6 锂离子电池先进电解液组分的性能优化

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Flammability of solvents (Flash point < than 39oC).
1.
Reaction of LiPF6 with the other materials in the electrolyte and with impurities such as water and acid. Instability: lack long lifetime characteristics (storage) No one mixture of the solvents has been shown to work well at temperature over‐50 to +80 oC). Reactive with the cathode surfaces and unstable at high voltages. We need to improve the high voltage stability up to 5V or even higher.
Reference Equivalent Electric Range Peak Pulse Discharge Power - 2 Sec / 10 Sec Peak Regen Pulse Power (10 sec) Available Energy for CD (Charge Depleting) Mode, 10 kW Rate Available Energy for CS (Charge Sustaining) Mode Minimum Round-trip Energy Efficiency (USABC HEV Cycle) ses Cold cranking power at -30癈,2 sec - 3 Pul miles 10 40 one system go 10 miles all electric. (½ hr discharge at 20 46 mph kW 50 / 45 / 38 kW 30 25 the other go 40 miles all electric. (2 hr discharge at 20 mph) kWh 3.4 11.6
Discharging If no side rxn at cathode: lithiate cathode and overly delithiate anode Over-discharge anode
The major problems of the state-of-theart electrolytes
Both systems require the capability to deliver ~ 45 kW kWh 0.5 0.3 of % 90 90 pulse power. kW 7 7 Density requirements (assuming 70% is 5,000 / 58 CD Life Energy / Discharge Throughput Cycles/MWh 5,000only / 17 for all electric driving) : CS HEVavailable Cycle Life, 50 Wh Profile Cycles 300,000 300,000
Comparison for conductivity and gas evolution
Conductivity of nonflammable electrolytes are comparable but lower than the Standard Comparison of volume of gas generated with temperature for the different electrolytes
Key Points: Requirements of End of Life Energy Storage Systems for PHEVs High Power/Energy Ratio High Energy/Power Ratio Performance and Characteristics at EOL (End of Life) life targets defined for two systems: Battery Battery
Possible reactions occurred within a cell
eE ELi Li+ + Constant Voltage (assume voltage changes with Li content) eeif products from anode are soluble + E E e-
MP based electrolyte
Methyl propionate containing electrolytes have displayed dramatically improved rate capability at -40oC compared to the baseline DOE formulation (i.e., 1.2M LiPF6in EC+EMC (30:70). Significantly higher capacity and operating voltage delivered at high rate .
Develop high voltage electrolytes that enable the dreamed 5 V Li Ion ChemistryEnergy density: New chemistries for HEV/PHEV • “Energy Quality”: Energy form • Conversion efficiency • Potential at which energy is delivered

Calendar Life, 35癈 Maximum System Weight Maximum System Volume Maximum Operating Voltage Minimum Operating Voltage Maximum Self-discharge
10-mile system: 121 Wh/L 40-mile system: 207 Wh/L
2. 3.
wk.baidu.com4.
New progresses made in electrolyte systems
New Solvents
Requirements:
Highly safety Low reactivity Wide liquid range
New Solvents

New fluoro solvents are being investigated as nonflammable solvents

Fluoro ether: is used as co-solvent to improve oxidation
potential in Hatachi.
K. Naoi, E. Iwama, Y. Honda and F. Shimodatein J. Electrochem. Soc., 157, A190(2010)
ELi ELi Li+
No side rxn. if no reaction at cathode! (unless voltage is flat on anode) + eE EPF6 e-
Chemical shuttle eE ELi EO + e-
or if anion reacts
ELi E Li+ PF6-
2012中国锂电池电解液研讨会---2012.11
锂离子电池先进电解液组分的性能优化
The optimization of electrolyte components used in lithium ion cells 郑 洪 河
苏州大学能源学院
华盛化学
PHEV Goals Announced by FreedomCAR

Long service life:

year kg Liter Vdc Vdc Wh/day
15 60 40 400 >0.55 x Vmax 50
15 120 80 400 >0.55 x Vmax 50
System Recharge Rate at 30癈
kW (120V/15A) 1.4 (120V/15A) the 40 mile system: at least 3000 cycles 1.4 to 80% capacity 癈 Unassisted Operating & Charging Temperature Range -30 to +52 -30 to +52 retention 癈 Survival Temperature Range -4680% to +66 the 10 mile system: around 5000 cycles to capacity -46 to +66 retention. Maximum System Production Price @ 100k units/yr $ $1,700 $3,400

Solvent with a F to H ratio >4 appears to have improved thermal properties, In the wick test the electrolyte containing the fluoro solvent didn’t catch fire.
or if oxide reacts
E LiM(3+)O2 1/2O 2 Li+ M(2+)O
Net loss of salt and solvent
Li+ Net loss of solvent and oxide
Constant Current
Li+ eE ELi Li+ eLi+ Charging If no side rxn at cathode: delithiate cathode and partially lithiate anode Loss of solvent Anode: Loss of lithium Loss of electrolyte/solvent Open Circuit If no side rxn at cathode: delithiate anode Self discharge Cathode: Dissolution of cations Oxygen release eLi+ e+ Li+ eE ELi + Li+ eE ELi Li+ e+

Absolute safety: No fire or explosion under any cases
The role of electrolytes in lithium ion batteries

Cycle life Shelf life Safety Working temperature Rate capability Reversible capacity Self-discharge properties Compared to the studies in Japan & USA less attention has been paid to the R&D of electrolyte systems in China

Fluoro solvents in conjunction with cyclic carbonates should exhibit improved thermal properties

Low temperature performance may suffer
• Fluoro-EC may be an alternative
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