WO2016178596A1 - Lithium-ion cell - Google Patents

Abstract

The invention relates to the electrical technology industry and may be used in the production of lithium-ion cells and batteries based thereon, intended for use as energy storage devices in electric transport, alternative energy, uninterruptible power supplies, power recovery systems and in balancing network loads. The design of the proposed lithium-ion cell combines a negative-electrode active material based on Li₄Ti₅O₁₂ and a positive-electrode active material based on Li₃V₂(PO₄)₃. The negative-electrode active material based on Li₄Ti₅O₁₂ may be doped with chromium at the titanium positions and takes the form of a compound having the composition Li₄Ti_5-xCr_xО₁₂, where 0 < х ≤ 0.2. The positive-electrode active material may be doped with sodium at the lithium positions, doped at the vanadium positions with one or more metals from a group containing magnesium, aluminum, yttrium and lanthanum, and doped at the phosphate positions with fluorine or chlorine, and takes the form of a compound having the composition Li_3-xNa_xV_2-yM_y(PО₄)_3-zHal_z/C, where M represents one or more metals from the group containing Mg, Al, Y and La; Hal = F, Cl; 0 < x ≤ 0.1; 0 < у ≤ 0.2; and 0 < z ≤ 0.16. Crystals of the active materials of the negative and positive electrodes may be coated with a surface layer of carbon, which may be produced by introducing a carbon-containing precursor, starch, into the mixture of initial reagents. The invention allows for creating lithium-ion cell designs having high energy storage capacity, and having enhanced power, safety and stability during cycling.

Description

 LITHIUM ION BATTERY

 FIELD OF TECHNOLOGY

The invention relates to the electrical industry and can be used in the production of lithium-ion batteries (LIA) and batteries based on them, intended for use as energy storage devices for electric vehicles, alternative energy sources, uninterruptible power supplies, energy recovery systems and equalization network loads.

BACKGROUND

Significant progress in lithium-ion battery technology (LIA) has made autonomous power supplies of this type the most energy-intensive among rechargeable electrochemical systems. The traditional material of the negative electrode (anode) in such batteries is carbon, which is capable of reversibly introducing lithium [1], and the material of the positive electrode (cathode) is lithiated cobalt oxide (lithium cobaltate, lithium-cobalt oxide) LiCo0 ₂ [2]. Despite the fact that LIA systems “carbon - lithium-cobalt oxide” currently occupy a significant part of the market for power supplies for portable electronics, their use for powering transport and energy is impossible due to a number of inherent disadvantages. The disadvantages of lithiated carbon as the anode material of LIA are [3-5]:

 - the probability of thermal acceleration and ignition with increasing temperature;

 - sharp degradation of the capacitance at an increased charge / discharge rate;

 - a very small residual capacity and the impossibility of charging the batteries at negative temperatures.

The disadvantages of lithium cobaltate when used as a cathode material LIA are [5-7]:

 - fire hazard at high temperatures;

 - degradation of capacity at high potentials, temperatures and cycling rates;

- short service life (no more than 800 cycles).

Batteries for electric vehicles and energy should combine such characteristics as energy intensity, power (i.e., ability to quickly charge and resistance to high load currents), a wide range of operating temperatures, long service life and safe operation, therefore, their creation requires the development and application of fundamentally new active electrode materials. Known anode materials based on lithium alloys with silicon [8]. The theoretical capacity of the richest lithium silicon compound (Li ₂ 2Si ₅ ) reaches 4200 mAh / g calculated on pure silicon or 201 1 mAh / g calculated on the compound Li2 ₂ Si ₅ . The main obstacle to the stable operation of the lithium-silicon intercalation electrode is the large volumetric changes that occur during lithium incorporation / extraction cycles. These changes reach 310% of the initial volume of silicon and are the cause of the mechanical instability of the material [9].

Known anode materials based on lithium alloys with tin [10]. Being in the same subgroup of the periodic system with silicon, tin forms similar crystalline structures and compounds similar in stoichiometry. It also fuses with lithium to form Li ₂₂ Sn ₅ . However, tin also has a larger unit cell volume than silicon, and therefore it suffers less from volume changes [11]. The disadvantage of the proposed solution is that tin is four times heavier than silicon, and the specific intercalated capacity of Li ₂₂ Sn ₅ is as much lower — 990 mAh / g versus 4200 mAh / g for Li ₂₂ Si ₅ [ll].

The possibilities of increasing the specific capacity of carbon-graphite materials have now been exhausted and correspond to the most lithium-rich compound LiC ₆ (372 mAh / g). A promising solution to the problem of limited carbon letter capacity is the use of Si-C, Sn-C, or Si-Sn-C letter composites [12]. The disadvantage of this solution is the high activity of lithium in the above materials, which determines their insufficient safety [13].

A promising anode material for use in LIA construction is a group of compounds with moderate capacitance values, in which lithium activity and, accordingly, electrode potential have an intermediate value between traditional anode and cathode materials. A typical example is lithium titanium spinel, or lithium titanate, Li ₄ Ti ₅ 0 ₁₂ [14]. This material has a theoretical capacity of 175 mAh / g and a charge-discharge curve plateau potential of -1.55 V. This potential is much higher than the recovery potentials of most organic solvents, therefore, solid electrolyte films with high resistance are not formed on the surface, and the release lithium metal on the anode is practically eliminated. Another advantage of Li ₄ Ti ₅ 0 ₁₂ in comparison with silicon and tin compounds is their small volume changes (less than 0.2%) during lithiation and delitration, which guarantees stability during long-term cycling. In addition to all of the above, the material has a high conductive properties of lithium ions: the value of specific conductivity is

8 1 1

is 5.8 x 10 ^"ohms" -see ^"even at room temperature [15].

To create a workable LIA design with an optimal combination of energy, power, service life and safety, it is necessary to select the active material of the positive electrode, which has a sufficiently high electrode potential, but at the same time devoid of all the disadvantages of lithium cobaltate. To a certain extent, these requirements are met by layered mixed lithiated oxides of nickel, cobalt and manganese of the composition LiNi _1-xy Co _x Mn _y 0 ₂ according to the patent [16]. This material has an energy intensity comparable to LiCo0 ₂ , surpassing it in power, safety and stability during cycling. The disadvantage of this material is a sharp drop in capacitance during cycling due to an increase in the resistance of the charge transfer reaction on the surface of the material due to its degradation [6]. In addition, the data of reaction calorimetry [5] indicate that the probability of occurrence of thermal acceleration in the LIA based on this active material is although significantly reduced, but rather.

Known material of the positive electrode LIA based on lithium-manganese spinel LiMn ₂ 0 ₄ [17], non-toxic, cheaper, powerful and safe to use in comparison with lithium cobalt. The disadvantages of lithium manganese spinel are the low specific capacitance and its irreversible drop due to dissolution of manganese during cycling, especially at elevated temperatures [6, 7], which makes this material unsuitable for the development of LIB for transport and energy.

The known material of the positive electrode LIA based on lithium ferrophosphate LiFeP0 ₄ [18], which has such advantages as non-toxicity, high capacity, stability and safety during cycling due to the fact that oxygen is chemically more strongly bonded in the phosphate structure than in the oxide structure. On the other hand, the structure of lithium ferrophosphate molecules causes a number of inherent disadvantages. Due to the specific features of the crystal structure, lithium ions can move only in one dimension [19] during charge and discharge of a battery, and not in three, as in traditional cathode materials based on transition metal oxides. This is the reason for the low conductivity of the cathode material, both ionic and electronic, which, in turn, leads to a lower specific energy (380 Wh / kg). In addition, due to the low conductivity of lithium ferrophosphate, there is a significant decrease in the capacity and power of LIB during operation at low temperatures [20, 21]. In addition, together with lithium titanate Li ₄ Ti ₅ 0 _12, lithium ferrophosphate LiFeP0 gives a low potential difference (1.9 V and lower) [22], which negatively affects the specific energy characteristics LIA. This, in turn, increases the mass and dimensions of rechargeable batteries, which is especially critical for electric vehicles, and also increases the cost of 1 kWh of energy stored by batteries due to the need to install more batteries to achieve acceptable voltage and energy levels.

Closest to the claimed battery is the solution according to the application [23], according to which it is proposed to use a combination of lithium titanate Li ₄ Ti ₅ 0i2 as a negative electrode material and lithium-cobalt phosphate LiCoP0 to create a battery with high energy intensity and power ₄ as a positive electrode material. The disadvantage of this solution is the impossibility of creating a stably working battery of this electrochemical system at the present stage of technology development due to low discharge capacitance, irreversible lithium losses and an accelerated drop in capacitance during cycling and the associated unacceptably small 1 Co0 resource ₄ electrodes (10 cycles) [24].

SUMMARY OF THE INVENTION

The objective of the invention was the development of LIA, combining in its design the active material of the negative electrode based on lithium titanate Li ₄ Ti ₅ 0 ₁₂ and the active material of the positive electrode, which has high values of electrochemical potential and specific capacity, and at the same time capable of long-term reversible cycling in a wide range of charge-discharge currents and temperatures. The use of such a combination of electrode materials makes it possible to design LIA-based energy storage devices suitable for use in electric transport, network load balancing systems, emergency power supply and uninterruptible power supply.

The technical result is the creation of a design of highly energy-intensive LIA with increased power, safety and stability during cycling.

The specified technical result is achieved in that the battery design uses a combination of the active material of the negative electrode based on lithium titanate Li ₄ Ti ₅ 0i ₂ and the active material of the positive electrode based on lithium vanadium phosphate (lithium phosphovanadate) Li ₃ V ₂ (P0 ₄ ) ₃ . In terms of specific energy, Li ₃ V ₂ (P0 ₄ ) _{3 is} comparable to oxide active materials, and in terms of safety, due to its phosphate structure, it is close to LiFeP0 ₄ , however, it has a number of distinctive features that make it advantageous. which include: - high theoretical value of specific capacity - 198 mAh / g and the ability to achieve practical values of specific capacity close to theoretical;

- higher average discharge voltage - 4.8 V rel. lithium for monoclinic structural modification and 4.3 V for rhombohedral (nasicon-like) structural type. Thus, in combination with lithium titanate, nasicon-like Li ₃ V ₂ (P0 ₄ ) ₃ gives a potential difference of the order of 2.8 V, and monoclinic Li ₃ V ₂ (P0 ₄ ) ₃ - of the order of 3.3 V;

 - increased cyclic life - up to 2500 charge-discharge cycles;

 - high specific power - 2000 W / kg;

 - high values of discharge currents - more than 40C.

The test results of the prototypes of the LIA system Li ₄ Ti ₅ 0 _{! 2} -Li ₃ V ₂ (P0 ₄ ) ₃ show their acceptable performance and cycling (Fig. 1 and 2).

The problem is also solved by the fact that the active material of the negative electrode based on Li ₄ Ti ₅ 0i _{2 is} doped with chromium at the positions of titanium and is a compound of the composition Li ₄ Ti _-x Cr _x Oi ₂ , where 0 <x <0.2. Partial substitution of titanium by chromium in the indicated amounts causes a change in the structure of the crystal lattice of the active material, which leads to an increase in the utilization factor, as a result, the preservation of capacity during cycling increases by 1.3%.

The indicated problem is also solved due to the fact that the active material of the positive electrode is doped with sodium at the positions of lithium, one or more metals from the group consisting of magnesium, aluminum, yttrium and lanthanum at the positions of vanadium, fluorine or chlorine at the positions of phosphate, and represents a compound of the composition Li ₃ _ _x Na _x V ₂ _ _y M _y (P0 ₄ ) _3-z Hal _z / C, where M is one or more metals from the group consisting of Mg, A1, Y, La; Hal = F, CI; 0 <x <0.1; 0 <y <0.2; 0 <z <0.16. Modification of the structure of lithium phosphovanadate in this way leads to an improvement in the electrical conductivity of the active material, as a result of which its discharge capacity and structural stability increase, which leads to an increase in the specific energy, power, and resource of LIB. As an example of the beneficial effects of doping lithium vanadium phosphate with magnesium in FIG. Figure 3 shows an increase in its discharge capacity during cycling with a current of 10–10 s.

The indicated technical result is also achieved by modifying the active materials used in the LIA design by applying a conductive carbon coating to the surface of their particles. As a result, the electrical resistance at the interface between the crystals of the active substance decreases, which leads to an increase in the surface conductivity of the active material, which, in turn, helps to improve its characteristics such as specific capacitance, coefficient of utilization of the active material. terial, power and cycleability. The result is also achieved through the use of starch as a carbon precursor, which during the synthesis of the active material forms a viscous medium that promotes the formation of particles of a particularly small size. As an illustration of the positive impact of the indicated technical solution on the properties of the active material in FIG. Figure 4 shows experimental data showing the ability of a composite of lithium-vanadium phosphate with carbon (1 zU ₂ (P0 ₄ ) s / C) to cycle with extremely high currents (up to 320 ° C).

Claims

CLAIM 1. A lithium-ion battery, characterized in that the active material of the negative electrode uses lithium titrated oxide Li ₄ Ti 0i ₂ , and the active material of the positive electrode is lithium vanadium phosphate Li ₃ V ₂ (P0 ₄ ) ₃ . 2. The lithium-ion battery according to claim 1, characterized in that the active material of the negative electrode is doped with chromium at the positions of titanium and is a compound of the composition Li ₄ Ti _5-x Cr _x Oi ₂ , where 0 <x <0.2. 3. The lithium-ion battery according to claim 1, characterized in that the active material of the positive electrode is doped with sodium at the positions of lithium, one or more metals from the group consisting of magnesium, aluminum, yttrium and lanthanum at the positions of vanadium, fluorine or chlorine at the positions of phosphate , and is a compound of the composition Li ₃ _ _x Na _x V ₂ _ _y M _y (P0 ₄ ) 3 _-z Hal _z / C, where M is one or more metals from the group consisting of Mg, A1, Y, La; Hal = F, CI; 0 <x <0.1; 0 <y <0.2; 0 <z <0.16.  4. The lithium-ion battery in p.p. 1 to 3, characterized in that the crystals of the active materials of the negative and positive electrodes are coated with a surface layer of carbon.  5. The lithium-ion battery according to claim 4, characterized in that the surface carbon layer on the crystals of active materials is obtained by introducing a carbon-containing precursor, starch, into the mixture of the starting reagents.