Lithium Trapping Research Articles

Capacity Fading Research on Si Anode in Lithium Ion Batteries

Lithium ion batteries are considered to be the best choice for future hybrid electric vehicles (HEV) and full electric vehicles (FEV). HEV and FEC require batteries with higher specific energy, energy density, and longer cycle life than those used in consumer electronics. The available lithium ion batteries materials cannot meet the requirements of batteries to be used in FEV and HEV. The commonly used anode material is graphite. The theoretical specific capacity of graphite is 372 mAh g-1 and the performance of commercial graphite materials almost reaches their limit. Silicon anode material has attracted more attention of late due to its high capacity for lithium. Si can form an alloy with lithium (Li4.4Si) with a theoretical capacity of 4200 mAh g-1. In the past several decades, although silicon has been considered for use in lithium ion batteries, capacity decay with cycling is still a barrier to its application. It is believed that the large volume changes of Si (～300%) during lithiation and delithiation leads to rapid decay of capacity. Repeated cycling results in pulverization of silicon, which causes structural change of the Si electrode, and newly exposed surface area, which accommodates side reactions [1]. In this presentation, we researched the side reaction rate and investigated the capacity fading mechanism of Si anodes coupled with a lithium iron phosphate (LFP) counter electrode. A composite electrode of Si (obtained from Umicore) was prepared by our previously reported method [2]. 2325 coin cells were assembled for electrochemical measurements. LiPF6-EC/DEC (1.2M, 3/7 wt)+30 wt% FEC was used as electrolyte. Cycle performance of Si/LFP full cell is shown in Fig.1 a. Capacity fading happened continuously with cycling. Although the average voltage on charge and discharge drops, the difference remains relatively constant, which means capacity fading is not due to resistance rise. From 3-electrode cell data (in Fig. 1 b), the charge process was limited by anode side, initially, and then switched to the cathode side with cycling. Lithium in the cathode was consumed gradually with cycling. We concluded that the lithium imbalance is one of the factors that lead to the capacity fading. For Si anode, consumed lithium may take part in SEI formation or be trapped in Si. Electron energy loss spectroscopy (EELS) results show that lithium accumulated in Si particles with cycling. Since there is no impedance rise with cycling, lithium accumulation is mainly from lithium trapping inside Si particles. Particle isolation is another factor in Si anodes to cause capacity fading. From charge and discharge end point data, we calculated capacity fading rate caused by particle isolation and side reactions. The rate of side reactions is higher than that of particle isolation. C-rate transition from C/10 to C/5 charge and C/3 discharge results in catastrophic particle isolation followed by high rates of side reactions. Eventually, the rate of side reactions drops to their initial rate and particle isolation drops to a low level but this is much past end of life. Reference: [1] C. Chan, H. Peng, Y. Cui et al, Nature Nanotechnology 2008, 3, 31-35. [2] N. Yuca, H. Zhao, X. Song, M. Dogdu, W. Yuan, Y. Fu, V. S. Battaglia, X. Xiao, G. Liu, ACS Applied Materials & Interfaces. 2014, 6, 17111-17118. Fig.1. Electrochemical performance of LFP/Si (a. cycle performance, b. voltage profile). Figure 1

Deformation of Lithium-Ion Battery Anodes during SEI Formation: a Probe for the Structure of the SEI

Lithium-ion batteries are ubiquitous in small, portable electronics, where the lifetime of the battery now exceeds the expected lifetime of the device (ca. 2 years). Capacity fade over time, however, remains a significant challenge hindering the use of lithium-ion batteries in more demanding applications with long life-time requirements, such as in electric vehicles. One of the primary contributors to capacity fade is lithium trapping within the solid-electrolyte interphase (SEI) on the anode, making understanding the SEI critical to the design of more reliable lithium-ion batteries. The size-scale (tens of nanometers) and reactivity of the SEI, though, make characterization of the SEI difficult. In this presentation, we present a new method to probe the structure of the SEI that is formed on lithium-ion battery anodes. A custom battery cell employs an unconstrained (i.e. not on a current collector) graphite composite electrode and allows optical access to the electrode during electrochemical cycling. Electrolyte is reduced on the electrode surface potentiostatically, and the resulting deformation of the electrode is measured using digital image correlation (DIC), an optical, full-field strain measurement technique. The amount of deformation of the electrode induced during SEI formation is related to the structure of the SEI layer. The strain measurements are then compared to galvanostatic cycling results, and the effects of different electrolyte salts, solvents, and additives on the SEI structure and battery capacity retention are evaluated. Figure 1

Long Term Cycling Performance of High-Capacity Lithium-Ion Full Cells with Li1.2Ni0.15Mn0.55Co0.1O2/Li4Ti5O12

High-capacity Li-ion battery systems bearing Li1.2Ni0.15Mn0.55Co0.1O2-based positive electrode and graphite-based negative electrode show severe capacity fade and large impedance rise during long term cycling.[1] Cell capacity fade mainly arises by lithium trapping in the solid electrolyte interphase (SEI) of the graphite-based negative electrode. The cells impedance rise and voltage fade are mainly from the Li1.2Ni0.15Mn0.55Co0.1O2-based positive electrode.[1-3]From a practical and scientific point of view, it is important to design and evaluate optimized Li-ion battery systems with minimal capacity fade and low impedance rise.Li4Ti5O12 is an attractive anode material and shows a well-defined 1.55 V plateau vs. Li+/Li.[4] This relatively high voltage plateau prevents conventional SEI formation.[5] Therefore, replacing graphite with Li4Ti5O12 in our current Li-ion battery system is expected to achieve good capacity retention during cycling. Adding a small amount of LiDFOB to the Gen 2 electrolyte is an additional strategy to improve the cell performance. LiDFOB can be oxidized and forms a protective layer on the positive electrode surface; this layer slows down the impedance rise during cycling. [2] Therefore, we evaluate cells with Li1.2Ni0.15Mn0.55Co0.1O2-based positive and Li4Ti5O12-based negative electrodes; the cells contain Celgard 2325 separator, and an EC: EMC (3:7, by wt.) + 1.2M LiPF6 + 2 wt% LiDFOB electrolyte. Cells are cycled between 0.75 to 3.15V at a ~C/3 rate, to 500 cycles. After 500 cycles, the capacity retention is better and impedance rise is lower than that of the graphite-bearing full cells.Electrochemical performance evaluations are conducted on the harvested positive and negative electrodes. We identify that impedance rise still mainly arises from the Li1.2Ni0.15Mn0.55Co0.1O2-based positive electrode, after 500 cycles. The impedance rise on the Li4Ti5O12-based negative electrode is negligible after aging. The capacities of the harvested positive and negative electrodes, measured at slow rates, are also similar to that of the pristine electrodes. The progression of voltage fade and its implications will be also discussed.[6, 7] References [1] Y. Li, M. Bettge, B. Polzin, Y. Zhu, M. Balasubramanian, D.P. Abraham, Journal of The Electrochemical Society, 160 (2013) A3006-A3019.[2] Y. Zhu, Y. Li, M. Bettge, D.P. Abraham, Journal of The Electrochemical Society, 159 (2012) A2109-A2117.[3] M. Bettge, Y. Li, B. Sankaran, N.D. Rago, T. Spila, R.T. Haasch, I. Petrov, D.P. Abraham, Journal of Power Sources, 233 (2013) 346-357.[4] T. Ohzuku, A. Ueda, N. Yamamoto, Journal of The Electrochemical Society, 142 (1995) 1431-1435.[5] H.F. Xiang, X. Zhang, Q.Y. Jin, C.P. Zhang, C.H. Chen, X.W. Ge, Journal of Power Sources, 183 (2008) 355-360.[6] M. Bettge, Y. Li, K. Gallagher, Y. Zhu, Q. Wu, W. Lu, I. Bloom, D.P. Abraham, Journal of The Electrochemical Society, 160 (2013) A2046-A2055.[7] I. Bloom, L. Trahey, A. Abouimrane, I. Belharouak, X. Zhang, Q. Wu, W. Lu, D.P. Abraham, M. Bettge, J.W. Elam, X. Meng, A.K. Burrell, C. Ban, R. Tenent, J. Nanda, N. Dudney, Journal of Power Sources, (2013).

Electrochemical lithiation and delithiation performance of SnSb–Ag/carbon nanonube composites for lithium-ion batteries

SnSb–Ag/Carbon nanonube (CNT) composites materials are synthesised using chemical reduction methods. The microstructure, morphologies and electrochemical properties of these materials are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), constant current charge/discharge tests and cyclic voltammetry tests. The results indicate that Ag promotes the entire charge–discharge process during the complex multi-step reaction process and, to some extent, prevent the reunion of nanoparticles. At the same time, CNTs, with a large space volume and form a network structure, prevent particles aggregation and increase the buffer space between the alloy particles, which greatly reduce the diffusion distance of lithium ions and the occurrence of lithium trapping in the active electrode materials. CNTs also have excellent mechanical properties and toughness, they effectively buffer enormous stresses during the volume expansion of alloy particles, weakening the forces between the particles and reducing the rate of formation of powder particles. All these factors cause the SnSbAg0.1/6% CNT composites exhibit excellent cycle life by controlling the lithiation of the anode material; the reversible capacity for the 50th cycle is 639.6 mAh g−1 between 0.05 and 1.5 V.

Understanding Long-Term Cycling Performance of Li1.2Ni0.15Mn0.55Co0.1O2–Graphite Lithium-Ion Cells

Lithium-ion cells containing lithium– and manganese– rich layered-oxides (LMR-NMC) have gained significant attention in recent years because of their ability to deliver high energy densities. In this article we report on a comprehensive performance and degradation study of cells, containing Li1.2Ni0.15Mn0.55Co0.1O2–based positive electrodes and graphite–based negative electrodes, on extended cycling. In addition to electrochemical measurements on full cells, characterization data on harvested electrodes by techniques that include scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), Raman spectroscopy, and secondary ion mass spectrometry (SIMS) are discussed. Our data show that cell capacity fade mainly results from lithium trapping in the solid electrolyte interphase (SEI) of the negative electrode. In addition, cell impedance rise and voltage fade mainly arise at the positive electrode and result from degradation processes in its oxide and carbon constituents. Processes that include the accumulation of transition metal elements at the negative electrode, and increasing misalignment of electrode capacity windows on extended cycling, also have a deleterious effect on cell performance. Identifying sources of performance degradation has enabled strategies to extend cell life, which include improved cell fabrication protocols, positive electrode coatings, and bifunctional electrolyte additives.

Positive Electrode Passivation by LiDFOB Electrolyte Additive in High-Capacity Lithium-Ion Cells

The effect of LiF2BC2O4 (LiDFOB) electrolyte additive on the capacity and impedance characteristics of cells with Li1.2Ni0.15Mn0.55Co0.1O2-based positive, graphite-based negative and LiPF6-based electrolyte is evaluated using a combination of electrochemical cycling and surface analysis techniques. The impedance rise in these cells occurs primarily at the positive electrode whereas the capacity loss results from lithium trapping at the negative electrode. The LiDFOB serves as a bifunctional additive and reduces both cell capacity loss and impedance rise by reacting at both electrodes; probable reaction mechanisms have been highlighted in this article. X-ray photoelectron spectroscopy (XPS) data show that the LiDFOB additive forms a thicker passivation layer that inhibits electrolyte oxidation and reduces dissolution of Mn, Ni, Co ions from the positive electrode. Secondary ion mass spectroscopy (SIMS) data show that a thinner but more robust SEI forms at the negative electrode, which helps maintain cell capacity. The synergistic effects of LiDFOB at both electrodes results in a marked improvement in cell electrochemical performance.

Evolution of Phase Transformation Behavior in Li(Mn1.5Ni0.5)O4 Cathodes Studied By In Situ XRD

In situ X-ray diffraction of Li(Mn1.5Ni0.5)O4 was performed using a novel electrochemical cell based on coin cell hardware. The pristine material had a cubic spinel structure with a Ni2+ oxidation state. As the cell was charged through its 4.75V plateau, a transition between spinels with Ni2+, Ni3+, and Ni4+ oxidation was observed. As the oxidation of the nickel increased, the lattice parameter of the corresponding spinel diminished. During discharge, the spinel reversed its phase changes until only the Ni2+ spinel was observed. As the discharge potential reached a plateau at 2.75V a tetragonal spinel phase was formed, which upon subsequent cell charging was completely converted back to a cubic spinel phase. Lattice parameter changes of each phase were calculated and showed a characteristic strain release during phase changes. After 15 full cycles the transition between cubic spinels was no longer complete and the formation of the tetragonal spinel phase was no longer detected. This suggests a gradual change from an ordered to disordered MNO structure and lithium trapping in the active material. These cycle-induced changes to phase transition behavior can be related to capacity fade and overall cell performance.

Preparation and Electrochemical Performance of SnSb-Ag Composite Alloy Anode Materials

SnSb-Ag composite alloy anode materials were synthesized using chemical reduction method. Their microstructures, morphologies and electrochemical properties were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), constant current charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The results indicated that the addition of Ag resulted in the formation of irregular layered structures and different void sizes after several charge/discharge cycles, which greatly reduced the distance of lithium ion diffusion and the occurrence of lithium trapping in the active electrode materials and increased the space available for volume expansion. Thus, the composite anode materials were protected from powdering and shredding, resulting in a greatly improved cycling stability. For example, the SnSbAg0.2 composite anode exhibited excellent cycle life by controlling the lithiation of the Ag, the reversible capacity for the 50th cycle was measured to be 518 mAh/g and the reversible capacity retention reached 82.04% between 0.1 V and 1.5 V.

Lithium recovery from highly concentrated solutions: Response surface methodology (RSM) process parameters optimization

Lithium recovery from aqueous solutions was studied by trapping lithium ions using a gel of aluminum hydroxide freshly prepared in situ under the reaction of a strong base. A 2 4 − 1 fractional factorial design and central composite design were employed for experimental design and analysis of the results. The combined effect of molar ratio Al/Li, pH and stirring time on lithium trapping at 25 °C was investigated and optimized using response surface methodology (RSM). The optimum values of these factors were found to be 4.7, 7.2 and 3 h respectively. In this case the lithium trapping percent is ∼ 95%. The obtained model is highly significant ( F obs > F tabulate and low p-value) with a correlation coefficient of 96.64%. On the other hand, linear, quadratic and interaction terms in this model have the largest statistical effect on the response (confidence level = 99.9%).

C(6)-Alkylation of 3-Hydroxypiperidine via Reductive and Homolytic Cleavage of N,S-Acetals

N-Carboxymethyl 3-hydroxypiperidine (6) undergoes substitution at C(6) via reductive cleavage of N,S-acetal 8a with lithium naphthalenide (LN) and trapping of the resulting carbanionic intermediate 9 with different electrophiles to give adducts 10. N,S-Acetal 8a also undergoes C-S homolysis and trapping of the resulting radical provides an alternative entry to 2-substituted-5-­hydroxypiperidines.

Lithium trapping by excess oxygen inWO3:A first-principles study

The process of lithium trapping by excess oxygen atoms in both crystalline and amorphous ${\mathrm{WO}}_{3}$ is studied by first-principles calculations. In both materials, the excess oxygen is incorporated in the bonding network by a peroxide-type bond. In both $c\ensuremath{-}{\mathrm{WO}}_{3}$ and $a\ensuremath{-}{\mathrm{WO}}_{3},$ breaking of this bond makes oxygen states available for the accommodation of the Li electrons. However, only in $a\ensuremath{-}{\mathrm{WO}}_{3}$ is this mechanism accompanied by a strong reduction in total energy as this material has the flexibility to accommodate (incorporate) the extra ${\mathrm{O}}^{2\ensuremath{-}}$ ion.

On the irreversible capacities of disordered carbons in lithium-ion rechargeable batteries

The irreversible capacity of disordered carbons, used as anodes of lithium-ion batteries, is known to result from their generally large surface area (leading to large volume of passivating layer) and from the presence of surface functional groups and of heteroatoms left from the precursor, which can react irreversibly with lithium. In this paper, we show that the irreversible capacity of disordered carbons can result from an additional mechanism: lithium trapping in the internal porosity. A series of carbon samples with low specific surface area and low heteroatom content has been investigated by X-ray diffraction, helium pycnometry, complex impedance spectroscopy and galvanostatic cycling. A clear correlation has been found between the irreversible capacity and the internal pore volume.

Lithium trapping at excess oxygen in sputter-deposited a-WO3 films

The initial stages of electrochemical intercalation of lithium in sputter-deposited tungsten oxide thin films were studied. The as-deposited films show a substantial irreversible uptake of lithium without an electrochromic effect. This trapping of lithium is associated with the presence of excess oxygen in the film. The experimental results are consistent with a reaction of lithium and interstitial oxygen to form a neutral Li2−Oi complex. Our findings are relevant for the manufacture of electrochromic devices, and the electrochemical titration method used may be applied to probe excess oxygen in other oxidic films as well.