The behavior of a many-particle electrode in a lithium-ion battery

Carbon-coated, anatase titanium dioxide nanotubes were prepared by carbonizing a polyacrylonitrile-based block copolymer grafted on the as-synthesized titanate nanotubes. As revealed by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS), this approach results in a very homogeneous and thin carbon coating, which is advantageous for those active materials storing lithium without undergoing significant volume changes upon ion (de-)insertion. As a matter of fact, thus prepared carbon-coated TiO 2 nanotubes presented an excellent long-term cycling stability for more than 500 cycles (0.02% capacity fading per cycle) and a very promising high rate performance (about 130 and 110 mAh g −1 at 10 C and 15 C, respectively). The influence of the tubular morphology on the rate performance is briefly discussed by comparing carbon-coated nanotubes and nanorods. Finally, the carbon-coated nanotubes were also investigated as sodium-ion anode material, showing very promising reversible capacities of around 170, 120, and 100 mAh g −1 at C/10, 1 C, and 2 C, respectively, rendering them as versatile anode material for lithium-and sodium-ion applications © The Author Efficient energy storage, prospected to pave the way for a fully electrified transportation system and the complete energy supply by renewables, is probably one of the major challenges modern society faces.1-3 Lithium-ion batteries and, very recently, sodium-ion batteries are considered as two of the most promising energy storage technologies to achieve these highly desired targets. However, further improvements in terms of energy density, rate capability, and safety are needed to make these devices finally suitable for such large-scale applications.4-14 With respect to stationary energy storage applications, for which weight and volume of the battery are not a real issue while long-term cycling stability, rate performance, and safety are of major importance, in particular, titanium-based materials are considered as highly promising candidates to replace the state-of-theart lithium-ion anode material graphite.15-18 Among these, anatase TiO 2 is certainly of special interest due to its natural abundance, low cost, environmental friendliness, non-toxicity, and large-scale availability.19-21 Additionally, it offers a rather large theoretical specific capacity of 335 mAh g −1 , corresponding to the reversible uptake and release of one lithium or sodium per formula unit of TiO 2 . The practical limit for micro-sized particles, however, is 0.5 lithium per TiO 2 unit (corresponding to a specific capacity of about 168 mAh g −1 ), due to diffusion limitation in the solid phase.22-25 Substantial improvements were realized in recent years by nanostructuring the primary particles [26][27][28][29][30] and the application of carbonaceous coatings 31-42 and matrices, [43][44][45] resulting commonly in enhanced rate capabilities, cycling stability, and increased specific capacities.46-48 One-dimensional nanostructures, such as nanowires,...

Section: Resultsmentioning

confidence: 99%

Carbon-Coated Anatase TiO₂Nanotubes for Li- and Na-Ion Anodes

Bresser

Oschmann

Tahir

et al. 2014

“…Dreyer et al investigated the single and multi-particle behavior during the phase transition of LFP. 21,23,24 During lithium insertion at low C-Rates, the bulk-material of the electrode behaves like a single particle due to slow kinetics indicated by a strong distinct maximum. During this phase transition, we get several different particle stages in the bulk according to a multi particle system.…”

Section: Resultsmentioning

confidence: 99%

Pressure Characteristics and Chemical Potentials of Constrained LiFePO₄/C₆Cells

Singer

Kropp

Kuehnemund

et al. 2018

Constraining lithium-ion cells increases the cyclic lifetime. However, depending on an expected volume expansion during charge and discharge cycling, defining the optimal constraining pressure range is not straightforward. In this study, we investigate a lithium iron phosphate/graphite pouch cell at four initial constraining pressure levels. As a function of C-Rate, the thermodynamic principle of the non-monotonic pressure curve during full charge and discharge cycles is evaluated. Using the rubber balloon model to calculate the chemical potential of lithium iron phosphate and discussing the relationship between the chemical potential and pressure, we illustrate the pressure curve qualitatively. By applying differential pressure analysis, we evaluate the resulting pressure curves of a single graphite stage. Approaching a fundamental understanding of reduced cycling lifetime of full cells with unknown material composition, we allocate the stages and stage transitions of graphite as well as the phase transition of lithium iron phosphate. Local extreme values in the differential pressure analysis indicate phase and stage transitions. These values can identify critical operating conditions that should be considered for defining the optimum initial constraining pressure range.

“…Regarding the cell potential, this becomes apparent by a hysteresis in the open circuit voltage between charging and discharging to the same SoC, which amounts to 10-20 mV. [39][40][41][42] For graphite electrodes, different lithium distributions for the same SoC have also been confirmed by electrooptical measurements. 43 To study the dependence of calendar aging on the charge-discharge history, an alternative procedure for reaching the storage SoC was examined, i.e., discharging Q discharge from the fully charged cells to reach the storage SoC.…”

Section: Methodsmentioning

confidence: 97%

Calendar Aging of Lithium-Ion Batteries

Keil

Schuster

Wilhelm

et al. 2016

407

288

In this study, the calendar aging of lithium-ion batteries is investigated at different temperatures for 16 states of charge (SoCs) from 0 to 100%. Three types of 18650 lithium-ion cells, containing different cathode materials, have been examined. Our study demonstrates that calendar aging does not increase steadily with the SoC. Instead, plateau regions, covering SoC intervals of more than 20%-30% of the cell capacity, are observed wherein the capacity fade is similar. Differential voltage analyses confirm that the capacity fade is mainly caused by a shift in the electrode balancing. Furthermore, our study reveals the high impact of the graphite electrode on calendar aging. Lower anode potentials, which aggravate electrolyte reduction and thus promote solid electrolyte interphase growth, have been identified as the main driver of capacity fade during storage. In the high SoC regime where the graphite anode is lithiated more than 50%, the low anode potential accelerates the loss of cyclable lithium, which in turn distorts the electrode balancing. Aging mechanisms induced by high cell potential, such as electrolyte oxidation or transition-metal dissolution, seem to play only a minor role. To maximize battery life, high storage SoCs corresponding to low anode potential should be avoided.