Colloidal-Crystal-Templated Synthesis of Ordered Macroporous Electrode Materials for Lithium Secondary Batteries

Abstract

This paper presents a general method of preparing three-dimensionally ordered macroporous ͑3DOM͒ electrode materials, including both cathode materials (V 2 O 5 and LiNiO 2 ) and an anode material (SnO 2 ). The method is based on templated precipitation of inorganic precursors within a colloidal crystal of poly͑methyl methacrylate͒ spheres and subsequent chemical conversion. 3DOM electrodes possess several features of interest in the design of novel battery materials, such as high accessible surface areas, continuous networks, and structural features on the nanometer scale. Optimal synthesis conditions and structural features of 3DOM electrode materials are described on the basis of X-ray diffraction, scanning electron microscopy, nitrogen adsorption, and chemical analysis.Conventional lithium secondary batteries experience large capacity losses when they are charged/discharged at high rates. This behavior is attributed to the rate-limiting step during the electrochemical processes, i.e., slow diffusion of lithium ions through the electrode materials. 1 At high charge/discharge rates, large Li ϩ insertion or extraction fluxes at the surface, and slow Li ϩ transport in the bulk result in concentration polarization of Li ϩ within the electrode material. This causes a rise/drop in battery voltage, which leads to termination of the charge/discharge before the maximum capacity of the electrode material is utilized. 2,3 Therefore, optimization of the electrode material parameters that influence ion kinetics is an important subject in battery research.Recently, numerous investigations have focused on processing of electrode materials with submicrometer grain sizes. 4-20 By several low-temperature preparation techniques ͑sol-gel methods, 4-13 wet chemical Pechini techniques 14-16 ͒ or fast microwave synthesis, 17-20 various ultrafine electrode materials have been prepared. Since the grain sizes ͑Ͻ1 m͒ of these electrode materials are much smaller than those produced from solid-state techniques ͑Ͼ10 m͒, the Li ϩ diffusion distances are correspondingly shorter; hence, less time is needed to achieve full charge or discharge at the same current density. In addition, the larger surface areas of these electrode materials lower the current density, resulting in a decrease of concentration polarization. Although the utilization of submicrometer-grained materials has the significant advantage of increasing rate capacity, it also leads to several drawbacks for practical applications. First, reducing average grain size, while keeping the mass constant, increases the grain boundary resistances of the electrode ͑internal resistance͒. To maintain the internal resistance at the same level, conductive additives ͑such as carbon black͒ are used, which decrease the energy density of the electrode. In addition, it is possible for very small grains to penetrate the porous membrane separating the electrodes, thereby short-circuiting the system and resulting in severe safety problems. Therefore, it is necessary to assemble the ultrafine electro...

Developments in Nanostructured Cathode Materials for High‐Performance Lithium‐Ion Batteries

“…[72] The method is based on soaking the poly(methyl methacrylate) (PMMA) colloidal crystals in the NaVO 3 solution so that the interstitial spaces are infiltrated with precursor solution, Y. Wang and G. Cao/Developments in Nanostructured Cathode Materials REVIEW followed by chemical conversion, drying, and sintering to remove polymer spheres. The resultant material possesses photonic-crystal structures composed of interconnected open pores with nanometer-sized thin walls.…”

Construction and Structural Estimation of Multilayered Organization of Polymer Nanosphere

“…The surface morphologies of transferred films were observed using a scanning probe microscope (Seiko Instrument, SPA300 with SPI-3800 probe station,) and microfabricated rectangular Si Figure 3 shows the π-A isotherm and AFM images of monolayer and single particle layer of PABA 5 . The surface morphology of the monolayer depends on the surface pressure.…”

“…These multilayered polymer nanospheres are similar to colloidal crystals. 5 They have long been used as major components of various industrial products such as foods, inks, paints, toners, coatings, papers, cosmetics, photographic films, and rheological fluids. Further, colloidal crystals, which comprise three-dimensional periodic arrays of submicron particles, have attracted considerable attention because of their novel photonic applications in the form of photonic crystals.…”

Porous Si-Al Composite Anode with Three-Dimensional Macroporous Substrate for Lithium-Ion Batteries

“…20 The major advantages of such a 3D architecture have been proved: (i) the large open pores allow easy transport of liquid electrolyte; (ii) it is beneficial for fast transferring of lithium ions due to short Li + diffusion length or pathway; (iii) the high specific surface area of 3D architecture ensures a large number of active sites for charge-transfer reactions and the active materials are not easy to fall off, thus improveing the electrical conductivity; (iv) it provides sufficient space to alleviate the volume change of active materials during lithiation/delithiation, relax the stress/strain, improve the mechanical stability of the electrode structure, and consequently improve cycle-life and coulombic efficiency of the electrode. 21 Aluminum exhibits high electrical conductivity, and is active to Li. The theoretic capacity of Al is 2234 mAh g -1 for Al 4 Li 9 .…”