Negative electrodes for Li-ion batteries

Graphitized carbons have played a key role in the successful commercialization of Li-ion batteries. The physicochemical properties of carbon cover a wide range; therefore, identifying the optimum active electrode material can be time consuming. The significant physical properties of negative electrodes for Li-ion batteries are summarized, and the relationship of these properties to their electrochemical performance in non-aqueous electrolytes, are discussed in this paper.     

TiO2(B) as a promising high potential negative electrode for large-size lithium-ion batteries

Needle-like TiO₂(B) powder was obtained from K₂Ti₄O₉ precursor by ion exchange to protons, followed by dehydration. The charge and discharge characteristics of the TiO₂(B) powder were investigated as a high potential negative electrode in lithium-ion batteries. It had a high discharge capacity of 200–250 mAh g⁻¹ at around 1.6 V vs. Li/Li⁺, which was comparable with that of TiO₂(B) nanowires and nanotubes prepared via a hydrothermal reaction in alkaline solution. It showed very good cycleability, and gave a discharge capacity of 170 mAh g⁻¹ even in the 650th cycle. It also had a high rate capability, and gave a discharge capacity of 106 mAh g⁻¹ even at 10 °C.     

Nanostructured Si/Sn-Ni/C composite as negative electrode for Li-ion batteries

A nanostructured composite with overall atomic composition Ni_0.14Sn_0.17Si_0.32Al_0.037C_0.346 has been prepared combining powder metallurgy and mechanical milling techniques for being used as anode material in Li-ion battery. Chemical and structural properties of the nanocomposite have been determined by X-ray diffraction (XRD), ¹¹⁹Sn Transmission Mössbauer Spectroscopy (TMS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite consists of Si particles with typical size ∼150 nm embedded in a poorly crystallized and complex multielemental matrix. The matrix is composed mostly by Ni_3.4Sn₄, and disordered carbon. Electrochemical evaluation shows a high reversible capacity of 920 mAh g⁻¹, with reasonable reversible capacity retention (∼0.1% loss/cycle) over 280 cycles.     

Electrodeposited porous-microspheres Li-Si films as negative electrodes in lithium-ion batteries

A porous-microspheres Li-Si film (PMLSF) is prepared by multi-step constant current (MSCC) electrodeposition on Cu foil. Its structure and morphology are characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). As negative electrodes of lithium-ion batteries, the PMLSF electrode delivers the first gravimetric and geometric charge capacities of 2805.7 mA h g⁻¹ and 621.9 μA h cm⁻² at the current density of 25.5 μA cm⁻², and its initial coulombic efficiency is as high as 98.2%. When the PMLSF electrode is cycled in VC-containing electrolyte, the superior cycling performance can be obtained. After 50 cycles, 96.0% of its initial capacity is retained at the current density of 50.0 μA cm⁻². Electrochemical impedance spectra (EIS) research confirms the positive effect of VC additive on the behavior of the PMLSF electrode.     

Preparation of high-capacity air electrode for lithium-air batteries

The research of advanced and green energy is getting more and more attention because the status quo of the energy shortage and the environment pollution is worse and worse, lithium-air batteries are attracting considerable interest for their high theoretical specific energy and pollution-free. Nevertheless their performance is restricted by many factors, for instance the transfer tunnel for the oxygen is blocked by the discharge products and then the discharge is over ahead of time. In this paper we had prepared the air electrode with double-layer structure which is usually used in proton exchange membrane fuel cell (PEMFC) to increase the discharge capacity, the discharge special capacity of the air electrode could reach 6587 mAh/g of carbon at the rate of 0.15 mA/cm².     

NiSb2 as negative electrode for Li-ion batteries: An original conversion reaction

The study of the electrochemical reaction mechanism of lithium with NiSb₂ intermetallic material is reported here. The nickel diantimonide prepared by classic ceramic route is proposed as possible candidate for anodic applications in Li-ion batteries. The electrochemical characterisation of NiSb₂ versus Li⁺/Li⁰ shows a reversible uptake of 5 lithium per formula unit, which leads to reversible capacities of 500 mAh g⁻¹ at an average potential of 0.9 V. From ex situ XRD and ¹²¹Sb Mössbauer measurements it was shown that during the first discharge the orthorhombic NiSb₂ phase undergoes a pure conversion process (NiSb₂ + 6 Li⁺ + 6e⁻ → Ni⁰ + 2Li₃Sb). During the charge process that follows, the lithium extraction from the composite electrode takes place through an original conversion process, leading to the formation of the high pressure NiSb₂ polymorph. This highly reversible mechanism makes it possible to sustain 100% of the specific capacity after 15 cycles.     

Electrochemical characteristics of manganese oxide/carbon composite as a cathode material for Li/MnO2 secondary batteries

Electrolytic manganese dioxide (EMD) recovered from a simulated leaching solution of spent alkaline batteries using a modified cyclone cell is tested as a cathode material for Li secondary batteries. An EMD/C(Super P) composite heat-treated at 400 °C after high-energy mechanical milling shows better electrochemical performance than that of pure EMD in terms of cycleability and capacity fading. The electrochemical characteristics of the EMD/C(Super P) composite are investigated by various analytical techniques. The irreversible capacity during the first cycle is mainly due to the formation of a Li₂MnO₃ phase. The carbon composite also retards the dissolution of Mn during cycling.     

Preparation of Co-Sn alloy film as negative electrode for lithium secondary batteries by pulse electrodeposition method

In order to easily and simply improve the cyclability of the Sn film negative electrode, we selected Co as a matrix metal and tried to prepare the Co-Sn alloy film negative electrode by a pulse electrodeposition method. The surface morphology of the deposit was almost the same as that of the Sn film, although aggregation partially occurred. The content rate of Co and Sn in the deposit was almost the same as the composition percentage in the electrodeposition bath. X-ray diffraction measurement showed that the deposited film could be assigned to a metastable Co-Sn alloy, while the co-deposition of crystalline Sn was not observed. The galvanostatic charge-discharge tests indicated that the discharge capacity and the charge-discharge efficiency of the Co_30.5Sn_69.5 alloy film electrode at the 1st cycle were 529.2 mAh g⁻¹ and 87.9%, respectively. Furthermore, the film electrode showed a good cyclability and discharge capacity of 470.5-617.5 mAh g⁻¹ during 50 cyclings. Alloying Sn with inactive Co could effectively improve the cyclability of the Sn film electrode prepared by the pulse electrodeposition method.     

SnCo nanowire array as negative electrode for lithium-ion batteries

Amorphous SnCo alloy nanowires (NWs) grown inside the channels of polycarbonate membranes by potentiostatic codeposition of the two metals (SnCo-PM) were tested vs. Li by repeated galvanostatic cycles in ethylene carbonate-dimethylcarbonate - LiPF₆ for use as negative electrode in lithium ion batteries. These SnCo electrodes delivered an almost constant capacity value, near to the theoretical for an atomic ratio Li/Sn of 4.4 over more than 35 lithiation-delithiation cycles at 1 C. SEM images of fresh and cycled electrodes showed that nanowires remain partially intact after repeated lithiation-delithiation cycles; indeed, several wires expanded and became porous. Results of amorphous SnCo nanowires grown inside anodic alumina membranes (SnCo-AM) are also reported. The comparison of the two types of NW electrodes demonstrates that the morphology of the SnCo-PM is more suitable than that of the SnCo-AM for electrode stability over cycling. Optimization of NW technology should thus be a promising route to enhancing the mechanical strength and durability of tin-based electrodes.     

Mesoporous carbon-encapsulated NiO nanocomposite negative electrode materials for high-rate Li-ion battery

In this study, a novel mesoporous carbon-encapsulated NiO nanocomposite is proposed and demonstrated for Li-ion battery negative electrode. The nanostructure of the electrode composes of an ordered mesoporous CMK-3 as a 3D nanostructured current collector with micorporous channels for Li⁺ transportation. In addition, exclusive formation of NiO nanoparticles in the confined space of the ordered mesoporous carbon is achieved using the hydrophobic encapsulation route. The half-cell assembled with the synthesized NiO/CMK-3 nanocomposite is able to deliver a high charge capacity of 812 mAh g⁻¹ at the first cycle at a C-rate of 1000 mA g⁻¹ and retained throughout the test with only 0.236% decay per cycle. Even the C-rate as high as 3200 mA g⁻¹, a charge capacity of 808 mAh g⁻¹ contributed by the NiO nanoparticles in CMK-Ni is obtained, which shows excellent rate capability for NiO with utilization close to 100%. The result suggests fast kinetics of conversion reaction for NiO with Li⁺. It also indicates the blockage of the pore channels by NiO nanoparticles does not take place in the synthesized NiO/CMK-3.     

Electrochemical performance of VOMoO4 as negative electrode material for Li ion batteries

Polycrystalline samples of VOMoO₄ are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO₄ electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g⁻¹) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li₄MoO₅ during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g⁻¹ is obtained after 80 cycles when cycling is performed at a current density of 120 mA g⁻¹.     

Vanadium diphosphides as negative electrodes for secondary Li-ion batteries

We report on the Li electrochemical reactivity of amorphous and crystalline VP₂, synthesized by ball-milling and by 600 °C heat treatment of a ball-milled sample, respectively. The amorphous sample can reversibly react with 3.5 Li per formula unit as compared to solely 2.5 for the crystalline one. However in both cases there is a rapid capacity decay upon cycling that is more pronounced in the case of the crystalline sample. Complementary X-rays, HTREM and NMR tend to show that the Li reactivity mechanism differs from the classical conversion reactions since neither V nanoparticles nor the formation of Li₃P were detected, as opposed to some of the other MP₂ compounds (M = Ni or Cu). Besides structural phase variations within the 3d metal-based binary phosphide series, the possibility of a change in the nature of the redox centre upon lithiation from cation (M) to anion (P) is evoked.     

Electrochemical evaluation of rutile TiO2 nanoparticles as negative electrode for Li-ion batteries

Nanosized rutile TiO₂ has been prepared by sol–gel chemistry from a glycerol-modified titanium precursor in the presence of an anionic surfactant. The sample has been characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and electrochemical tests. Nanosized rutile TiO₂ has been electrochemically investigated using two potential windows: 1.2–3 V and 1–3 V. It exhibits excellent high rates capabilities and good cycling stability.     

Improvement of cyclability of Si as anode for Li-ion batteries

Silicon working as anode for Li-ion batteries has attracted much attention due to its high capacity (∼4200 mAh g⁻¹). However, due to the large volume expansion during lithiation, the capacity of silicon fades very fast. In this systematic study, we focus on the issue to fight the capacity fading. Results show that Si with sodium carboxymethyl cellulose (Na-CMC) as a polymer binder exhibits a better cyclability than that with poly(vinylidene fluoride) (PVDF). Yet differing from the system used in PVDF, the addition of vinylene carbonate (VC) does not improve or even worsens the performance of the system using Na-CMC. In addition, the small particle size of Si, a large amount of carbon black (CB), the good choice of electrolyte/conducting salt and charge-discharge window also play important roles to enhance the cyclability of Si. It is found that electrode consisting of 40 wt.% nano-Si, 40 wt.% carbon black and 20 wt.% Na-CMC (pH 3.5) displays the best cyclability, and in the voltage range from 0 to 0.8 V, after 200 cycles, its capacity can still keep 738 mAh g⁻¹ (C/2, in 1 M LiPF₆ ethylene carbonate/diethyl carbonate electrolyte, with VC-free), almost twice as that of graphite.     

High performance Si/C@CNF composite anode for solid-polymer lithium-ion batteries

The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with carbon nanofiber (CNF) was examined as an anode for solid-polymer lithium-ion batteries. Nano-Si powder was firstly coated with carbon by pyrolysis of PVC and then mixed with CNF (referred to as Si/C@CNF) using a rotation mixer. The composite exhibited good cycling performance, but suffered from a large irreversible capacity loss of which the retention was less than 60%. In order to reduce the loss, a thin lithium sheet was attached to the Si/C@CNF electrode surface as a reducing agent. The irreversible capacity of the first cycle was lowered to as much as 0 mAh g⁻¹ and after the third cycle, the lithium insertion and extraction efficiency was almost 100%. A reversible capacity of more than 1000 mAh g⁻¹ was still maintained after 40 cycles.     

Electrochemical characteristics of Sn film prepared by pulse electrodeposition method as negative electrode for lithium secondary batteries

In order to improve the cyclability of Sn negative electrode, we tried preparing the Sn film negative electrode by a pulse electrodeposition. Based on the SEM observations, the crystal grains of the Sn film after the pulse electrodeposition were comparatively homogeneous and their grain size was ca. 1 μm. The discharge capacity and the charge–discharge efficiency at the 1st cycle were 679.3 mAh g⁻¹ and 93.0%, respectively. The charge–discharge tests indicated that the initial electrochemical characteristic of Sn film electrode prepared by a pulse electrodeposition was much better than that of the Sn film electrode prepared by a constant current electrodeposition. The GD-OES profile suggested that Li⁺ ions were easily extracted during the discharge reaction. In addition, it was found that no exfoliation of the film was observed after the 1st discharge though the cracking in the film was observed after the 1st discharge. Consequently, the Sn film electrode prepared by a pulse electrodeposition exhibited a better cyclability for the initial 10 cycles compared to the Sn film electrode prepared by a constant current electrodeposition. By reducing the particle size and repressing the morphological change, the initial electrochemical characteristics were considerably improved.     

SiOx-graphite as negative for high energy Li-ion batteries

Negative electrodes containing SiO_x were investigated as alternative negative electrodes to carbon for Li-ion batteries. The results obtained on the effect of binders and carbon additives on the electrochemical performance (i.e., reversible capacity, coulombic efficiency, charge-discharge rate capability) of the SiO_x-graphite electrode and SiO_x electrode are presented. SEM analysis that utilizes facilities for in situ and ex situ studies were applied to better understand the performance and cycle life of the SiO_x-based electrodes. The SEM analysis clearly showed that the SiO_x particles expand and contract during charge-discharge cycling, and that some of the particles undergo mechanical degradation during this process. The SiO_x-graphite electrode with polyimide binder exhibited a stable capacity of 600 mAh g⁻¹ during high-rate charge-discharge from C/4 to 1C. These results suggest that the use of a flexible binder like polyimide and reasonably small SiO_x particles (nano-particles) facilitates improved cycle life and higher rate capability.     

Magnesium silicide as a negative electrode material for lithium-ion batteries

Mg₂Si was synthesized by mechanically activated annealing and evaluated as a negative electrode material. A maximum discharge capacity of 830 mAh/g was observed by cycling over a wide voltage window of 5–650 mV versus Li, but capacity fade was rapid. Cycling over the range 50–225 mV versus Li produced a stable discharge capacity of approximately 100 mAh/g. X-ray diffraction (XRD) experiments showed that lithium insertion converts Mg₂Si into Li₂MgSi after lithium intercalation into Mg₂Si. Electrochemical evidence of Li–Si reactions indicated that the Li₂MgSi structure can be converted to binary lithium alloys with extensive charging.     

β-FeOOH thin film as positive electrode for lithium-ion cells

β-FeOOH thin film was prepared on the surface of a foamed Ni substrate by liquid phase deposition (LPD) method with a chemical equilibrium reaction between metal-fluoro complex and oxyhydroxide to make a low-cost and environmentally friendly positive electrode for high-power batteries. The new film electrode, with a thickness of 316 nm, was found out to give a large discharge capacity of 260 mAh g⁻¹ at 0.05 C rate even without an electro-conductive material. Furthermore, the electrode also showed good discharge performance with the retention of 69.9% at 10-0.05 C current rate, which means a promising positive active material for high-power use.     

Carbothermal synthesis of Sn-based composites as negative electrode for lithium-ion batteries

The composite [Sn-BPO₄/xC] to be used as negative electrode material for the storage of electrochemical energy was obtained by dispersing electroactive tin species onto a BPO₄ buffer matrix by carbothermal reduction of a mixture of SnO₂ and nanosized BPO₄. This composite material was thoroughly characterized by X-ray diffraction, Scanning Electron Microscopy, ¹¹⁹Sn Mössbauer spectroscopy and Raman spectroscopy. The electrochemical tests of this new material highlight its very interesting electrochemical properties, i.e., a discharge capacity of 850 mAh g⁻¹ for the first cycle and reversible capacity around 585 mAh g⁻¹ at C/5 rate. These electrochemical performances are attributed to the very high dispersion and stabilisation of tin metal particles onto the BPO₄ matrix. The irreversible capacity observed for the first charge/discharge cycle is due the reduction of interfacial Sn^II species and to the passivation of the anode surface by liquid electrolyte decomposition (formation of the SEI layer).