Additive for electrochemical energy storages and electrochemical energy storage

Abstract

An additive for electrochemical energy storages is disclosed, wherein the additive contains at least one silicon- and alkaline earth metal-containing compound V1 which in contact with a fluorine-containing compound V2 in the energy storage forms at least one compound V3 selected from the group consisting of silicon- and fluorine-containing, lithium-free compounds V3a, alkaline earth metal- and fluorine-containing, lithium-free compounds V3b, silicon-, alkaline earth metal- and fluorine-containing, lithium-free compounds V3c and combinations thereof. Also disclosed is an electrochemical energy storage containing the additive.

Claims

1. An electrochemical energy storage, comprising: a liquid electrolyte; and an additive in the liquid electrolyte, the additive containing at least one silicon- and alkaline earth metal-containing compound V1 which in contact with a fluorine-containing compound V2 in the energy storage forms at least one compound V3 selected from the group consisting of silicon- and fluorine-containing, lithium-free compounds V3a, alkaline earth metal- and fluorine-containing, lithium-free compounds V3b, silicon-, alkaline earth metal- and fluorine-containing, lithium-free compounds V3c and combinations thereof, wherein said at least one silicon- and alkaline earth metal-containing compound V1 is a powder comprising at least the following constituents (in % by weight): TABLE-US-00015 SiO.sub.2 15-68 BaO 10-80 ZrO.sub.2  0-15 Li.sub.2O greater than 0-25 P.sub.2O.sub.5 greater than 0-20 Al.sub.2O.sub.3  greater than 0-1.1 CaO  0-30 MgO  0-30 MgO + BaO + CaO ≥20 NiO  0-10 PbO  0-10 ZnO  0-10 F  0-5, a molar ratio of one or more alkaline earth metal oxides to silicon dioxide is in a range from 0.65 to ≤1.0, and wherein said at least one silicon- and alkaline earth metal-containing compound V1 does not contain any B.sub.2O.sub.3.

2. The energy storage of claim 1, wherein the liquid electrolyte is selected from the group consisting of a nonaqueous electrolyte, an electrolyte based on carbonate solvents, and an electrolyte containing at least LiPF.sub.6.

3. The energy storage of claim 1, wherein said energy storage is a lithium ion cell.

4. The energy storage of claim 1, wherein the energy storage contains an anode, a cathode and a separator.

5. The energy storage of claim 1, wherein the molar ratio of one or more alkaline earth metal oxides to silicon dioxide is a molar ratio of BaO/SiO.sub.2.

6. The electrochemical energy storage of claim 1, wherein the compound V1 comprises 60-80% by weight of BaO.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The sole FIGURE is a graph that depicts a decrease in the HF concentration under potential load for both material a and material b.

PREFERRED EMBODIMENTS OF THE INVENTION

EXAMPLES

(2) A glass powder as additive (working examples WE 1 to WE 25) is described in the following.

(3) The glass powder was introduced into a battery electrolyte and allowed to stand at 60° C. for seven days. After separating off the electrolyte and drying the material, the BaSiF.sub.6 formed (e.g. at the surface of the glass powder) can be confirmed by means of XRD (X-ray powder diffraction); as an alternative and in the case of formation of noncrystalline phases also by EDX and SEM.

(4) Compositions in which BaSiF.sub.6 was detected (table 1): CE 1 Comparative example with 100% Al.sub.2O.sub.3 n.d. not determined

(5) TABLE-US-00009 TABLE 1 Composition [% by weight] CE 1 WE 1 WE 2 WE 3 WE 4 WE 5 SiO.sub.2 55.0 29.0 26.3 31.6 36.2 ZrO.sub.2 5.7 2.7 2.8 Al.sub.2O.sub.3 100 10.0 1.0 B.sub.2O.sub.3 10.0 BaO 25.0 66.5 67.0 65.7 61.0 ZnO Li.sub.2O 0.9 P.sub.2O.sub.5 2.7 F PbO 1.0 Ratio of — 0.18 0.9 1.0 0.81 0.66 BaO/SiO.sub.2 (on a molar basis) Main phase — n.d. n.d. BaSiF.sub.6 BaSiF.sub.6 BaSiF.sub.6 in the XRD analysis of the filter cake Glass transition — 665 620 767 742 729 temperature Tg [° C.] Composition [% by weight] WE 6 WE 7 WE 8 WE 9 WE 10 WE 11 SiO.sub.2 28.3 29.0 27.1 28.2 27.2 27.2 ZrO.sub.2 6.1 6.1 Al.sub.2O.sub.3 1.0 1.0 1.0 B.sub.2O.sub.3 BaO 64.6 62.4 63.1 63.7 65.2 61.8 ZnO Li.sub.2O 0.6 1.7 1.7 P.sub.2O.sub.5 8.0 8.1 6.6 8.3 F 1.0 1.0 PbO Ratio of 0.89 0.85 0.91 0.88 0.94 0.89 BaO/SiO.sub.2 (on a molar basis) Main phase BaSiF.sub.6 BaSiF.sub.6 BaSiF.sub.6 BaSiF.sub.6 BaSiF.sub.6 BaSiF.sub.6 in the XRD analysis of the filter cake Glass transition 718 620 577 719 711 594 temperature Tg [° C.] Composition [% by weight] WE 12 WE 13 WE 14 WE 15 WE 16 WE 17 SiO.sub.2 29.5 28.6 29.2 29.0 28.9 26.6 ZrO.sub.2 5.5 Al.sub.2O.sub.3 1.0 1.0 1.0 1.1 1.0 B.sub.2O.sub.3 BaO 67.9 65.4 66.9 66.5 66.1 67.9 ZnO Li.sub.2O 0.3 0.9 1.5 0.6 1.2 P.sub.2O.sub.5 1.3 4.1 1.4 2.8 2.8 F PbO Ratio of 0.9 0.9 0.9 0.9 0.9 1.0 BaO/SiO.sub.2 (on a molar basis) Main phase BaSiF.sub.6 BaSiF.sub.6 n.d. BaSiF.sub.6 n.d. BaSiF.sub.6 in the XRD analysis of the filter cake Glass transition n.d. 627 n.d. 655 605 790 temperature Tg [° C.] Composition [% by weight] WE 18 WE 19 WE 20 WE 21 WE 22 WE 23 SiO.sub.2 29.9 28.2 30.2 27.6 28.5 28.8 ZrO.sub.2 1.2 Al.sub.2O.sub.3 1.0 1.0 1.0 1.0 B.sub.2O.sub.3 BaO 65.7 67.5 66.8 66.0 65.3 66.2 ZnO Li.sub.2O 0.6 0.6 0.6 0.6 0.9 0.9 P.sub.2O.sub.5 2.8 2.7 1.4 4.9 4.1 4.1 F PbO Ratio of 0.86 0.94 0.86 0.94 0.9 0.9 BaO/SiO.sub.2 (on a molar basis) Main phase n.d. n.d. n.d. n.d. n.d. n.d. in the XRD analysis of the filter cake Glass transition 651 635 n.d. 637 n.d. n.d. temperature Tg [° C.] Composition [% by weight] WE 24 WE 25 WE 26 WE 27 WE 28 SiO.sub.2 28.2 28.3 45 63.6 63.6 ZrO.sub.2 1.2 Al.sub.2O.sub.3 1.0 1.0 B.sub.2O.sub.3 BaO 64.6 64.7 55 ZnO Li.sub.2O 0.8 0.9 P.sub.2O.sub.5 4.1 4.2 F 0.9 PbO MO CaO36.4 MgO36.4 Ratio of 0.61 0.85 MO/SiO.sub.2 (on a molar basis) Ratio of 0.9 0.9 0.48 BaO/SiO.sub.2 (on a molar basis) Main phase n.d. n.d. n.d. n.d. n.d. in the XRD analysis of the filter cake Glass transition n.d. n.d. 685 n.d. n.d. temperature Tg [° C.]

(6) The electrolyte used is essentially a mixture of one or more nonaqueous solvents, preferably carbonate solvents, and at least one fluoride-based electrolyte salt. LiPF.sub.6 was preferably used as electrolyte salt.

(7) Possible solvents are, for example:

(8) propylene carbonate (PC), ethylene carbonate (EC), butylene carbonates (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), vinylene carbonate (VC), methyl ethyl carbonate (EMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), ethyl acetate (EA), 1,3-dioxolane (DOL), tetrahydrofuran (THF), tetra(ethylene glycol) dimethyl ether (TEGDME), tri(ethylene glycol) dimethyl (TEGD). Preference is in principle given to using PC, EC, γ-BL, DMC, DEC, EMC or DME.

(9) The solvents can be used either alone or as suitable mixtures. Examples of mixtures are EC/DMC in a ratio of 50/50 (% by weight) or electrolyte mixtures having a ratio of EC to (DMC+EMC) of <1. LiPF.sub.6 can be used either alone or in combination with other electrolyte salts. The latter encompass, by way of example, LiBF.sub.4, LiAsF.sub.6, LiClO.sub.4, LiB(C.sub.6H.sub.5).sub.4, LiCH.sub.3SO.sub.3, LiCF.sub.3SO.sub.3, LiN(SO.sub.2CF.sub.3).sub.2, LiC(SO.sub.2CF.sub.3).sub.3, LiAlCl.sub.4, LiSiF.sub.6, Li[(OCO).sub.2].sub.2B, LiDFOB, LiCl, and LiBr.

(10) The concentration of LiPF.sub.6 or electrolyte salt mixtures in the nonaqueous solvents is not limited but should preferably remain within the following ranges: from 0.1 M (mol/dm.sup.3) to 5.0 M, preferably from 0.5 M to 3.0 M.

(11) The electrolyte consisting of solvent and electrolyte salt has, for example, the following composition:

(12) 1 mol of LiPF.sub.6 in EC/DMC 1:1 (% by weight)

(13) The invention is illustrated by the following working examples.

(14) The glass powder WE 17 has the following composition in mol %:

(15) TABLE-US-00010 SiO.sub.2: 47.5 BaO: 47.5 ZrO.sub.2: 5

Example 1

(16) The inorganic material (a: Al.sub.2O.sub.3 BET surface area from 7 to 8 m.sup.2/g, particle size D50, purity for batteries; b: WE17 BET surface area from 7 to 8 m.sup.2/g, particle size D50, purity for batteries) introduces the same amount of surface water (2000-3000 ppm) into the system on integration into the LIB cell. Material b releases this to the smallest extent in the cell, in particular the electrolyte compared to the electrode materials. This can be seen from cyclovoltammetry (CV) results:

(17) The respective material is dried and then introduced into the test cell consisting of two Pt electrodes as counterelectrode and working electrode which is uncoated.

(18) In the cyclovoltammograms, the peak at 2.2 V indicates the existence of free water in the cell. This is not present in the case of materials a and b in the first cycle. During the further course of the experiment (cycles 5 and 10), a small water peak is detected in the case of material a and no water peak is detected in the case of material b.

Example 2

(19) Materials a and b are admixed with a mixture of electrolyte and water in order to reinforce the formation of damaging HF and examined by means of cyclovoltammetry. The reference is an electrolyte (ethylene carbonate:dimethyl carbonate (1:1) containing 1 mol/l of LiPF.sub.6) without addition of an inorganic material. The effect of the binding of HF is shown by evaluation of a peak characteristic of HF at 2.9 V in the cyclovoltammogram. The decrease in the HF concentration is apparent under potential load for both materials, viz. a and b, while in the system of electrolyte with water the amount of HF even increases toward the end of the experiment (see the sole FIGURE).

(20) The cathode material LiMn.sub.2O.sub.4 (LMO) was additionally added to the respective abovementioned CV measurements in the next step. LMO is destroyed by reaction with HF, with Mn being leached from the crystal composite. Here too, evaluation of the CV data (plotting of the peak heights) shows that the inorganic filler materials scavenge HF in the presence of an electrode material. After the CV measurement, the supernatant solution was analyzed for Mn.sup.2+ by means of ICP-OES. It can be seen here that significantly less Mn has been leached from the cathode material in the case of the sample with material b compared to material a and the system without inorganic additive.

(21) Mn.sup.2+ content in mg/I in water-moistened electrolyte after 25 cycles (determined using ICP-OES)

(22) TABLE-US-00011 Electrolyte 40 Electrolyte + Al.sub.2O.sub.3 40 Electrolyte + WE17 20

(23) Furthermore, the getter action of the material b commences only after a particular time (in CV, further significant decrease in the HF peak after 5 cycles). This is necessary since small amounts of HF are required during activation of an LIB cell in order to form the SEI and also to passivate the Al current collector for the cathode.

(24) For the calendar identification of HF scavenging, materials a and b were storaged in moistened electrolyte for 7 days and the fluoride content was subsequently determined by means of ion chromatography. Material b binds HF significantly during downtimes.

(25) F content in mg/I (calendar effect) in electrolyte moistened with 1500 ppm of water after 7 days

(26) TABLE-US-00012 Electrolyte 1300 ± 130 87% (corresponds to 1300 ppm) 13% scavenged Electrolyte + Al.sub.2O.sub.3 1500 ± 150 100% (corresponds to 1500 ppm) 0% scavenged Electrolyte + WE17  900 ± 100 60% (corresponds to 900 ppm) 40% scavenged

Example 3

(27) When additional water is introduced into an LIB cell, materials a and b bind water from the system. This occurs both under potential load and also during downtimes.

(28) The calendar effect was detected: an electrolyte composed of EC:DMC with 1 M LiClO.sub.4 (suppression of reaction of the anion with water to form HF) and 1000 ppm of water is mixed with the inorganic materials a and b. After standing for 7 days, the residual amount of water is determined by means of Karl-Fischer titration. Both materials withdraw water from the electrolyte.

(29) H.sub.2O content in mg/kg of solvent (calendar effect) in electrolyte moistened with 1500 ppm of water after 7 days

(30) TABLE-US-00013 Electrolyte 997 ± 10 100% (corresponds to 997 ppm) 0% scavenged Electrolyte + Al.sub.2O.sub.3 917 ± 10 92% (corresponds to 917 ppm) 8% scavenged Electrolyte + WE17 894 ± 10 89% (corresponds to 894 ppm) 11% scavenged

(31) Working example of an electrochemical energy storage containing as additive at least one silicon- and alkaline earth metal-containing compound V1 which in contact with a fluorine-containing compound in the energy storage forms at least one compound V3 which is a fluorine-containing, lithium-free alkaline earth metal compound V3b, in this case BaF.sub.2.

(32) A separator coated with the additive (glass powder) was installed in cathode half cells (Li/LP30/glass-polyethylene separator/LP30/cathode material; 1) lithium manganese oxide (LMO) 2) lithium nickel cobalt manganese oxide (NCM)) for a battery test. Swagelok cells were used together with a lithium reference for the experiment. Cycling was carried out according to a CC-CV method. At the beginning, 5 activation cycles are carried out at a current for C/10 (corresponds to one charging or discharging step of 10 h), and the cells are subsequently charged and discharged with a current of 1 C (corresponds to the time of 1 h). The voltage range was from 3.0 to −4.4 V. After 60 cycles, the cells were dissembled and the separator coating was examined by means of XRD. This shows that BaF.sub.2 was formed. The electrolyte LP30 [EC:DMC (1:1)+1 mol/l of LiPF.sub.6] was dry (H.sub.2O<20 ppm).

(33) The glass powder used had the following composition in mol %:

(34) TABLE-US-00014 SiO.sub.2: 47.5 BaO: 47.5 ZrO.sub.2: 5