Frequently Asked Questions (FAQ)

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Basic Principles and Basic Terminology of Batteries

What are the differences between primary batteries and secondary batteries?

The main difference lies in the active materials. The active materials of secondary batteries are reversible, while those of primary batteries are not. Primary batteries have much lower self-discharge than secondary batteries, but their internal resistance is much higher, resulting in lower load capacity. In addition, the gravimetric capacity and volumetric capacity of primary batteries are both higher than those of typical rechargeable batteries.

NiMH batteries use nickel oxide as the positive electrode, hydrogen storage alloy as the negative electrode, and an alkaline solution (mainly KOH) as the electrolyte.

During charging:

  • Positive electrode reaction: Ni(OH)₂ + OH⁻ → NiOOH + H₂O – e⁻

  • Negative electrode reaction: M + H₂O + e⁻ → MH + OH⁻

During discharging:

  • Positive electrode reaction: NiOOH + H₂O + e⁻ → Ni(OH)₂ + OH⁻

  • Negative electrode reaction: MH + OH⁻ → M + H₂O + e⁻

The main component of the cathode in lithium-ion batteries is LiCoO₂, while the anode is mainly carbon (C). During charging:

  • Cathode reaction: LiCoO₂ → Li₁₋ₓCoO₂ + xLi⁺ + xe⁻

  • Anode reaction: C + xLi⁺ + xe⁻ → CLiₓ

  • Overall reaction: LiCoO₂ + C → Li₁₋ₓCoO₂ + CLiₓ

During discharging, the reverse of the above reactions takes place.

Common IEC standards for batteries: the standard for nickel-metal hydride (NiMH) batteries is IEC61951-2:2003; the lithium-ion battery industry generally follows UL or national standards.

Common national standards for batteries: the standards for NiMH batteries are GB/T15100-1994 and GB/T18288-2000; the standards for lithium batteries are GB/T10077-1998, YD/T998-1999, and GB/T18287-2000. In addition, commonly used standards for batteries also include the Japanese Industrial Standards (JIS C) related to batteries.

IEC, the International Electrotechnical Commission, is a global standardization organization composed of national electrotechnical committees. Its purpose is to promote standardization in the field of electrical and electronic engineering worldwide. IEC standards are the standards established by the International Electrotechnical Commission.

The main components of NiMH batteries are: positive electrode plate (nickel oxide), negative electrode plate (hydrogen storage alloy), electrolyte (mainly KOH), separator, sealing ring, positive electrode cap, and battery casing, etc.

The main components of lithium-ion batteries are: cathode plate (active materials include lithium cobalt oxide, ternary materials, or lithium iron phosphate), separator (a special type of composite film), anode (active material is carbon), organic electrolyte, and battery casing (which can be steel case, aluminum case, or aluminum-plastic composite film).

It refers to the resistance encountered by current flowing inside the battery during operation. It consists of two parts: ohmic resistance and polarization resistance. A large internal resistance will cause the battery’s discharge operating voltage to drop and shorten the discharge time. The internal resistance is mainly affected by factors such as battery materials, manufacturing process, and cell structure. It is an important parameter for evaluating battery performance. Note: Internal resistance is generally specified in the charged state. The measurement of battery internal resistance requires a dedicated internal resistance tester and cannot be performed using the ohm range of a multimeter.

The nominal voltage of a battery refers to the voltage exhibited during normal operation. The nominal voltage of secondary nickel-cadmium and nickel-metal hydride batteries is 1.2V; the nominal voltage of secondary lithium batteries is generally 3.7V.

Open-circuit voltage refers to the potential difference between the positive and negative terminals of a battery when it is not operating, that is, when no current flows through the circuit. Operating voltage, also called terminal voltage, refers to the potential difference between the positive and negative terminals of a battery when it is operating, that is, when current flows through the circuit.

For nickel-metal hydride (NiMH) rechargeable batteries, the discharge plateau generally refers to the voltage range where the battery’s operating voltage remains relatively stable during discharge under a certain discharge regime. Its value is related to the discharge current—the higher the current, the lower the value. For lithium-ion batteries, the discharge plateau is generally defined as the discharge time when the battery, after being fully charged to 4.2V at constant voltage and with a current less than 0.01C, rested for 10 minutes, is discharged to 3.7V at any given discharge current. The discharge plateau is an important criterion for evaluating battery quality.

  • Low cost.

  • Good fast-charging performance.

  • Long cycle life.

  • No memory effect.

  • Non-polluting, environmentally friendly (green) battery.

  • Wide operating temperature range.

  • Good safety performance.

  • High energy density.

  • High operating voltage.

  • No memory effect.

  • Long cycle life.

  • Non-polluting.

  • Lightweight.

  • Low self-discharge.

Lithium iron phosphate batteries are mainly used as power batteries, and their advantages are mainly reflected in the following aspects:

  • Ultra-long lifespan.

  • Safe to use.

  • Capable of high-current fast charging and discharging.

  • High-temperature resistance.

  • Large capacity.

  • No memory effect.

  • Compact size and lightweight.

  • Environmentally friendly (green).

  • No leakage problem, as the battery contains no liquid electrolyte and uses a gel-like solid electrolyte.

  • Can be made into thin batteries, with thickness as low as 0.2 mm.

  • Can be designed in various shapes.

  • Can be bent or deformed: polymer batteries can be bent up to approximately 90°.

  • Can achieve high voltage in a single cell: batteries with liquid electrolytes require multiple cells in series to obtain high voltage, whereas polymer batteries can achieve high voltage in a single cell.

  • Because there is no liquid inside, multiple layers can be combined within a single cell to reach high voltage.

  • Capacity can be twice that of a lithium-ion battery of the same size.

Battery Performance and Testing

What aspects are generally included in the performance of secondary batteries?

They mainly include voltage, internal resistance, capacity, self-discharge rate, cycle life, sealing performance, safety performance, storage performance, appearance, etc.

They mainly include: cycle life, discharge characteristics at different rates, discharge characteristics at different temperatures, charge characteristics, self-discharge characteristics, over-discharge characteristics, temperature cycling test, drop test, vibration test, capacity test, mechanical shock test, and high-temperature/high-humidity test.

Pulse charging generally adopts a charge-and-discharge method, that is, charging for 5 seconds and then discharging for 5 seconds. During this process, most of the gas generated in the charging process is reduced back into the electrolyte during the discharge pulse. This not only limits the amount of electrolyte vaporization inside the battery, but also, for older batteries that are already heavily polarized, using this charge-and-discharge method 5–10 times can gradually restore or approach their original capacity.

Trickle charging is used to compensate for the capacity loss of a battery caused by self-discharge after it is fully charged. This is generally achieved by charging with a small current, for example, at 0.01C.

Charging efficiency refers to the measure of the extent to which the electrical energy consumed during the charging process is converted into chemical energy stored in the battery. It is mainly affected by the battery manufacturing process and the working environment temperature of the battery.

Discharge efficiency refers to the ratio of the actual capacity delivered when discharging to the end-point voltage under certain discharge conditions to the rated capacity. It is mainly affected by factors such as discharge current and ambient temperature. In general, the higher the discharge rate, the lower the discharge efficiency. The lower the temperature, the lower the discharge efficiency.

The output power of a battery refers to its ability to deliver energy per unit time. It is calculated based on the discharge current I ,and the discharge voltage U, using the formula P=U×I, with the unit being watts.

The smaller the internal resistance of the battery, the higher the output power. The internal resistance of the battery should be smaller than that of the appliance; otherwise, the power consumed by the battery itself would exceed that consumed by the appliance, which is uneconomical and may also damage the battery.

Self-discharge, also known as charge retention capability, refers to the ability of a battery to retain its stored charge under certain environmental conditions when in an open-circuit state. In general, self-discharge is mainly affected by manufacturing processes, materials, and storage conditions. It is one of the main parameters for evaluating battery performance. Generally speaking, the lower the storage temperature of the battery, the lower the self-discharge rate. However, it should also be noted that excessively low or high temperatures may cause battery damage and make it unusable.

Charged-state internal resistance refers to the internal resistance of a battery when it is fully charged (100%), while discharged-state internal resistance refers to the internal resistance of a battery after it has been fully discharged.

In general, discharged-state internal resistance is less stable and relatively higher, whereas charged-state internal resistance is lower and more stable. During battery usage, only the charged-state internal resistance has practical significance. In the later stages of battery life, due to electrolyte depletion and reduced activity of internal chemical substances, the internal resistance of the battery will increase to varying degrees.

It refers to the internal gas pressure of a battery, caused by gases generated during the charge and discharge processes of a sealed battery. It is mainly affected by battery materials, manufacturing processes, and battery structure. The primary cause is the accumulation of gases produced by the decomposition of internal moisture and organic solvents within the battery.

Generally, the internal pressure of a battery remains at a normal level. Under overcharge or over-discharge conditions, the internal pressure may rise. For example, during overcharging:

  • Positive electrode: 4OH⁻ – 4e⁻ → 2H₂O + O₂↑ ①

  • The generated oxygen reacts with hydrogen evolved at the negative electrode to form water: 2H₂ + O₂ → 2H₂O ②

  • If the reaction in step ② proceeds slower than that in step ①, the oxygen generated cannot be consumed in time, resulting in an increase in the battery’s internal pressure.

Common Battery Issues and Analysis

Which certifications have the company’s products obtained?

The company has obtained ISO9001:2000 quality management system certification and ISO14001:2004 environmental management system certification. Its products have received the European CE certification and North American UL certification, and have passed SGS environmental testing. In addition, the company’s products are globally insured by PICC.

Currently, nickel-cadmium (NiCd), nickel-metal hydride (NiMH), and lithium-ion (Li-ion) rechargeable batteries are widely used in various portable devices such as laptops, camcorders, and mobile phones. Each type of rechargeable battery has its own unique chemical properties.

The main difference between NiCd and NiMH batteries is that NiMH batteries have a higher energy density. Compared with batteries of the same model, the capacity of NiMH batteries is roughly twice that of NiCd batteries. This means that using NiMH batteries can significantly extend device operating time without adding extra weight to the device. Another advantage of NiMH batteries is that they greatly reduce the “memory effect” present in NiCd batteries, making NiMH batteries more convenient to use. NiMH batteries are also more environmentally friendly than NiCd batteries because they contain no toxic heavy metals.

Lithium-ion batteries have rapidly become the standard power source for portable devices. Li-ion batteries can provide the same energy as NiMH batteries but reduce weight by approximately 35%, which is crucial for devices such as camcorders and laptops. The absence of “memory effect” and the lack of toxic substances are also important reasons that make Li-ion batteries the preferred standard power source.

The discharge efficiency of NiMH batteries decreases significantly at low temperatures. In general, the charging efficiency increases with rising temperature. However, when the temperature exceeds 45°C, the performance of the battery materials degrades under high temperature, and the cycle life of the battery is significantly shortened.

Rate discharge refers to the relationship between the discharge current (A) and the rated capacity (A·h), expressed as a multiple. Hour-rate discharge refers to the number of hours required to discharge the rated capacity at a specified output current.

In digital cameras, the activity of battery active materials is greatly reduced at very low temperatures, which may prevent the battery from supplying the normal operating current required by the camera. Therefore, when shooting outdoors in cold regions, special attention must be paid to keeping the camera or battery warm.

It is not recommended to combine batteries of different capacities. The reasons are as follows:

  1. Uneven discharge: Batteries of different capacities have different discharge rates and voltage drop curves. Smaller-capacity batteries will be depleted first, which may cause the circuit to shut down prematurely or result in over-discharge.

  2. Impact on lifespan: Repeated deep discharge of smaller-capacity batteries accelerates their aging, while larger-capacity batteries may not be able to deliver their full capacity due to current limitations.

  3. Safety risks: Capacity mismatch may cause increased internal pressure, overheating of the electrolyte, or even leakage, posing safety hazards.

If it is necessary to combine batteries of different capacities, ensure that they have the same brand, chemical system, and voltage, and preferably use a professional Battery Management System (BMS) for balance control.

An external short circuit occurs when the two terminals of a battery are connected by any conductor. Different types of batteries may experience varying degrees of consequences from a short circuit, such as increased electrolyte temperature and elevated internal gas pressure. If the internal pressure exceeds the pressure tolerance of the battery cap, the battery may leak, causing severe damage. If the safety valve fails, it may even lead to an explosion. Therefore, batteries must never be externally short-circuited.

  1. Charging: When selecting a charger, it is best to use one equipped with proper charge termination devices, such as overcharge protection timers, negative delta voltage (-dV) cut-off, and overheat sensors, to prevent battery lifespan reduction due to overcharging. In general, slow charging prolongs battery life more effectively than fast charging.

  2. Discharging:
    a. Depth of discharge is the main factor affecting battery life. The deeper the discharge, the shorter the battery’s lifespan. In other words, reducing the depth of discharge can significantly extend battery life. Therefore, batteries should not be over-discharged to very low voltages.
    b. Discharging at high temperatures shortens battery life.
    c. If an electronic device cannot completely stop all current, leaving the battery inside while the device is unused for a long time may lead to excessive consumption due to residual current, causing over-discharge.
    d. Mixing batteries of different capacities, chemical compositions, charge levels, or ages may also result in excessive discharge and even reverse charging.

  3. Storage environment: Long-term storage of batteries at high temperatures can reduce electrode activity and shorten battery life.

  • External short circuit, overcharge, or reverse charge (forced over-discharge) of the battery.

  • High-rate, large-current continuous overcharging, causing the battery core to swell and direct contact short circuit between the positive and negative electrodes.

  • Internal short circuit or micro-short circuit, such as improper placement of positive and negative plates causing electrode contact short circuit, or contact between positive and negative electrode plates.

  • Whether any single cell has zero voltage.

  • Short circuit or open circuit at the connector, or poor connection with the connector.

  • Leads detached from the battery, cold solder joints, or poor soldering.

  • Internal battery connection errors, such as missing solder, cold solder joints, or detached connections between connecting tabs and the battery.

  • Incorrect connection or damage of internal electronic components within the battery.

  • The battery has aged and its capacity has degraded after storage or use.

  • Insufficient charging or no charging.

  • Ambient temperature is too low.

  • Low discharge efficiency, for example, during high-current discharge, ordinary batteries may experience a rapid voltage drop because the diffusion rate of internal materials cannot keep up with the reaction rate, preventing effective discharge.

  • The battery is not fully charged, for example, due to insufficient charging time or low charging efficiency.

  • The discharge current is too high, causing reduced discharge efficiency and thus a shorter discharge time.

  • The ambient temperature during discharge is too low, resulting in decreased discharge efficiency.

Battery Types and Application Fields

What types of batteries are there?

Chemical Batteries:

  • Primary Batteries: carbon-zinc dry batteries, alkaline-manganese batteries, lithium batteries, activated batteries, zinc-mercury batteries, cadmium-mercury batteries, zinc-air batteries, zinc-silver batteries, and solid electrolyte batteries (silver-iodine batteries), etc.

  • Secondary Batteries: lead-acid batteries, nickel-cadmium (Ni-Cd) batteries, nickel-metal hydride (Ni-MH) batteries, lithium-ion (Li-ion) batteries, sodium-sulfur batteries, etc.

  • Other Batteries: fuel cells, air batteries, thin batteries (paper batteries), light batteries (photoelectric batteries), nano batteries, etc.

Physical Batteries:

  • Solar cells.

A smart battery contains a built-in chip that not only supplies power to the device but also controls its main functions. This type of battery can display remaining capacity, the number of cycles completed, temperature, and other information. However, smart batteries are not yet available on the market, but they are expected to dominate the market in the future—especially in portable camcorders, cordless phones, mobile phones, and laptop computers.

A paper battery is a new type of battery, which also consists of electrodes, electrolyte, and a separator. This innovative paper battery is made from cellulose paper embedded with electrodes and electrolyte, with the cellulose paper serving as the separator. The electrodes are carbon nanotubes incorporated into the cellulose and metallic lithium coated on a film made of cellulose, while the electrolyte is a lithium hexafluorophosphate solution. This type of battery is foldable and has a thickness comparable to that of paper.

A photoelectric cell is a semiconductor device that generates electromotive force when exposed to light. There are many types of photoelectric cells, commonly including selenium cells, silicon cells, thallium sulfide cells, and silver sulfide cells. They are mainly used in instruments, automated telemetry, and remote control applications. Some photoelectric cells can directly convert solar energy into electrical energy; these cells are also called solar cells.

A fuel cell is an electrochemical system that directly converts chemical energy into electrical energy. The most common method of classification is based on the type of electrolyte. According to this, fuel cells can be divided into:

  1. Alkaline fuel cells, which use potassium hydroxide as the electrolyte;

  2. Phosphoric acid fuel cells, which use concentrated phosphoric acid as the electrolyte;

  3. Proton exchange membrane fuel cells, which use fully fluorinated or partially fluorinated sulfonic acid proton exchange membranes as the electrolyte;

  4. Molten carbonate fuel cells, which use molten lithium-potassium carbonate or lithium-sodium carbonate as the electrolyte;

  5. Solid oxide fuel cells, which use solid oxides as oxygen ion conductors, such as yttria-stabilized zirconia membranes as the electrolyte.

Fuel cells can also be classified according to their operating temperature:

  • Low-temperature fuel cells (operating below 100°C), including alkaline fuel cells and proton exchange membrane fuel cells;

  • Medium-temperature fuel cells (operating between 100–300°C), including Bacon-type alkaline fuel cells and phosphoric acid fuel cells;

  • High-temperature fuel cells (operating between 600–1000°C), including molten carbonate fuel cells and solid oxide fuel cells.

A nano battery is a battery made using nanomaterials (such as nano MnO₂, LiMn₂O₄, Ni(OH)₂, etc.), where “nano” refers to 10⁻⁹ meters. Nanomaterials possess special microstructures and unique physicochemical properties, such as quantum size effects, surface effects, and quantum tunneling effects. Currently, the most mature nano battery technology in China is the nano activated carbon fiber battery. It is mainly used in electric vehicles, electric motorcycles, and electric-assisted bicycles. This type of battery can be recharged and cycled 1,000 times, with continuous usage lasting about 10 years. A single charge takes only about 20 minutes, allowing a flat-road range of 400 km, with a weight of 128 kg. This already surpasses the level of battery vehicles produced in the U.S., Japan, and other countries, whose nickel-metal hydride batteries require approximately 6–8 hours to charge and achieve a flat-road range of 300 km.

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