Some notes on batteries.

There are 2 types: primary cells (non-rechargeable) and secondary cells (rechargeable)

Lithium Ion[edit | edit source]

Lithium Ion batteries (Li-Ion, LIB) is a type of battery that uses lithium ions. Lithium Ion Polymer (LiPo) batteries are also included in this category, but are constructed with a polymer electrolyte.

Lithium-ion battery consists of 3 primary components:

  1. The negative electrode (anode) is made with carbon and is typically graphite. This acts as the host for lithium ions.
  2. The positive electrode (cathode) can be one of:
    • Lithium Cobalt Oxide (LCO), the traditional Li-ion battery consisting of 60% cobalt oxide and 40% lithium
    • Lithium Nickel Manganese Cobalt (NMC), traditionally a 1:1:1, moving to 5:2:3, and perhaps a 8:1:1 blend. R&D goal is to reduce cobalt oxide and increase nickel content.
    • Nickel Cobalt Aluminum (NCA), aluminum replaces manganese. 80% Nickel, 15% cobalt, 5% aluminium. The 'Panasonic/Tesla battery'
    • Lithium Iron Phosphate (LFP)
    • Lithium Manganese Oxide (LMO)
  3. The electrolyte which can be in liquid (as lithium salts) or solid form (as lithium metal oxides).

There are five prevalent materials used in the making of these batteries and are known as the core "Battery Materials": Cobalt, Graphite, Lithium, Nickel, Manganese. Some of these metals especially in cobalt are from conflict-affected or high-risk areas that have serious human right abuses, child labour, or high environmental impacts.

While discharging, lithium ions carry the current from the negative to the positive electrode.

While charging, an external power source applies an over voltage in the same polarity. Most Lithium Ion batteries charge to 4.2 volts. Unless otherwise specified, batteries should be charged at 0.5C, where C is the rated capacity of the battery. (For example, a 3400mAh battery should be charged at 1700mA). Charge is terminated at 3% of the initial charge current. During charging, current within the battery flows from the positive to the negative electrode.

Type Discharged Voltage Charged Voltage
Lithium metal oxides (eg. LiCoO2) 2.7 - 3.0V 4.2V
lithium iron phosphate (eg LiFePO4) 1.8 - 2.0V 3.6 - 3.8V

Note: A 3.7V Lithium Ion battery can be charged up to 4.2V. 3.7V is the voltage the battery will output for the bulk of its discharge.

18650[edit | edit source]

18650s are cylindrical lithium-ion rechargeable batteries that are 18mm in diameter an 65mm in length. These are most commonly found inside laptop batteries and are used in various applications such as ebikes.

Internal resistance of a battery can be calculated with the DC load method. By measuring the initial voltage (Vi), the voltage under load some resistive load(Vl), and the resistance of the load (R) and applying it to the following formula, we can calculate the ohmic resistance of the battery.

When comparing the internal resistance of batteries using this method, batteries should have the same charge. Good batteries at half charge could have the same internal resistance as a bad battery at full charge. In general, new batteries should have a internal resistance less than 100 mΩ while bad batteries have over 350 mΩ.

High internal resistance will cause the battery's output voltage to drop under load and heat up as current draw increases.

See also:

Chargers[edit | edit source]

TP4056[edit | edit source]

The TP4056 can charge a battery at 1 amp. The current is set to 1 amp with the 1.2K resistor connected to the PROG pin.

I ordered 10 TP4056 modules with output protection for about CAD$4. The modules without output protection are slightly cheaper.

See Also[edit | edit source]

Nickel Cadmium[edit | edit source]

Nickel Cadmium (NiCd, or NiCad) is a rechargeable battery that uses nickel oxide hydroxide and metallic cadmium as electrodes.

Nickel Metal Hydride[edit | edit source]

Nickel Metal Hydride (NiMH, Ni-MH) is a rechargeable battery similar to a Nickel Cadmium, rather than using cadmium in the negative electrode, it uses a hydrogen-absorbing alloy instead. This yields a higher energy density around 2-3x that of a nickel-cadmium and can approach that of a lithium-ion.

Each cell has a nominal voltage of 1.2V.

Charging voltage is in the range of 1.4–1.6V per cell. Trickle charging is possible, but should be done at C/40 or possibly lower. Chargers should terminate a charge when a negative voltage delta is detected or when the temperature begins rising. Overcharging a NiMH battery will cause hydrogen gas to form from the electrolyte which can possibly rupture the cell.

Lead Acid[edit | edit source]

A lead-acid battery is a rechargeable battery that uses lead (Pb, negative) and lead oxide (PbO2, positive) plates submerged in sulfuric acid (H2SO4). When discharged, both plates become lead sulfate (PbSO4) and the acid dilutes as it becomes primarily water.

The construction of a lead-acid battery typically requires a separator between the plates to prevent dendrites from forming between the plates and causing a short circuit.

A lead-acid cell has a nominal voltage of 2.1V. Charging a lead-acid requires at a minimum of 2.15V per cell. It is possible to charge a lead-acid with a higher voltage (eg. 2.5V) without damage so long as it is not near its fully charged state.

Overcharging a lead-acid battery will cause electrolysis of the water in the electrolyte, producing hydrogen and oxygen. This happens only when any of the lead sulfate or sulfuric acid has been reacted and unavailable.

As lead-acid batteries are cycled, its capacity will be reduced due to sulfation where the lead sulfate does not combine with the electrolyte. The result of this is a reduction in the amount of lead on the negative plate.

USB Power Banks[edit | edit source]

Most USB power banks use Lithium Ion batteries in the form of 18650. The rated capacity is usually based on the 3.7V of the internal battery rather than at the 5V output voltage.

A 20000mAh battery at 3.7V will provide 74000mWh (or 74Wh) of power (assuming 100% efficiency).

A Raspberry Pi using 0.5A at 5V will use 2.5W. Using the battery above, 74Wh/2.5W = 29h run time.