1

LITHIUM ION BATTERIES

2

Lithium ion batteries (LIBs)

Overview

• Structure & Mechanism

• Trends (application, topics)

Technical terms

• Material / Electrode / Cell

Materials for LIBs

• Active materials / Electrolyte / Separator

3

Lithium ion batteries

4

Battery capacity for HEV, PHEV, BEV

5

Overview

1. General structure / Operation mechanism of LIB

2. Application

3. Current topics

General structure of LIBs

: anode | electrolyte/separator | cathode

: Li ions travels back and forth between two electrodes

ex) Li1+Co3+O2 ↔ Li1+1-xCo(3+x)+O2 + xLi+ + xe- (Positive E)

6xC + xLi++ xe- ↔ xLiC6 (Negative E)

(where, →: charging, ←: discharging)

: Li+ moves through electrolyte

(generally liq. solution: ex) 1M of LiPF6 in EC+DMC)

: Separator blocks direct contact of anode and cathode, provides path of Li+ ions (PE, PP)

: current collector (Cu, Al foil), binder, conductive agent…

Applications

: energy storage for mobile devices, electric vehicle, energy storage system for power plant…

Current topics

: capacity(specific/volumetric), power, safety, longevity, environment, cost…

6

Structure, Charging/Discharging reaction

Separator

1. 조립 직후 (방전 상태): C (graphite) LiCoO2

2. 충전: LiCoO2 → Li1-xCoO2 + xLi+ + xe-

xLi+ + xe- + 6xC → xLiC6

3. 방전: xLiC6 → xLi+ + xe- + 6xC

Li1-xCoO2 + xLi+ + xe- → LiCoO2

7

수압

흐른 물의 총량

수압

흐른 물의 총량

올라간 물 양: “충전용량”

충전

방전

내려간 물 양: “방전용량”비가역 용량

비가역 용량

가역 용량

8

비가역 용량

① 1st 충전

③ 2nd 충전

② 1st 방전

④ 2nd 방전

FIG : 일반적인 충/방전 곡선

☞ 용량②/용량① = 효율

9

FIG : 일반적인 1st 충방전 곡선 (NCA, NCM111). Cutoff voltage: 3.0-4.3V vs. Li/Li+

☞ 충전 cutoff: 4.3V. 층상구조 활물질 (LCO, NCM, NCA 등)의 이론 용량은 거의 같으며,

다만 주어진 cutoff 조건에서 사용하는(뽑아내는) 리튬의 양이 다름. (LCO: ~55%, NCA: ~70%)

“ state of charge (SOC)”, 커질수록 불안정