GB2316800A

GB2316800A - Method of fabricating of a safe material for electrodes for secondary batteries

Info

Publication number: GB2316800A
Application number: GB9617837A
Authority: GB
Inventors: Alexander G Maximov; Peter Ya Novak; Vadim S Gorshkov
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-08-27
Filing date: 1996-08-27
Publication date: 1998-03-04
Also published as: GB9617837D0

Abstract

Method of fabricating a safe material for electrodes comprising formation of spacial coherency function of an electron states of atoms of a material which provides a double battery protection from current, mechanical and thermal overloads. Electrode material exemplified includes lithium, vanadium, oxygen and sulphur.

Description

METHOD OF FABRICATING OF A SAFE MATERIAL FOR ELECTRODES FOR SECONDARY BATTERIES This invention relates to a method of fabricating of a safe material for electrodes for secondary batteries.

Rapid development of different types of portable electron devices and the necessity to replace internal combustion engines for environmentally clean electric motors challenge vital interest among consumers to secondary batteries. This problem, in its turn, brings up an issue of providing protection against fireand/or explosion of batteries which are in use. Traditionally, the issue of batteries safety was considered at the design and technological developments stage. This approach can never be a guarantee for a complete safety as it does not exclude the major possibility of uncontrolled oxidation-reduction reactions which cause its explosion and/or ignition. The complexity of the issue lies in the fact that said reactions appear while changing microscopic characteristics of electrode materials which are impossible to control at said design stage. As a result there might occur fire and explosion hazzard reactions that take place spontaneously or under electrical current, mechanical or thermal effects on a battery, or due to a wrong doing. The only way to provide a battery safety is to undertake protective measures at the microscopic level in order to form an elcctron structure of elctrode materials which would exclude the very possibility of having uncontrolled oxidation-reduction reactions and effects of the battery heating by electrical current.

It is an object of said invention to provide safety and reliabilty of secondary batteries.

Said object is achieved by special method of fabricating a safe electrodes material for secondary batteries. Said method allows to set up a two level battery protection using essential features of the electron structure of electrode matrials and, in particular, the dependency of spacial coherency function of electron states of electrode materials on kinetic energy of electrons participating in the process of electrotransport and active ions kinetic energy. The first protection level provides a battery safety at short circuit or high current loads. Growth of current density going through the electrode material increases kinetic energy of mobile elcctrons and causes electron states synchronization breakdown. Electron states synchronization breakdown causes dramatic increase of internal electrode resistance with increase of current density in a battery which provides automatic current restriction. The second protection level provides safety at thermal overloads and at mechanical battery damages which can cause dangerous chemical reactions with high energy release. This level of protection is implemented through selective elctrochemical activity of the elecrode material to oxidationreduction reactions by the level of their coherency. As a result active ion kinetic energy increase causes the loss of spacial coherency of electron states of the elctrode material which, in its turn, stops oxidation-reduction process on the elctrode.

Physical-chemical processes in any battery bring to changes of electron states of elctrode materials atoms. Changes of electron states can be divided into two types according to the following conditions. To the first type we refer elcctron transitions between conditions of an atom which differ from each other by the main quantum number value. For example, ns' o nsO, nd3 o nd2, etc. These electron transitions are the basis of all oxidation-reduction reactions as such, i.e. these reactions are nothing but electron transitions from the state with one main quantum number value into the state with another main quantum number value. In wave mechanics said type of transitions is defined as the variation of proper oscillations frequency of electron states and is characterised by time coherency function. The second type is related to the changes of electron state characteristics as such. In quanatum mechanics it has the name of electron transitions by additional quntum numbers (spin-orbital and spin spin traransitions). This type of electron states changes defines the conditions of proceeding of chemical reactions. For low-energy chemical reactions, i.e. when the energy of initial and final states is slightly different this particular type of changes of electron states is responsible for the the direction of oxidation-reduction reactions, and for the nature of the formed chemical bonds. In wave mechanics this type is defined as the change in the function of spacial coherency of proper oscillations which can be accompanied by frequency deviation and by the changes of degeneration level of proper oscillations. Main electrode materials feature of secondary batteries is low energy difference between electron states of electrode material atoms in charged and discharged conditions. That is why the second type of electron characteristic changes defines the general battery operation, and, accordingly, defines its safety. In practical use of microwave technique it is customary to use the term "frequency" for describing time coherency and the term "phase" for defining spacial coherency of electromagnetic fields. In particular the terms "frequency" and "phase" in this meaning will be used further. Thus, the term used in the text: "frequency and phase assignment of electron state" means assignment of time and spacial coherency function for the described electron state. Any electron configuration of an isolated atom or ion has a defined function of time coherency (frequency of proper oscillation of electron states or proper energy values) and function of spacial coherency (it is also called wave function or function of state). Function of spacial coherency (phase) of group of atoms, connected by chemical bond can be defined through the interrelated change of electron states of atoms of this group. It is found out that spacial coherency of electron states is not only the parameter of a theory but can be directly measured experimentally by the method of electron spin resonance (ESR). Generally the methodology of defining the phase of elctron states by ESR-spectrometer is the foregoing. Alternating radio-frequency field with variable spacial coherency function is applied to a sample placed into a constant magnetic field. For these purposes electromagnetic field generators with tunable time coherency are used. With the terms matching to the conditions of the electron spin resonance the spectrometer registration system registrates ESR signal which intensity depends on the selected function of spacial coherency of variable radio-frequency field. This methodology allows to selectively record spectrum of various electron states and to unambiguously identify them. It makes possible to register elcctron states participating in chemical bonds which is not possible with traditional methods of ESR spectroscopy. The spacial coherency function of electron state of material can be expressed through the following spectral parameters: spin-spin and spin-lattice relaxation time of electron states, time of coherency of these states, atoms quantity with said phase of electron states and electron configuration of these atoms. The function of spacial coherency can be used for certification and identification of manufactured materials. Serial production of ESR spectroscopy equipment and short time expenditure for taking measurements and spectrums processing make the above mentioned parameters definitions quite available for manufacturers. Registration of spacial coherency of electron states allows to separate oxidation-reductions reactions on secondary batteries electrodes into reactions of two types. Coherent oxidationreduction reactions which energy completely transforms into the elcctrical current energy and is characterised by its high ion-selectiveness and which is identified by its selective activity of the electrode to the phase of electron states of mobile ion - current carrier. Said reactions take place, if the phase of electron states of electrode material is stable and fully defined. Noncoherent oxidation-reduction reactions are reactions which energy is released in the heat form. These reactions take place, if the phase of electrode material is not completely defined. As a result oxidation-reducation reactions depend on the mobile ion kinetic parameters and local stable phases of electron states of separate groups of electrode material atoms. Noncoherent reactions in the batteries are parasitic as they are responsible for uncontrolled electrochemical processes in batteries and for all the cases of fire-explosure hazards. It is experimentally determined that with the absense of control of electron states phase of electrode materials with different chemical composition and crystalline structure, statistical distribution of charge-discharge cycles numbers of up to 50% of electrochemical cells capacity losses by cell numbers is random. This distribution is described by Lorentz distribution - in case of thermodynamic equilibrium electrode material and by Gauss distribution in case of thermodynamic nonequilibrium electrode materials. All the electrode differences by its chemical composition and crystallic structure are revealed in the value of a ratio of halfwidth to the height of distribution. Hence, chemical composition of electrode material and/or its crystalline structure can not be a substential issue for classification of batteries elctrodes and their identification. This conclusion is supported by direct measurements of electron states phase of electrode material by ESR spectroscopy. Spacial coherency of electron states of any material consisting of one element of periodic system or any combination of different elements of periodic system is an extrastructural charactristic. It is determined by spacial coherency of microscopic fields of electron shells in electrode material atoms and spacial coherency of outer electromagnetic fields at the moment of formation of chemical bonds between these atoms. Components used for manufacturing of electrode material are not certified by spacial coherency parameters. Presently standartization system for this parameter does not exist. As the result the spread of spacial coherency parameters values of any electrode component of a given chemical composition and structure depends on the volume of used product and is increasing with the increase of the quantity of used product of one and the same manufacturer. The spread is significantly increased in case of using the products from different manufacturers, technologies and raw materials sources. It explains random nature of statistic distribution charge-discharge cycles number by the cells quantity. Similar situation happened at the beginning of the 20th century when manufacturers did not control materials elements composition under production and certification of the material by this parameter did not exist. The necessity of proceeding of this type of certification by the parameter of spacial coherency of electron states is directly connected with the batteries safety and reliability. Otherwise random character of electrode electrochemical properties at mass production can be the reason of hazzard situations.

Method described herinwith for fabricating materials of safe elctrodes for secondary batteries consists of three stages: Stage 1. Initial components of electrode material go through a preliminary certification by the parameters of their spacial coherency with the help of ESR spectroscopy.

Stage 2. Variating temperature modes, composition and ratios of solid state components, composition and partial pressure of gas phase components (if any), liquid phase composition (if any) in the working reactor zone, spectrum parameters of produced subproducts are determined. On the basis of the data received the sequence of operations is defined and the final product is manufactured.

Stage 3. The quality control of the final product with ESR spectroscopy. During this stage the safety level of electrode material is determined by the quantity of material atoms with electron states having the given function of spacial coherency parameters.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 show typical ESR-spectrum of initial vanadium pentoxide.

Figure 2 illustrates typical ESR-spectrum of subproduct (1 - signal from electron configurations 3d2 singlet of vanadium ions, 2 - signal from electron configurations 3d3 of vanadium ions) Figure 3 shows typical ESR-spectrum of final product (single line from configurations 3d3 of vanadium ions with low resolution of the fine and superfine structure) Fabricating positive elctrode material for lithium batteries on the basis of periodic system elements - vanadium, oxigen, sulphur. A basic operational trransition of electrochemical reaction in a lithium battery is determined by changing quadruplet state of vanadium atom with electron configuration 3d3 in charged condition into a triplet-singlet state of vanadium atom with electron configuration 3d2 in discharged condition. The main goal is to form such electron state function in an electrode material that would exclude the possibility of appearance of singlet vanadium atoms states (3d2) and that would provide only low energy difference in energy between quadruplet - 3d3 and triplet - 3d2 states. This is achieved by synchronization of vanadium atoms electron states (3d3/3d2) and oxigen atoms electron states (2p3 /2p6).

To provide synchronization electron shells of sulphur atoms are used. They act as connection lines" with nonlinear transmission coefficient between the electron states of vanadium and oxigen atoms. "Connection lines" creation occurs due to the fact that sulfur is an acceptor for vanadium ions and in the same time is electron donor for oxygen ions. Said spacial coherency function can be formed by the following: The main component of initial row material - vanadium pentoxide goes through preliminary certification by the parameter of its spacial coherency with the help of standard method of ESR. Typical spectrum of initial vanadium pentoxide obtained by the spectrometer ERS- 220 (frequency 9.3 GHz) is on the Figure 1. In this case all electron states of vanadium have electron configuration 3d2- singlet. Next step is to take 181.88 grams of vanadium pentoxide, 32.06 grams of sulphur both are in powder state and are thoroughly mixed, and to heat in 5 2 medium in closed volume. The heating temperature has to be set up in the range of 150;300 OC depending on the value of the phase of subproducts obtained. Parameters of subproducts have to be checked by ESR. Figure 2 presents tipical ESR-spectrum of subproduct. On this stage electron states of vanadium ions is a mixture of electron configurations 3d2 - singlet, 3d2 - triplet and 3d3 - quadruplet. Electron states 3d2- triplet can not be detected by ESRspectrometer due to large initial splitting, so that spectrum (Fig. 2) consist of two lines from the electron states configurations 3d2 - singlet and 3d 3 - quadruplet. It is important to get minimum intensity of 3d2 - singlet line and maximum intensity of 3d3- quadruplet line by variation of temperature regime. Such a spectrum is a final product sign. The final product contains from 4.2 to 4.8 moles of oxigen and up to 1 mole of sulphur per 2 moles of vanadium. Typical ESR-spectrum of final product represented on Figure 3. It is a single line from of 3d3- quadruplet states of vanadium ions with low resolution of the fine and superfine structure. Secondary lithium battery with this elctrode material can withstand short circuit and is resistant to thermal and deformative overloads and nonsensitive to overrecharging. Hence, the battery satisfies to the main requirements of maintenance safety. Measured capacity for such a battery ranges from 200 to 220 mA h/g at variations in the voltage from 3.4 V to 1.9 V which is acceptable for their profitable production.

Claims

1. Method of fabricating a safe material for electrodes comprising the formation of spacial coherency function of electron states of material atoms providing double battery protection from current, mechanical and thermal overloads.

2. Method claimed in claim 1, wherein determination and control of said spacial coherency function of electron states for initial, intermediate and final materials atoms are provided by ESR spectroscopy.

3. Method claimed in claims 1 and 2 of fabricating a positive electrode for lithium batteries from periodic system elements - vanadium, oxigen, sulphur, wherein safe elctrode material contains from

4.2 to 4.8 moles of oxigen and up to 1 mole of sulphur per 2 moles of vanadium. Essential feature of this material is synchronization of vanadium atoms electron states in quadruplet (3d3) and triplet (3d2) states; and oxigen atoms with electron configurations 2p3 and 2p6; whereas electron shells of sulphur atoms act as "connection lines" with nonlinear transmittance coefficient for providing this synchronization.