Development of a bipolar Li/composite polymer electrolyte/pyrite battery for electric vehicles V. Livshits, A. Blum, E. Strauss, G. Ardel, D. Golodnitsky * , E. Peled School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel Received 29 June 2000; accepted 11 December 2000 Abstract To demonstrate the concept of rechargeable polymer electrolyte bipolar lithium batteries, laboratory-type bipolar Li/pyrite 3-cell batteries were fabricated and tested. The unoptimized 5 V, 10 cm 2 3-cell battery had a capacity of 30±40 mAh with 100% Faradaic ef®ciency. The long-term projection for a prototype sealed bipolar Li/composite polymer electrolyte/pyrite Li/CPE/FeS 2 ) battery, with a 45 mm-thick cathode is 250 Wh/kg speci®c energy. The performances of monopolar and bipolar battery designs are compared. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Polymer electrolyte bipolar battery; Faradaic ef®ciency; Li/pyrite batteries 1. Introduction Lithium and lithium-ion battery usage is gradually spreading to large-scale battery systems, such as power sources for electric vehicles EV) and energy storage for load leveling. Electric vehicles need batteries that are affordable, meet or exceed current safety standards and satisfy customer expectations for performance. The lithium polymer battery is considered to be one of the best long-term solution for powering electric vehicles. Lithium polymer batteries have been under development since the late 1970s and have been shown to be a promising technology [1]. One of the major obstacles to the commercialization of lithium polymer-electrolyte and lithium-ion batteries for EV appli- cation is their high cost [2]. The cost of materials for the Li/ composite polymer electrolyte/pyrite Li/CPE/FeS 2 ) battery is about $40/kWh excluding the case), a sixth of that for lithium ion batteries and for other lithium polymer electro- lyte batteries estimated at $250/kWh) [3±5]. There are two reasons for such low cost similar to that of the lead-acid battery: the use of lithium iodide as a salt at $20/kg, as opposed to lithium hexa¯uorophosphate or lithium imide at about $250/kg, and the use of a natural ore pyrite) as cathode material at $0.5/kg. The Li/CPE/FeS 2 battery has many attractive properties. This all-solid-state battery utilizes metallic lithium as its anode and a thin composite polymer electrolyte which acts both as a separator and electrolyte. The ¯exible, multi- laminate structure of the polymer electrolyte battery makes possible very high power and energy densities. The use of a solid polymer as the electrolyte is particularly advantageous because it does not leak and emit dangerous gases. Pyrite was found to be fully compatible with the polymer electro- lyte components up to 3008C [3]. The Li/CPE/FeS 2 battery operates over a moderate temperature range of 75±1408C.At C/10 discharge rate, thin-cathode cells operating at 908C deliver 50% of their 1358C capacity. More than 500 100% DOD cycles at C/3 rate) with a capacity-fading rate of less than 0.1%/cycle were carried out in small 1 cm 2 area) laboratory prototype cells with 10 mm-thick cathodes [4]. It was shown [5] that cells with FeS 2 -composite cathodes show identical electrochemical behavior and performance characteristics, independent of the pyrite source. Internal electrochemical overcharge/overdischarge pro- tection mechanisms were shown for the Li/CPE/FeS 2 battery [4]. Up to 100% overcharge and discharge down to 0.3 Vare possible in this system with no signi®cant negative effects. The existence of the buffer capacities is a very important battery feature against accidental damage. Overcharge and overdischarge protection becomes particularly important in the design of high-voltage multi-cell bipolar batteries. The bipolar battery design minimizes IR losses between adjacent cells in a cell-stack and provides uniform current and Journal of Power Sources 97±98 2001) 782±785 * Corresponding author. Tel.: 972-3-640-92-93; fax: 972-3-640-68-79. E-mail address: glod@post.tau.ac.il D. Golodnitsky). 0378-7753/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0378-775301)00608-5