Solid State Ionics 184 (2011) 62–64

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Solid State Ionics

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Protected anodes for lithium-air batteries

Gleb Yu. Aleshin a,⁎, Dmitry A. Semenenko a, Alina I. Belova a, Tatyana K. Zakharchenko a, Daniil M. Itkis a,b,Eugene A. Goodilin a,b, Yurii D. Tretyakov a,b

a Department of Material Science, Lomonosov Moscow State University, Moscow, 119991, Russiab Department of Chemistry, Inorganic Chemistry Division, Lomonosov Moscow State University, Moscow, 119991, Russia

⁎ Corresponding author. Tel.: +7 495 939 47 29; faxE-mail address: glebkms@gmail.com (G. Yu. Aleshin

0167-2738/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.ssi.2010.09.018

a b s t r a c t

a r t i c l e i n f o

Article history:Received 16 May 2010Received in revised form 9 September 2010Accepted 10 September 2010

Keywords:Lithium-air batteryLithium anodeLAGP

A new protected anode for lithium-air batteries is designed using lithium foil and lithium–aluminium–

germanium–phosphorus glass–ceramics (LAGP)with improved specific conductivity exceeding 3.1⋅10−4 S cm−1

at 80 °C and 1.4⋅10−4 S cm−1 at −20 °C. Prevention of anode or electrolyte degradation provided stability ofthe battery characteristics for at least 10 cycles. In particular, a lithium-air battery with the protected anode andan activated carbon cathode modified with α-MnO2 nanorod catalyst showed a specific capacity of about3000 mAh g−1.

: +7 495 939 09 98.).

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© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Effective energy storage is highly demanded for different applica-tions such as consumer electronics and pure electric vehicles (EV). Inthis sense lithium-air batteries are the most prominent solution dueto their high specific energy and huge capacity overcoming lithium-ion batteries by one order of magnitude.

Pioneering works of Bruce et al. [1–3] in the field of lithium-airbatteries have recently demonstrated growing promises and increasingattention worldwide. Lithium-air batteries with a lithium conductingpolymer electrolyte have been already reported in 1996 by Abrahamand Jiang [4]. This prototype cell showed anopencircuit voltage of about3 V and an oxygen electrode capacity of 1600 mAh g−1. A catalystaddition to the carbon cathode material makes the cell much moreefficient and reversible. The reversible capacity of about 3000 mAh g−1

for an α-MnO2 nanorod catalyst was shown [2]. Recently, Kuboki et al.reported an extremely high capacity of 5360 mAh g−1 when usingcobalt phtalocyanine as a catalyst [5].

Unfortunately, lithium-air batteries are still underestimated andcould not be deployed because of safety issues and their fast degra-dation under ambient conditions. In particular, the highly reactivelithium must somehow be isolated from water vapor and oxygenpermeating to the anode part of the cell from the surroundingatmosphere. Recently, NASICON-type lithium conductors and theircomposites with PEO-based polymers and LIPON were supposed toprotect lithium anodes inside lithium-air batteries with aqueouselectrolytes [6–10]. In the present work, we suggest a new protected

lithium anode based on a glass-ceramic NASICON-type electrolyte andlithium foil for rechargeable lithium-air batteries.

2. Experimental

The solid lithium conductor Li1.5Al0.5Ge1.5(PO4)3 (LAGP) wasprepared by a technique described in [11]. Li2CO3, Al(OH)3, GeO2

and NH4H2PO4 were mixed in an agate mortar in stoichiometric ratio.For further homogenization the reactants were milled in a planetarymill for 1 h (Fritsch PULVERISETTE) under heptane. Such preparedprecursor powder was annealed at 950 °C for 12 h. The resultingproduct was fused by water plasma at about 2500–3000 °C andsubsequently quenched between rotating metallic cylinders. Finally,the obtained glass flakes were crystallized by heat treatment for 2 h at630 °C.

Laboratory-scale protected lithium anodes were prepared fromlithium foil pressed onto a nickel mesh placed inside polypropylenetubes and sealed with LAGP glass-ceramic pieces and epoxy resin. Thecathode was prepared by mixing 85 wt.% of activated carbon (Norit),5 wt.% of polyvinylidene fluoride and 10 wt.% of α-MnO2 nanorodsprepared according to ref. [12]. The cathode slurry was deposited ontoconductive carbon paper (Torray).

LAGP glass–ceramics was characterized by XRD (Rigaku D/MAX2500 X-ray; Cu-Kα radiation; 10–60° 2θ range at 0.02° increments).SEM images (LEO Supra 50 VP) were taken using freshly cleavedglass-ceramic flakes. Thermal analysis was performed using typically10 mg of LAGP glass (Netzsch STA 409).

Ionic conductivity was measured by means of AC-impedancespectroscopy within a frequency range of 10 Hz–1 MHz (10 mVamplitude) using an Autolab PGSTAT 302 analyzer. A standard two-electrode cell with blocking platinum electrodes was used. Collected

Fig. 1. DSC curve of quenched LAGP glass. Glass transition starting at 530 °C and LAGPcrystallization peak at 625 °C are indicated.

63G. Yu. Aleshin et al. / Solid State Ionics 184 (2011) 62–64

impedance spectra were fitted in Z-View software package fromScribner Associates.

Electrochemical tests of lithium-air cells were performed at roomtemperature utilizing a multichannel galvanostat with cut-off valuesof 2.0 and 4.2 V. Charge and discharge currents were held at 100 mAper 1 g of cathode material.

Fig. 2. (a) SEM micrograph of LAGP glass–ceramics, (b) XRD pattern of LAGP glass–ceramics. AlPO4 impurity phase reflections are marked with asterisks.

3. Results and discussion

The samples obtained by quenching were found to be transparentthin flakes of about 1 cm in width showing no clear X-ray diffractionmaxima. Differential scanning calorimetry revealed a glass transitionstarting at about 530 °C and showing a strong peak at 625 °Cthat could correspond to crystallization of the LAGP phase (Fig. 1).Annealing of glass for 2 h at 630 °C led to the formation of a well-crystallized product (Fig. 2a). This 100 μm-thick piece of LAGP glass–ceramic has no open porosity and this evidently prevents gaspermeation.

An XRD pattern of annealed glass is shown in Fig. 2b evidencingcrystallization of the known LiGe2(PO4)3 rhombohedral phase (PDFcard #80-1924) with unit cell parameters a=8.298(12)Å andc=20.64(3)Å. A slight increase of the parameters compared toLiGe2(PO4)3 would be expected for partial substitution of Ge4+ withAl3+. A small amount of AlPO4 as an impurity phasewas also detected.A Williamson–Hall analysis of diffraction peak broadenings for both

Fig. 3. (a) Impedance spectra of LAGPmembranes at 80 °C (circles), 20 °C (squares) and−20 °C (rhombs). Inset shows an equivalent circuit that was used to fit experimentaldata. (b) Temperature dependence of specific ionic conductivity of LAGP glass–ceramicsgiven as Arrhenius plot.

Fig. 4. (a) Scheme of the lithium-air cell with LAGP-based protected anode and activatedcarbon cathode. (b) Charge and discharge curves in the 4.2–2.0 V range. α-MnO2

nanorods were used as a catalyst. (c) Capacity retention for the first 10 cycles. Cyclingwas performed in the 4.2–2.0 V range. Capacity is calculated per 1 g of cathodematerial,current was maintained at a 100 mA g−1 level.

64 G. Yu. Aleshin et al. / Solid State Ionics 184 (2011) 62–64

phases gives an approximate crystallite size of 70 nm for LAGP and5–10 nm for AlPO4. The presence of AlPO4 nanocrystalline precipi-tates is quite beneficial since a contribution of surface conductivity ofsuch impurity nanocrystals can raise the total ionic conductivity ofthe system [13].

AC-impedance spectra of the Pt/LAGP/Pt cell (Fig. 3a) can befitted well with the model of a traditional R–RC–RC-chain. TheArrhenius plot presented in Fig. 3b shows the temperaturedependence of LAGP glass–ceramics with a specific ionic conduc-tivity of about 2.24 ⋅10−4 S cm−1 at room temperature. This valueremains high enough even at −20 °C slightly decreasing down to1.41 ⋅10−4 S cm−1. Obviously such a level of conductivity seems tobe promising for application of these membranes for lithiumrechargeable batteries fabrication.

The design of a lithium-air battery with a protected lithium anodeis shown in Fig. 4a. Lithium foil acting as an anode material remainedshiny with no traces of corrosion even after one week of exposure to100% humidity environment. In order to demonstrate the perfor-mance of the protected anode it was tested within a cell assembledwith an activated carbon cathode. The recently reported α-MnO2

nanorod catalyst [2] was added to activated carbon in order toincrease cell capacity and improve its reversibility.

A typical charge/discharge curve is demonstrated in Fig. 4b. Thespecific discharge capacity was shown to be about 3000 mAh per 1 gof the cathode material. Moreover, the cell was recharged 10 timeswithout a significant loss of capacity. An average discharge voltage ofabout 2.7 V was stable for all the cycles, thus we have to conclude thatthe developed technique provides sufficient stability of both theelectrodes.

4. Conclusions

The lithium–aluminium–germanium–phosphorus glass–ceramics(LAGP) prepared in this study with improved specific conductivityexceeding 3.1⋅10−4 S cm−1 at 80 °C and 1.4⋅10−4 S cm−1 at −20 °Ccould play an important role in the design of lithium-air batteries.First of all, it allows to prevent anode or electrolyte degradation andenhance the stability of the battery for at least 10 cycles. Secondly, suchprotection enhances the temperature range of effective discharge ofthe battery down to negative temperatures. Finally, a combinationof protected anodes with an activated carbon cathodemodified with anα-MnO2 nanorod catalyst allows to achieve a specific capacity of about3000 mAh g−1 making it possible to promise future practical applica-tions of such an enhanced power source.

Acknowledgement

The work was supported by the Russian Foundation of BasicResearch and Federal R&D Program (project # 02.516.11.6200).

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