battery blog

Comparison of Cobalt and Manganese as positive electrodes

Chemicals and additives help to balance the critical trade-off between high energy density, long storage time, extended cycle life and safety. High energy densities can be achieved with relative ease. For example, adding more nickel in lieu of cobalt increases the ampere/hours rating and lowers the manufacturing cost but makes the cell less safe. While a start-up company may focus on high energy density to gain quick market acceptance, safety, cycle life and storage may be compromised. Reputable manufacturers, such as Dell,IBM,Compaq,NEC,Sony,Toshiba,HP,Acer,Apple, Fujitsu,Asus and E-One Moli place high importance on safety.

Lithium-ion cells cause less harm when disposed than lead or cadmium based batteries. Among the lithium-ion battery family, the spinel is the friendliest in terms of disposal.

Charging the Li-ion battery

The lithium-ion charger is a voltage-limiting device that is similar to the lead acid Dell 310-6321 battery , Dell 310-6322 battery charger with the differences of a higher voltage per cell, tighter voltage tolerance and the absence of trickle or float charge at full charge.

Whereas the Valve Regulated Lead Acid (VRLA) offers some flexibility in terms of voltage cut off, the manufacturers of lithium-ion Dell Inspiron 9300 battery are very strict about the voltage choice. When first introduced, the charge voltage limit of the graphite system was 4.10 volts per cell. Although higher voltages deliver increased energy density, cell oxidation severely limited the service life in the early graphite cells if charged above the 4.10V/cell threshold. This effect has now been solved with chemical additives, and most new lithium-ion cells are now set to 4.20V. The tolerance on all lithium-ion batteries is a tight +/- 0.05 volts per cell.

The charge time of all lithium-ion Dell 312-0068 battery , Dell 6Y270 battery is about 3 hours at a 1C initial charge current, and the battery remains cool during charge. Full charge is attained after the voltage reaches the upper voltage threshold, and the current drops and levels off at about 3% of its nominal rating, or about 0.03C.

Increasing the charge current on a lithium-ion charger does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer. Figure 3 shows the voltage and current signature of a charger as the lithium-ion cell passes through stage one and two.

Figure 3:  Charge stages of a Li-ion Battery.
Increasing the charge current on a lithium-ion charger does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer.

Claims of fast charging a Li-ion Dell Inspiron 500m battery,Dell Inspiron 510m battery in one hour or less usually results in lower charge levels. Such a charger simply eliminates stage two and goes directly into ‘ready’ once the voltage threshold is reached at the end of stage one. The charge level at this point is about 70%. The topping charge typically takes twice as long as the initial charge.

No trickle charge is applied because the Li-ion is unable to absorb overcharge. Trickle charge could cause plating of metallic lithium, a condition that makes the cell unstable. Instead, a brief topping charge is applied to compensate for the small amount of self-discharge the Dell Inspiron 5100 battery , Dell 6T473 battery and its protective circuit consume.

Depending on the charger and the self-discharge of the Dell Inspiron E1505 battery , a topping charge may be implemented once every 500 hours or 20 days. Typically, the charge kicks in when the open terminal voltage drops to 4.05 volts per cell and turns off when it reaches 4.20V/cell.

Protection circuit

Commercial lithium-ion HP Pavilion DV1000 battery , HP PF723A battery packs contain redundant protection devices to assure safety under all circumstances. Typically, a solid-state switch opens if the charge voltage of any cell reaches 4.30V, and a fuse activates if the cell temperature approaches 90°C (194°F). In addition, a pressure switch in each cell permanently interrupts the charge current if a safe pressure threshold is exceeded, and internal voltage control circuits cut off the battery at low and high voltage points. Exceptions are made to prismatic and cylindrical spinel packs containing one or two cells only.

The lithium-ion is typically discharged to 3 volts per cell. The lowest 'low-voltage' power cut-off is 2.5V/cell. During prolonged storage, however, a discharge below this voltage level is possible. Manufacturers recommend a 'trickle' charge to raise such a HP Pavilion dv2000 battery , HP HSTNN-LB31 battery gradually back up into the 'acceptable' voltage window. Not all chargers are designed to apply a charge once a lithium-ion battery has dipped below 2.5V/cell.

Some batteries feature an ultra-low voltage cutoff that permanently disconnects the pack if a cell dips below 1.5 volts. This precaution is done to prohibit recharge if a battery has dwelled in an illegal voltage state. A deep discharge causes copper plating, which can lead to short circuit in the cell.
Most manufactures do not sell the lithium-ion cells by themselves but make them available in a battery pack, complete with protection circuit. This precaution is understandable when considering the danger of explosion and fire if the HP F4486B battery ,F4486A ,HP CGR-B1870AE battery is charged and discharged beyond safe limits.

A major concern arises if static electricity or a faulty charger has managed to destroy the battery's protection circuit. Such damage often causes the solid-state switches to fuse to a permanent ON position without the user's knowledge. A battery with a faulty protection circuit may function normally but will not provide the required safely. If charged beyond safe voltage limits with a poorly designed accessory charger, the battery may heat up, then bulge and in some cases vent with flame. Shorting such a HP PP2182D battery , HP 338794-001 battery , HP PP2182L battery can also be hazardous.

Analyzers for the Lithium Ion batteries

In the past, battery analyzers were used to restore batteries affected by 'memory'. With today's nickel-free batteries, memory is no longer a problem and the emphasis of an analyzer is shifting to battery performance verification, quality control and quick-test.

Conventional wisdom says that a new HP Pavilion ZT3000 battery , HP 337607-001 battery , HP 337607-003 battery always performs flawlessly. Yet many users have learned that a battery fresh from the shrink-wrap does not always meet the manufacturer's specifications. With a battery analyzer, all incoming batteries can be checked as part of a quality control procedure. In addition, warranty claims can be made if the capacity drops below the specified level at the end of the warranty period.

A typical life of a lithium-ion is 300-500 discharge/charge cycles or about three years from time of manufacturing. The loss of battery capacity occurs gradually and often without the knowledge of the user. Although fully charged, the battery eventually regresses to a point where it may hold less than half of its original capacity. The function of the battery analyzer is to identify these weak Sony VGP-BPS3 battery , Sony VGP-BPS5 battery  and "weed' them out.

A battery analyzer can also be used to troubleshoot the cause of short runtimes, some can simulate the load signature of a digital device and verify the runtime based on the available PA3107U-1BRS , PA3383U-1BRS , PA3384U-1BRS  capacity.
An important feature of modern battery analyzers is its ability to read the internal battery resistance, a test that only takes a few seconds to complete. As part of natural aging, the internal resistance of the cobalt lithium-ion gradually increases due to cell oxidation. The higher the resistance, the less energy the battery can deliver. On the manganese lithium-ion, the resistance stays low but the capacity drops.

A more reliable method of measuring the state-of-health of a battery is through quick-test methods. Cadex has developed a system that uses an inference algorithm to test battery capacities. The QuickTest™ algorithm is made battery-specific by using a trend-learning algorithm that resembles the thinking process of the human brain. QuickSort™ uses a generic matrix and services the vast pool of single cell lithium-ion A1175 , A1185 , M9324 , M8403 , M7318 for cell phones.

Summary

Lithium-ion has found a strong market niche for portable devices demanding small form-factor and light weight. The high energy cobalt version is popular for cell phones, cameras and laptop computers; the rugged but lower energy-dense manganese and phosphate variants are employed for high current applications such as power tools, medical instruments, and soon also the hybrid car and electric vehicle.

Lithium-ion has proven less favorable for a laptop that is mostly powered by AC. High heat on a fully charge A1079 , A1078 cause premature aging. Most battery chemistries suffer from this phenomenon