Enhanced Capacity and Rate Capability of Carbon Nanotube Based Anodes with Titanium Contacts for Lithium Ion Batteries

Abstract

Carbon nanotubes are being considered for adoption in lithium ion batteries as both a current collector support for high-capacity active materials (replacing traditional metal foils) and as free-standing electrodes where they simultaneously store lithium ions. The necessity to establish good electrical contact to these novel electrode designs is critical for success. In this work, application of nickel and titanium as both separable and thin film electrical contacts to free-standing single-wall carbon nanotube (SWCNT) electrodes is shown to dramatically enhance both the reversible lithium ion capacity and rate capability in comparison with stainless steel. Scanning electron microscopy showed that evaporation of Ni and Ti can effectively coat the SWCNT bundles in a bulk electrode which is capable of providing an improved electrical contact. A thin film of titanium emerged as the preferred electrical contact promoting the highest capacity ever measured for a SWCNT free-standing electrode of 1250 mAh/g. In addition, the titanium contacting approach demonstrated a 5-fold improvement in lithium ion capacity at extraction rates greater than 1C for a high-energy density Ge-SWCNT electrode. The overall performance improvement with Ti contacts is attributed to a lower contact resistance, nanoscale "wetting" of SWCNT bundles to improve contact uniformity, and effective electron coupling between Ti and SWCNTs due to work function-energy level alignment. The experimental results provide the basis for a Ragone analysis (power vs energy parameters), whereby Ge-SWCNT-Ti anodes paired with a LiFePO(4) cathode can lead to a 60% improvement over conventional graphite anodes in both power and energy density for a complete battery.

Anodes for Li-Ion Batteries

“…The highest reversible capacity is predicted for SWCNTs and is estimated to be 1116 mAh g À1 in stoichiometry LiC 2 owing to the intercalation of lithium into stable sites located on the surface of pseudographitic layers and inside the central tube as well [119][120][121][122]. This theoretical prediction is confirmed by experiments, since purified SWCNTs, produced by laser vaporization procedure, yield a capacity larger than 1050 mAh g À1 [123], the largest capacity obtained with SWCNT anodes. This performance has been obtained for a purified SWCNT obtained by laser vaporization.…”

Rock‐Salt‐Templated Mn3O4 Nanoparticles Encapsulated in a Mesoporous 2D Carbon Matrix: A High Rate 2 V Anode for Lithium‐Ion Batteries with Extraordinary Cycling Stability

“…At first, the electrochemical properties of commercial LiFePO 4 has been investigated in half cell configuration vs Li/Li + . A first cycle discharge capacity of 128 mAh g ‐1 is found at a current density of 0.1 mA cm ‐2 (Figure S9, supporting information), a result comparable with the previously reported literature . Figure a shows the cyclic voltammograms of the LiFePO 4 //Mn 3 O 4 @C‐T full cell for the first five consecutive scans recorded at 1 mV s ‐1 in the potential window of 1.0‐3.6 V. Second cycle onwards, the voltammograms nearly overlap with one another indicating excellent reversibility of the charge/ discharge processes.…”

Novel felt pseudocapacitor based on carbon nanotube/metal oxides

“…The performance of energy storage devices is commonly compared on a Ragone chart [37] where the specific energy is plotted versus the specific power. Figure 9 shows the Ragone plot where the performances of our electrodes are compared with commercial devices and some selected reports.…”