(1) DME, (2) DEE, (3) DMC, (4) DEC 1.0 M LiClO 4, PC-mixed with various solvents (1:1) 1.0 M LiClO 4, EC-mixed with various solvents (1:1) 1.0 M LiPF 6, PC-mixed with various solvents (1:1) 1.0 M LiPF 6, EC-mixed with various solvents (1:1) Mixed solvent electrolyte for high voltage lithium metal secondary cells
conductivity using each 1.0 M solute EC/DMC electrolyte. (1) LiClO 4, (2) LiBF4, (3) LiPF 6, (4)LiAsF 6. conductivity using (1) 1.0M-LiPF 6 -EC/DMC and (2) 1.5M-LiPF 6 -EC/DMC. Cycling performance of Li/LiMn 1.9 Co 0.1 O 4 cells using (1) 1.0M-LiPF 6 -EC/DMC and (2) 1.5M- LiPF 6 -EC/DMC. 1.5M-LiPF 6 -EC/DMC are less advantageous than those of 1.0M-LiPF 6 -EC/DMC. conductivity is LiAsF 6 > LiPF 6 > LiClO4 > LiBF 4 > electrolyte. Cycling performance of Li/LiMn 1.9 Co 0.1 O 4 cells using each 1.0 M solute EC/DMC electrolyte. (1) LiClO 4, (2) LiBF 4, (3)LiPF 6.
μ is the molality that corresponds to the maximum conductivity, κ(max), and a, b constants. the curves to the calculated according to Eq. (1) values. Eq. (1) Dependence of conductance, κ, on molality, m. 15 o C 20 o C 25 o C 30 o C 35 o C 40 o C
LiAsF 6 LiPF 6 LiClO 4 LiBF 4 at 25 ◦ C LiAsF 6 LiPF 6 LiClO 4 LiBF 4 specific capacity for Li/Li 1.05 Mn 2 O 4 cells with electrolyte solutions 1m salt in PC 50.7%–DEC 49.3% (temperature 25 ◦ C). The higher conductivities of LiAsF 6 and LiPF 6 can be explained with the larger anion radius of these salts, compared with that of LiClO 4 and LiBF 4, which means that the ionic dissociation ability of LiAsF 6 and LiPF 6 is higher than that of LiClO 4 and LiBF 4 as the coulombic force between Li + and the anion is weaker for larger radii.
The lithium polymer electrolytes have a full plastic structure. Such plastic lithium ion batteries are expected to be less expensive and more easily scaled up than their liquid counterparts. In addition, the absence of free liquid allows packaging in light- weight plastic containers unlike conventional batteries which require metallic casing. Finally, since the electrolyte membrane and the associated plasticized electrodes can be formed as 1aminates, the plastic battery can be fabricated in any desired shape or size, a target difficult to be achieved with liquid electrolyte cells. All these features make the plastic lithium battery a very appealing product. The key component of the plastic battery is the polymer electrolyte membrane that has to fulfill a series of stringent requirements, including among others: i) good mechanical properties (to assure easy battery fabrication), ii) high ionic conductivity (to assure low internal resistance), iii) high lithium ion transport (to avoid concentration polarization), iv) wide electrochemical stability (to be compatible with high voltage electrodes), v) low cost (in order to fill a large market), and vi) benign chemical composition (to be environmentally compatible). Lithium polymer electrolytes
Solid Polymer Electrolytes (No volatile organic solvents) Basic unit of polymer matrix chains for polymer electrolytes Lithium salts have been used LiClO 4, LiCF 3 SO 3, LiPF 4, LiPF 6 X Low solubility. σ(25 o C)~10 -7 LiC(CF 3 SO 2 ) 3, LiN(SO 2 CF 2 CF 3 ) 2 σ(25 o C)~10 -5 Plasticizers Poly(ethylene glycol)-dimethacrylate (PEGMA) Poly(ethylene glycol)-monomethacrylate (PME)
Two kinds of gelled polymer electrolytes 加熱與攪拌 polymer Lithium salts solvent additive 加熱與攪拌 polymer Lithium salts solvent additive gel formed Liquid electrolyte Soaking gel into liquid electrolyte
Composite polymer electrolytes based on PAN, LiClO 4 and α-Al 2 O 3 To prepare the electrolyte, first, an appropriate amount of PAN was dissolved with a small amount of DMF. Then, the required quantity (F=[LiClO 4 ]/[CN], where F represents the the molar ratio of salt fed to a PAN repeat unit) of the lithium salt was added, and the solution was stirred well. A designed amount of α-Al 2 O 3 powder was then added and the PAN/LiClO4/α-Al 2 O 3 solution was stirred continuously by a high intensity ultrasonic finger directly immersed in the solution for 24 h to disperse the particles. After this, the solution was cast on a flat glass and dried in a vacuum oven at a proper temperature to remove the solvent for at least 24 h. The mechanically stable membranes obtained have average thickness of about 100 μm. The DMF residue in the membranes estimated from TGA measurement was less than 10 wt.%. The dried samples were stored in an argon-filled glove box (water is less than 5 ppm) to avoid moisture contamination. melting of the microcrystalline domains. Tg
NF6A7.5 LiClO 4 =0.6 wt.% of Al 2 O 3
Effect of concentration and grain size of alumina filler on the ionic conductivity enhancement of the (PEO) 9 LiCF 3 SO 3 :Al 2 O 3 composite polymer electrolyte The nanoporous Al 2 O 3 powder have a pore size 5.8 nm, particle size 104 μm, surface area 155 m 2 /g and acidic surface groups, and the Al 2 O 3 powder have grain size<10 μm, 37 and 10–20 nm.
Variation of ionic conductivity at 30 o C with specific surface area of alumina grains for the composite polymer electrolyte PEO 9 LiTf t -Al 2 O 3. the nano-porous alumina grains with 5.8 nm pore size and 150 m 2 /g specific area and 15 wt.% filler concentration exhibited the maximum enhancement.
The composite polymer electrolyte system at low filler concentrations may be imagined as a conducting medium where filler grains are randomly and uniformly distributed throughout the volume. The presence of the filler grains could give rise to additional favourable conducting pathways in the vicinity of the surface of the grains as described earlier. The number of such additional high conductivity pathways is expected to increase with increasing filler surface area. At low enough filler concentrations, where the grains are still well separated these surface interactions can therefore account for the observed conductivity increase with increasing filler concentration. At somewhat higher filler concentrations, however, the blocking effect or the geometrical constrictions imposed bythe more abundant alumina grains could make the long polymer chains more ‘‘immobilized’’ leading to a lower conductivity. This would lead to the appearance of the first conductivity maximum and the subsequent drop in conductivity. As the filler concentration is further increased, the filler grains get close enough to each other so that the high conducting regions in the vicinity of the grain surfaces start to get interconnected. The migrating ionic species can now travel along and between these interconnected high conducting pathways giving rise to the second increase in the conductivity. Finally, at still higher filler concentrations, the grains get so close to each other that the blocking effect due to the neutral filler becomes large and the conductivity starts to drop. This can explain the existence of the second maximum in the variation of the conductivity versus composition plots.
Sketch depicting how PEO chains enter the nanoporous tunnels of alumina grains in a PEO based nano-composite electrolyte. The observed conductivity enhancement has been attributed to Lewis acid–base type surface interactions of ionic species with O/OH groups on the filler surface, with an additional contribution below 60 o C coming from the retention of an increased fraction of the amorphous phase due to the presence of the filler. The conductivity versus filler concentration curves exhibit two conductivity maxima which has been explained in terms of the surface interactions, blocking effect and grain consolidation. The conductivity enhancement appears to saturate beyond 100 m 2 /g grain surface area.
Time evolution of the conductivity of LiPF 6 /DMC/PAN +6wt%Al 2 O 3 composite gel electrolyte Time (days) Impedance response at various temperatures of the LiPF 6 /DMC/PAN +6wt%Al 2 O 3 composite gel electrolyte. Adding of Al 2 O 3 improve the stability of the electrolyte
Li/EC/LiClO 4 /PAN5+1%Al 2 O 3 /LiFePO 4 電壓 V.S 時間 充放電平台表現圖 利用交流阻抗分析電池介面， 發現添加 α-Al 2 O 3 有效降低介面 阻抗，介面阻抗包含 SEI 與電 荷轉移阻抗，添加 α-Al 2 O 3 對於 降低 SEI 明顯有所幫助，而且 隨添加比重越高電路模擬的擬 合阻抗值越低，電荷轉移阻抗 則是推論因掃描範圍原因，無 法完整檢測阻抗隨比例變化， 但還是對於阻抗降低有所幫助。
Schematic representation of conductivity at ambient temperature; contributions from ion hopping and polymer chain motion and transport number. Conductivity (arbitrary units) Transfer number Contribution from hopping Measured conductivity Contribution from polymer chain motion Volume fraction of ceramic phase 1.0 0.75 0.5 0.25 0.0 0.25 0 0.75 0.5 1.0
不合適當添加物 The ceramic particles, depending upon the volume fraction, would tend to minimize the area of lithium electrode exposed to polymers containing O, OH species and thus reduce the passivation process. It is also foreseeable that smaller size particles for a similar volume fraction of the ceramic phase would impart improved performance compared to larger size particles because they cover more surface area. The formation of an insulating layer of ceramic particles at the electrode surface is probable at higher volume fraction of a passive ceramic phase. The experimental evidence is numerous and consistently show that the lithium-composite electrolyte interfaces are more stable and efficient than lithium-polymer electrolyte interfaces. Schematic diagram of lithium-composite electrolytes (a) larger size particles, and (b) smaller size particles.