Project Subjects
R&D for Safe and Reliable Solvent-free Lithium-Ion Polymer Batteries
Background and Objective
Research and development of large size rechargeable battery for the main power source of advanced
electric vehicles, stabilized power sources of photovoltaic and wind power systems are expected to contribute toa low-carbon society.
On this subject, CEIEPI is developing a solvent-free lithium-ion polymer battery (LIPB) which exhibitshigh energy efﬁciency and reliability. The target area of the battery is stationary use to correspond the highly diffused renewable energy in the system. In 2009FY, the improvement operation life of anode and rate properties ofcathode characteristics was reported. In addition, energy density calculation procedure of the kWh-scale battery
module was developed and validated the procedure to apply the conventional lithium-ion battery (LIB).

Main results
1. Trial production of ﬂat-type LIPB using electrode coating system
Flat-type LIPB was fabricated using electrode coating system in the dry room (dew point of <-70 ºC) at
the Akagi Testing Center (Fig.1).
2. Improvement of rate properties of cathode in LIPB
A cathode/solid polymer electrolyte (SPE) interface was optimized by adjusting the lithium salt concentration in the SPE (minimum region in Fig.2). Although the optimized salt concentration was inconsistent tothat of ionic conductivity in the polymer electrolyte, we conﬁrmed that the battery performance was ruled by theoptimized condition of cathode/SPE interface (Fig.3) [Q09001].
3. Improvement of cycle properties of carbon anode by the modiﬁcation of electrode components
Binder material in the anode electrode was changed from conventionally used PVDF to SBR. The carbon
anode using SBR binder and SPE exhibited 700 cycles long cycle performance and it was twice as long as thatusing PVDF binder (Fig.4) [Q09010].
4. Energy density estimation of LIB
Energy density estimation procedure of LIB was proposed by integrating electrode and current collectormaterial thickness, density, etc. The estimated maximum energy density of LIB using conventional electrodematerials was 20% higher than that of commercially available LIB with the highest energy density, and 2-3 times
higher than that of LIB for electric vehicles. Further higher energy density battery than LIB system was estimatedusing LIPB (Fig.5). Therefore, developing LIPB exhibited a potential for higher energy density than that of conventional LIB with reliability [Q09006].

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Environmental and Energy Utilization Technology[Electrode coating system][Cathode coating step][Electrode laminating step]
Fig. 1 LIPB preparation equipments in the dry room and schematic of prototype ﬂat-cell preparation

Fig. 2 Relationship between Li salt concentration in SPE and cathode / SPEinterfacial impedance
Minimum interfacial impedance was found at a ratioof [Li] / [O]=0.1 at any state of charge (SOC).

Fig. 3 Main factor image of cell rate performance
Li+ mobility at cathode / SPE and rate performance showedmaximum value at a ratio of medium concentration of Li+ inSPE.

than current large LIB

Fig. 4 Capacity retention versus operation
cycles of carbon anode using different
binders
PVDF: Polyvinylidene diﬂuoride
SBR: Styrene-butadiene rubber

Fig. 5 Energy and volume densities of LIBand LIPB
Energy and volume densities of various LIB and LIPB
were evaluated using developed cell energy density
estimation procedure.

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