Single-Wall Carbon Nanotube Anodes for Lithium Cells

In recent experiments, highly purified batches of single-wall carbon nanotubes (SWCNTs) have shown promise as superior alternatives to the graphitic carbon-black anode materials heretofore used in rechargeable thin-film lithium power cells. The basic idea underlying the experiments is that relative to a given mass of graphitic carbon-black anode material, an equal mass of SWCNTs can be expected to have greater lithium-storage and charge/discharge capacities. The reason for this expectation is that whereas the microstructure and nanostructure of a graphitic carbon black is such as to make most of the interior of the material inaccessible for intercalation of lithium, a batch of SWCNTs can be made to have a much more open microstructure and nanostructure, such that most of the interior of the material is accessible for intercalation of lithium. Moreover, the greater accessibility of SWCNT structures can be expected to translate to greater mobilities for ion-exchange processes and, hence, an ability to sustain greater charge and discharge current densities

In Situ Measurements of Stress Evolution in Silicon Thin Films During Electrochemical Lithiation and Delithiation

We report in situ measurements of stress evolution in a silicon thin-film electrode during electrochemical lithiation and delithiation by using the Multi-beam Optical Sensor (MOS) technique. Upon lithiation, due to substrate constraint, the silicon electrode initially undergoes elastic deformation, resulting in rapid rise of compressive stress. The electrode begins to deform plastically at a compressive stress of ca. -1.75 GPa; subsequent lithiation results in continued plastic strain, dissipating mechanical energy. Upon delithiation, the electrode first undergoes elastic straining in the opposite direction, leading to a tensile stress of ca. 1 GPa; subsequently, it deforms plastically during the rest of delithiation. The plastic flow stress evolves continuously with lithium concentration. Thus, mechanical energy is dissipated in plastic deformation during both lithiation and delithiation, and it can be calculated from the stress measurements; we show that it is comparable to the polarization loss. Upon current interrupt, both the film stress and the electrode potential relax with similar time-constants, suggesting that stress contributes significantly to the chemical potential of lithiated-silicon.Comment: 12 pages, 3 figure

Monolithic Composite Electrodes Comprising Silicon Nanoparticles Embedded in Lignin-derived Carbon Fibers for Lithium-Ion Batteries

We report direct manufacturing of high-capacity carbon/silicon composite fiber electrodes for lithium-ion batteries produced via a flexible low-cost melt processing route, yielding low-cost stable silicon particles coated in situ by a 10 nanometer thick protective silica layer. The core–shell silicon/SiO2 islands are embedded in electrochemically active and electronically conductive carbon fiber derived from lignin precursor material. The silicon–silica–carbon composites exhibit capacities exceeding 700 mAh g−1 with Coulombic efficiencies in excess of 99.5 %. The high efficiency, stability, and rate capability are linked to the nanocrystalline structure and abundant, uniform nanometer-thick SiO2 interfaces that are produced during the spinning and subsequent pyrolysis of the precursor blend

Inexpensive method for producing macroporous silicon particulates (MPSPs) with pyrolyzed polyacrylonitrile for lithium ion batteries

One of the most exciting areas in lithium ion batteries is engineering structured silicon anodes. These new materials promise to lead the next generation of batteries with significantly higher reversible charge capacity than current technologies. One drawback of these materials is that their production involves costly processing steps, limiting their application in commercial lithium ion batteries. In this report we present an inexpensive method for synthesizing macroporous silicon particulates (MPSPs). After being mixed with polyacrylonitrile (PAN) and pyrolyzed, MPSPs can alloy with lithium, resulting in capacities of 1000 mAhg−1 for over 600+ cycles. These sponge-like MPSPs with pyrolyzed PAN (PPAN) can accommodate the large volume expansion associated with silicon lithiation. This performance combined with low cost processing yields a competitive anode material that will have an immediate and direct application in lithium ion batteries

A mini-review on the development of Si-based thin film anodes for Li-ion batteries

This review provides a summary of the progress in research on various Si-based thin films as anode materials for lithium-ion batteries. The lithiation mechanism models, different types of materials from pure monolithic Si thin film to Si-based three-dimensional structured composite thin films, the effect of liquid and solid-state electrolytes on the performance of Si were considered and various available preparation techniques were discussed. A table summarizing important information on such systems including the thin film features, preparation methods and conditions, electrochemical test conditions and obtained results in order to elucidate the approaches used to prepare a stable thin film anode with high capacity and long cycle life is provided. We believe that this review will help the researchers to find some answers and induce some new ideas

Predicting fracture evolution during lithiation process using peridynamics

Silicon is regarded as one of the most promising anode materials for lithium-ion batteries due to its large electric capacity. However, silicon experiences large volumetric change during battery cycling which can lead to fracture and failure of lithium-ion batteries. The lithium concentration and anode material phase change have direct influence on hydrostatic stress and damage evolution. High pressure gradient around crack tips causes mass flux of lithium ions which increases the lithium-ion concentration in these regions. Therefore, it is essential to describe the physics of the problem by solving fully coupled mechanical-diffusion equations. In this study, these equations are solved using peridynamics in conjunction with newly introduced peridynamic differential operator concept used to convert partial differential equation into peridynamic form for the diffusion equation. After validating the developed framework, the capability of the current approach is demonstrated by considering a thin electrode plate with multiple pre-existing cracks oriented in different directions. It is shown that peridynamics can successfully predict the crack propagation process during the lithiation process

Mechanical mismatch-driven rippling in carbon-coated silicon sheets for stress-resilient battery anodes

High-theoretical capacity and low working potential make silicon ideal anode for lithium ion batteries. However, the large volume change of silicon upon lithiation/delithiation poses a critical challenge for stable battery operations. Here, we introduce an unprecedented design, which takes advantage of large deformation and ensures the structural stability of the material by developing a two-dimensional silicon nanosheet coated with a thin carbon layer. During electrochemical cycling, this carbon coated silicon nanosheet exhibits unique deformation patterns, featuring accommodation of deformation in the thickness direction upon lithiation, while forming ripples upon delithiation, as demonstrated by in situ transmission electron microscopy observation and chemomechanical simulation. The ripple formation presents a unique mechanism for releasing the cycling induced stress, rendering the electrode much more stable and durable than the uncoated counterparts. This work demonstrates a general principle as how to take the advantage of the large deformation materials for designing high capacity electrode

Nanostructured Hybrid Silicon/Carbon Nanotube Heterostructures: Reversible High-Capacity Lithium-Ion Anodes

Lithium ion batteries have become the major flagship power sources for compact and portable electronics owing to their high energy and improved power density. The current lithium ion technology consists predominantly of graphite (theoretical capacity of 372mAh/g) as the anode and LiCoO 2 as the cathode. However, for applications such as electric or hybrid electric vehicles and grid energy storage, much higher capacities are required for which silicon with a theoretical capacity of 4200 mAh/g has been identified as a promising anode. Poor capacity retention that occurs during long term cycling for silicon based anodes due to large volume expansion-contraction (~400%) during lithium alloying-dealloying processes can be solved by various ways. Si/C based nanocomposites prepared by our group using high energy mechanical milling (HEMM) exhibited high reversible capacities of ~1000mA/g and excellent capacity retention In this work, amorphous carbon coated nanocomposites comprising of graphite/VACNT/silicon are synthesized by chemical vapor deposition (CVD) as well as high energy mechanical milling. Thin films/droplets of silicon were first deposited either directly on graphite or on vertically aligned carbon nanotubes (VACNTs). A simple 2-step liquid injection approach was employed in which m-xylene (with ferrocene as catalyst) and silane (SiH 4 ) were used as the CNT and silicon feedstocks, respectively. An amorphous carbon was deposited on silicon by decomposing m-xylene in the absence of catalyst. These hetereostructures developed on quartz were scraped off and slurries were made using a conductive additive and binder. Alternatively, additive and binder free electrodes were also developed by first growing VACNTs on Inconel 600 alloy over which silicon was deposited by thermal cracking of silane and finally coating with an amorphous carbon layer by xylene decomposition. The as-prepared electrodes were tested directly in a prototype test cell without using a conductive additive and binder. The silicon obtained from thermal cracking of silane was found to be nanocrystalline as confirmed by HRTEM. The nc-Si/graphite based electrodes, synthesized by HEMM, showed a reversible capacity of ~1000mAh/g upto 50 cycles while capacities more than 2500mAh/g were achieved from the nc-Si/VACNT based electrodes. The binder free nc-Si/VACNT electrodes showed a first discharge capacity of 1600mAh/g and capacities close to 1400mAh/g at the end of 30 th cycle. All these electrodes showed very low (10-16%) irreversible loss. Based on the high capacity retention and low irreversible loss of these heterostructured electrodes, the nc-Si/graphite/MWCNT based composite electrodes can be seen as promising anodes for the next generation lithium ion batteries. Acknowledgements: The authors gratefully acknowledge financial support of the DOE-BATT (DE-AC02-05CHl1231) and NSF-CBET programs. The authors also acknowledge the Edward R. Weidlein Chair Professorship funds for support of this research. Abstract #288, 219th ECS Meeting