Future cathode materials for lithium rechargeable batteries

Lithium rechargeable batteries are now well established as power sources for portable equipment, such as portable telephones or computers. Future applications include electric vehicles. However before they can be used for this, or other price-sensitive applications, new cathode materials of much lower cost are needed. Possible cathode materials are reviewed.     

Vapor-grown carbon fiber anode for cylindrical lithium ion rechargeable batteries

A lithium ion rechargeable battery based on carbon anode that is a viable replacement for lithium metal anode has been developed. In this investigation, the Vapor-Grown Carbon Fiber was used as the anode material of a cylindrical battery. The charge/discharge experiments were carried under various temperatures and current densities. Excellent cyclability was obtained at 21°C at a charge/discharge of 0.8 C with three cathode materials (LiCoO₂, LiMn₂O₄, and LiNiO₂). High discharge capacity was obtained at low temperature (0°C). Good cyclability was also obtained at high temperature (40°C). At the charge/discharge rate of 4.0 C, energy density did not decay significantly. Good cyclability was obtained for rates ranging from 0.8 C to 4.0 C. Self-discharge was investigated at 3 temperatures (21, 40 and 60°C). The measured self-discharge was 8, 15 and 31% per month at 21, 40 and 60°C, respectively.     

Sulfur-graphene composite for rechargeable lithium batteries

Sulfur-graphene (S-GNS) composites have been synthesized by heating a mixture of graphene nanosheets and elemental sulfur. According to field emission electron microscopy, scanning electron microscopy with energy dispersive X-ray mapping, Raman spectroscopy, and thermogravimetric analysis, sulfur particles were uniformly coated onto the surface of the graphene nanosheets. The electrochemical results show that the sulfur-graphene nanosheet composite significantly improved the electrical conductivity, the capacity, and the cycle stability in a lithium cell compared with the bare sulfur electrode.     

Boron doped lithium trivanadate as a cathode material for an enhanced rechargeable lithium ion batteries

Boron was doped into lithium trivanadate through an aqueous reaction process followed by heating at 100 °C. The B-LiV₃O₈ materials as a cathode in lithium batteries exhibits a specific discharge capacity of 269.4 mAh g⁻¹ at first cycle and remains 232.5 mAh g⁻¹ at cycle 100, at a current density of 150 mAh g⁻¹ in the voltage range of 1.8–4.0 V. The B-LiV₃O₈ materials show excellent stability, with the retention of 86.30% after 100 cycles. These result values are higher than those previous reports indicating B-LiV₃O₈ prepared by our synthesis method is a promising candidate as cathode material for rechargeable lithium batteries. The enhanced discharge capacities and their stabilities indicate that boron atoms promote lithium transferring and intercalating/deintercalating during the electrochemical processes and improve the electrochemical performance of LiV₃O₈ cathode.     

LixNiO2, a promising cathode for rechargeable lithium batteries

Lithiated nickel oxide has been prepared and studied with the aim of using it as the positive active reversible material in rechargeable lithium batteries. This paper describes the particular features of this material, and discusses the results that demonstrate its interest as cathode in practical cells, using carbon as the negative electrode. Specific energy and energy density of more than 130 Wh/kg and 320 Wh/l were obtained in prototypes, and a cycleability of over 1000 cycles was demonstrated.     

Anatase as a cathode material in lithium—organic electrolyte rechargeable batteries

A preliminary investigation of anatase, TiO₂, as a positive electrode material in secondary lithium—organic electrolyte batteries is reported.Up to 0.6 lithium equivalents can react with 1 mole of TiO₂. However, optimum cycling behaviour is obtained for regimes involving compositions between 0.15 and 0.45 Li/TiO₂ mole ratio.Under these conditions, prolonged cycling at 0.25 – 0.5 mA cm^?2 gives satisfactory results.     

New inverse spinel cathode materials for rechargeable lithium batteries

The synthesis, characterization, and electrochemical properties of LiNi_yCo_{1 − y}VO₄ (0 ≤ y ≤ 1) as the new cathode materials for rechargeable lithium batteries were investigated. A series of LiNi_yCo_{1 − y}VO₄ (y = 0.1 − 0.9) compounds were synthesized by either a solid-state reaction of LiNi_yCo_{1 − y}O₂ and V₂O₅ at 800 °C for 12 h or a solution coprecipitation of LiOH · H₂O, Ni(NO₃)₂ · 6H₂O, Co(NO₃)₂ · 6H₂O and NH₄VO₃, followed by heating the precipitate at 500 °C for 48 h. The products from both preparation methods were analyzed by scanning electron microcopy and inductively-coupled plasma-atomic emission spectroscopy. These compounds are inverse spinels based on the results from Rietveld analysis and the fact that the cubic lattice constant a is a linear function of stoichiometry y in LiNi_yCo_{1 −y}VO₄. Either a 1 M LiC1O₄-EC + PC (1:1) or 1 M LiBF₄-EC + PC + DMC (1:1:4) electrolyte can be used as the electrolyte for Li/LiNi_yCo_{1 − y}VO₄ cells up to y = 0.7. The charge and discharge capacity of a Li/1 M LiBF₄-EC + PC + DMC (1:1:4) /LiNi_0.5Co_0.5VO₄ cell were 43.8 and 34.8 mAh/g, respectively, when the cathode material was prepared by the low temperature coprecipitation method.     

Synthesis of polyaniline/graphite composite as a cathode of Zn-polyaniline rechargeable battery

The characteristics of polyaniline/graphite composites (PANi/G) have been studied in aqueous electrolyte. PANi/G films with different graphite particle sizes were deposited on a platinum electrode by means of cyclic voltammetry. The film was employed as a positive electrode (cathode) for a Zn-PANi/G secondary battery containing 1.0 M ZnCl₂ and 0.5 M NH₄Cl electrolyte at pH 4.0. The cells were charged and discharged under a constant current of 0.6 mA cm⁻². The assembled battery showed an open-circuit voltage (OCV) of 1.55 V. All the batteries were discharge to a cut off voltage of 0.7 V. Maximum discharge capacity of the Zn-PANi/G battery was 142.4 Ah kg⁻¹ with a columbic efficiency of 97–100% over at least 200 cycles. The mid-point voltage (MPV) and specific energy were 1.14 V and 162.3 Wh kg⁻¹, respectively. The constructed battery showed a good recycleability. The structure of these polymer films was characterized by FTIR and UV–vis spectroscopies. Electrochemical impedance spectroscopy (EIS) was used as a powerful tool for investigation of charge transfer resistance in cathode material. The scanning electron microscopy (SEM) was employed as a morphology indicator of the cathodes.     

A novel composite gel polymer electrolyte for rechargeable lithium batteries

Composite polymer electrolyte (PE) films comprising of thermoplastic polyurethane (TPU) and polyacrylonitrile (PAN) (denoted as TPU–PAN) have been prepared by two different processes. Scanning electron microscope (SEM) of the films reveal the differences in morphology between them. The electrochemical properties of composite electrolyte films incorporating LiClO₄–propylene carbonate (PC) were studied. TPU–PAN based gel PE shows high ionic conductivity at room temperature. Thermogravimetric analysis informs that the composite electrolyte possesses good thermal stability with a decomposition temperature higher than 300 °C. Electrochemical stability in the working voltage range from 2.5 to 4.5 V was evident from cyclic voltammetry. Cycling performances of Li/PE/LiCoO₂ cells were also performed to test the suitability of the composite electrolyte in batteries.     

Sn nanocrystal/carbon composites as high-capacity anode materials for lithium rechargeable batteries

High-capacity lithium-storage materials in metal composite form are being extensively researched, which can replace the carbon-based lithium intercalation materials currently commercialized as the negative electrode of lithium rechargeable batteries. Herein, Sn nanocrystals and Sn nanocrystal/carbon composites with various particle sizes are prepared by the chemical reduction method where surfactant can control the resultant particle size because the particle size of metal-based materials is the main underlying factor for their electrochemical enhancement. The chemical reduction approach using surfactants is very effective for varying the particle size of Sn nanocrystals. Sn nanocrystals with the optimized particle size in terms of anodic properties are made into a composite with carbon acting as an agglomeration preventer as well as an electronic conductor. The controlled size of the Sn nanocrystal in the carbon is associated with their drastically improved electrochemical performance retaining above 65% of the initial capacity after 30 cycles.     

Sulfides organic polymer: Novel cathode active material for rechargeable lithium batteries

Two novel sulfide polymers, poly(2-phenyl-1,3-dithiolane) and poly[1,4-di(1,3-dithiolan-2-yl)benzene], were prepared via facile oxidative-coupling polymerization under ambient conditions, characterized by FT-IR, XRD, TGA and elemental analysis, and were tested as cathode materials in rechargeable lithium battery. The charge–discharge tests showed that the specific capacity of poly[1,4-di(1,3-dithiolan-2-yl)benzene)] was 378 mAh g⁻¹ at the third cycle, and retained at 300 mAh g⁻¹ after 20 cycles. The specific capacity of poly(2-phenyl-1,3-dithiolane) was 117 mAh g⁻¹ at the second cycle, and retained at 100 mAh g⁻¹ after 20 cycles. The results indicated that thiolane group could be used as cathode active function group for lithium secondary batteries and the novel electrode reaction is proposed tentatively.     

New anions as supporting electrolytes for rechargeable lithium batteries

Each of the two most commonly used salts in ambient-temperature rechargeable lithium batteries has problems involving safety and long-term stability. For example, solutions of LiClO₄ in 1,3-dioxolane are shock sensitive while LiAsF ₆/ether electrolytes degrade (both thermochemically and electrochemically) with time. Studies have been undertaken on the solubility, conductivity, and stability towards lithium of seven new lithium salts in both tetrahydrofuran (THF) and sulfolane. Of the seven salts, LiTaF₆, Li₂C₂F₄(SO₃)₂ and Li₂C₄F₈ (SO₃)₂ provide reasonable conductivities and good stability in sulfolane at 70 °C.     

Nickel sulfides as a cathode for all-solid-state ceramic lithium batteries

The nickel sulfide, Ni₃S₂, was examined as a potential cathode material of the all-solid-state-lithium-batteries using thio-LISICON, Li₂S–GeS₂–P₂S₅, as the solid-electrolyte. Ni₃S₂and Li₂S–GeS₂–P₂S₅ system, was synthesized with a new sintering system, which proceed under a flowing argon in the reusable quartz tube. The highest ionic conductivity 2.39×10⁻³$2.39\times 10^{-3}$ S cm⁻¹ was observed for a sample prepared at 700 °C with 10% of excess P₂S₅, and bear comparison with the maximum conductivity reported for the thio-LISICON, Li_3.35Ge_0.35P_0.65S₄. An all-solid-state-lithium-battery based on, Ni₃S₂/Li_3.35Ge_0.35P_0.65S₄/Li–Al alloy, showed electrochemical capacities of greater than ∼$\sim$300 mAh g⁻¹ after 30 cycles. The cycling performances of the cells were found to be dependent on the Ni₃S₂/thio-LISICON compositions in the cathode mixture, with a cell containing 60 wt.% of Ni₃S₂ exhibiting the most stable reversible capacities. As the depth of the first discharge capacity also influences the cycling properties, Ni₃S₂ consumed during the discharge reaction may play an important role in the nickel reduction mechanism.     

Multi-functional additive PFPN for rechargeable lithium sulfur battery with composite cathode materials

由于具有极高的比容量和丰富的硫资源储量,锂硫电池已成为下一代可充电池研究的热点之一。但锂硫电池中存在较大的安全性隐患,这将阻碍其实际应用。一种高效的阻燃添加剂,乙氧基五氟环磷腈（PFPN）被首次用于锂硫电池。添加5%质量分数的PFPN使得高度易燃的碳酸酯电解液完全不燃,同时减小极化电压,并显著提高硫基复合材料的倍率性能。上述结果表明,PFPN是一种适用于可充锂硫电池的多功能添加剂。     

Scale-up of lithium rechargeable batteries

Small-size lithium rechargeable cells in an envelope format were reported at the 20th International Power Sources Symposium [1,2]. This design offers the possibility of making cells using much lighter packing than cells with metal cans. The prismatic format allows good packing in rectangular boxes. Hence they offer the potential for high gravimetric and volumetric energy densities. The cells have now been developed to a size sufficient to form components of a large battery, built to power Army man-portable equipment. Lithium-ion cells have been manufactured using lithium cobalt oxide cathodes and other cathode materials are under investigation. Individual cells up to the 3 A h size have been successfully cycled, with further development possible. A 24 V battery has been constructed and its performance and prospects are described.     

Polytriphenylamine: A high power and high capacity cathode material for rechargeable lithium batteries

Polytriphenylamine (PTPAn) was chemically synthesized and tested as a cathode material for high-rate storage and delivery of electrochemical energy. It is found that the polymer has not only superior high power capability but also high energy density at prolonged cycling. At a moderate rate of 0.5C, PTPAn gives a high average discharge voltage of 3.8 V and quite a high capacity of 103 mAh g⁻¹, which is very close to the theoretical capacity (109 mAh g⁻¹) as expected from one electron transfer per triphenylamine monomer. Even cycled at a very high rate of 20C, the polymer can still deliver a capacity of 90 mAh g⁻¹ at 1000th cycle with a nearly 100% coulombic efficiency. The excellent electrochemical performances of PTPAn are explained from the structural specificity of the polymer where the radical redox centers are stabilized and protected by conductive polymeric backbone, making the radical redox and charge-transporting processes kinetically facile for high-rate charge and discharge.     

Improvement of cycle property of sulfur-coated multi-walled carbon nanotubes composite cathode for lithium/sulfur batteries

A novel sulfur-coated multi-walled carbon nanotubes composite material (S-coated-MWCNTs) was prepared through capillarity between the sulfur and multi-walled carbon nanotubes. The results of the TEM and XRD measurements reveal that S-coated-MWCNTs have a typical core-shell structure, and the MWCNTs serve as the cores and are dispersed individually into the sulfur matrices. The charge–discharge experiments of the lithium/sulfur cells demonstrated that the S-coated-MWCNTs cathode could maintain a reversible capacity of 670 mAh g⁻¹ after 60 cycles, showing a greatly enhanced cycle ability as compared with the sulfur cathode with simple MWCNTs addition (S/MWCNTs) and the cathode using sulfur-coated carbon black composite (S-coated-CB). The EIS and SEM techniques were used to define and understand the impact of the microstructure of the composite electrode on its electrochemical performance. Derived from these studies, the main key factors to the improvement in the cycle life of the sulfur cathode were discussed.     

Comparative thermal stability of carbon intercalation anodes and lithium metal anodes for rechargeable lithium batteries

An accelerating rate calorimeter has been used to probe the thermal stability of Li_xC₆ in electrolyte as a function of specific surface area, lithium content, and solvent choice. The exotherm can be qualitatively modelled based on the reaction which produces the passivating film on the carbon surface.     

Lithium manganese oxides for rechargeable lithium batteries

Lithium manganese spinel compounds HT-LiMn₂O₄ (HT means high temperature) synthesized at > 700 °C have high capacity in the 4 V range (Li_xMn₂O₄, x ⩽ 1), However, lithium manganese oxides LT-LiMn₂O₄ (LT means low temperature) synthesized at temperatures lower than 400 °C, resemble to the spinel structure and tend to have a reduced capacity in the 4 V range. We investigated the factor of potential difference between the 4 V type and the 3 V type by using ⁷Li nuclear magnetic resonance (NMR) and electron spin resonance (ESR) measurements. It was found by using ⁷Li-NMR that there were two kinds of spectrum in these materials; in the 4 V type, the spectrum having about 530 ppm of chemical shift with spinning side band was mainly observed. On the other hand, in the 3 V type, the broad spectrum having about 760 ppm of chemical shift without spinning side band was mainly observed. There are two different lithium sites in the manganese spinel compound (space group of Fd3m), one is at the 8a site located far from the manganese ion and the other one is at the 16c site located close to the manganese ion. It is presumed that the spectrum having 530 ppm of chemical shift with spinning side band is corresponding to the 8a site, and the broad spectrum having 760 ppm of chemical shift without spinning side band is corresponding to the 16c site, with taking into consideration the influence of paramagnetic character of manganese on the lithium site which is closely related to the distance from the manganese ion.     

Organic electrolyte solutions for rechargeable lithium batteries

Several combinations of organic solvents and lithium salts have been examined as electrolytes for ambient-temperature, rechargeable lithium batteries. Ethers (1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, etc.) have been used as the base solvents, as they are electrochemically stable and have a low reactivity towards lithium metal. In the main, mixed-solvent systems have been adopted to improve the solubility of electrolytes and, hence, the electrolytic conductivity of the solution. The charge/discharge characteristics of the lithium negative electrode have been examined in these electrolytes. The cycling characteristics of Li/TiS₂ cells with the electrolytes containing crown ethers have also been investigated. The electrochemical properties of the electrodes and the charge/discharge characteristics of these cells are markedly influenced by the composition of the electrolyte.

The electrode reaction mechanisms are briefly discussed for these systems.