MXPA98000869A - Lithium ion battery, rechargeable, low resistance - Google Patents

Abstract

The present invention relates to a perforated current collector element (21), fitted with at least one of its polymeric intercalation electrodes (23), reduces the internal resistance of a rechargeable, flexible lithium-ion battery (2).

Description

LITHIUM ION BATTERY, RECHARGEABLE, LOW RESISTANCE RELATED APPLICATIONS This application is a continuation in part of the US Patent Application Serial Number 08 / 160,018, filed on November 30, 1993, now US Patent 5,460,904 issued on October 24, 1995, which was a continuation in part of the U.S. Patent Application Serial Number 08 / 110,262, filed August 23, 1993, now U.S. Patent 5,418,091, issued May 23, 1995, which in turn was in itself a continuation in part of the U.S. Patent Application Number of Series 08 / 026,904, filed on March 5, 1993, now US Patent 5,296,318, issued on March 22, 1994. The foregoing applications, assigned to the assignee of this application, are hereby incorporated by reference in their entirety .

BACKGROUND OF THE INVENTION The present invention relates to electrolytic cells comprising electrodes of polymeric film composition and separating membranes and to a REF: 26805 way to use these cells to provide economical and highly efficient batteries. In particular, the invention relates to rechargeable, unitary lithium battery cells comprising an intermediate buffer element containing an electrolyte solution through which lithium ions from a source electrode material move between the electrodes of the cell during the charge / discharge cycles of the cell The invention is particularly useful for making these cells in which the ion source electrode is a material, such as a transition metal oxide, capable of intercalating the lithium ions , and wherein a membrane separating the electrodes comprises a polymeric matrix made ionically conductive by the incorporation of an organic solution of a dissociable lithium salt that provides ionic mobility. More specifically, the present invention relates to the construction and arrangement of these battery cell elements that significantly reduce the internal resistance of the resulting battery while substantially improving the level of power capacity available in this battery. The rechargeable, rechargeable lithium-ion battery cells, as described in the incorporated descriptions, have been constructed in general by means of electrode lamination and separator / electrolyte cell elements that are individually prepared by coating, extrusion, or otherwise, from compositions comprising polymeric materials, for example, a plasticized polyvinylidene fluoride (PVdF) copolymer. For example, in the construction of a lithium ion battery, an aluminum foil or grid current collector layer was covered with a positive electrode film or membrane prepared separately as a coated layer and a dispersion of the electrode composition. of intercalation, for example, a LiMn204 powder in a copolymer matrix solution, which was dried to form the membrane. A separating membrane / electrolyte formed as a dry coating of a composition comprising a solution of the copolymer and a compatible plasticizer was then coated on the film of the positive electrode. A negative electrode membrane formed as a dry coating of a powdered carbon dispersion in a copolymer matrix solution was similarly coated in the separator membrane layer, and a copper collector sheet or grid was deposited in the layer of the negative electrode to complete a cell assembly. This assembly was then heated under pressure to effect a hot melt bond between the plastified copolymer matrix components and the collector grids to thereby achieve the lamination of the cell elements in a flexible battery cell structure., unitary The resulting laminated battery structure, which comprised a significant measure of homogenously distributed organic plasticizer, particularly in the extract of the separating membrane, was devoid of hygroscopic electrolyte salt and, as a result, could be stored at ambient conditions, either before or after being formed or further processed, without being interested in the deterioration of the electrolyte due to the reaction with atmospheric humidity. When it was desired to activate a battery in the final stage of manufacture, the laminated cell structure was immersed or otherwise contacted with an electrolyte salt solution which was absorbed into the copolymer matrix to provide substantially the same improvement of ionic conductivity such as that achieved by a hybrid, preformed separator / electrolyte film containing this solution of electrolyte salts.

In order to facilitate the absorption of the electrolyte solution during activation, it is generally preferred that a substantial portion of the plasticizer is previously removed from the copolymer matrix. This can easily be achieved at any time after the rolling operation by immersing the cell laminate product in a low boiling point solvent, inert to the copolymers, such as diethyl ether or hexane, which selectively removes the plasticizer without affecting Significantly, the copolymer matrix of the stratum of the elements of the cell. The extraction solvent can then be simply evaporated to produce a dry, inactive battery cell that will readily absorb an effective amount of the electrolyte solution that essentially replaces the extracted plasticizer. As with any electrolytic cell, a lithium ion cell generally prepared in the above manner exhibits an internal electrical resistance, characteristic which is ordinarily a function of the various materials of the composition and amounts, i.e. the mass or thickness of each one employed in the cell. Therefore, it was particularly surprising the discovery that the internal strength and performance of these cells having elements of substantially similar composition and mass could be significantly varied by means of the physical structure of the cell and the arrangement of the materials components inside the cell. The arrangement of the components of the cell according to the present invention has allowed a remarkable reduction in the internal resistance of the battery cells without compromising the activity and specific stability.

BRIEF DESCRIPTION OF THE INVENTION The previous polymeric battery cells have been typically structured to have a layer or membrane of separator / electrolyte element, interposed between the layers of the positive and negative electrodes, respectively, with that subassembly disposed between the sheets of the conductive elements, electric current collectors, much in the manner shown in FIG. 1. As described above, in the electrolyte-activated cells at least one, preferably both, of the collecting elements are crosslinked, for example, in the form of a metal sheet grid, extended, to provide an access of the extraction and electrolytic fluids to the polymer matrices of the cell. A cell structure according to the present invention, on the one hand, comprises in its simplest form, a similar arrangement in which at least one of the layers of the positive or negative electrode covers its respective collecting grid as shown in the figure 2. The significant decrease in the internal resistance of the cell evident in this array is believed to be due in large part to the average distance shortened through the electrode layer to the collector, thereby providing a more expedient flow of electrons. Of particular note is the fact that the specific capacity of the cell does not decrease, despite the displacement of approximately half of the composition material of the divided electrode outside the current collector element. As will be seen from the last description, other embodiments of the invention, as depicted in the drawings, produce a substantial increase in the capacity of the cell compared to previous construction cells having equivalent amounts of the active electrode materials .

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described with reference to the accompanying drawings of which: Figure 1 is a schematic representation of a typical laminated lithium ion battery cell structure used prior to the present invention; Figure 2 is a schematic representation of a laminated lithium ion battery cell structure typical of the present invention; Figure 3 is a schematic representation of an elevation view of the longitudinal cross section of an electrode / collector element of the present invention; Figure 4 is a schematic representation of a multi-cell battery structure of the present invention; Figure 5 is a schematic representation of a processing process for preparing a battery cell structure of the present invention; Figure 6 is a schematic representation of a laminated lithium ion battery cell structure, variant of the present invention; Figure 7 is a diagram of the comparative internal resistances of the laminated lithium-ion batteries of Figures 1, 2 and 4; Figure.8 is a graph of the specific comparative capacities of the laminated lithium-ion batteries of Figures 1 and 4 as a function of the charge / discharge cycle speed; Y Figure 9 is a graph of the total comparative capacities of the laminated lithium ion batteries of Figures 1, 2 and 4 as a function of the charge / discharge cycle speed.

DESCRIPTION OF THE INVENTION Lithium ion cell batteries, useful, have been made economically available through the technological advances described in the patent specifications, incorporated in the above references. The basic structure of this cell 10 is represented in FIG. 1 and essentially comprises the layer elements 13, 17 of the positive and negative electrode, between which there is interposed a separating element / electrolyte comprising a polymeric matrix, preferably a polyvinylidene fluoride copolymer, in which a lithium salt electrolyte solution will eventually move. These electrodes respectively comprise a lithiated intercalation compound, for example, LixMn2Δ4, and a complementary material capable of reversibly intercalating lithium ions, for example, carbon in the form of petroleum coke or graphite, each dispersed in a similar polymer matrix. The electrically conductive current collectors 11, 19, preferably of aluminum and copper, contact the respective electrode elements 13, 17, and are joined, such as by thermal lamination, to the remaining elements of the cell to form a battery cell, unit. In order to facilitate the subsequent processing of the cell, for example, to incorporate the lithium salt electrolyte, at least one of the collecting elements is permeable to fluids such as in the form of an expanded, perforated metal grid 12. To provide the contacts of the simple battery terminals, the current collector elements can be extended as tabs 12, 18. By comparison, the substance of the present invention can be easily seen in Figure 2, where the composition layer of the The positive electrode is divided into two elements 23, 23 which are placed on the respective surfaces of the grid 21 of the current collector. The resulting composite electrode / collector element is then laminated with the separator element 25, the layer 27 of the negative electrode, and the sheet 29 of the negative collector to form the unitary battery cell 20, in a substantially similar manner, that used to prepare the anterior cell 10. The composite electrode / connector structure can be seen in greater detail in Figure 3 which generally represents the result of the preferred thermal lamination of the layers of the electrode or membrane composition 23, 23 with the grid 21 of the collector, interposed. Although the grid 21 is shown to be located centrally within the laminated electrode layer, it should be understood that by preferential selection of the composite membranes 23 of different thicknesses the collector can be placed at any depth within the electrode composition , as desired. Also, the invention allows the use of electrode membranes 23 of different composition, for example, variable proportions of the intercalation component, active, to achieve for example, a compound electrode of graduated power capacity. Of particular interest in this laminated incorporation of the manifold is the manner in which the composition of the polymeric electrode of the membranes 23 penetrates the perforated grid to form a coherent, individual electrode layer within which the collecting grid 21 essentially engages. In addition to establishing in this way the ionic conductivity through the electrode composition, this lamination ensures intimate electronic contact between the electrode elements and the collector, and furthermore, advantageously provides the physical reinforcement and the bonding of firm polymer matrix for the element of the reticulated collector, relatively fragile. This added integrity is particularly useful when designing compact, high capacity multi-layer batteries by repeated or concentric folding of an elongated flexible cell. A useful, additional embodiment of the invention that provides a battery 40 having a significant increase in specific capacity is shown in Figure 4. This arrangement essentially incorporates a duplicate pair of structured cells as shown in Figure 2, with one element 49 of current collector, blade or grid, common that serves both cell members. In the assembly of this battery, the electrode / manifolds 41, 43 can be laminated in turn with separating membranes 45, electrodes 47 and collector 49, preferentially, a laminated sub-assembly of collector 49 and electrodes 47 can be separated to be later laminate with spacer membranes 45 and one electrode pair / sub-assembly manifolds 41, 43. In this preferred method, the use of a grid for the negative element 49 results in an embedded collector electrode of the type shown in Fig. 3, and provides the final battery with the additional benefit of the invention. As shown in Figure 4, the duplicate electrode / manifold is preferably one of positive polarity, since the manifold 41 used with the composition of the positive electrode 43 is usually made of low density aluminum, while the negative collector 49 is copper more dense In this way, although the arrangement of the electrodes of a particular plurality is not critical to the operation of the battery, a significant advantage in the weight and a proportional improvement of capacity in the represented arrangement are realized. A number of electrolytic cell laminate products with similar compositions, still varying in structure according to the above description, were prepared and tested for adequate electrolytic and physical capacity for use in rechargeable battery cells. The following examples are illustrative of this preparation and use.

EXAMPLE 1 A separator / electrolyte membrane coating solution was prepared by dispersing 6 g of a copolymer of vinylidene fluoride (VdF): hexafluoropropylene (HFP) 88:12 of approximately 380xl03 MW (Kynar FLEX 2801, Atochem) and 4 g of fumed silica, silanized in approximately 40 g of acetone and by adding approximately 10 g of dibutyl phthalate (DBP) to this mixture. The finished mixture was heated to about 50 ° C to facilitate the dissolution of the copolymer and homogenized in a laboratory ball mill for about 6 hours. A portion of the resulting slurry was coated on a glass plate with a doctor blade device with a separation of about 0.5 mm. The coated film was allowed to dry inside the coating enclosure under dry air flowing moderately at room temperature for about 10 minutes to produce a flexible, hard film that was removed from the glass plate. The film was approximately 0.1 mm thick and was easily cut into rectangular, separating elements that could be stored for days at ambient conditions without significant loss of weight.

EXAMPLE 2 A positive electrode composition was prepared by homogenizing in a stainless steel mixer, covered with lid for about 10 minutes at 4000 rpm, a mixture of 44 g Li Li + xMn 20, where 0 < x < 1 (for example, Lij..os n20 prepared in the manner described in US Pat. No. 5,266,299), screened through 53 μm, 11.8 g of the VdF copolymer: HFP (FLEX 2801) of Example 1, 18 g of phthalate of dibutyl, 4.7 g of conductive carbon (Super-P Black, MMM Coal, Belgium), and approximately 75 g of acetone. The resulting thick suspension was degassed by briefly applying reduced pressure to the mixing vessel, and then a portion of a glass plate was coated with a doctor blade device spaced at about 0.8 mm. The coated layer was allowed to dry inside the coating enclosure under dry air flowing moderately at room temperature for about 10 minutes to produce a flexible, hard film that was removed from the glass plate. The film was approximately 0.25 mm thick and easily cut into rectangular electrode elements that could be stored for days at ambient conditions without significant loss of weight.

EXAMPLE 3 A negative electrode composition was prepared by homogenizing a mixture of 21 g of a commercial petroleum coke (MCMB 25-10, Osaka Gas), milled in a stainless steel mixer capped for about 10 minutes at 4000 rpm. with a ball mill and sieved through 53 μm, 6.0 g of the VdF copolymer: HFP (FLEX 2801) of Example 1, 9.4 g of dibutyl phthalate, 1.12 g Super-P conductive carbon of approximately 36 g of acetone. The resulting thick suspension was also degassed by briefly applying a reduced pressure to the mixing vessel, and then, a portion was coated on a glass layer with a doctor blade device spaced at approximately 0.5 mm. The coated layer was allowed to dry inside the coating enclosure under dry air flowing moderately at room temperature for approximately 10 minutes to produce a hard, flexible film that was easily removed from the glass plate. The film was approximately 0.15 mm thick and easily cut into rectangular, electrode elements that could be stored for days at ambient conditions without significant loss of weight. Similarly, suitable electrode and separator compositions were obtained with vinylidene fluoride copolymers of 8-25% hexafluoropropylene, such copolymers were purchased from other commercial sources (e.g., Solef 21-series, Solvay) and copolymers of vinylidene fluoride with similar proportions of chloro trifluoroethylene (Solef 31-series, Solvay). These compositions of the copolymer matrix worked well with compatible plasticizers homogeneously incorporated in the range of about 20-70%. In addition, the intercalation compounds of LixCo02 and LixNi02 were effective substitutes for LixMn204 as the active component of the positive electrode compositions. The rechargeable battery structures were easily assembled from the component electrode and separator elements, prepared in the manner of the previous examples. The conditions of the preparation of the electrode can vary, either in the consistency of the coating composition or in the thickness of the coated layer, to obtain a weight-based ratio of the active intercalation material in the positive electrode combination: negative between about 2.1 and 3.5, preferably about 2.2 when using petroleum coke or about 3.0 with graphite. Similarly, various assembly lamination methods can be employed using for example flatbed, heated presses or, preferably, assembly lines with heated, continuous process rolls, as generally shown in Fig. 5 with a cell of the type shown in Figure 2. Here, a laminated product negative electrode / manifold 57, 59 is formed in station 52 between heated rollers 56 at approximately 150 ° C and approximately 4 x 104 Pa of pressure, a product laminate 51, 53 of positive electrode / collector is likewise formed in station 54, and then the sub-assembly pair is laminated with separator membrane 55 in station 58. Additional lamination stations can be included to conform to manufacture described of extended batteries of the type shown in Figure 4.

EXAMPLE 4 A battery cell 10 of the above, basic structure shown in Figure 1 was prepared in the following manner. A 80 x 40 mm copper current collector sheet 19, preferably in the form of an open mesh grid of approximately 30 μm thickness (e.g., MicroGrig precision expanded foil, Delker Corp.), was cut out at one end to form a tongue 18 which would subsequently serve as a convenient battery terminal. To improve the subsequent adhesion to its associated electrode element, the grid 19 is cleaned on the surface by immersing it for a few seconds in a common "copper luster" solution (HN03, H2SO4, diluted, mixed), rinsing in water, drying with air, coating by immersion in a 0.5% acetone solution of the VdF: HFP copolymer of Example 1, air drying and heating in an oven at about 350 ° C for 5-10 seconds. A negative electrode element 17 of carbon 60 x 40 mm, cut from the film prepared in example 3, was coated on the grid 19 of the pair of elements and the pair of elements was placed between the cushion sheets of the polyethylene terephthalate adherent (not shown). The assembly was then passed through a rolling station, as in 52 in Figure 5, which essentially consists of a commercial card stamping laminator. The positive electrode element 13, of similar size, as prepared in example 2, and the aluminum collector grid 11, cleaned with acetone were similarly laminated, as in 54 (FIG. 5), the pair The resultant electrode / collector was laminated with an interposed separating membrane 55, as in 58 (FIG. 5). The laminated battery structure was extracted from a substantial amount of the DBP plasticizer comprising the polymer matrices of the laminated layers, particularly the separator / electrolyte, by immersion for about 10 minutes in stirred diethyl ether. The extracted battery structure was then activated in the preparation for the immersion charge / discharge cycle test, under a substantially moisture free atmosphere, in a 1M electrolyte solution of LiPF6 in ethylene carbonate (EC): dimethyl carbonate (DMC) 50:50 for approximately 20 minutes, during which the battery absorbed an amount of solution that substantially replaced the extracted plasticizer. The activated battery was then hermetically sealed, but to extend the terminal tabs 12, 18, in a hermetic enclosure of moisture-proof barrier material, such as a polyolefin laminate / aluminum / polyester sheet product, commercially used for enclosures of food.

EXAMPLE 5 A battery cell 20 having a structure of the present invention, as depicted in Figure 2, was prepared in the following manner. A portion of the composition of the positive electrode of Example 2 was similarly coated and processed to a dry film thickness of about 0.12 mm.

Two 60 x 40 mm sections were cut from the film to form the positive electrode elements 53, 53 (Figure 5) which were then mounted with a grid 51 of the aluminum manifold and laminated with the negative electrode elements, collector and separator, remaining from Example 4 in the manner shown in Figure 5. The resulting cell is further processed with removal and activation of the electrolyte as described in Example 4 to provide a test battery.

EXAMPLE 6 An extended battery 40 of the present invention, as depicted in Figure 4, was prepared with the additional positive electrode film sections 43 of Example 5 following the laminated manufacturing example described above, in which each of the three electrode / manifold sub-assemblies were pre-laminated, as in station 54 of figure 5, prior to final lamination with separators 45, as in station 58. Extraction, activation with electrolyte and packing as described in the previous examples finished the manufacture of test battery.

EXAMPLE 7 A highly versatile variant of the present invention as shown in Figure 2 is shown in Figure 6 and comprises the grid current collectors 61, 69 that are both interposed between the elements of the laminated cell 60. In addition to the socket of the manifold 61 inside the positive electrode 63, the collector 69 is laminated within the negative electrode 67 substantially between the face of the separator element 65, or in a similar location that will provide an optimum balance of the inter-collector and intra-electrode distances, average. This configuration of cell elements, in addition to reducing the inter-collector space, also provides each collector grid element with an integral polymer reinforcement, both of these conditions are advantageous in the fabrication of structures in which a elongated cell in transverse axes to reform a compact, numerous, concentric laminated battery that has a specific capacity. The pre-lamination of the collecting elements with the layers of the electrode composition, respectively, in the previously described manner is also preferred, since this operation serves to ensure the complete incorporation of the collectors in the final laminated structure without the pre-treatment of the surface of the grid. Batteries prepared from cells 10, 20 and 40 were tested comparatively in charge / discharge cycles at various speeds (a speed 2C designates a two-hour charge or discharge cycle segment) over the range of approximately 4.5 V to 2.5 V. During the previous stage of this test; the internal resistance of each battery was measured by the common voltage drop method, and it was determined to be 6.3 O, 3.0 O, and 0.95 O, respectively, as shown in Figure 7. The dramatic improvement in this property apparently appears of the structure of the fitted manifold of the present invention. However, the unusually high specific capacity exhibited by these cells is particularly surprising, considering the physical arrangement of a considerable proportion of the active electrode material beyond the current collectors they encompass. The persistence of the improved specific capacity of the new battery structure on the increasing cycle speeds, as shown in Figure 8, and the improved stability of this capacity at these increasing speeds, as is evident in the comparative lines of the figure 9, testifies to the additional advantageous effects of the present invention. It is noted that in relation to this date, the best method known by the applicant to carry out the present invention, is the conventional one for the manufacture of the objects to which it refers. Having described the invention as above, the content e is claimed as property. the following:

Claims (12)

1. A rechargeable lithium-ion battery structure comprising positive and negative electrode layer elements having a spacer element positioned therebetween and current collectors associated therewith, each of the elements comprising a film composition of polymer matrix, flexible and joining adjacent elements in their respective faces to form a flexible, unitary structure, characterized in that: a) this positive electrode layer element comprises a composition of a lithium ion intercalation compound selected from from the group consisting of LixMn204, LixCo02, and LixNi02; and b) at least one of the current collectors is fitted within its associated electrode layer.

2. A battery structure according to claim 1, characterized in that the fitted manifold is substantially extensive with its associated electrode and is perforated, whereby the composition of the electrode penetrates the conductor to maintain the ionic conductivity through the electrode layer.

3. A battery structure according to claim 2, characterized in that the nested collector is placed substantially equidistant from the surfaces of the electrode layer, thereby minimizing the internal strength of the structure.

4. A battery structure according to claim 1, characterized in that at least one of the current collectors is fitted within the electrode layer in a location adjacent to an electrode / spacer interface.

5. A battery structure according to claim 4, characterized in that the electrode layer comprises a composition of a lithium intercalation material consisting essentially of carbon.

6. A battery structure according to claim 2, characterized in that each of a plurality of collectors is fitted within its respective associated electrode.

7. A battery structure according to claim 6, characterized in that the plurality of electrodes comprises a pair of similar polarity placed symmetrically around an opposite polarity electrode.

8. A rechargeable lithium-ion battery structure characterized in that it comprises: a) a plurality of positive electrode elements made of a flexible polymer composition containing a lithiated intercalation compound; b) a negative electrode element made of a flexible polymer matrix composition contains carbon as a material capable of intercalation with lithium, wherein the negative electrode element is placed between each of the positive electrodes; c) a plurality of separating elements composed of a flexible polymeric film composition capable of being an ionically conductive ax by the incorporation of an organic solution of a dissociable lithium salt that can provide ionic mobility, at least one of the separating elements that is place on either side of the negative electrode, thereby separating the negative electrode from the positive electrodes; d) a plurality of current collectors, wherein a current collector is fitted into each of the positive electrodes and the negative electrode; and e) wherein each of the elements joins the contiguous elements to form a flexible, unitary structure.

9. A battery structure according to claim 8, characterized in that the current collectors are made of aluminum or copper.

10. A battery structure according to claim 9, characterized in that the current collectors are perforated.

11. A battery structure according to claim 10, characterized in that the current collectors are made of a metal sheet grid.

12. A battery structure according to claim 8, characterized in that the flexible polymer matrix film composition is a plasticized, polyvinylidene fluoride copolymer.