Rational Design of Effective Binders for LiFePO4 Cathodes

Polymer binders are critical auxiliary additives to Li-ion batteries that provide adhesion and cohesion for electrodes to maintain conductive networks upon charge/discharge processes. Therefore, polymer binders become interconnected electrode structures affecting electrochemical performances, especially in LiFePO4 cathodes with one-dimensional Li+ channels. In this paper, recent improvements in the polymer binders used in the LiFePO4 cathodes of Li-ion batteries are reviewed in terms of structural design, synthetic methods, and working mechanisms. The polymer binders were classified into three types depending on their effects on the performances of LiFePO4 cathodes. The first consisted of PVDF and related composites, and the second relied on waterborne and conductive binders. Profound insights into the ability of binder structures to enhance cathode performance were discovered. Overcoming the bottleneck shortage originating from olivine structure LiFePO4 using efficient polymer structures is discussed. We forecast design principles for the polymer binders used in the high-performance LiFePO4 cathodes of Li-ion batteries. Finally, perspectives on the application of future binder designs for electrodes with poor conductivity are presented to provide possible design directions for chemical structures.

Novel zwitterionic Polymer Binder with Enhanced Ionic Conductivity for Water-processable LiFePO4 Cathodes

Current olivine structure LiFePO4 possesses poor conductivity, which makes it unsuitable for unparalleled battery applications. This issue can be solved by improved design concepts of binder systems. Herein, an original...

Effect of the pyrolysis temperature after hydrothermal reaction on the structure of electrode material LiFexCo1􀀀xPO4 (0.1 x 0.5) and electrochemical evaluation of this material in Li-ion half-cell

High voltage cathode LiCoPO4 has been taken great interest for high power Li-ion batteries (LIBs). Though Co enhance the cyclability, capacity of materials, Co concentration should be reduced in electrode materials due to its high cost and toxic. In this work, the solvo-thermal reaction following by pyrolysis in inert Ar was investigated to synthesize the electrode materials LiFexCo1-xPO4 (0.1 <= x <= 0.5) for LIBs. The structure of the materials after calcinated at 600 oC, 700 oC and 800 oC was analyzed by X-ray diffraction (XRD). The results indicated that the olivine structure was obtained for all Fe contents, except for x = 0.5. At the content of 0.1 and 0.5, the intensity of impurity peaks in the samples increased with the pyrolysis temperature. Meanwhile, other samples did not display the obvious change of olivine structure. Electrochemical properties of the materials were evaluated via cyclic voltammetry (CV) and Galvanostatic charging-discharging. CV curves of the samples with Fe content of 0.2x0.4 all displayed high intensity and reversible redox peak of Co3+/Co2+ locating at 4.8 V and another peak of Fe3+/Fe2+ locating at 3.5 V. As the Fe content increased, the former peaks decreased while the latter increased due to the change of active species concentrations. Unfortunately, the specific capacities obtained for Fe-substituted materials were lower than the pristine material (70 mAh/g versus 120 mAh/g) and gradually declined during cycling. The results could be due to the electrolyte decomposition in the first charging. However, the sample with x = 0.1 exhibited the best performance with discharge capacity of 70 mAh/g and 73% capacity retention obtained after 25 cycles, which was better than the sample with x = 0.2 and unsubstituted sample.

Multistage origin of dunite in the Purang ophiolite, southern Tibet, documented by composition, exsolution and Li isotope characteristics of constituent minerals

The Purang ophiolite, which crops out over an area of about 650 km2 in the western Yarlung–Zangbo suture zone, consists chiefly of mantle peridotite, pyroxenite and gabbro. The mantle peridotite is comprised mainly harzburgite and minor dunite. Locally, the latter contains small pods of chromitite. Pyroxenite and gabbro occur as veins of variable size within the peridotite; most of them strike northwest, parallel to the main structure of the ophiolite. Three types of dunite occur in the Purang ophiolite: dunite that envelopes podiform chromitite (1) and lenses of dunite with either Cr-rich spinel (2) or Cr-poor spinel (3) in a harzburgite host. The constituent minerals of dunite envelopes around podiform chromitite are similar in composition to those of transition-zone dunite (Fo91.01−91.87 in olivine; Cr/(Cr+Al) (Cr#) =41.5–47.0 and Mg/(Mg+Fe2+) (Mg#) =58.9–63.0 in Cr-spinel). Forsterite contents in olivine decrease from type 2 lenses with Cr-rich spinel (91.9–93.0) to type 1 dunite enveloping chromitite (91.7–93.7) to type 3 lenses with Cr-poor spinel (95.3–96.0). Similarly, Cr# in spinel decreases from type 2 (66.9–67.9) to type 1 (41.5–47.0) to type 3 (19.8–20.6). In addition, Al2O3 in clinopyroxene is highest in type 2 (3.48–5.24 wt %) and decreases to type 1 (1.56–3.29 wt %) and type 3 (0.78–0.86 wt %). Olivine in type 1 dunite enveloping podiform chromitite has Li concentrations and δ7Li values of 1.48–1.71 ppm and 6.19 ‰–7.98 ‰, respectively. Type 2 dunite lenses with Cr-rich spinel contain olivine with Li =0.98–1.64 ppm and δ7Li =6.77 ‰–10.99 ‰. The type 3 dunite lenses with Cr-poor spinel show the highest values of Li =0.94–1.40 ppm and δ7Li =10.25 ‰–14.20 ‰. Exsolution lamellae of clinopyroxene and magnetite occur as oriented intergrowths in olivine of type 3 dunite lenses with Cr-poor spinel. We suggest that the Purang ophiolite developed during two main stages of formation. In the first stage, abyssal peridotites formed in a mid-ocean-ridge environment. During the second stage, hydrous high-Mg boninitic melts were produced by high degrees of partial melting in a supra-subduction zone mantle wedge, which reacted with peridotite to form type 2 dunite pods with high-Cr# spinel. At lower degrees of partial melting in the same mantle wedge, Al-rich melts were produced, which reacted with peridotite to form type 3 dunite pods that contain low-Cr# spinel. These Al-rich melts were also relatively rich in Ti4+, Ca2+ and Fe3+, which were incorporated into the olivine structure by appropriate substitutions. During cooling, these elements exsolved as lamellae of magnetite and clinopyroxene.

Effects of BaCu(B2O5) additives on the crystal structures and dielectric properties of CaMgGeO4 ceramics for LTCC applications

A CaMgGeO4 (CMG) ceramic with an olivine structure was fabricated by the traditional solid-phase reaction method; this material was dense at 1300 °C/6 h and exhibited excellent dielectric properties (εr = 6.83, Q × f = 125 432, f = 14.9 GHz).

Storage performance of Mg2+ substituted NaMnPO4 with an olivine structure

Magnesium ions have a strong impact on the storage performance of olivine-type NaMnPO4.

High valence transition metal-doped olivine cathodes for superior energy and fast cycling lithium batteries

High-valence transition metals are inserted into the olivine structure, thus enhancing the specific capacity and rate capability of cathodic materials.

Synthesis and crystal structure determination of the new olivine-type compound Mn2SnSe4

The Mn2SnSe4 compound was synthesized by the melt and annealing technique and its structure was refined by the Rietveld method using X-ray powder diffraction data. This compound crystallizes in the olivine-type structure with unit cell parameters a = 12.9028(2) Å, b = 7.9001(1) Å, c = 6.5015(1) Å, V = 662.72(2) Å3 in the orthorhombic space group Pnma (Nº 62). This olivine structure can be described from a hexagonal close-packing of selenium atoms where manganese atoms occupy ½ of the octahedral sites while thin atoms lay in ⅛ of the tetrahedra.

Structure and Electrochemical Behavior of Minor Mn-Doped Olivine LiMnxFe1−xPO4

In the recent years, olivine LiFePO4 has been considered as a prospective cathode material for lithium-ion batteries. However, low conductivity is an obstacle to the commercialization of LiFePO4; doping the transition metal such as Mn and Ni is one of the solutions for this issue. This work aimed to synthesize the Mn-doped olivines LiMnxFe1−xPO4 at low content of Mn (x = 0.1, 0.2) via the hydrothermal route followed by pyrolyzed carbon coating. The synthesized olivines were well crystallized in olivine structure, with larger lattice parameters compared with LiFePO4. The EXD and TGA results confirmed the coated carbon of 4.14% for LiMn0.1Fe0.9PO4 and 6.86% for LiMn0.2Fe0.8PO4. Both of Mn-doped olivines showed higher diffusion coefficients of Li+ intercalation than those of LiFePO4 that led a good performance in the cycling test. LiMn0.2Fe0.8PO4 exhibited a higher specific capacity (160 mAh/g) than LiMn0.1Fe0.9PO4 (155 mAh/g), and the Mn content is beneficial for the cycling performance as well as ionic conductivity.