Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
1999-12-29
2004-12-21
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C324S427000, C429S090000
Reexamination Certificate
active
06833707
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to high-energy electrochemical cells, such as lithium-based cells, other secondary cells, and batteries constructed therefrom. More particularly, the present invention relates to systems and methods for characterizing electrochemical cells and for predicting the response of such cells to thermal, mechanical or electrical abuse based on power functions obtained from calorimetry.
BACKGROUND OF THE INVENTION
Rechargeable electrochemical cells are currently used to power a wide variety of portable electronic devices, including laptop computers, cell phones, cameras, and personal organizers, for example. The increased use of such mobile devices has placed a greater demand on the battery manufacturing industry to provide high powered cells that may be used safely in a wide spectrum of consumer and industrial applications. In order to minimize size and weight, battery technologies with high-energy density are normally used. Larger versions of such technologies may, for example, be used in hybrid or all-electric vehicles. High-energy density cells store large amounts of energy in relatively small volumes. If this energy is released quickly and in an uncontrolled manner, however, thermal runaway is possible, leading to safety concerns.
Lithium-ion and lithium-ion polymer cells (collectively referred to as lithium-ion cells in the following discussion), for example, exhibit the largest energy density of all ambient-temperature rechargeable cell technologies. Lithium-ion cells are carefully engineered to meet a variety of safety test standards, including, for example, UL-1642 (Underwriters Laboratories) and IEC-61960 (International Electrotechnical Commission) standards. The tests defined by these standards include oven exposure, short-circuit, forced overcharge, forced discharge, shock and vibration. Other proposed tests include nail penetration tests. It is desirable that cells and batteries constructed from such cells do not emit smoke or flame when subjected to thermal, electrical, and mechanical stress associated with the above-identified tests.
In addition to the electrical energy which lithium-ion cells can deliver during discharge, these and other high-energy cells can also evolve a considerable amount of heat due to the reaction of the electrode materials with the electrolyte. During short-circuiting of a cell, for example, both the electrical energy of the cell and the chemical heat resulting from the electrode/electrolyte reactions are dissipated as heat within the cell. Thermal runaway can occur if the sum of these thermal powers is greater than the power that can be transported from the cell to the environment.
The UL and IEC oven exposure tests probe the severity of electrode/electrolyte reactions. These reactions are most severe when the cell is fully charged. In accordance with these oven exposure tests, a fully charged cell is placed into an oven and exposed to a temperature of 150° C. (UL) or 130° C. (IEC) for a predetermined duration of time. Short-circuiting of the cell under test normally does not occur and the cell temperature rises above the oven temperature to the point where the power generated by electrode/electrolyte reactions is equal to the power that can be transferred to the environment. However, if the former is always larger than the latter, thermal runaway occurs. It is noted that, although cells in consumer use are typically not placed in ovens at high temperature, they may be exposed to 85° C. environments in battery cases that inadvertently are thermally well-insulated. If electrode/electrolyte reactions proceed significantly at such temperatures, insulated batteries could exhibit thermal runaway.
The total power generated by the electrode/electrolyte reactions (under a specific set of circumstances) is proportional to the total volume of the cell. That is, if two cells have the same chemistry, the same construction details and the same charging history, but one has twice the volume of the other, then the larger cell will evolve twice the power due to electrolyte/electrode reactions at elevated temperature than the smaller one. The power that can be transferred to the environment, however, is proportional to the cell surface area. Therefore, it is expected that the cell surface area to volume ratio should be maximized to optimize cell safety. This is not always possible due to cell manufacturing constraints or physical size limitations of a device within which the cell will be housed.
Given the issues discussed above, it can be appreciated that cell designers are faced with a complex task. The cell designer is often asked to maximize cell performance, cell energy density, and cell safety. Design changes that maximize energy density may, however, adversely compromise safety. Design changes to cell shape and cell size also affect safety. Selection of the electrode materials and electrolyte affect performance and safety.
Typically, designers are able to make simple cell performance and energy density estimates based on projections from data collected in lab cells. However, it has heretofore not been possible to reliably predict safety test results of practical cells (e.g., full-scale consumer batteries) based on test results at the lab scale. In order to conduct reliable safety studies, prototyping of a potential product in actual cell hardware, followed by extensive testing, is presently necessary. Moreover, large quantities of electrode materials must be produced in order to properly construct prototype cells for safety testing and evaluation. Conventional cell/battery design and development techniques typically require the production and availability of 10 kilograms or more of sample electrode material. Those skilled in the art readily appreciate that designing, developing, and testing electrochemical cells and batteries, particularly those having a custom, non-industry standard configuration, using conventional approaches is extremely time consuming and costly.
There is a need in the battery manufacturing industry for systems and methods that assist in the design of electrochemical cells and batteries of varying technologies, and which require the production of small quantities of sample electrode materials. There exists a further need for such systems and methods that eliminate the present need to construct full-scale cell/battery prototypes in order to fully evaluate the safety aspects of a given cell/battery design. The present invention fulfills these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to methods and apparatuses for characterizing electrochemical cell components and for characterizing a response of an electrochemical cell to a specified operating condition. According to one embodiment of the present invention, characterizing electrochemical cell components involves preparing a sample of an electrode material in contact with an electrolyte. Self-heating, power-temperature or power-time data is obtained for the sample using a calorimetry technique, such as by use of an accelerating rate calorimetry technique or a differential scanning calorimetry technique, for example. Obtaining self-heating data, for example, may involve obtaining temperature versus time data of the sample during substantially adiabatic reaction.
A power function is developed for the sample using the self-heating, power-temperature or power-time data. The power function is representative of thermal power per unit mass of the sample as a function of temperature and amount of reactant remaining from a reaction of the sample electrode material and electrolyte.
In general, preparing the electrode material sample involves preparing the sample using less than about 100 grams of the electrode material. According to one embodiment, preparing the electrode material sample involves preparing the sample using between about 1 gram and about 10 grams of the electrode material. In another embodiment, preparing the electrode material sample involves preparing the sample using between about 1
Dahn Jeffery R.
Hatchard Timothy D.
MacNeil Dean D.
3M Innovative Properties Company
Deb Anjan K.
Hollingsworth Mark A.
Pastirik Daniel R.
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