The KOH electrolyte

Ni-Cd batteries (+): 2NiOOH + 2H2O + 2e- 2Ni(OH)2 + 2OH- (0.5 V) (-): Cd + 2OH- Cd(OH)2 + 2e- (0.8 V) ------------------------------------------------------------ Cd + 2NiOOH + 2H2O Cd(OH)2 + 2Ni(OH)2 (1.3 V) In KOH 6~8M electrolyte

The KOH electrolyte

The KOH electrolyte

Ni-Cd batteries (+): 2NiOOH + 2H2O + 2e- 2Ni(OH)2 + 2OH- (0.5 V) (-): Cd + 2OH- Cd(OH)2 + 2e- (0.8 V) ------------------------------------------------------------ Cd + 2NiOOH + 2H2O Cd(OH)2 + 2Ni(OH)2 (1.3 V) The solids are insoluble in KOH electrolyte. --Longer life than Pb-acid batteries (for UPS: no acid vapor, but more expensive!!) --But shorter life than Ni-MH batteries

KOH + LiOH: The electrolyte high rate discharge performance cycle life high temperature performance The current collectors and can are typically Ni or Ni-plated steel!

The discharge performance

The discharge performance

Ni plated steel case

The drawbacks Cd pollution Lower capacity vs. that of Ni-MH batteries Poor charge retention Memory effects

Poor charge retention

Voltage depression (memory effect) --a reversible failure Especially at high temperature Two-step discharge (lower capacity)

Cd may undergo a physical change, increasing the cell resistance. Cutoff voltage is important. Practically, performing discharge before charging. The charger (to match the batteries) is critical.

Ni-Cd batteries (+): 2NiOOH + 2H2O + 2e- 2Ni(OH)2 + 2OH- (0.5 V) (-): Cd + 2OH- Cd(OH)2 + 2e- (0.8 V) ------------------------------------------------------------ Cd + 2NiOOH + 2H2O Cd(OH)2 + 2Ni(OH)2 (1.3 V) In KOH 6~8M electrolyte

Ni-Cd batteries (+): 2NiOOH + 2H2O + 2e- 2Ni(OH)2 + 2OH- (0.5 V) (-): Cd + 2OH- Cd(OH)2 + 2e- (0.8 V) ------------------------------------------------------------ Cd + 2NiOOH + 2H2O Cd(OH)2 + 2Ni(OH)2 (1.3 V) The solids are insoluble in KOH electrolyte. --Longer life than Pb-acid batteries (for UPS: no acid vapor, but more expensive!!) --But shorter life than Ni-MH batteries

The drawbacks Cd pollution Lower capacity vs. that of Ni-MH batteries Poor charge retention Memory effects

Poor charge retention

Voltage depression (memory effect) --a reversible failure Especially at high temperature Two-step discharge (lower capacity)

Ni-Metal Hydride (Ni-MH) batteries

Ni-metal hydride (Ni-MH) batteries Using hydrogen instead of Cd. The hydrogen is in metal hydrides (the hydrogen storage materials).

The energy storage mechanism It is rechargeable! No H2O is involved in the reaction, so the cycle life is better. Also using 6~8 M aqueous KOH as the electrolyte.

Ni-metal hydride (Ni-MH) batteries Advantages: higher energy density than Ni-Cd free of Cd memory effect longer cycle than Ni-Cd ~1.3 V high safety simple, convenient, low cost than LIB

Ni-metal hydride (Ni-MH) batteries Disadvantages : inferior rate performance than Ni-Cd less tolerant of overcharge higher cost than Ni-Cd (due to MH, e.g. LaNi5) heavy

於充放電過程中氫在鎳氫電池電解液中的移動及電荷轉移情況 Expensive & heavy

儲氫合金材料 (hydrogen storage alloy) M+H2 MHX+ Η 系列代表合金備註 AB5 LaNi5 MmNi5 AB2 TiCr2 TiMn2 AB TiFe TiNi 以荷蘭飛利浦公司之專利為代表 以美國 Ovonics 公司之專利為代表 A2B Mg2Ni Ti2Ni

The important properties of hydrogen storage alloy

儲氫合金材料吸氫機構示意圖

LaNi5 型儲氫合金材料之結晶結構與氫化物形成時氫原子所佔據的位置

鎳氫電池的內部結構包括 正極材料 : 氫氧化鎳 負極材料 : 儲氫合金 電解質 : 氫氧化鉀為主的水溶液 ( 濃度約為 7 M) 正 負極片之間的隔離板 附註 : 一般來說, 適當的隔離板材料須有以下性能 :(1) 在強鹼電解質中要有抗腐蝕性 ;(2) 多孔性, 便於離子之傳導 ;(3) 吸附力強, 減少電解液的使用量 ;(4) 電絕緣性, 防止正 負極間漏電或短路

The safety concern -- electrode design

The safety concern -- electrode design

The larger anode: prevent H2 evolution and avoid high pressure.

Polarity reversal during over-discharge

The charge retention

Charging the Ni-MH betteries

Charging the Ni-MH betteries

Techniques for charge control (1) Timed charge: inexpensive, suitable for applications where the batteries are usually fully discharged (but at low rates). (2) -ΔV(10~20 mv): preferred for Ni-Cd O2 recombination 放熱 T resistance V (3) Temperature (T) detection: usually set at 45, but is influenced by ambient temperature, cell design, charge rate (4)ΔT: the influence of ambient temperature is minimized. (5)ΔT/Δt: preferred for Ni-MH batteries

Moreover, charge methods should match the types of batteries from different manufacturers.

Cost: Li-ion > Ni-MH > Ni-Cd Cell voltages are different

Li-ion batteries Commercialization by Sony in 1990, employing Li intercalation compounds as the positive and negative materials. The rocking-chair batteries.

Li-ion batteries Lithium-ion (Li-ion) batteries are comprised of cells that employ lithium intercalation compounds as the positive and negative materials. As a battery is cycled, lithium ions (Li) exchange between the positive and negative electrodes. They are also referred to as rocking-chair batteries as the lithium ions rock back and forth between the positive and negative electrodes as the cell is charged and discharged. The positive electrode material is typically a metal oxide with a layered structure, such as lithium cobalt oxide (LiCoO2), or a material with a tunneled structure, such as lithium manganese oxide (LiMn2O4), on a current collector of Al foil. The negative electrode material is typically a graphitic carbon, also a layered material, on a Cu current collector. In the charge/ discharge process, lithium ions are inserted or extracted from interstitial space between atomic layers within the active materials.

(Al) (Cu)

(~4 V)

Li4Ti5O12