How rechargeable batteries, charge and discharge cycles work

Batteries store electrical energy in the form of chemical energy, which in turn can be converted into electrical energy. The process of converting chemical energy into electrical energy is called discharge. The chemical reaction during discharge causes electrons to flow through an external load connected to the terminal, resulting in a current flow of electrons in the opposite direction.
Some batteries can return these electrons to the same electron by applying a reverse current, a process called charging. Batteries that are able to recycle electrons on the same electrodes are called rechargeable batteries, and if they cannot do so, they are called non-rechargeable batteries.
In a battery, the electrode where the reduction occurs is called the cathode, and the electrode where the oxidation occurs is called the anode.

There are three types of rechargeable batteries commonly used in the market.

1. Lead-acid batteries
2. NiCd battery
3. NiMH batteries
4. Lithium Ion Battery

Lead-acid batteries

First, lead-acid batteries were invented in 1859 by French physicist Gaston Plante. This is a negative electrode (anode) which is made of sponge or porous lead. The positive electrode (cathode) consists of lead oxide. Both the anode and cathode electrodes are immersed in an electrolyte of sulfuric acid and water (dilute sulfuric acid).

Discharging lead-acid batteries

Pb + HSO4-ーーーー> PbSO4 + h + 2e- Reaction at negative electrode
PbO2 + HSO4-+ 3H + + 2e-ーーーー> PbSO4 + 2H2O Reaction at positive electrode
Overall reaction Pb + PbO2 + 2h2so4ーーーー> 2PbSO4 + 2H2O

The discharge of lead-acid batteries causes the formation of lead sulfate (PbSO4) crystals on the positive (cathode) and negative (anode) electrodes and releases electrons due to the change in lead's valence charge. This method of forming lead sulfate uses sulfuric acid, which is the electrolyte in batteries, to form sulfate. This results in a lower concentration of sulfuric acid when fully discharged, both electrodes are covered with lead sulfate and water, and there is no sulfuric acid around the electrodes. At full discharge, the electrodes are completely covered by the same material, which is lead sulfate, so there is no chemical potential or voltage between the two electrodes. In practice, there is a cut-off voltage to stop the discharge long before this point.
Let's look at the discharge rate, lead-acid batteries are usually specified at 8, 10, or 20 hours at a rate of c/8, c/10, c/20. If you find battery 12v 200Ah/10h or c/10.
c/10 = 200 Ah/10 h = 20A
The specific time after the c/10m voltage is cut off, here 10 hours is c/10.

Charging of lead-acid batteries

When charging begins, the charger is connected to the positive and negative terminals. Lead-acid batteries convert lead sulfate (PbSO4) into lead (Pb) at the negative electrode and lead sulfate (PbSO4) into lead oxide at the positive electrode. Chemical reaction reverses during discharge

Charging of lead-acid batteries

PbSO4 + 2H2O Reaction at positive electrode ーーーーー> PbO2 + HSO4-+ 3H + + 2e-
PbSO4 + h + + 2e-ーーーーーー> Pb + HSO4- Reaction at negative electrode
Full reaction 2pbso4 + 2H2O ーーーーー> Pb + PbO2 + The 2H2SO4
charging current electrolyzes water from the electrolyte, and both hydrogen and oxygen produce this process, called the "gas" of the battery. This gas emission causes several problems with the battery. This is unsafe due to the explosive nature of the hydrogen produced. This also reduces water in the battery, which can be replaced manually, but it adds a maintenance factor. Gas emissions can cause shading of the active species in the electrolyte, permanently reducing battery capacity, which is why batteries should not be regularly charged beyond the voltage that causes gas emissions. Bleeding voltage can vary with charging rate
There are several ways to charge lead-acid batteries. But we should take the best way to reduce the chance of gassing for maximum battery life and capacity. The list of methods is given below.

1. Constant Voltage:- As a name, this method will provide a constant voltage until the current of the battery is zero. it takes a long time
2. Constant Current:- As a name, this method will supply a constant current until the voltage reaches its specified bleed voltage. It also takes a long time.
3. Multi-stage Constant Current Charge Current:- In this method, the charge current is kept constant until the voltage reaches the bleed voltage, and then the current starts to gradually decrease to keep the voltage below the bleed voltage. This charger is complicated to manufacture.
4. Improved constant voltage and constant current:- In this method the battery is charged in three stages. The first stage is the constant current stage, in which current is applied to the battery until the voltage reaches its specified gassing voltage. In the second stage, the voltage remains constant until the current decreases to around 0.1 c20 (also known as C20/10). The voltage is lowered to the float voltage (typically 2.25 v to 2.27 v) to keep the battery charged.
   The charging current and charging voltage can be found on the label of the battery, as you can see in the picture there are two modes to choose the charging voltage and current, which are standby use and cycle use. Cycling refers to the use of batteries that require rapid charge and discharge. Standby use is when the battery is charged and used when needed. 0.1 c means 0.1 times the total capacity of the battery. If you have a 40ah battery then 0.1 c is 0.1 x 40 = 4 a. 0.25c = 0.25 x 40 = 10A.
   

Instructions for Use of
Lead-Acid Batteries Life Cycle of Lead-Acid Batteries The life-cycle
of lead-acid batteries depends on many factors. Generally, shallow-cycle batteries have about 200-300 charge-discharge cycles, but this number can be increased or decreased. The life cycle of such a battery depends on three factors: depth of discharge, correct charge cycle and temperature. A deep cycle battery can maintain a life cycle of around 1000, but what is a yellow cycle and a deep cycle? , you can find it below.

depth

Depth of discharge (DOD) means how much the battery is discharged. Let's assume you have a 100ah battery, you have discharged 20 minutes at 50A, so the depth of discharge is given as follows Concealment
time in hours = 20/60
Calculated discharge time = 50x20/60 = 16.7 a
discharge depth = (discharge/ Capacity) x100 = (16.7/100) x100 = 16.7%
According to the needs of batteries, they are divided into two categories, namely batteries with more than 50% on-demand capacity, deep cycle batteries, and
deep cycle batteries even if the depth of discharge exceeds 50%. Can maintain a life cycle of around 1000, while shallow cycle batteries can maintain their life cycle well, as shown in the figure below.

Shallow cycle battery capacity, depth of discharge and cycle life
Charging: If not charged correctly, it can lead to overcharging or undercharging, which also reduces the capacity of the battery.

Temperature: Temperature also affects the life cycle of the battery, the capacity of the battery is reduced in low temperature operation, and the high temperature operation increases the aging rate of the battery.

NiCd battery

First, the nickel-cadmium battery was invented in 1899 by Waldemar Jungner. Its positive electrode (cathode) is made of basic nickel oxide (NiO(OH)) and its negative electrode (anode) is made of metal cadmium (Cd). The electrolyte used was 30% potassium hydroxide in distilled water. The electrolyte level is maintained above the electrodes. There was no significant change in the electrolyte during charging and discharging.

Discharge of NiCd Batteries

This battery has about 2000 discharge/charge cycles.
Its nominal voltage is 1.2 volts per cell, its charging voltage is 1.55 volts, and it is fully discharged when the voltage drops to 1.1 volts, which can be increased by connecting cells in series. The capacity of the battery is determined by the manufacturer, and the capacity of the general AA battery is close to 1000mah.
Discharge of NiCd Batteries
When a load is connected to the terminal, the battery begins to discharge. Potassium hydroxide in potassium hydroxide (KOH) decomposes into potassium ions and hydroxyl ions. Hydroxyl (OH-) ions move towards the negative electrode. The negative electrode releases electrons and the positive electrode receives electrons through an external connection. This causes current to flow from positive to negative through the load.
Cd + 2OH ーーーー> Cd(OH)2 + 2e- Reaction on Negative Electrode
NiO(OH) + H2O + 2e- ーーーーーー> Ni(OH)2 + OH- Reaction on Positive Electrode
Full Reaction Cd + 2NiO (OH ) + 2H2O ーーーー> 2Ni(OH)2 + Cd(OH)2
The discharge rate varies with the size of the battery, a normal AA battery can provide about 1.8 amps, and a d-sized battery can provide about 3.5 amps.
Charging of NiCd Batteries
During charging, the charger is connected at the terminals. The reaction proceeds in reverse by discharge. The positive electrode converts nickel hydroxide to nickel hydroxide and releases electrons. Negative electrons gain electrons from external connections and convert Cd(OH)2 to Cd.

Charging
Ni(OH)2 + OH-ーーーーー> NiO(OH) + H2O + 2e - Reaction on Positive Electrode
Cd(OH)2 + 2e - ーーーーー> Reaction on Cd + 2OH Negative Electrode
Total Reaction 2ni (OH)2 + Cd (OH)2ーーー> Cd + 2NiO (OH) + 2H2O
At the end of the charge cycle, the battery will outgas, which can also happen when the battery is overcharged. From this gas, water in the electrolyte will be split into hydrogen at the negative electrode and oxygen at the positive electrode. This gas evolution depends on the voltage and temperature at which the battery is charged. To fully charge the nickel-cadmium battery, a small amount of gassing must be carried out to utilize part of the water in the electrolyte concentration.
There are two ways to charge NiCd batteries: slow charge and fast charge.

1. Slow charging:- The slow charging current is about 0.1 c, it will not damage the battery after full charge. This method is also used to overcome the self-discharge phenomenon of NiCd batteries.
2. Fast Charge:- During fast charge, the battery is charged at a constant current of about 1 degree Celsius. is the capacity of the battery, if you are using a 4ah battery then 1c means 1 x 4 = 4A. Once it is fully charged, it can be detected by the charge detection algorithm given below. The current will be reduced to 0.1 degrees Celsius, and trickle charging will be used. Trickle charging refers to charging at the same rate as the battery self-discharges. This will keep the battery fully charged.
   The full charge detection algorithm can use a two-factor negative increment v or temperature.
   If the temperature detection algorithm is used, the temperature is 45 degrees when fast charging and 50 degrees when slow charging.
   In the negative delta v detection algorithm, the voltage drops after full charge. Detection of such droplets can be used to detect the full charge state. This method is called negative increment v. This method provides accurate full charge detection.
   Nickel-metal hydride battery
   First, in 1967, the Battelle-Geneva Research Center invented the nickel-metal hydride battery. In 2005, Sanyo launched the Eneloop brand. In this type of battery, the positive electrode (cathode) is made of basic nickel oxide and the negative electrode (metal hydride). The electrolyte used was potassium hydroxide concentrated with distilled water.
   

NiMH battery
This battery has about 180-2000 discharge/charge cycles. It depends on various factors how you charge or discharge the battery.
This battery is almost similar to a nickel-cadmium battery. NiMH batteries have a nominal voltage of 1.2 v for a single cell. But when fully charged, the voltage is 1.5 v, and the fully discharged voltage is 1.0 v. The current capacity of this battery varies with its size, and a single AA battery can have a capacity close to 2000mah.
Discharge of NiMH Batteries
When a load is connected to the terminal, a discharge reaction begins. Metal hydride (MH) reacts with OH ions to form m and water, also releasing an electron. The electrons are carried away by NiO(OH) through the applied load. This causes current to flow through the load.

Charging of NiMH batteries
MH + OH - ーーーーーーーー> Reaction in m + H2O + e-
NiO(OH) + H2O + e- ーーーーーー> Ni(OH)2 + OH- Reaction on positive electrode
Overall reaction NiO(OH) + MH ーーー> Ni(OH)2 + m
Normally, NiMH batteries have a discharge rate of 3c (where c is the capacity of the battery, but high quality batteries can discharge at rates up to 15c.
NiMH batteries are charged
at When a charger is attached to the end of the battery, the charge reaction is the opposite of the discharge reaction. The positive electrode converts the nickel hydroxide to water and an electron is released. This electron is taken from the outer wire by the negative electrode and it from the MH again.

Charging of NiMH battery
Ni(OH)2 + OH-ーーーー> NiO(OH) + H2O + e- Reaction on positive electrode
Negative electrode m + H2O + e-ーーーーーー> MH + OH- reaction
Overall reaction Ni(OH) 2 + m ーーーーー> NiO (OH) + MH
Ni-MH battery charging chemistry using constant current and constant voltage algorithms, can be divided into four parts given below.

1. Charging:- When the battery is deeply discharged, the voltage of each battery is less than 0.9V. The maximum constant current used to charge the battery is 0.1 degrees Celsius, and this current is called trickle charging.
2. Constant Current:- When the voltage of each cell is higher than 0.9v, apply a constant current in the range of 0.2c to 1c for constant current charging.
3. Charging Terminal:- A fully charged battery can be detected by a complete charging detection algorithm, which is explained below. When fully charged, trickle charging is used at the rate of self-discharge to keep the battery fully charged.
   The full charge detection algorithm can use a two-factor negative increment v or temperature.
   If the algorithm uses temperature to detect, then the temperature will detect a full charge between 45 degrees and 50 degrees.
   In the negative delta v detection algorithm, the voltage drops after full charge. Detection of such droplets can be used to detect the full charge state. This method is called negative increment v. This method provides accurate full charge detection.

Lithium Ion Battery

First, Akira Yoshino developed a lithium-ion battery in 1985. The positive electrode (cathode) is made of lithium cobalt oxide and the negative electrode (anode) is made of graphite. Lithium salts are used as electrolytes as an organic solvent. Separator is used to separate the electrodes

Lithium-ion battery
The discharge/charge cycle of this battery is about 400-1200 cycles. It depends on various factors how you charge or discharge the battery.
Lithium-ion batteries are rated at 3.60 v. When the battery is fully charged, the voltage is about 4.2 v, and when the battery is fully discharged, the voltage is about 3.0 v. Lithium-ion batteries come in different sizes and shapes, and their capacities are also available on demand.
Discharging Li-Ion Batteries When the
battery is discharging, the load is connected to the terminal battery. Lithium ions are released from the negative electrode into the electrolyte. This lithium ion is absorbed by the positive electrode. The negative electrode also releases electrons that pass through the outer wire to the positive electrode. This supplies current to our circuit.

Discharge
of Li-ion battery (Li-ion battery discharge)
Lic6ーーーーー>C6+Li+e-Reaction on negative electrode
Coo_2+Li+e- ーーーーー>LiCoo_2Reaction on positive electrode
Full reaction LiC6+coo_2ーーーーー>C6+
LiCoO2Lithium Ion batteries can be discharged at a rate of 10c (where c is the capacity of the battery). If your battery can provide 1000mah then the discharge rate will be 10x1000 = 10000mAh.
Charging the
Li-Ion Battery When charging the Li-Ion battery, the battery is connected to the charger. The positive electrode loses a negatively charged electron. To maintain the charge balance on the negative electrode, equal amounts of positively charged ions are dissolved into the electrolyte solution. These lithium ions move to the positive electrode, where they are absorbed by the graphite. This absorption reaction also deposits electrons onto the graphite anode to "bind" lithium ions.

Charging of Lithium-Ion Batteries

Licoo2 ーーーーーーー> coo_2 + Li + e- Reaction on positive electrode
C6 + Li + + e- ーーーーー > lic6 Reaction on negative electrode
Full reaction C6 + licoo2 ーーーーー> LiC6 + CoO2
Li-ion battery charging chemistry using constant current and constant voltage The algorithm can be divided into four parts.
Charging:- When the batteries are deeply discharged, each battery is below 3.0 v. The maximum constant current used to charge the battery is 0.1 degrees Celsius, and this current is called trickle charging.
Constant Current:- When the voltage is higher than 3.0v per cell, apply constant current in the range of 0.2c to 1c for constant current charging.
Constant Voltage:- Constant current charging when the voltage reaches 4.2V per battery. Constant voltage until the battery's current drops to zero, which maximizes the battery's performance.
End-of-Charge: - End-of-Charge Detection Algorithm, detect current range drop to 0.02c to 0.07c or use timer method. It detects when a constant voltage phase starts and it terminates the charger after 2 hours of the constant voltage phase.

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