Technical Field The present invention relates to an electrochemical device, preferably a lithium secondary battery, which uses inorganic particles having lithium ion conductivity as additive for an electrode, and thus shows improved safety under overcharge or high-temperature storage conditions with no degradation in the battery quality. Background Art Recently, many attempts are made to continuously downsize and lighten portable electronic instruments including portable computers, portable phones, camcorders, etc. At the same time, it is required for hthium secondary batteries used in such electronic instruments as power sources to have a higher capacity, more compact size, lighter weight and a smaller thickness. A lithium secondary battery comprises a cathode, anode, separator and an electrolyte. Such lithium secondary batteries are capable of repeating charge/discharge cycles, because hthium ions reciprocate between a cathode and anode in such a manner that lithium ions deintercalated from a cathode active material upon the first charge cycle are intercalated into an anode active material such as carbon particles and then deintercalated again from the anode active material, while serving to transfer energy. When a hthium secondary battery is overcharged to a voltage exceeding a predetermined drive voltage range or when an exothermic reaction proceeds between a cathode and electrolyte in a charged state at high temperature, reactivity between the cathode and electrolyte increases, resulting in degradation of the cathode surface and oxidation of the electrolyte. Additionally, there are problems related with lack of battery safety, for example, lithium dendrite growth followed by breakage of a separator, rapid exothermic reaction and explosion of the battery. To solve the above problems, Korean Laid-Open Patent No. 2000-0031096 discloses the use of molecular sieves or finely divided fumed silica added to an electrode or electrolyte of a lithium ion battery for stabilization of the battery. However, as the amount of additives increases, the amount of cathode active material decreases. Further, when viewed from the point of electrolyte, it seems that the electrolyte is adversely affected by addition of non-reactive materials. Therefore, the above additives cause a problem of degradation in the battery quality. In addition, Korean Patent Publication Nos. 0326455, 0326457 and 0374010 disclose methods for coating inorganic oxide particles on a cathode active material in order to improve the safety of a battery. However, such methods have a disadvantage in that they cause degradation in the battery quality in proportion to the amount of added inorganic oxide particles, even if the battery safety may be improved. Disclosure of the Invention The present invention has been made in view of the above-mentioned problems. We have found that when inorganic particles having lithium ion conductivity are added to an electrode active material forming an electrode of a lithium secondary battery, the battery safety can be improved while minimizing degradation in the battery quality caused by the use of additives. Therefore, it is an object of the present invention to provide an electrode capable of improving the safety of a battery and preventing degradation in the battery quality caused by the use of additives. According to an aspect of the present invention, there is provided an electrode obtained from electrode slurry comprising: (a) an electrode active material capable of lithium intercalation/deintercalation; and (b) inorganic particles having hthium ion conductivity. According to another aspect of the present invention, there is provided an electrochemical device, preferably a lithium secondary battery, including the same electrode. Hereinafter, the present invention will be explained in more detail. The present invention is characterized in that an electrode for an electrochemical device (for example, a lithium secondary battery) includes not only a conventional electrode active material known to one skilled in the art but also inorganic particles having lithium ion conductivity, which serve as supplement for the electrode active material. According to the above characteristic of the present invention, it is possible to obtain the following effects: (1) Because conventional inorganic particles added to an electrode in order to improve the safety of an electrochemical device are inert, lithium ion conductivity in the device are decreased, resulting in degradation in the quality of the electrochemical device. On the contrary, the electrode according to the present invention uses inorganic particles having lithium ion conductivity as additive for an electrode. Therefore, it is possible to minimize a drop in lithium ion conductivity in an electrochemical device caused by the use of additives, and thus to prevent degradation in the quality of an electrochemical device. (2) Additionally, the electrode obtained by adding such inorganic particles significantly reduces the amount of electrolyte to be in contact with the surface of a charged electrode, and thus inhibits an exothermic reaction between the electrode active material and electrolyte, such exothermic reaction resulting in the lack of thermal safety of an electrochemical device. Therefore, it is possible to improve the safety of an electrochemical device. Particularly, the inorganic particles inherently experience no change in physical properties even under a high temperature of 200°C or higher. In other words, the inorganic particles have excellent heat resistance. Accordingly, the electrode according to the present invention causes no degradation in the safety under severe conditions including high temperature, overcharge, etc. According to the present invention, any inorganic particles may be used as additive for an electrode when forming electrode slurry, as long as they have lithium ion conductivity as described above. As used herein, "inorganic particles having lithium ion conductivity" are referred to as inorganic particles containing lithium elements and having a capability of transferring lithium ions without storing lithium. In general, currently used electrode active materials are in a crystal system, and thus have a structure capable of storing lithium in a lattice, for example a unique lattice structure such as a layered structure or spinel structure. On the contrary, the inorganic particles having lithium ion conductivity according to the present invention may be in a non-crystal system as well as a crystal system. More particularly, even though the inorganic particles used according to the present invention have the same crystal system as a general electrode active material, the inorganic particles cannot store lithium ions in the lattice structure but can move and transfer lithium ions through the defects or vacancies present inside the lattice structure. Accordingly, although the inorganic particles having lithium ion conductivity used according to the present invention have a similar apparent structure to the structure of a conventional cathode active material known to one skilled in the art, they are not suitable to be used as electrode active materials that store lithium ions and intercalates/ deintercalates lithium ions into/from the lattice structure. However, because the inorganic particles according to the present invention can transfer and move lithium ions through the defects present inside the lattice structure of the inorganic particles, it is possible to improve the overall lithium ion conductivity in a battery, compared to other electrode additives serving as inert fillers, by virtue of the lithium ion conductivity of the inorganic particles, and thus to prevent degradation in the battery quality. Non-limiting examples of such inorganic particles having lithium ion conductivity include: lithium phosphate (Li3P04), lithium titanium phosphate (LixTiy(P04)3, 0