Showing papers on "Lithium-ion battery published in 1999"

Battery set structure and charge/discharge control apparatus for lithium-ion battery

Abstract: In a battery-driven portable computer, a battery pack is constituted by m battery sets connected in series each including n lithium-ion secondary battery cells connected in parallel. A voltage monitor for monitoring the voltage of the terminal electrode of each battery set and a charger for independently appropriately charging each battery set in accordance with a monitor result are arranged, thereby realizing battery driving by a lithium-ion secondary battery pack having a large capacity.

AC impedance and state-of-charge analysis of a sealed lithium-ion rechargeable battery

Abstract: A 7.2V, 1.25 Ah sealed lithium-ion rechargeable battery has been studied for estimating its state-of-charge (SOC) by AC impedance. The dispersion of impedance data over the frequency range between 100 kHz and 25 mHz comprises an inductive part and two capacitive parts. As the inductive behaviour of the battery is attributed to the porous nature of the electrodes, only the capacitive components have been examined. The data obtained at several SOC values of the battery have been analyzed by a non-linear least-squares fitting procedure. The presence of two depressed semicircles in the capacitive region of the Nyquist plots necessitated the use of an electrical equivalent circuit containing constant phase elements instead of capacitances. The impedance parameters corresponding to the low-frequency semicircle have been found useful for predicting the SOC of the battery, mainly because the magnitude of these parameters and their variations are more significant than those of the high-frequency semicircle. The frequency maximum (f(max)) of the semicircle, the resistive component (Z') corresponding to f(max), the phase angle (phi) in the 5.0 Hz-0.1 Hz frequency range, the equivalent series resistance (R-s) and the equivalent series capacitance (C-s) have been identified as suitable parameters for predicting the SOC values of the lithium-ion battery.

Corrosion of Lithium‐Ion Battery Current Collectors

Abstract: The primary current‐collector materials being used in lithium‐ion cells are susceptible to environmental degradation: aluminum to pitting corrosion and copper to environmentally assisted cracking. Localized corrosion occurred on bare aluminum electrodes during simulated ambient‐temperature cycling in an excess of electrolyte. The highly oxidizing potential associated with the positive‐electrode charge condition was the primary factor. The corrosion mechanism differed from the pitting typically observed in aqueous electrolytes because each site was filled with a mixed metal/metal‐oxide product, forming surface mounds or nodules. Electrochemical impedance spectroscopy was shown to be an effective analytical tool for characterizing the corrosion behavior of aluminum under these conditions. Based on X‐ray photoelectron spectroscopy analyses, little difference existed in the composition of the surface film on aluminum and copper after immersion or cycling in electrolytes made with two different solvent formulations. Although Li and P were the predominant adsorbed surface species, the corrosion resistance of aluminum may simply be due to its native oxide. Finally, copper was shown to be susceptible to environmental cracking at or near the lithium potential when specific metallurgical conditions existed (work hardening and large grain size). © 1999 The Electrochemical Society. All rights reserved.

Battery cell bypass topology

Abstract: When the cell of a battery, most notably a lithium ion battery, fails and human intervention is unavailable to correct the problem. a system is provided for optimizing the energy storage capacity of the battery. At least two strings (46, 48), each including a plurality of battery cells (52), connected electrically in series. All strings (46, 48, 50) contain the same number of battery cells (52) and are electrically connected in parallel to form a battery array (42) powering a load (44). A sensor (56) detects the condition of each battery cell (52) and sends a signal of the detected condition to a controller (54) for operating the battery array (42) for powering the load (44). A switching arrangement (62) is responsive to the sensor (56), upon failure of a battery cell (52) in one string (46), for disconnecting at least one other battery cell (52) of the battery array such that, thereafter, the modified battery array continues to power the load with reduced but optimized capacity. In one instance, the switching arrangement (62) is operable, upon failure of the battery cell (52) in one string (46) to disconnect that cellular string (46) from the remaining cellular strings (48,50) which, thereafter, alone continue to power the load. In another instance, the switching arrangement (62) is operable, upon failure of the battery cell (52) in one cellular string (46), to disconnect a battery cell (52) from each of the remaining cellular strings (48, 50) whereby all of the cellular strings continue, as originally, to have an equal, albeit reduced, number of active battery cells (52), the modified battery array (42) continuing to power the load (44).

In situ Characterization of a Graphite Electrode in a Secondary Lithium-Ion Battery Using Raman Microscopy:

Abstract: A Raman microscopy study of lithium intercalation into the graphite electrode of a lithium-ion battery is presented. An in situ spectroelectrochemical cell was designed for direct observation of the electrode/electrolyte interface. The performance of this cell is discussed in terms of the results of a calibration experiment performed at a single defined point on the electrode surface. The electrode was made of TIMREX SFG 44 synthetic graphite with polyvinylidene fluoride binder. The electrolyte was lithium perchlorate, LiClO4, dissolved in a mixture of ethylene carbonate and dimethyl carbonate. In the region of the carbonyl stretching vibrational modes of the electrolyte components, changes in the band profile have been observed. At electrode potentials negative to 180 mV vs. Li/Li+, a new band evolved at about 1850 cm-1. This band has tentatively been assigned to a complex between lithium ions and decomposition products of the ethylene carbonate electrolyte component. The maximum intensity of this new band is observed at 5 mV vs. Li/Li+; its intensity decreases with increasing potential upon lithium de-intercalation. Raman mapping of the graphite electrode under potentiostatic conditions indicates that lithium intercalation does not proceed homogeneously over the graphite electrode surface at a potential of 200 mV vs. Li/Li+. An additional Raman mapping study was performed under galvanostatic conditions. With this method, the presence of "blind spots" on the electrode surface can be detected. These points lag behind in the process of lithium intercalation. Furthermore, information on changes in the carbon component of the electrode can be inferred from these measurements.

Battery charger for charging a stack of multiple lithium ion battery cells

Abstract: A battery charging apparatus for charging a stack of multiple lithium ion battery cells charges the stack by a combination of switched capacitance cell balancing and cell voltage monitoring to provide a charge cycle that starts with a nominally constant current charging and easily shifts to constant voltage taper charging.

Battery cell bypass module

Abstract: A battery cell bypass module comprises a sensor for detecting an operating condition of a battery cell such as voltage or temperature and a controller connected across the battery cell of a lithium ion battery, for example, and having a conductive mode and a normally non conductive mode The controller is operable to change to the conductive mode when an operating condition of the battery cell exceeds a predetermined value to thereby shunt current around the battery cell The sensor may be a temperature transducer such as a thermistor for measuring battery cell temperature and a cell temperature comparator such as an operational amplifier is operable to generate a temperature excessive signal when the signal from the temperature transducer exceeds a predetermined value, the controller then being operable to change to the conductive mode and thereby shunt current around the battery cell The sensor may also be a voltage comparator, also an operational amplifier, for measuring voltage across the cell, the controller being operable in response to a voltage excessive signal to change the controller to the conductive mode and thereby shunt current around the battery cell The controller includes a voltage limiting operational amplifier operable for transmitting a voltage excessive output signal when the input thereto exceeds a predetermined value and a transistor having a predetermined gate voltage allowing bypass current flow, the transistor being responsive to the voltage excessive output signal from the voltage limiting operational amplifier to shunt current around the battery cell

State of charge indicator

Abstract: A state of charge indicator of a lithium ion battery computes a state of charge (SOC) corresponding to a cell open circuit voltage from a SOC-cell open circuit voltage characteristic map, and displays the SOC on a display device. Herein, the SOC-cell open circuit voltage characteristics are obtained by defining the battery charge amount when the open circuit voltage of the cell is 3.9 V as SOC=100%, and defining the battery charge amount when the open circuit voltage of the cell is 3.5 V as SOC=100%. By defining SOC=100% and SOC=0% in this way, the SOC can be correctly computed and displayed even if the battery has deteriorated.

Anodic dissolution of aluminium in organic electrolytes containing perfluoroalkylsulfonyl imides

Abstract: Electrochemical dissolution of aluminium has been investigated in various solutions composed of organic solvents and 1 m lithium bis(perfluoroalkylsulfonyl) imide salts. Potentials of the onset of transpassive dissolution and repassivation as well as dissolution currents have been measured for several systems by using voltammetric methods. Empirical correlation between the composition of the solvent and the dissolution current has been established for mixtures of ethylene carbonate and ethylmethyl carbonate. The effect of the perfluoroalkyl chain length on the dissolution rate has also been studied and the result has been elucidated with the help of considerations on the structure of the ions. Mechanistic information obtained from electrochemical impedance spectra revealed that at least two adsorbed intermediates have to be included in the dissolution mechanism. Conditions of application of lithium perfluoroalkylsulfonyl imides in lithium ion batteries are briefly discussed.

Doped tin oxides as potential lithium ion battery negative electrodes

Abstract: Recently some work has shown that tin oxide compounds can be promising anode materials in rechargeable lithium batteries. These materials show a higher capacity compared to the graphite that is used commercially. The present studies are focused on zinc doped tin oxides as anode materials, especially on the effect of ball-milling on the anode capacity. Different ratios of ZnO and SnO2 with different times of ball-milling have been used as active materials. The inverse spinel, Zn2SnO4 has been prepared by both hand-grinding and ball-milling, followed by sintering and has also been investigated as an active material. Individual ball-milling of the oxides was observed to increase capacity, co-milling was fairly neutral and ball-milling before solid state reaction was observed to have a detrimental effect.

Lithium-ion battery charge control method

Abstract: A technique of operating a lithium-ion (Li-ion) battery is proposed for maximizing battery life. In a first instance, this technique calls for charging the battery at a lower temperature than the temperature at which discharge begins. Preferably, the battery is charged at a temperature T1 in the range between about +5°C and -20°C; and discharged at a temperature T2, in the range of about +5°C to +30°C, T2 being higher than T1. In another instance proposed by the invention, the battery is charged to an elevated state of charge which is above an initial state of charge at a temperature T1 between about +5°C and -20°C which is lower than a temperature T2, in the range of about +5°C to +30°C, at which discharge begins. In still another instance proposed by the invention, after the battery has been charged and discharged during the eclipse season, it is then charged to an intermediate charge level between about 40% and about 60% state of charge over a relatively long lapsed duration of time, about one month to about six months, and thereafter, the battery is maintained at this intermediate charge level.

Lithium ion polymer electrolytes

Abstract: A dimensionally stable, highly resilient, hybrid copolymer solid-solution electrolyte-retention film for use in a lithium ion battery in one preferred embodiment has a predominantly amorphous structure and mechanical strength despite contact with liquid solvent electrolyte. The film is a thinned (stretched), cast film of a homogeneous blend of two or more polymers, one of which is selected for its pronounced solvent retention properties. A very high surface area inorganic filler dispersed in the blend during formation thereof serves to increase the porosity of the film and thereby enhance electrolyte retention. The film is soaked in a solution of liquid polymer with liquid organic solvent electrolyte and lithium salt, for absorption thereof. Use of a cross-linked liquid polymer enhances trapping of molecules of the electrolyte into pores of the film. The electrolyte film is sandwiched between flexible active anode and cathode layers to form the lithium ion battery. Novel methods are provided for forming the electrodes, the polymer substrate, and other elements of the battery.

Lithium ion battery utilizing carbon foam electrodes

Abstract: A lithium ion battery (200) has at least two carbon foam electrodes (54, 56). Each of the electrodes (54, 56) is fitted with a plate (60, 62 respectively) formed from an electrically conductive material. The plate (60, 62) has an underside which is formed so as to be attached to one end of the carbon foam electrode (54, 56). The plate (60, 62) may be fixed to the electrode by crimping or a similar deforming process or may be fitted thereto by an electrically conductive adhesive.

Electrode for rechargeable lithium-ion battery and method of fabrication

Abstract: An electrode for a rechargeable lithium-ion battery is formed by mixing stanous oxide (SnO) and lithium nitride (Li 3 N) in a stoichiometric ratio of 2 moles of Li 3 N to 3 moles of SnO to form a mixture, milling the mixture to obtain a milled powder, and processing the milled powder in accordance with an electrode-forming technique. The electrode forming technique can be any one of die pressing, spraying, doctor-blading and rolling. Conductive additives, such as carbon and binders (PVDF, cellulose and Teflon), can be introduced during the processing step. Preferably, the method is carried out in a dry, inert atmosphere of argon or helium. As a result of the invention, a smaller, lighter and more efficient lithium-ion battery is produced.

Positive electrode material for lithium battery and its manufacture

Abstract: PROBLEM TO BE SOLVED: To improve heat stability of a LiNiO2 base positive electrode material for a lithium battery with high discharge capacity without decreasing discharge capacity. SOLUTION: This positive electrode material for a lithium ion battery containing an oxide of at least one kind element Z of B and P in an atomic ratio (a) of Z/(Ni+M) satisfying 0.001<=a<=0.1 in a lithium composite oxide represented by composition formula: LixNi1-yMyO2 (M is at least one of Mn, Fe, and Al, 0.95<=x<1.1, 0<=y<=0.5) is manufactured by mixing a Z element source to a Ni compound or a Ni+M element compound and calcinating the mixture to produce an oxide containing Z, then mixing a Ni source to this and then calcinating the mixture. The Z element is concentrated on the grain boundary of crystal grains of a lithium composite oxide having an average crystallite size of 100-1000 Å, and a material whose 95% or more of lithium site is occupied by lithium is obtained. In the case where granular powder is formed by spray-drying a mixture before calcination or baking, drop in discharge capacity can be prevented.