MXPA99005927A - Method and anode for improving the power density of lithium secondary batteries - Google Patents

Abstract

The invention relates to a method and anode for improving power density of lithium secondary batteries, specially those containing solid polymer solutions. This is done by employing boric acid esters and/or boric acid derivatives or the compounds thereof as additives. Lithium compounds in corresponding complexes are specially added. The invention also includes anodes for use in galvanic cells, specially in lithium ion secondary batteries and those with solid polymer solutions, which contain boric acid esters and/or boric aid ester derivatives or the compounds thereof as additives in the anode.

Description

METHOD AND NODE TO IMPROVE THE POWER DENSITY OF LITHIUM SECONDARY BATTERIES Description of the Invention The invention relates to a method and anode for improving the power density of secondary lithium batteries, in particular those with solid polymer solutions. In groupings of cells and other groupings a better use of the material is desired in order to satisfy the requirements of the consumers. The fact that in a secondary battery the charge of the anode to the cathode material is preponderantly transported by an electrolyte or an electrolyte solution is due to the fact that any materials are transported with a potential. Therefore also the positively charged ions are transported through the electrolytes to the negative charge electrode. The opposite is applicable to anions. The current density of electrolytes is expressed as: I = LE (? F +? I t? R •? Μi) (1) being that LE is the conductivity of the electrolytic solution,? F is the potential difference between the anode material and the cathode material, tir is the reduced transport magnitude of the transport species "i", and? μi is the difference of the chemical potential of the species "i" between the anode material and the cathode material. Because all the materials are diluted in a defined way at the anode, yes? μ¿ is then approximately 0 for the common batteries, then an equivalence of Ohm's first law will be produced, as it is exemplarily explained (1). Voltages greater than those expected for the system may occur. This can lead to risks and damages that should be avoided in a preventive manner. Finally, the polymer link is inconvenient, the anions are not immobilized. The magnitude of lithium transport is unsatisfactory. Therefore the task of the present invention is to provide, predominantly for the secondary batteries of lithium an addition that increases the density of the power taking into consideration the safety of operation, which obtains a positive derivation of the first Ohm's law, which decreases the emptying of the salt, and that it increases the number of cycles or the cyclic resistance. It was also necessary to elaborate method steps that would result in the improvements described. The task is solved by the distinctive features in accordance with the patent claims. Accordingly, for the improvement of the power density of secondary lithium batteries, in particular those with solid polymeric solutions, boric acid esters and / or boronic acid esters or their compounds are added as additives. The addition causes what is known as salt drainage to be reduced (figure 3), a high magnitude of lithium transport is reached and a positive derivation of the salt results. Law of Ohm (figure 4). This also results in a higher cyclic resistance of the battery system, as well as an increase in power density for established potentials. The system of cells used is detached from the figures. In particular, esters of boric acid and / or ester derivatives of boric acid are used as lithium compounds in complexes of the formula and / or p and / or wherein the radical groups Ri and R2 can be aromatic and / or aliphatic, and that in formula III M is a transition metal, and that the cyclopentadienyl groups can also have fluorine instead of H. The transition metals are those elements whose atoms have an incomplete sublayer d or which can form one or more cations with incomplete sublayers. According to this and in accordance with the notation recommended by the IUPAC, the transition metals belong in the 4th period the elements Sc to Zn with the atomic numbers 21-30, in the 5. period Y to Cd (39-48) ), in the 6th period The a Hg including the lanthanides in which the sublayer 4f is filled (atomic numbers 57-80), and in the 7. Ac period, the actinides up to Lr (89-103). Preferably, esters of boric acid are used. The radical groups determine the electrochemical stability and the solubility in the organic solvent. Due to large and bulky radical groups, the negative charge is distributed. This has the consequence that it is very unlikely that lithium + forms pairs of ions or complex species. Because of this, the salt is dissolved or dissociated in the organic solvent. Preferably the additives are added on the anode side. The additives are added in amounts of >0 to 20% by weight, preferably 5 to 15% by weight. The anode according to the invention, in particular in the secondary lithium ion batteries and those with solid polymeric solutions, contains at the anode additions of boric acid esters and / or ester derivatives of boric acid or its compounds. This achieves a comparatively high current by selecting a reduced potential, which in particular has the effects of a stable system and obtains a greater number of cycles or a greater cyclic resistance. The anode is constituted by a substance which may include lithium and / or lithium ions and conductive salts which are dissolved in solvents and / or polymeric binding agents and / or conductive carbon black and / or the additive. Particularly suitable are those anodes which contain, as an additive, boric acid boric acid esters and / or ester derivatives of boric acid in the form of complex compounds of the formulas I p and / or Suitably the additives are contained in the anodes in amounts greater than 0 and up to 20% by weight, preferably 5 to 15% by weight. The invention will now be explained in more detail with reference to the accompanying drawings. In the drawings, FIG. 1 shows a schematic representation of a battery, exemplary LiC / PEO lithium-ion battery, lithium salt / LiMn2Os without salt drain, with very small electric currents during short intervals (idealized case Figure 2 shows a schematic sectional representation of the same system, unlike Figure 1 in this case the curve diagrams show the behavior when using larger currents, Figure 3 again a schematic representation in section of the same system, the graphs show the behavior in the case of small and large currents, there is no emptying of salt, Figure 4 trends in the diagrams of curves for minor, medium and major currents, Figure 5 diagram of curves as in Figure 4, but however in the ideal case with immobilized anions, Figure 6 diagrams of exemplary schematic curves on how the resistance can be increased cyclic based on the case of the use of polyethylene oxide (PEO). Figure 7 diagram of curves of the positive derivation of the 1. Ohm's law achieved by the application of addition substances, in comparison with the trajectory of the curve without positive derivation; 8 shows a schematic representation of anodes / electrolyte / cathodes for the case of the use of addition substances and without the use of them; Figure 9 current-voltage diagram to represent the results of the examples. In the groupings, as shown schematically in figure 1, there are no emptying of salt in the case of very small currents during short time pulses. This is applicable in particular for the lithium ion batteries sketched which are represented in the ideal case according to Figure 1, the anions are not immobilized. That is why it is only possible to take small currents during short intervals without a gradient. Figure 2 reproduces the conditions in the case of higher currents in the same system of a lithium ion battery used as an example, local salt voids are presented. Because there is a mass balance of lithium ions, their concentration is approximately constant (A). The anions move towards the electrolyte against a positive electrode. By virtue of the fact that the electrodes do not produce more anions, a concentration gradient (B) is produced. In accordance with Kohlrausch's law, the conductive capacity of the ions is a function of the concentration of the electrolyte. When the concentration decreases, the conductive capacity also decreases. Furthermore, with the appearance of a concentration gradient, a gradient of the conductive capacity (C) results. By decreasing the conductive capacity of the electrolyte, the local resistance of the electrolyte increases. With an increase in the local resistance of the electrolyte, a potential drop occurs (D). According to FIG. 3, according to the invention the anions are now immobilized in the polymer matrix of the electrolyte. In this way large and small currents can be used without having problems with the emptying of salt and thereby register potential drops, as also shown in figure 5 as a trend in the curve diagrams in the ideal case with immobilized anions. For the minor, medium and major currents the described trends are summarized in the curve diagrams of Figure 4. The ideal case with immobilized anions illustrated according to Figure 5 will be explained below in more detail in an exemplary manner. The anions are not mechanically immobilized, but their transport magnitude is very small in relation to lithium. If the anions are mechanically immobilized, then the constant of the complex is very large, the magnitude of lithium transport decays. The total conductivity decays because the complex constant between anions and lithium is large. If the anions are chemically immobilized, then the complex constant between Li + and anion is very high, the total conductivity is very low. If, however, the transport of anions is very small in comparison with the magnitude of transport of Li +, then there are no significant complexes between the anions and the cations.

In this way a high conductivity results. Figure 6 is based on the fact that if a large current is needed, a high potential has to be used. High potentials only give small amounts of cycles or only a conditioned cyclic resistance. This is illustrated in figure 6 with the PEO solvent ple. Figure 6 also shows how the sustained currents according to the invention are obtained with then reduced potentials that are within quantities in which the PEO solvent is stable. The cyclic capacity could be increased by using the substances according to the invention by the reduced potentials obtained in this way, but thus obtaining an invariable current. The reduced potential increases the number of cylinders or the cyclic resistance. In the system of a lithium ion battery taken as exemplary basis according to FIG. 1, according to the invention the particular advantage was achieved that with the addition of the substances according to the invention to the electrolyte binding material in the anode according to the claims could reduce the potential as illustrated exemplarily in figure 6, without reducing the density of the current. In a series of tests it was possible to increase the power density of the system and present the verification of it. Thus, figure 7 schematically shows the so-called positive derivation of the first Ohm law that was obtained, together with the graphs of the normal curve of Ohm's first law for ordinary batteries in the described lithium-ion battery systems. For research the potential was invariably established. The complexes of the additives or the discovered substances were added, and a positive derivation of Ohm's first law was proved. That means a higher current compared to the curve normally achievable according to Ohm's first law. "Therefore the density of the power of the system was increased by the equation specified in figure 8, as well as by the drawing it is derived that the magnitude of transport of the anions is approximately equal to 0. Therefore, the difference in chemical potential does not influence in any way the density of the current.When adding a lithiated derivative of boric acid ester, the partial surplus energy of the Lithium ions invariably become positive, this is based on a higher current density as well as a greater amount of lithium transportation.

Then d ti2 i + d ln x Li RT dx dx and? i t? r? μi »... > Or volt (2).

This gives a positive derivation of Ohm's first law. For cell designs and established potentials, a larger current can be taken for an external current circuit if the system positively disagrees with Ohm's first law. This means therefore, an increase in power density ple 1 (Comparative ple) Recipes without lithium-bis [1,2-benzoldiolate (2-) -0, 0 'Jborate (1-) (LiBSE) Active material percent by weight graphite (type KS6) 90.29 carbon black conductive (super P type) 4.74 Teflon binder 4.97 (total mass of the electrode 13.9 mg, active mass of KS6: 12. 55 mg; equivalent to 4.67 mAn) ple 2 Recipes with lithium-bis [1,2-benzoldiolate (2-) -0, O '] borate (1-) (LiBSE) Active material percent graphite weight (type KS6) 82.08 black conductive smoke (super P type) 4.30 Teflon binder 4.53 LiBSE 9.09 (total electrode mass 11.3 mg, active mass of KS6: 9.3 mg, equivalent to 3.46 mAn) In both ples the measurements were carried out in a lithium composite cell with an active surface area of approximately 1 cm2 (standard LP electrolyte) : EC.DMC (1: 1); 1 m LiPF6; feed speed 0.1 * mV / s). To prepare the electrodes, the corresponding active materials were mixed in a mortar and pressed on the nickel grid. A cyclovoltamogram with these two compositions was produced in a controllable potentiometer, as can be seen in figure 9 (current-voltage diagram).

From this figure 9 it is derived that the currents of the cathode and of the anode were increased. From this it is derived that the capacity in the system with LiBSE (example 2) is increased compared to the system without LiBSE (example 1) -

Claims (1)

1. CLAIMS Method for improving the power density of secondary lithium batteries, in particular those with solid polymeric solutions, characterized in that boric acid esters and / or boric acid esters or their derivatives are added to the anode as additives. compounds Method according to claim 1, characterized in that the esters of boric acid and / or ester derivatives of boric acid are present as lithium compounds in complexes of the formulas I p and / or wherein the radical groups Ri and R2 can be aromatic and / or aliphatic, and that in formula III M is a transition metal, and that the cyclopentadienyl groups can also have fluorine instead of H. Method according to claim 1 and 2, characterized in that the additives are added in amounts of more than 0 and up to 20% by weight, preferably 5 to 15% by weight with respect to the anode. Anode for batsrias of. lithium-polymer, in particular in secondary batteries of lithium ions and those with solid polymeric solutions, characterized in that the anode contains boric acid esters and / or ester derivatives of boric acid or its compounds as additives. Anode according to claim 4, characterized in that it contains as additives boric acid esters and / or ester derivatives of lithic acid lithiated in the form of complex compounds of the formulas and / or p and / or node according to claim 4 and 5, characterized in that the additives are contained in amounts of more than 0 and up to 20% by weight, preferably 5 to 15% by weight with respect to the anode.