounds were observed regardless of test temperature, test duration, and state-of-charge. On the negative electrode laminates lithium alkyl carbonates (ROCO 2 Li) and Li 2 CO 3 were found in addition to the above-mentioned compounds. Decomposition of lithium alkyl carbonates to Li 2 CO 3 occurred on negative electrodes stored at elevated temperature. Initial depth-profiling results suggest that the surface layer thickness is greater on positive electrode samples from cells stored at high temperature than on samples from cells stored at room temperature. This observation is significant because positive electrode impedance, and more specifically, chargetransfer resistance at the electrode/electrolyte interface, has been shown to be the main contributor to impedance rise in these cells.
Electrode–solution interactions in Li-ion batteries: a short summary and new insights
Journal of Power Sources, 2003
This paper is aimed at reviewing and discussing several selected surface phenomena related to Li-ion batteries. Accumulated data from in situ XRD, in situ AFM, SEM, and electrochemical measurements of graphite electrodes comprising different types of graphite particles (in terms of morphology and 3D structure) converge to a description of failure mechanisms of graphite electrodes, which involve deactivation by insulating surface films that surround cracked particles. It appears that the performance of the cathodes is also, to a large extent, surface film controlled. Hence, aging of Li-ion batteries relates mostly to surface phenomena that increase the electrodes' impedance, especially at elevated temperatures. Attempts to improve the performance of Li-ion battery systems by introduction of new salts and reactive additives are reviewed. The impact of elevated temperatures (up to 80 8C) is also discussed.
Electrode Degradation in Lithium-Ion Batteries
ACS Nano
Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2−5 times higher than that of conventional intercalation materials (e.g., LiCoO 2 and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.
The Cathode Surface Composition of a Cycled Li–O 2 Battery: A Photoelectron Spectroscopy Study
The Journal of Physical Chemistry C, 2012
A layer of reaction products, dominantly built up of C and O in the form of ethers and lithium alkyl carbonates, is formed on the surface of the carbon cathode during discharge of a Li−O 2 battery in an electrolyte of 1 M LiPF 6 in PC. The results are based on a detailed surface analysis combining the use of in house X-ray photoelectron spectroscopy (XPS) and synchrotron based hard X-ray photoelectron spectroscopy (HAXPES). The Li−O 2 batteries were investigated at uncycled state (stored), after the first discharge, after the first charge, and at the end of life (discharge state). The results showed little to no Li 2 O 2 and/or Li 2 O among the discharge products. The surface layers on the cathode were dominantly removed during charging of the battery. At the end of battery life, no complete discharge product layer is formed. The cathodes showed a strong indication of binder decomposition during cycling of the Li−O 2 cell. Overall, the results obtained in this investigation show that the whole cathode formulation as well as the electrolyte composition need a completely new approach for the realization of a recyclable Li−O 2 battery.
A Comprehensive Analysis of Material Revolution to Evolution in Lithium-ion Battery Technology
Turkish Journal of Materials, 2023
Lithium-ion batteries (LIBs) have significantly impacted our lives and are now found in various devices such as cell phones, laptops, and electric vehicles. An appropriate electrolyte was produced in LIBs via a twisting route, which relates to the progress of electrode chemistry. Based on recent research and discoveries, LIB has emerged as the technology of choice for storing electrical energy for use in mobile products and electric vehicles. This is due to LIBs' desirable qualities, such as their lightweight, high-energy density, small size, little memory effect, extended lifespan, and low pollution. In this method, a metal oxide is the cathode, and porous carbon is the anode. The electrochemical interaction of lithium with anode materials can generate intercalation products that are the basis for innovative battery systems. At room temperature, structural retention makes this reaction quick and reversible. This concise overview examines the progress of LIB technology and the impact of the materials used in different technologies on cell performance. The section summarizes the evolution of LIB cells and Li + ion storage into various materials and intercalation chemistry.