Power Batteries Basics

Ⅰ. The definition of power batteries

Power batteries are batteries that provide power for tools, mostly referring to batteries that provide power for electric vehicles, electric trains, electric bicycles, and golf carts.

At present, power batteries are mainly divided into two categories: one is lead-acid batteries, nickel-cadmium batteries and lithium-ion batteries; the other is fuel cells (including hydrogen-oxygen fuel cells, solid oxide fuel cells and methanol reforming hydrogen production ethanol) and other types of hybrid vehicle engines.

Power batteries are the core components of new energy vehicles and an important direction for future energy transformation.

Ⅱ. The structure of the power batteries

Power batteries are mainly divided into battery packs, modules, and batteries.

1. Battery pack

A battery pack is generally composed of a battery module, a thermal management system, a battery management system (BMS), an electrical system, and structural components.

2. Module

The battery module can be understood as the intermediate product of the battery cell and the pack formed after the combination of lithium-ion cells in series and parallel, and the addition of a single battery monitoring and management device. Its structure must support, fix and protect the battery core. Its basic components include: module control (commonly known as BMS slave board), battery cells, conductive connectors, plastic frame, cold plate, cooling pipes, pressure plates at both ends and a set of fastening components that combine these components pieces. In addition to gathering the single cells and providing a certain pressure, the pressure plates at both ends often also design the fixed structure of the module in the battery pack on it. The module is designed to facilitate battery management by BMS, improve battery safety, and facilitate maintenance and repair.

3. Battery

The battery cell is the smallest unit of a power battery and also an electrical energy storage unit. It must have a high energy density to store as much electrical energy as possible, so that electric vehicles have a longer cruising range. In addition, the battery life is also the most critical factor. The damage of any battery cell will lead to the damage of the whole battery pack.

The main working principle of the cell is to charge and discharge by the migration of lithium ions between the positive and negative electrodes. The charging process requires external energy, that is, grid power, which is equivalent to storing the grid's power in the battery. The discharge process can be completed spontaneously, which releases the stored energy. Batteries are divided into cylindrical batteries, pouch batteries and square batteries according to different structures.

Ⅲ. The basic concept of power batteries

1. Battery lifespan

The lifespan of the battery is divided into two parameters: cycle lifespan and calendar lifespan.

(1) The cycle lifespan refers to the number of times the battery can be charged and discharged, that is, the number of cycles experienced when the battery capacity decays to 80% when the battery is charged and discharged at the rated charge and discharge current under ideal temperature and humidity.

(2) Calendar lifespan refers to the time in which the battery reaches the end-of-life condition (generally, the capacity decays to 80%) under actual use conditions and after specific use conditions.

2. Energy/Power

Battery energy is an important indicator to measure the work done by the battery-driven equipment, and the capacity cannot determine the amount of work done. The battery is discharged according to a certain standard, and the energy (E) that the battery can release is in Wh (watt-hour) or KWh (kilowatt-hour), and 1KWh=1 kilowatt-hour.

There are basic concepts in physics books, E=U*I*t, which is also equal to the battery voltage multiplied by the battery capacity. The formula for power is, P=U*I=E/t, which represents the energy that can be released per unit time. Units are W (watts) or KW (kilowatts). Like a battery with a capacity of 1500mAh, the nominal voltage is generally 3.7V, so the corresponding energy is 5.55Wh.

3. Depth of Discharger (DOD)

The percentage of the capacity released by the battery to the rated capacity. Generally, the deeper the discharge depth of lithium batteries, the shorter the battery lifespan.

4. The consistency of the battery

Consistency is one of the manifestations in power batteries. After single batteries of the same specification and model form a battery pack, there are certain differences in parameters such as voltage, charge capacity, capacity and its decline rate, internal resistance and its change rate, life, temperature influence, and self-discharge rate. The consistency of lithium batteries refers to the convergence of these parameters, which is a relative concept. It is best for multiple strings of cells in the same battery pack and each parameter to be within a small range for good consistency. According to the reasons for the inconsistency of the power battery pack in use and the way it affects the performance of the power battery pack, we can divide the consistency of the power battery into capacity consistency, internal resistance consistency and voltage consistency.

5. Power and power density

① Power refers to the energy output by the battery per unit time under a certain discharge system, and the unit is W or kW.

② Power density, also known as specific power, is the output power of a battery per unit mass or unit volume, and the unit is W/kg or W/L. Specific power is an important indicator to evaluate whether batteries and battery packs meet the acceleration and climbing capabilities of electric vehicles.

6. Battery energy

Battery energy is the energy stored in the battery, energy (W h, watt hour) = voltage (V) * battery capacity (A h, ampere hour), for example: a battery marked as 3.6V/10A h, its energy is 36W·h. If we connect such four batteries in series, a battery pack with a voltage of 14.4V and a capacity of 10A h is formed. Generally peaking, if such four batteries are connected in parallel, a battery pack with a voltage of 3.6V and a capacity of 40A·h is formed. Although they have different forms, the total energy reaches 144 W h.

7. Energy density

Energy density is a commonly used parameter for power batteries. If it is a unit volume, that is, the volume energy density (the ratio of energy to volume), sometimes it is directly called the energy density, and the unit is W h/L; if it is a unit mass, that is, the mass energy density (the ratio of energy to weight), Sometimes also called specific energy, the unit is W·h/kg.

8. Capacity

Battery capacity refers to how much electricity the battery can store. Capacity is an important indicator of battery electrical performance, which is determined by the active material of the electrode. Capacity refers to the amount of electricity that can be obtained from battery lithium under certain discharge conditions. The capacity unit of the battery is specified as Ah (Ampere Hour) or mAh (milliampere Hour), which means that a 1AH battery can be discharged for 1 hour with a current of 1A when it is fully charged.

(1) Rated capacity: measured under specified conditions, the battery capacity given by the manufacturer.

(2) Usable capacity: the amount of electricity released from a fully charged battery under specified conditions.

(3) Theoretical capacity: Assuming that the active material is fully utilized, the capacity that the battery can release.

(4) Unit: The capacity is expressed in C, and the unit is expressed in Ah (Ampere Hour) or mAh (milliampere Hour).

Formula: C=It, that is, battery capacity (Ah) = current (A) x discharge time (h).

Influencing factors: The actual capacity of the battery mainly depends on the following factors: the quantity and quality of the active material, and the utilization rate of the active material.

9. Voltage

The voltage of the battery generally refers to the nominal voltage (also called the rated voltage) of the lithium battery. The nominal voltage of an ordinary lithium battery is generally 3.7V, and we also call its voltage platform 3.7V. The voltage we are talking about generally refers to the open circuit voltage of the battery.

① Open circuit voltage: refers to the voltage of the battery when it is not connected to an external circuit or external load. The open circuit voltage has a certain relationship with the remaining energy of the battery, and the power display uses this principle.

② Discharge cut-off voltage: refers to the voltage reached when the battery is fully charged and discharged (if it continues to discharge, it is over-discharged, which will damage the life and performance of the battery).

③ Limited charging voltage: The charging voltage changes from constant current to constant voltage during charging.

④ Working voltage: It refers to the potential difference between the positive and negative electrodes of the battery when the battery is in the working state, that is, when there is current flowing in the circuit, also known as the load voltage. In the working state of battery discharge, when current flows through the battery, it must overcome the resistance of internal resistance. Therefore, the operating voltage is always lower than the open circuit voltage.

10. Charge-Rate/Discharge-Rate

It indicates how much current to charge and discharge. Generally, it is calculated as a multiple of the nominal capacity of the battery, which is called a few C.

Like a battery with a capacity of 1500mAh, it is stipulated that 1C=1500mAh. If it is discharged at 2C, it is discharged at a current of 3000mA, and at 0.1C, it is charged and discharged at a current of 150mA.

11. Resistance

Since it cannot be equivalent to an ideal power supply when charging and discharging, it has a certain internal resistance. Internal resistance consumes energy, of course, the smaller the internal resistance, the better. The unit of battery internal resistance is milliohm (mΩ).

Ⅳ. The advantages of power batteries

1. Renewable energy

Power batteries can be combined with environmentally friendly energy sources such as solar and wind power. This means electric vehicles can be charged using cleaner and renewable energy sources, reducing the need for fossil fuels.

2. Be recycled

Power batteries can be recycled and reused through a special recycling system, which reduces the emission of harmful substances, and the recycled materials can also be used to produce new batteries. This recycling method helps reduce the impact of waste on the environment.

3. Reduce noise pollution

The popularity of power batteries can reduce noise pollution. The noise produced by the engine of traditional fuel vehicles has brought a lot of trouble to urban life. Electric vehicles are driven by electric motors, which run more quietly, effectively reduce traffic noise, and are also beneficial to the physical and mental health of residents.

4. No greenhouse gas emissions

Because electric vehicles use batteries for power, they emit almost no tailpipe emissions. In contrast, exhaust emissions from conventional vehicles are one of the main sources of greenhouse gases. Therefore, the popularization of electric vehicles can reduce greenhouse gas emissions and help mitigate climate change.

In short, power batteries have significant advantages in reducing greenhouse gas emissions, reducing noise pollution, charging with renewable energy, and recyclability. By adopting electric vehicles and energy storage systems, we can reduce carbon emissions and create a better living environment for our future.

Ⅴ. Features of the power battery industry

The power battery industry has the following features:

1. Corporate profitability will return to a steady state

Under the pressure of the slowdown in the growth rate of domestic electric vehicles and the cost reduction of auto companies, the gross profit margin of domestic power battery companies has fluctuated and declined. At present, the gross profit margin of mainstream enterprises such as Ningde Times and Guoxuan Hi-Tech is above 25%, and the steady-state gross profit rate is expected to be between 20% and 25%.

2. Industry concentration continues to increase

Whether domestic or foreign, the power battery industry has shown a trend of increasing concentration. In the domestic market, Ningde Times is the only one; in the global market, Ningde Times and LG Chem are currently in the first group. In terms of technology research and development, scale, cost, and customers, industry leaders have obvious advantages, strong anti-risk capabilities, and their status is difficult to shake.

Due to the capital-intensive and technology-intensive characteristics of the power battery industry, the leading position is expected to continue to strengthen, and the market share of the top five in the global industry is expected to reach more than 80% in the future.

3. High capital barriers

In terms of capital expenditure, a 1GWh battery production line requires an investment of 300-400 million yuan. Generally speaking, power batteries need to build a production capacity of more than 5GWh to have economies of scale. The capacity planning of global mainstream battery companies such as LG Chem, Samsung SDI, SKI, Panasonic, Ningde Times, BYD, etc. has reached more than 100GWh.

4. The scale of the industry is growing rapidly

With the acceleration of the transformation of automobile electrification at home and abroad, the installed capacity of batteries is expected to continue to maintain rapid growth. It is estimated that from 2020 to 2025, the compound growth rate of the industry will exceed 45%. In 2020, the global installed capacity of power batteries will be 137GWh. It is estimated that by 2025, the global power battery installed capacity will reach 940GWh, with a compound growth rate of more than 45%. As the scale of batteries continues to expand, the price of power batteries will continue to decline. If calculated according to the price of 0.45 yuan/Wh in 2025, the global scale of power batteries will be close to 420 billion yuan in 2025, and the industry is booming.

5. Fast technology iteration

From the perspective of technical considerations, there are mainly indicators such as low cost, high energy density, long life, and high safety. Lithium iron phosphate is expected to have strong competitiveness in low-endurance models. For high-end models, battery life is an important indicator. In the long run, the high-nickel ternary route will still be the mainstream development route. It is expected that the two technical routes will coexist in a long period of time in the future. Due to cost and safety considerations, the domestic passenger car market tends to turn to lithium iron phosphate in the short to medium term, while overseas still uses high-nickel ternary batteries as the main technical route.

In addition, the structure and process improvement of batteries are also the focus of enterprises. For example, the integrated design of the battery pack is to reduce the number of modules used or even not use modules, and install them directly from the battery cell to the battery pack (CTP) in one step. The battery technology iterates quickly, which means that continuous investment in research and development is required to maintain the leading and forward-looking technology. Small and medium-sized enterprises have disadvantages in technology research and development and capital, and the first-mover advantage of leading companies is expected to be maintained for a long time.

Ⅵ. What is the power rating of a battery?

The capacity of a battery is generally rated and labelled at the 1C Rate (1C current), this means a fully charged battery with a capacity of 10Ah should be able to provide 10 Amps for one hour.

Ⅶ. What is 12V and 24V battery?

What Does “12V” Mean? 12V tells us that the battery supplies 12 volts under a nominal load. The same principle holds for a 24V battery bank in that it provides 24 volts. As we discussed before, most car and RV batteries are 12V.

Ⅷ. What is a cell in a battery?

A cell is a single-unit device which converts chemical energy into electric energy. A battery usually consists of a group of cells. Depending on the types of electrolytes used, a cell is either reserved, wet or dry types.