RU33000U1 - Current source for implantable medical devices - Google Patents

Description

The invention relates to an improved cell with an organic electrolyte, in which the cathode is fluorinated carbon and the anode is lithium metal. Since elements of this type are characterized by high energy, good persistence and a stable level of discharge voltage, they are widely used in various kinds of electronic devices, in particular in medical implantable devices. However, attempts to force the discharge of such current sources lead, in particular, to a large heat release, which can result in thermal acceleration, failure of the element, destruction of the powered equipment and the creation of an emergency.

Since a medical device, together with a current source, is implanted in a living organism, naturally, increased safety and reliability requirements should be imposed on the current source during long-term operation.

A current source for implantable medical devices of a similar electrochemical system 1,2 is known, including fluorinated carbon, lithium metal and an organic electrolyte. However, the safety of the current source is not resolved in this invention, and the discharge curve has an incident shape.

The objective of the invention is to increase the reliability and fire and explosion safety of the current source in case of unauthorized external or internal short circuit, as well as to obtain a flat discharge characteristic, which is more preferable for the operation of the electronics unit in a medical device.

The proposed current source solves this problem due to the fact that the current source contains a housing of a corrosion-resistant material, a lithium anode, a solid cathode of fluorinated carbon that separates them

a separator and a non-aqueous electrolyte, a cathode of a current source including fluorinated carbon, an electrically conductive additive in the form of graphite or soot, and a binder is made porous. The fraction of fluorinated carbon (with an active fluorine content of 55-60%) in the cathode mass is 95-98%, the conductive additive is 1-3% and the binder is 1-3%. The cathode porosity is 60 - 65%, and the density 3 - 3.5 g / cm. Since the operation of implantable devices is designed for a long time (in particular, a pacemaker for 8 - 10 years), the current consumption does not exceed 30 100 μA. The cathode of this composition fully provides such current consumption at a sufficiently high (2.9 - 3.0 V) level of discharge voltage. At the same time, the specified ratio of the components in the cathode (fluorinated carbon, graphite and binder) provides a sufficiently high specific capacity of the current source in a given volume, and the indicated porosity and density of the cathode maintains the passage of current at a minimum load, in particular with a short circuit, at a low level of 40 mA due to diffusion restrictions on the electrolyte in the cathode pores as the accelerated discharge of the current source. Since the used fluorocarbon tends to expand as it discharges (up to 30–40%), so that the separator does not break, the separator is double-layer. Moreover, the first layer in contact with the cathode is made of non-woven polypropylene material with a thickness of 90-110 microns. and a pore size of 25 + 5 μm., and the outer layer in contact with the lithium anode is made of a microporous polypropylene film with a thickness of 20 -25 μm. and a pore size of 0.025 +0.003 microns. The porosity and thickness of the first separator provide the necessary filling and retention of the electrolyte in the interelectrode space. And since a porous layer of polyethylene 1-3 microns thick is applied to the surface of a thin separator, when the current source is heated, the polyethylene layer melts, closes the pores on the separator surface and the film conductivity decreases by more than 10 times, which naturally leads to a sharp drop in current flowing through

SOURCE of current. In addition, the tensile strength of the specified separator is 1000 kg / cm, which ensures its integrity during the expansion of the cathode during the discharge.

In FIG. 1 shows an electrode and current collector for manufacturing a cathode; figure 2 presents the assembled cathode, placed in a double polypropylene separator and connected to a pressure connection on the cover of the current source; Fig. 3 shows an assembled current source.

The current source is made as follows: fluorinated carbon powder is dry biased with acetylene carbon black in a ball mill. In this case, 1000 g is taken. fluorocarbon and 21g. soot. After this, the finished mixture is subjected to liquid mixing in ethanol with the addition of 24 g. (27.5 ml) of an aqueous suspension of F4D fluoroplast. Then, after pressing the alcohol, the mass is rolled on rollers into a 1.75 mm thick tape, from which two electrodes of a U-shaped cathode are cut. After preliminary drying of the electrodes, they begin to manufacture the cathode itself directly. For this, two electrodes (1) are coated on one side with an alcoholic solution of colloidal graphite (25 g / l) and the coated side is laid on a titanium current collector (2), also previously coated with colloidal graphite. The assembled cathode is pressed with a force of 100-130 kgf / cm. Then, by contact welding, a titanium current collector of the cathode (2) is welded to the hermetic outlet (6) in the lid (3), an insulating gasket (7) made from lavsan is placed between the lid and the cathode. The cathode (4) is sealed into a double separator (5) by hot welding around the perimeter of the cathode .. After preliminary drying of the components in a dry argon atmosphere, a current source is collected: the cathode in the separator (9) is pre-welded to the hermetic outlet (6) on the cover (3) with an insulating gasket (7) is placed in a shaped body (10), along the wide walls of which a 0.7 mm thick lithium anode (8) is laid. After welding the cover of the current source (3) with the housing (10), vacuum filling the cell with non-aqueous electrolyte and the final sealing of the gas station GS -f //

. ;; L (/: - / and I hole in the cover (3) with a ball (11) using a pressure test method and negative lead (12) over the ball using laser welding, the element was subjected to a short circuit at the temperature after incoming inspection. The results are shown in Fig. .4. The temperature rise from the ambient temperature does not exceed. Then after 90 minutes the temperature of the current source is compared with the ambient temperature and does not change throughout the rest of the short circuit time. Thus, in conditions of prolonged external short circuit um overheating of the current source, depressurization, changes in overall dimensions, destruction of the housing.

Thus, the technical result is that the reliability and safety of the current source are improved both during storage and during long-term operation in an implantable medical device.

Figure 5 shows the discharge curve of the current source to the load of 5 kOhm; it can be seen that the curve has a flat appearance almost throughout the entire discharge time, even at a load 20 times higher than the actual load in the pacemaker (100 kOhm).

The current source works as follows: when the terminals of the current source are closed on the lithium anode, positive lithium ions transition into the solution and their diffusion in the electrolyte solution to the fluorocarbon cathode. The electrons freed up in this case are sent through an external circuit to the positive terminal of the current source. As a result of the electrochemical reaction at the cathode, lithium fluoride and amorphous carbon are formed: xLi + CFx - xLiF + С

The reaction continues until one of the electrodes is consumed. Due to the occurrence of this reaction inside the element, an electric current is observed in the external circuit.

Sources of information taken into account: 1. US patent .№ 6,150,057, cl. Н01М 10/40, November 21, 2000

Claims (3)

1. A current source comprising a housing made of a corrosion-resistant material, a lithium anode, a solid fluorinated carbon cathode, a separator separating them and a non-aqueous electrolyte, characterized in that the cathode is made porous, while the electrically conductive additive and a binder are included in it, the proportion of fluorinated carbon is 95-98% with an active fluorine content of 55-60%, a conductive additive of 1-3% and a binder of 1-3%, while the cathode porosity is 60-65%, and the density is 3-3.5 g / cm ³ . 2. The current source according to claim 1, characterized in that the cathode is made of two electrodes connected together by a solution of colloidal graphite and located on a titanium current collector. 3. The current source according to claim 1, characterized in that the separator is made of two layers, the inner layer of nonwoven polypropylene material 90-110 microns thick and pore size 25 ± 5 microns, and the outer layer of microporous polypropylene film 20-25 microns thick and pore size 0.025 ± 0.003 μm.